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tag:theconversation.com,2011:/africa/topics/rivers-1725/articles Rivers – The Conversation 2020-03-05T19:08:36Z tag:theconversation.com,2011:article/133004 2020-03-05T19:08:36Z 2020-03-05T19:08:36Z Sure, save furry animals after the bushfires – but our river creatures are suffering too
The hellish summer of bushfires in southeast Australia triggered global concern for our iconic mammals. Donations flooded in from at home and around the world to help protect furry species.

But there's a risk the government and public responses will not see the fish for the koalas.

Of the 113 priority fauna species identified by the federal government as worst impacted by bushfires, 61 (54%) are freshwater species that live in or around our inland rivers, such as fish, frogs, turtles and the iconic platypus.

These animals and ecosystems were already struggling due to prolonged drought and mismanagement of the Murray Darling Basin. Saving koalas and other mammals is of course important, but freshwater species should also be a priority for post-fire environmental programs.

A picture of devastation

The government's priority species list includes three turtle species, 17 frogs, 22 crayfish, 17 fish and the platypus. Rounding out the list is an alpine stonefly, although many other invertebrates are also likely to be affected (as well as other species that depend on moist, streamside forest habitats).

Excluding tropical savannah, the recent bushfires burnt more than 7.7 million hectares in Victoria, South Australia, New South Wales, Queensland and Western Australia. Rainforests and riparian (riverside) forests were extensively damaged along the Australian east coast and alps. These are normally moist environments, which are not adapted to fire.

Plant and animal species at the edge of waterways, in peat wetlands and in riverside forests are likely to have been burnt or killed by heat, such as crustaceans , lizards, and corroboree and mountain frogs in the alps and east coast rainforests.

   Read more: Fire almost wiped out rare species in the Australian Alps. Feral horses are finishing the job

Burnt riverside forests no longer shade the water, making water temperatures hotter and leading to increased evaporation that may stress surviving wildlife. The loss of vegetation cover also leaves prey exposed to predators.

Following recent rain, water flowing into rivers has washed ash into streams. This clogs fish gills and brings nutrients that drive algal blooms. Sediment washed into waterways fills in the gaps between rocks and holes in river beds – places where many species shelter and breed. For instance, the River Murray catchment's last population of Macquarie perch was impacted as rain washed ash and sediment into Mannus Creek in southern NSW.

Fires tend to burn forests in patches, sometimes leaving refuges for land-based animals. However fire damage to waterways flows downstream, systematically degrading the habitat of aquatic animals by leaving little clean water to hide in.

 <img alt="" src="https://images.theconversation.com/files/318786/original/file-20200305-127918-1013akc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/318786/original/file-20200305-127918-1013akc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=374&fit=crop&dpr=1 600w, https://images.theconversation.com/files/318786/original/file-20200305-127918-1013akc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=374&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/318786/original/file-20200305-127918-1013akc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=374&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/318786/original/file-20200305-127918-1013akc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=470&fit=crop&dpr=1 754w, https://images.theconversation.com/files/318786/original/file-20200305-127918-1013akc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=470&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/318786/original/file-20200305-127918-1013akc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=470&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 Bushfire silt clogging the usually pristine Tambo river in the Victorian high country in January. David Crosling/AAP

Long-term damage

The devastating impact of the fires in river environments may be long-lived.

When aquatic animals species are wiped out in particular rivers, they may not be able to recolonise from surviving populations in other unconnected rivers.

Some species will invariably now be closer to extinction. For example many key peat swamp habitats of the critically endangered northern corroboree frog have been burnt in the Bogong Peaks and Brindabella mountains of NSW and the ACT.

   Read more: The sweet relief of rain after bushfires threatens disaster for our rivers

And after fires, fast-growing young eucalyptus forests transpire much more water than older burnt trees. This may reduce inflows into streams for a century.

The recent bushfires followed several years of extreme drought across much of Australia. In the Murray-Darling Basin, these challenges were compounded by poor water management that contributed to dried-up rivers and mass fish deaths.

Water-sharing rules in the basin determine how much water is allocated to agriculture and the environment. Current water-sharing plans do not explicitly include allocations to manage losses due to climate change, and as the plans will only be updated once a decade, it is questionable whether they will be adjusted to sustain flows needed to conserve threatened species.

 <img alt="" src="https://images.theconversation.com/files/318788/original/file-20200305-127904-15dxl51.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/318788/original/file-20200305-127904-15dxl51.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/318788/original/file-20200305-127904-15dxl51.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/318788/original/file-20200305-127904-15dxl51.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/318788/original/file-20200305-127904-15dxl51.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/318788/original/file-20200305-127904-15dxl51.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/318788/original/file-20200305-127904-15dxl51.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 Much corroboree frog habitat was destroyed during the fires. Melbourne Zoo

Here's what to do

After the fires, government officials and scientists rescued a number of "insurance" populations of threatened aquatic animals such as turtle and fish species, and took them to captive breeding facilities, such as the stocky galaxias fish in the alps. We must ensure healthy habitat is available for these animals to re-establish viable populations when released.

In the short term, we must protect surviving and regenerating habitat. Government programs are off to a good start in promising to cull feral predators such as cats and foxes, as well as grazing animals such as pigs, deer and goats. The NSW and Victorian governments must also remove feral horses in the Australian Alps that are damaging the swamp habitats and streams.

Now so many infested riverside forests are accessible, it is a key time to control weed regrowth.

   Read more: Last summer's fish carnage sparked public outrage. Here's what has happened since

In the medium term, we should expand programs to fence livestock out of waterways, install other watering points for these animals and revegetate stream banks.

Deep holes in rivers and streams with cool water are important refuges for aquatic animals, and ways to restore them should be investigated.

Impediments to fish migration, such as weirs, should be removed or fish "ladders" installed to aid fish movement. Aquatic species often won't breed unless the water is the right temperature in the right season; to prevent the release of overly cold water from the bottom of dams, better water release structures should be installed.

 <img alt="" src="https://images.theconversation.com/files/318789/original/file-20200305-127909-lqng9c.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/318789/original/file-20200305-127909-lqng9c.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/318789/original/file-20200305-127909-lqng9c.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/318789/original/file-20200305-127909-lqng9c.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/318789/original/file-20200305-127909-lqng9c.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/318789/original/file-20200305-127909-lqng9c.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/318789/original/file-20200305-127909-lqng9c.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 Years of drought meant rivers and aquatic life were already vulnerable before the fires. Dean Lewins/AAP

An opportunity for change

Successive governments have been asleep at the tiller when it comes to threatened aquatic animals. Official recovery plans for many fire-affected species have not been adequately funded or implemented.

In the Murray-Darling Basin for example, a native fish strategy was shelved in 2013 after the NSW government reportedly pulled funding.

The impending release of a new fish strategy, and other post-fire recovery actions, are an opportunity for governments to right past wrongs and ensure our precious freshwater species thrive into the future.

Jamie Pittock is a member of advisory boards for a number of Australian environmental non-government organizations who fund conservation of biodiversity, including responding to the impacts of bush fires.
 Fish, frogs, turtles and platypus at major risk of extinction following the bushfires. So why aren't they getting much attention? Jamie Pittock, Professor, Fenner School of Environment & Society, Australian National University Licensed as Creative Commons – attribution, no derivatives. tag:theconversation.com,2011:article/130770 2020-02-24T13:47:51Z 2020-02-24T13:47:51Z Mine waste dams threaten the environment, even when they don't fail

The January 2019 collapse of a dam in Brumadinho, Brazil, sent mining tailings and mud over the landscape for miles, destroying this bridge and killing 300 people.  Andre Penner/AP

Scars from large mining operations are permanently etched across the landscapes of the world. The environmental damage and human health hazards that these activities create may be both severe and irreversible.

Many mining operations store enormous quantities of waste, known as tailings, onsite. After miners excavate rock, a processing plant crushes it to recover valuable minerals such as gold or copper. The leftover pulverized rock and liquid slurry become tailings, which often are acidic and contain high concentrations of arsenic, mercury and other toxic substances.

Mining companies store tailings forever, frequently behind earth-filled embankment dams. Over the past 100 years, more than 300 mine tailing dams worldwide have failed, mainly due to foundation weakening, seepage, overtopping and earthquake damage.

We are research scientists studying how humans affect rivers. In our view, the damage caused by stored mine waste often outweighs the benefits that mining provides to local economies and the technology industry.

This issue is especially urgent now in a region of the Pacific Northwest where Alaska and British Columbia meet. This zone, known as the Golden Triangle, is studded with mineral claims and leases. We believe that rivers in this area could be severely damaged if proposed mega-projects are allowed to proceed.

Footage of the Mt. Polley tailing spill in Canada.

Catastrophic failures renew old worries

Tailings dam failures range from the 1966 Aberfan disaster that buried a Welsh village to multiple spills over the past decade in Canada, China, Chile and the United States. The International Commission on Large Dams, a nongovernmental organization, warned in 2001 that the frequency and severity of tailings dam failures was increasing globally.

Two catastrophic and highly publicized failures at the Mt. Polley dam in Canada in 2014 and the Brumadinho dam in Brazil in 2019 finally catalyzed a response. The International Council on Mining and Metals, the United Nations Environment Programme and the independent organization Principles for Responsible Investment drafted a "global standard for the safe and secure management of mine tailings facilities." The first public review of the standard was completed in December 2019, and its authors plan to finalize their recommendations by the end of March 2020.

 <img alt="" src="https://images.theconversation.com/files/316684/original/file-20200222-92518-hl8w9w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/316684/original/file-20200222-92518-hl8w9w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=401&fit=crop&dpr=1 600w, https://images.theconversation.com/files/316684/original/file-20200222-92518-hl8w9w.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=401&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/316684/original/file-20200222-92518-hl8w9w.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=401&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/316684/original/file-20200222-92518-hl8w9w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/316684/original/file-20200222-92518-hl8w9w.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/316684/original/file-20200222-92518-hl8w9w.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 Crews and a sniffer dog search for buried bodies 99 days after the Jan. 25, 2019 collapse of the Corrego do Feijao mining dam in Brumadinho, Brazil. Douglas Magno/AFP via Getty Images

The standard aspires to achieve "zero harm to people and the environment and zero tolerance for human fatality." Reducing the likelihood of future dam failures and minimizing damage if one does break are appropriate goals, but our research suggests that the concept of "zero harm" is false and potentially dangerous.

Why? Because once in place, tailings dams and their toxic reservoirs require maintenance forever. Even if there is no catastrophic failure, these dams and their surrounding infrastructure can cause ecological harm in multiple ways. They require artificial water diversions and releases, which upset natural flow patterns in surrounding streams and modify water temperature and concentrations of metals. And polluted groundwater seepage from unlined reservoirs or failing liners is often hard to detect and treat.

These ecosystem modifications directly affect organisms on land and in the water downstream. Every decision to allow a mine to proceed with a tailings storage facility indelibly transforms rivers and their ecosystems for hundreds to thousands of years.

 <img alt="" src="https://images.theconversation.com/files/316658/original/file-20200221-92533-idvzfx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/316658/original/file-20200221-92533-idvzfx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=424&fit=crop&dpr=1 600w, https://images.theconversation.com/files/316658/original/file-20200221-92533-idvzfx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=424&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/316658/original/file-20200221-92533-idvzfx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=424&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/316658/original/file-20200221-92533-idvzfx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=533&fit=crop&dpr=1 754w, https://images.theconversation.com/files/316658/original/file-20200221-92533-idvzfx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=533&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/316658/original/file-20200221-92533-idvzfx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=533&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 Mining dominates the Iskut River area of British Columbia. Each red segment represents a separate mining claim. BC Mining Law Reform

International rivers at risk

Today these decisions loom large in the Golden Triangle, home to the Taku, Stikine and Unuk Rivers – three of the longest undammed rivers in North America. Salmon from these rivers have supported indigenous communities for millennia, generate tens of millions of dollars in economic activity annually and provide a dependable source of food for organisms ranging from insects to brown bears.

We calculate that 19% of the total drainage area of these three rivers is staked with mineral mining claims or leases. This includes 59% of the Unuk River watershed, along with the entire Iskut River corridor, the largest tributary to the Stikine River.

We have identified dozens of mines in exploratory or production phases. Some industry representatives call these statistics irrelevant because only a small portion of the claims will convert to economically viable projects. But from our perspective, the fact that vast areas of these watersheds are included in initial explorations implies that few rivers in this region are safe from potential mining development.

Most proposed projects in the Golden Triangle will require open pit mining and tailings storage. As one indicator of their potential scale, the Red Chris Mine, which has operated since 2015 in the headwaters of the Stikine River, maintains a tailings reservoir dam that is permitted to ultimately stand 344 feet (105 meters) high and contain approximately 107 billion cubic feet (305 million cubic meters) of tailings. The heights of the failed dams at Mt. Polley and Brumadinho were 131 feet (40 meters) and 282 feet (86 meters), respectively.

Those heights pale in comparison to dams proposed for three metal mines in the Stikine and Unuk watersheds, including KSM, Galore Creek, and Schaft Creek. The tallest of four dams planned for KSM would measure 784 feet (239 meters) – one of the highest dams in North America, and the second highest in Canada.

At KSM, economically viable ore will be transported from open pits to a processing facility and tailings storage reservoir, accessed via twin tunnels built under a glacier. After what the project proponent calls the 53-year "life of mine," Seabridge Gold proposes to treat runoff water from the piled waste rock for at least 200 years.

Each component of these proposed mines is an incredible engineering feat that will cost billions of dollars to construct and more to clean up later. From the perspective of maintaining an ecologically healthy watershed, the life of the mine is just beginning when operations close.

In contrast to more conventional water storage dams, which are licensed and built for a finite operating life, tailings dams must hold back their slurry forever. The likelihood of leaks or dam failure compounds over this multigenerational time period as facilities age and projects no longer generate revenue.

Accurately assessing risk

Rivers are the arteries of coastal Alaska and northwestern Canada, draining pristine snow and ice-covered mountains and pumping out cold, clean water to support fish, wildlife and people. Here and elsewhere, we believe that regulators should take a measured and cautious view of current and planned tailings facilities.

Dam failures are increasing in frequency, and often are so large that true cleanup or reclamation is not possible. Before more are built, we see a need for independent science to provide a means of honestly assessing the risk of storing mining waste.

[Insight, in your inbox each day. You can get it with The Conversation's email newsletter.]

Christopher Sergeant receives funding from Wilburforce Foundation.

Julian D. Olden does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
 Dams built to hold enormous quantities of toxic mining waste have a long history of spills. Decisions in the Pacific Northwest threaten three free-flowing rivers there. Christopher Sergeant, Research Scientist, Flathead Lake Biological Station, The University of Montana Julian D. Olden, Professor of Aquatic and Fishery Sciences, University of Washington Licensed as Creative Commons – attribution, no derivatives. tag:theconversation.com,2011:article/132116 2020-02-20T13:15:54Z 2020-02-20T13:15:54Z Beavers are set to recolonise the UK – here's how people and the environment could benefit
For an animal that looks like a soggy fur ball with the feet of a duck in need of a pedicure and a tail cut from an old tyre, the beaver's public image is doing rather well lately.

That's despite centuries of hunting that caused the Eurasian beaver (Castor fiber) to disappear from the UK during the 1500s. Now they're back. In 2015, two beaver families were released on the River Otter in Devon. Researchers followed this reintroduced population and tracked their distribution and health. They also monitored how the amphibious rodents affected river flow and other wildlife, along with any disruption on adjacent land. By 2019, there were at least seven breeding pairs that had spread throughout the river catchment, well beyond the release sites.

The results of the five-year trial are striking. The beavers built dams, creating wetland and ponds that slowed down peak river flows that might have caused flooding. Their engineering holds back water in the catchment area, stopping it from running off the land quickly and overloading the river, creating a bottle neck in towns downstream.

This glowing report on the flood prevention skills of beavers couldn't be better timed. Two winter storms, Ciara and Denis, have recently brought flooding to thousands of homes in the UK. In November 2019, the National Trust, a charity more associated with stately homes, released beavers on Exmoor, also in Devon, with much of the publicity at the time touting the likely benefits they'll bring to flood-prone homes nearby.

Wildlife has benefited from the beavers too. The small pools created by the dams had 37% more fish than comparable stretches of the river. That's helped local birds that eat fish, while rare water voles have been able to find refuge from invasive mink in newly wetted channels. Young trout prefer the faster water of washed out dams and have been spotted leaping over intact dams during high river flows.

The River Otter backs up data from shorter term studies set over smaller areas that show beaver dams benefit the diversity of freshwater invertebrates, reduce nutrient levels in outflow, filter pollution and allow sediment to settle out and bury carbon.

 <img alt="" src="https://images.theconversation.com/files/316168/original/file-20200219-11023-13x0uls.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/316168/original/file-20200219-11023-13x0uls.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/316168/original/file-20200219-11023-13x0uls.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/316168/original/file-20200219-11023-13x0uls.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/316168/original/file-20200219-11023-13x0uls.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/316168/original/file-20200219-11023-13x0uls.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/316168/original/file-20200219-11023-13x0uls.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 Beavers build dams – like this one in North America – which help create wetlands, slowing flood water, reducing drought and creating micro-habitats like shallow pools which benefit biodiversity. Chase Dekker/Shutterstock

Reconciling ranchers and rewilders

Just as importantly, the report doesn't shy away from raising the challenges of returning a large mammal to a landscape heavily altered by humans. Beavers burrowed and blocked some culverts, while some of the trees they felled blocked paths. They ate some maize crop (£1.33 worth, gross) and gnawed an orchard tree.

The greatest potential drawback was flooding of productive farmland. There's a risk that these outcomes cause people to rapidly degenerate into two mutually hostile camps – those with an anti-beaver outlook that portray rewilders as naïve townies, trying to force their eco-warrior views on country folk versus a pro-beaver lobby that sees opponents as habitat-wrecking landowners who don't care about the environment and are only interested in animals they can shoot. Thankfully, there is none of this in the River Otter report. Instead, there's recognition of concern and examples of rapid action that can deal with problems.

   Read more: Give beavers permanent residence – we'd be dam stupid not to

The recent report feels a far cry from the one produced after the first official beaver reintroduction trial, which ran in Knapdale, Scotland from 2009-2014. From start to finish the Knapdale project was circumscribed with cautious language, and the beavers were described as fenced in and heavily monitored. These legally permitted beavers were allowed but only under strict guard. Despite this, illegal beavers started appearing elsewhere, most conspicuously on the River Tay, also in Scotland, perhaps since 2011, according to the "Save the Free Beavers of the Tay" Facebook group.

 <img alt="" src="https://images.theconversation.com/files/316159/original/file-20200219-11040-1bwaeff.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/316159/original/file-20200219-11040-1bwaeff.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/316159/original/file-20200219-11040-1bwaeff.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/316159/original/file-20200219-11040-1bwaeff.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/316159/original/file-20200219-11040-1bwaeff.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/316159/original/file-20200219-11040-1bwaeff.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/316159/original/file-20200219-11040-1bwaeff.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 After a five-year study gave the River Otter beavers and their ecosystem benefits a glowing review, signs like these are likely to pop up elsewhere in Britain. Paul J Martin/Shutterstock

Their presence caused the usual mix of delight and anger, and in 2010 Scottish Natural Heritage planned to remove them. But the death of a Scottish beaver called Erica that had been rounded up was a public relations mess. Once an animal has a name and can endear human observers, you better be sure it doesn't die in your custody. Bowing to public pressure, the Scottish government granted beavers full legal protection in 2019.

Beavers look to be on the way back, all over the UK. Quite how they will get around isn't entirely clear yet, but there seems to be widespread public and political support, and it may be that they will spread by themselves.

That will surely be better than the 1948 reintroduction of beavers in Idaho, in the US. Here, the hapless rodents were boxed up and the crates dropped by parachute from low flying aeroplanes.

The plan worked, apart from the one beaver that managed to climb onto the top of its airborne box only to jump off at the last minute. As the Chronicles of Narnia showed, tea and cakes are more a beaver's thing than extreme sports.

Mike Jeffries does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
 Coming to a river catchment near you: a rodent crack team ready to reduce flooding and boost biodiversity. Mike Jeffries, Associate Professor, Ecology, Northumbria University, Newcastle Licensed as Creative Commons – attribution, no derivatives. tag:theconversation.com,2011:article/127876 2020-02-02T13:39:21Z 2020-02-02T13:39:21Z Climate change, pollution and urbanization threaten water in Canada

If we're not careful, water may not be clean enough or available when we need it.  (Shutterstock)

In recent years, the daily news has been flooded with stories of water woes from coast to coast to coast.

There are melting glaciers and ice sheets in northern and western Canada and lead in drinking water in the older neighbourhoods of many cities in Canada. We see toxic blue green algae threatening pets, livestock and drinking water as well as catastrophic floods, droughts and fires.

In 2018, parts of British Columbia experienced devastating floods, followed by wildfires a couple of months later.

Our water resources are under threat from contamination, land use, urbanization and climate change. If we're not careful, it may not be clean enough or available when we need it.

An opportunity to lead

The public supports environmental — and water — leadership in Canada. Many political pundits have suggested the federal election result of October 2019 was a clear call for climate action.

   Read more: Canadians in every riding support climate action, new research shows

And yet Canada is on the front lines of rapid climate changes that affect the water cycle. Where, when, and how much rain, snow or freezing rain falls is changing across Canada.

 <img alt="" src="https://images.theconversation.com/files/311505/original/file-20200123-162210-1ailoak.jpg?ixlib=rb-1.1.0&rect=140%2C95%2C4109%2C2726&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/311505/original/file-20200123-162210-1ailoak.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/311505/original/file-20200123-162210-1ailoak.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/311505/original/file-20200123-162210-1ailoak.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/311505/original/file-20200123-162210-1ailoak.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/311505/original/file-20200123-162210-1ailoak.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/311505/original/file-20200123-162210-1ailoak.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 We cannot have good health if we do not have clean and accessible water. (Shutterstock)

This is the water that we depend upon to replenish our groundwater, rivers and lakes, which continue to have a significant and increasing impact on water availability and quality in Canada and around the world.

However, Canadians remain divided on energy policy and resource development, and on appropriate solutions that balance environmental, economic and social needs. As Canadians, we must move beyond this and implement changes to better manage our water resources sustainably.

Water front and centre

We must manage our water sustainably because water is central to environmental, social and economic sustainability and therefore sustainable societies. This is the focus of the UN's Sustainable Development Goals. These 17 goals identify targets that must be achieved for livelihoods, health, education, environment, cities, oceans, equity and partnership.

It's important to understand that these goals are not isolated, but interrelated. This is why, even though there is a goal for water (SDG 6), there are 40 targets in the other 16 goals that relate directly to water.

 <img alt="" src="https://images.theconversation.com/files/311501/original/file-20200123-162210-ysexjy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/311501/original/file-20200123-162210-ysexjy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=431&fit=crop&dpr=1 600w, https://images.theconversation.com/files/311501/original/file-20200123-162210-ysexjy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=431&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/311501/original/file-20200123-162210-ysexjy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=431&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/311501/original/file-20200123-162210-ysexjy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=542&fit=crop&dpr=1 754w, https://images.theconversation.com/files/311501/original/file-20200123-162210-ysexjy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=542&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/311501/original/file-20200123-162210-ysexjy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=542&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 The river system that the Grassy Narrows First Nation in northern Ontario relies on for food and water has been contaminated with mercury for almost 50 years. Since November 2015, 88 long-term drinking water advisories have been lifted across the country; 55 remain in place. THE CANADIAN PRESS/Paul Chiasson

For example, we cannot have good health if we do not have clean and accessible water, and children cannot go to school or adults to work, if they are not healthy. With water often at the heart of many social and economic inequities, it is critical to address water quantity, quality and access issues in order to meet all of the goals and to achieve the global sustainable development vision.

The recipe for managing Canada's water resources in a sustainable and equitable manner requires all of us to urgently recognize our changing climate and water resources, including drinking water, and act appropriately.

It requires federal co-ordination and leadership on water to overcome challenges of fragmented jurisdiction, such as following through with their commitment to create a Canada Water Agency, develop a national flood forecasting system and ensure universal access to adequate drinking water supplies.

   Read more: Urban floods: We can pay now or later

Research institutions must also step up to advance our knowledge, develop and assess decision support tools and solutions, and communicate their findings to communities, governments and economic sectors.

Finally, it requires reconciliation through shared nations' governance of water resources and recognition of the long history of successful, sustainable management of natural resources through Indigenous Knowledge and historical local knowledge.

Getting our own house in order

Canada could support the world in achieving water sustainability, but it must first get its own house in order and achieve the UN's water goals nationally.

 <img alt="" src="https://images.theconversation.com/files/305557/original/file-20191206-39032-17fwb9c.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/305557/original/file-20191206-39032-17fwb9c.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/305557/original/file-20191206-39032-17fwb9c.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/305557/original/file-20191206-39032-17fwb9c.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/305557/original/file-20191206-39032-17fwb9c.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/305557/original/file-20191206-39032-17fwb9c.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/305557/original/file-20191206-39032-17fwb9c.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 Canada's water opportunities and challenges. (Global Water Futures)

Canada still has not reached universal access to reliable, potable water supplies for everyone, especially First Nations communities. Lead pipes, disinfection byproducts and aging infrastructure are interrupting drinking water service and negatively affecting human health.

   Read more: Lead-tainted water: How to keep homes, schools, daycares and workplaces safe

These water threats also cost our economy big time — as much as $28 billion between 2010 and 2017 — and those costs are rising.

The bottom line

Canada already has the expertise, technologies, industries and research capacity to make good on a commitment to water sustainability and universal achievement of the UN's water goals for all Canadians. But it needs leadership to advance research and practice to expand our existing strengths, and export these internationally.

Canadian research institutions have a role to play in bringing the country together by showing Canada and the world the solutions and benefits of achieving these goals.

There are significant long-term benefits at stake, including the enhanced health and well-being of current and future generations, as well as expanded economic opportunity. But, to achieve these, political leadership needs to transcend partisan lines in order to do what is right.

Ultimately, we have an opportunity to make where we live a better place and to get our own watersheds in order. This will help us create a better, more just, equitable and sustainable world for all. The alternative is, quite simply, unthinkable.

Corinne Schuster-Wallace receives funding from Global Water Futures and the Canadian Tri-Agency. She is co-chair of the Working Group on Climate Change for the Canadian Coalition for Global Health Research.

Robert Sandford receives partial funding from the Global Water Futures program at the University of Saskatchewan.

Stephanie Merrill is a volunteer board member of the Saskatchewan branch and National board of the Canadian Water Resources Association and the Nashwaak Watershed Association.
 The water that replenishes groundwater, rivers and lakes is under threat from climate change, pollution and aging infrastructure. Corinne Schuster-Wallace, Associate Professor, Department of Geography and Planning, University of Saskatchewan Robert Sandford, Chair in Water and Climate Security, United Nations University Stephanie Merrill, Research Scientist, Knowledge Mobilization, Global Insitute for Water Security, Global Water Futures Program, University of Saskatchewan Licensed as Creative Commons – attribution, no derivatives. tag:theconversation.com,2011:article/126484 2020-01-22T13:37:24Z 2020-01-22T13:37:24Z Stoneflies and mayflies, canaries of our streams

The presence of mayflies and stone flies indicates clean water is nearby. Andrew/flickr, CC BY-NC

Experienced anglers recognize that for a trout, the ultimate "steak dinner" is a stonefly or mayfly. That's why fly fishing enthusiasts will go to extreme lengths to imitate these graceful, elegant and fragile insects.

I share their passion, but for different reasons. As a an entomologist who has studied stoneflies and mayflies for over 40 years, I've discovered these insects have value far beyond luring trout – they are indicators of water quality in streams and are a crucial piece of the larger food web. And they are in trouble.

Collecting bugs

I have served as director of the C. P. Gillette Museum of Arthropod Diversity since 1986. The greatest thrill of my career has been collecting and adding mayflies and stoneflies to our collection.

 <img alt="" src="https://images.theconversation.com/files/309127/original/file-20200108-107219-1r624aq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/309127/original/file-20200108-107219-1r624aq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=900&fit=crop&dpr=1 600w, https://images.theconversation.com/files/309127/original/file-20200108-107219-1r624aq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=900&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/309127/original/file-20200108-107219-1r624aq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=900&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/309127/original/file-20200108-107219-1r624aq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1131&fit=crop&dpr=1 754w, https://images.theconversation.com/files/309127/original/file-20200108-107219-1r624aq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1131&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/309127/original/file-20200108-107219-1r624aq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1131&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 Boris Kondratieff collecting aquatic insects in Oregon with former student Chris Verdone.

To find specimens, I have traveled to pristine streams in every U.S. state, Canada, Mexico, Central America, Brazil, Ecuador, the Arabian Peninsula and Europe. My collecting trips have yielded more than 100 new species of mayflies and stoneflies.

One of my favorites literally fell into my lap as I was beating lush foliage along a pristine stream in southern Oregon during May 2014. The beating sheet is an efficient means of sampling dense, streamside vegetation, where adult insects hide. The sheet itself is made of sturdy canvas stretched over two wooden cross members. A stick is used to knock the insects from the vegetation onto the canvas, where they are collected.

When I saw a large yellow and black insect drop onto my sheet, I knew immediately it was a new stonefly species, previously unknown to science. I was ecstatic. My colleagues and I subsequently described it as Kathroperla siskiyou, after the Siskiyou mountains of southern Oregon.

Mayflies and stoneflies thrive in unpolluted water – a fact my colleagues and I have witnessed firsthand on our numerous expeditions. Not only do we see greater overall abundance of these insects in clean streams, but more diversity of species, as well. In polluted areas, we observe the exact opposite. Without a doubt, the presence or absence of mayflies and stoneflies in a stream is a reliable indicator of the quality of its water.

The role of mayflies and stoneflies in the food chain is fundamental, as well. Immature mayflies and stoneflies consume algae, living plants, dead leaves, wood and each other. In this nymph phase, when they have gills and live exclusively underwater, they are an important food source for many animals further up the food chain, including fish and wading birds. When the mayflies and stoneflies emerge from the water as adults, they are essential food for spiders, other insects such as dragonflies and damselflies, and many kinds of birds and bats.

 <img alt="" src="https://images.theconversation.com/files/308425/original/file-20200103-11914-1yaa33q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/308425/original/file-20200103-11914-1yaa33q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/308425/original/file-20200103-11914-1yaa33q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/308425/original/file-20200103-11914-1yaa33q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/308425/original/file-20200103-11914-1yaa33q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/308425/original/file-20200103-11914-1yaa33q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/308425/original/file-20200103-11914-1yaa33q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 Mayflies are on the menu for this hungry fledgling. Keith Williams/flickr, CC BY-NC

Currently, scientists estimate that 33% of all aquatic insects are threatened with extinction worldwide. Many of these species are mayflies and stoneflies. The mayfly species Ephemera compar has already gone extinct in Colorado, and several other species of aquatic insects are threatened in my home state.

Life drains into a stream

Less than 1% of Earth's water is potable and available for human use. Maintaining water quality has become an ever increasing challenge because of the large number of chemicals people use in everyday life and in commerce. Common contaminants such as sediment, organic enrichment including fertilizers and animal waste and heavy metals are constantly making their way into the waters, as well. Declining water quality is like a police siren alerting humanity to current, ongoing and emerging pollution problems.

 <img alt="" src="https://images.theconversation.com/files/308428/original/file-20200103-11914-jlv768.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/308428/original/file-20200103-11914-jlv768.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/308428/original/file-20200103-11914-jlv768.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/308428/original/file-20200103-11914-jlv768.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/308428/original/file-20200103-11914-jlv768.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/308428/original/file-20200103-11914-jlv768.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/308428/original/file-20200103-11914-jlv768.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 Native plantings along a waterway can reduce storm water runoff. Sheryl Watson/Shutterstock.com

One of my great passions is to enlighten others on how to protect the most valuable natural resource of the planet: streams and rivers. Individually, citizens can make a difference. Storm water is the number one water quality problem nationally. Enhancing and planting riparian buffers – that is, planted areas near streams – can help to prevent precipitation and sprinkler runoff. People can also prioritize using only native plants; decreasing mowing areas; recycling or composting yard waste; using less or no fertilizer; avoiding the use of pesticides; and bagging pet waste. Insisting that environmental laws be enforced and strengthened will also help reduce water pollution.

Without clean water, life on Earth will become difficult or impossible for mayflies and stoneflies, not to mention people.

[ You're smart and curious about the world. So are The Conversation's authors and editors. You can read us daily by subscribing to our newsletter. ]

Boris Kondratieff receives funding from National Park Service, Agricultural Experiment Station, and National Science Foundation..
 Mayflies and stone flies are extremely vulnerable to water pollution, which has implications for the larger food chain. Boris Kondratieff, Professor of Entomology and Curator of the C. P. Gillette Museum of Arthropod Diversity, Colorado State University Licensed as Creative Commons – attribution, no derivatives. tag:theconversation.com,2011:article/128441 2019-12-09T15:15:09Z 2019-12-09T15:15:09Z Many urban rivers are hidden underground – 'daylighting' them would bring nature back to cities

Two small rivers meet in the 'Cathedral' under Bradford city centre. Martyn Sutcliffe, Author provided

Ever noticed how few rivers you can see in most city centres? It's easy enough to spot the big, usually tamed, main river such as the Thames in London, the Seine in Paris, the Aire in Leeds or the Don in Sheffield. But you will be hard pressed to find any of their tributaries.

The lost rivers of London are well known, but all cities have them. In my home city of Bradford there is virtually no trace of the small main river, the Bradford Beck, or most of its urban tributaries. In Bradford alone, more than 25km of streams have been covered over and now flow within an engineered structure known as a culvert.

 <img alt="" src="https://images.theconversation.com/files/305775/original/file-20191209-90569-16bbzon.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/305775/original/file-20191209-90569-16bbzon.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=451&fit=crop&dpr=1 600w, https://images.theconversation.com/files/305775/original/file-20191209-90569-16bbzon.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=451&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/305775/original/file-20191209-90569-16bbzon.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=451&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/305775/original/file-20191209-90569-16bbzon.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=567&fit=crop&dpr=1 754w, https://images.theconversation.com/files/305775/original/file-20191209-90569-16bbzon.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=567&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/305775/original/file-20191209-90569-16bbzon.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=567&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 The Bradford Beck flows through – but mostly beneath – the city.

Rivers were put in culverts partly to contain the smell. Bradford grew from a town of 15,000 in 1800 to 100,000 by 1860 as it became the richest city in England on the back of the wool trade, yet the first mile of public sewer was not laid until 1862 and first sewage works not completed until a decade later. Until then much of the sewage and industrial waste ended up in the Beck or canal which must have smelt appalling – it is said the canal was so putrid that it could be set on fire.

Rivers were also put in culverts to make flat land available. Buildings were constructed over the river itself, combined with raising the boggy land of the flood plain with ashes and other wastes. In Bradford at least, most of the culverts are under buildings rather than roads or public spaces. They often have a wall down the centre of the river, indicating that the two owners built out to the edge of their property.

Culverts were mostly built by the Victorians

"Daylighting" is the action of returning a culverted river to open water. At its simplest it is taking the lid off the culvert, but most designs aim to create a more natural river shape and re-introduce ecological habitats.

It makes sense to do this now that the benefits of Victorian-era culverting have given way to modern problems of old age, pollution, capacity and blockage, and the loss of the pleasure of water. No engineering structure will last for ever – culverts have to be maintained and eventually replaced if the buildings and infrastructure above are to be safe.

Victorian culverts were built when cities were smaller and less of the ground was paved. Nowadays flood runoff is much greater even before we consider climate change, but the culverts' flood capacity has not increased. This can have serious consequences, as in Newcastle a few years ago when an overwhelmed culvert collapsed and washed out the foundations of two blocks of flats built over it. An open river will have a higher flood capacity than a culvert, and a slight overflow certainly won't have the catastrophic consequences of a blockage or collapse.

Culverts also help conceal pollution sources. For example, Bradford has more than 50 sewer overflows and many more frequently unmapped drains from roads and factories. Most of these discharge into culverts without anyone seeing them.

It is not surprising that there is widespread pollution from misconnected drains and malfunctioning sewage infrastructure that we don't discover until the river eventually emerges downstream into the daylight. This problem is definitely not unique to Bradford or to the UK. If rivers were daylighted and visible the pollution would more obvious and easier to fix.

Dawn of daylighting

Colleagues and I have been researching the impact of "deculverting" for a over a decade now, most recently in a review of evidence published in 2018.

In the 96 urban projects the review looked at, daylighting was mostly driven by a desire to create new habitats, to reduce flood risk, provide new amenities and as part of regeneration projects. Water gives a sense of place in a city, and often becomes to focus for civic activities. Wildlife will return to the city – even if it is just ducks.

Many successful daylighting projects have been suburban or parkland sites such as the opening of 900 metres of the River Alt in Liverpool. Major urban daylighting projects are rarer – the opening of the Roch in the centre of Rochdale to reveal the river and a 14th-century bridge is a notable recent example.

One particularly impressive example is the Saw Mill River in Yonkers, a suburb of New York City, where US$34 million was allocated to opening the river to create a public park and habitat for migratory fish. Consequential redevelopment along the new corridor is reshaping the city.

A lovely small example is the creation of a pocket park on the Porter Brook in Sheffield, costing a more modest £400,000. As a senior Sheffield City Council official said to me, having this completed example has made it easier to explain the idea and value of daylighting to developers, and further projects are now planned in the city.

Earlier generations culverted – and killed – their rivers for reasons which were good at the time. But times have changed. Daylighting offers the opportunity to reduce flood risk and bring water and nature back to towns and cities.

David Lerner discussed his "daylighting rivers" research on a recent episode of BBC Radio 4's Start the Week.

David N Lerner has received funding from EPSRC, NERC, BBSRC, EU, the Environment Agency and various water utilities. He is a trustee of the Aire Rivers Trust and the Chair of the Friends of Bradford's Becks.
 The Victorians placed rivers in underground culverts to contain the smell and create new land for buildings. David N Lerner, Emeritus Professor of Environmental Engineering, University of Sheffield Licensed as Creative Commons – attribution, no derivatives. tag:theconversation.com,2011:article/127010 2019-11-26T18:40:37Z 2019-11-26T18:40:37Z 'New Bradfield': rerouting rivers to recapture a pioneering spirit

Waters from the Herbert River, which runs toward one of northern Australia's richest agricultural districts, could be redirected under a Bradfield scheme. Patrick White, Author provided

The "New Bradfield" scheme is more than an attempt to transcend environmental reality. It seeks to revive a pioneering spirit and a nation-building ethos supposedly stifled by the bureaucratic inertia of modern Australia.

This is not a new lament. Frustrated by bureaucracy, politicians in North Queensland have long criticised the slow pace of northern development.

   Read more: You can't boost Australia's north to 5 million people without a proper plan

In 1950, northern local governments blamed urban lethargy. One prominent mayor complained:

… these young people lack the pioneering spirit of their forebears, preferring leisure and pleasure to hardships and hard work.

These sentiments were inspired by an agrarian nostalgia that extolled toil and toughness. Stoic responses to the challenges of life on the land are part of the Australian legend.

With drought devastating rural and urban communities and a state election looming in Queensland in 2020, both sides of politics have proposed a "New Bradfield" scheme.

An idea with 19th-century origins

Civil engineer John Bradfield devised the original scheme in 1938. His plan would swamp inland Australia by reversing the flow of North Queensland's rivers. Similar proposals go back to at least 1887, when geographer E.A. Leonard recommended the Herbert, Tully, Johnstone and Barron rivers be turned around to irrigate Australia's "dead heart".

 <img alt="" src="https://images.theconversation.com/files/302057/original/file-20191117-66921-mj64sz.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/302057/original/file-20191117-66921-mj64sz.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/302057/original/file-20191117-66921-mj64sz.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/302057/original/file-20191117-66921-mj64sz.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/302057/original/file-20191117-66921-mj64sz.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/302057/original/file-20191117-66921-mj64sz.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/302057/original/file-20191117-66921-mj64sz.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 Blencoe Falls, on a tributary of the Herbert River, North Queensland, during the dry season. Patrick White, Author provided

As the "dead heart" became the "Red Centre" in the 1930s, populist writers revived the dreams of big irrigation schemes.

These schemes have always been contested on both environmental and economic grounds. A compelling history of Bradfield's proposal reveals many errors and miscalculations. But what the scheme lacked in substance it made up for in grandiose vision.

Water dreaming has been a powerful theme in Australian history. The desire to transform desert into farmland retains appeal and discredited schemes like Bradfield keep reappearing.

   Read more: The keys to unlock Northern Australia have already been cut

Contempt for nature and country

While less ambitious than the original plan, the "New Bradfield" scheme still engineers against the gradient of both history and nature. It would have irreversible consequences for Queensland's environment, society and culture.

What's more, the new scheme manifests much the same mindset as the old.

It's an attitude that privileges the conquest of nature: in this case literally up-ending geography by turning east-flowing rivers westward. Its celebration of the human struggle against defiant nature reprises the pioneering ethos.

Like many pioneers, "New Bradfield" proposals disregard the interests and land-management practices of Indigenous people. The bushfires ravaging the eastern states show the folly of ignoring traditional ways of caring for country .

Overlooking native title realities can also cost governments and communities.

   Read more: Remote Indigenous Australia's ecological economies give us something to build on

Polarising debate neglects more viable projects

"New Bradfield" is promoted as "an asset owned by all Queenslanders for all Queenslanders". But environmental destruction and disputes over water sales in the Murray-Darling Basin sound a warning.

The Queensland Farmers Federation has cautiously welcomed the new scheme. Others have dismissed it as a "pipe dream".

Thus, northern Australia again sits amid a polarised debate about its utility to the nation. Such polarising contests diminish the likelihood of more viable projects being implemented.

Extravagant expectations of "untapped" northern resources have been proffered for nearly two centuries. Distant governments have fantasised the Australian tropics as a land of near-limitless potential. Northern communities have many times been disappointed by the results.

Today's promises to "drought-proof" large areas of Queensland rely on similar images. "Drought-proofing" aims to keep people on the land but often defies economic and social reality.

   Read more: We can't drought-proof Australia, and trying is a fool's errand

Dam developments have an underwhelming record

The "New Bradfield" rhetoric echoes the inflated expectations of myriad disappointing northern development plans in the past. The Ord River project was touted as an agricultural wonder that would put hundreds of thousands of farmers into the Kimberley. Its success lies forever just over the horizon.

Much closer to the present proposal is the Burdekin Falls Dam. It sits in the lower reaches of the same river earmarked for the Hells Gates Dam that would feed the "New Bradfield" scheme. Damming Hells Gates has been advocated since at least the 1930s and has new supporters.

 <img alt="" src="https://images.theconversation.com/files/302055/original/file-20191117-66921-zna3a6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/302055/original/file-20191117-66921-zna3a6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/302055/original/file-20191117-66921-zna3a6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/302055/original/file-20191117-66921-zna3a6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/302055/original/file-20191117-66921-zna3a6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/302055/original/file-20191117-66921-zna3a6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/302055/original/file-20191117-66921-zna3a6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 The proposed site for Hells Gates Dam is on Gugu Badhun country on the Burdekin River. Dr Theresa Petray, Author provided

Back in the 1950s, damming the Burdekin was expected to generate hydro-electric power and irrigate vast swathes of farmland. After decades of political squabbling, the dam was completed in 1988. It does not generate hydro power. Although it irrigates some land downstream, the anticipated huge agricultural expansion never happened.

The Burdekin Falls Dam has helped the regional economy and could help to overcome the water shortages of the nearby city of Townsville. But it has not met the inflated expectations widely proffered decades earlier. The benefits that would flow from another dam further upstream are likely to be even more meagre.

   Read more: Damming northern Australia: we need to learn hard lessons from the south

Grandiose visions of northern development have a habit of failing. A "New Bradfield" scheme, animated by an old pioneering ethos, is unlikely to be different.

Drought-affected communities would derive more benefit from sober proposals that acknowledge the past, integrate Indigenous knowledge and incorporate agricultural innovation.

Patrick White receives funding from an Australian Government Postgraduate Award.

Janine Gertz's PhD Doctoral research was funded by a JCU Australian Postgraduate Award and a JCU Prestige Indigenous Research Award. Janine provides administrative support to the Gugu Badhun Aboriginal Corporation RNTBC. Gugu Badhun Aboriginal Nation is participating in a Nation-Building research project "Prerequisite conditions for Indigenous nation self-government" which is funded by an ARC Discovery Grant, led by the Jumbunna Institute for Indigenous Education and Research, University of Technology Sydney. Gugu Badhun is also a research partner on a native food project with the ARC Training Centre for Uniquely Australian Foods, University of Queensland.

Russell McGregor does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
 The 'New Bradfield' scheme seeks to revive a nation-building ethos supposedly stifled by bureaucratic inertia. But there are good reasons the scheme never became a reality. Patrick White, PhD Candidate in History and Politics, James Cook University Russell McGregor, Adjunct Professor of History, James Cook University Licensed as Creative Commons – attribution, no derivatives. tag:theconversation.com,2011:article/125323 2019-11-14T15:31:21Z 2019-11-14T15:31:21Z Botswana's Okavango Delta is created by a delicate balance, but for how much longer?

The Delta's rich array of wildlife makes it a popular tourist destination Ger Metselaar/Shutterstock

The Okavango Delta in northern Botswana is a mosaic of water paths, floodplains and arid islands. The delta sits in the Okavango river basin, which spans three African countries: Angola, Namibia and Botswana.

Because it's an oasis, in a semi-arid area, it hosts a rich array of plants and attracts a huge variety of wildlife.

As a unique ecosystem, in 2014 it was placed on UNESCO's World Heritage list and it is an iconic tourist destination, which generates 13% of Botswana's GDP.

 <img alt="" src="https://images.theconversation.com/files/298349/original/file-20191023-119438-prx01q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/298349/original/file-20191023-119438-prx01q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=401&fit=crop&dpr=1 600w, https://images.theconversation.com/files/298349/original/file-20191023-119438-prx01q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=401&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/298349/original/file-20191023-119438-prx01q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=401&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/298349/original/file-20191023-119438-prx01q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/298349/original/file-20191023-119438-prx01q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/298349/original/file-20191023-119438-prx01q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 Aerial view of the Okavango Delta. Vadim Petrakov/Shutterstock

But it's a fragile natural area. It's controlled by deformations of the Earth's crust over a long time (thousands to millions of years) and by annual water flows and evaporation. The size of the flooded delta from year to year varies between 3,500km² and 9,000km² because of weather fluctuations which control its water supply.

Any change to the processes that form the delta will have an impact on the wildlife and local economic activities. Its grassy floodplains are food for grazing animals in the dry period. Losses of this habitat will cause declines in wildlife and livestock. It's therefore imperative to understand what creates and sustains the delta for the future management of the system.

We have conducted several studies that cover how the Okavango basin was formed and the way dissolved chemicals are withdrawn from the delta's surface.

The dynamic history of the Okavango Delta's waterways and floodplains tells us that the interplay between geology, water and plants makes the delta resilient, but vulnerable.

Some imminent changes are expected that are of concern. One is higher temperatures, which will boost evaporation and transpiration. Another is the pumping of water for irrigation in Namibia. Both of these changes will reduce the water needed to sustain the delta's floodplains.

An oasis

The Okavango Delta is a generally flat area which is under constant change with phases of flooding and drying. A variety of geographical and natural processes have formed it and sustain it.

It's in a depression which was created by fault lines cutting the Earth's surface. This means water flows into it. The fault lines are created by the spread of the East African Rift – a major fracture, created over millions of years, which crosses the eastern part of Africa.

The origin of the islands in the delta is attributed to two mechanisms: the construction of termite mound spires; and formation of elevated ridges where former channels deposited sand. Both act as the starting point for vegetation to take root.

 <img alt="" src="https://images.theconversation.com/files/298350/original/file-20191023-119419-mp4xtl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/298350/original/file-20191023-119419-mp4xtl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=402&fit=crop&dpr=1 600w, https://images.theconversation.com/files/298350/original/file-20191023-119419-mp4xtl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=402&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/298350/original/file-20191023-119419-mp4xtl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=402&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/298350/original/file-20191023-119419-mp4xtl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=505&fit=crop&dpr=1 754w, https://images.theconversation.com/files/298350/original/file-20191023-119419-mp4xtl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=505&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/298350/original/file-20191023-119419-mp4xtl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=505&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 Termite mound in the delta. PIXEL to the PEOPLE/Shutterstock

The water supply comes from the Cubango and Cuito rivers in Angola. This reaches the delta between March and June and peaks in July. There's also local rainfall in the Okavango area from November to February (about 450mm a year) which adds to this.

About 98% of the water that goes into the delta is eventually lost through evaporation and plant transpiration, when water moves through the plant and evaporates from leaves, stems and flowers.

Even though the subtropical sun generates intense evaporation, the delta's water is fresh, not salty. This is surprising because water samples from the middle parts of the islands have very high chemical and salt concentrations. This chemical concentration occurs in thousands of islands.

The reason the water is fresh is that trees on the edges of the islands have created a barrier of natural filters between the inner part of the islands and the floodplain.

Possible changes

The Okavango Delta is continually being shaped by complex interactions of natural processes. If something happens to change the balance of these processes, it could destabilise the system.

The most important dynamic for the delta is inflowing water. The two main rivers in Angola, the Cubango and the Cuito, join to form the Okavango river, which feeds the delta. These two rivers are hydrologically quite different. The Cubango, to the west, first flows rapidly down steep, narrow paths characterised by incised valleys, rapids, waterfalls and valley swamps. The Cuito, to the east, with shallow valleys and large floodplains, gets its water from groundwater seepage.

The manipulation of these rivers – in the form of dams and irrigation – will affect the water flow and change its annual distribution. Both of these form part of current and future development planning in Angola and Namibia.

A decrease in water supply will affect the vegetation growth and the wildlife. An increase in water would inundate the islands and could dissolve the salts at the centre of them, releasing chemical elements that would change the water quality.

In addition to declines in water flow induced by global warming and human activities, ground deformation is also happening because of shifting continental plates. This could change the paths of the water flowing by changing the ground slopes. Measurements of ground deformation with Global Positioning Systems displays reveal very slight changes in local slopes that can modify the paths of the water flowing to the delta.

To sustain the Okavango Delta it's imperative that management integrate all the components of the system. All governments are involved and must integrate scientific expertise, from upstream catchment to downstream Delta.

Michael Murray-Hudson receives funding from the University of Botswana for monitoring island groundwater and earth surface deformation in the Okavango Delta.

Olivier Dauteuil a reçu des financements de l'université de Rennes 1 et du CNRS.
 It's imperative that we understand what creates and sustains the delta for the future management of the system. Michael Murray-Hudson, Senior Research Fellow, Okavango Research Institute, University of Botswana Olivier Dauteuil, Directeur de Recherche au CNRS, Université Rennes 1 Licensed as Creative Commons – attribution, no derivatives. tag:theconversation.com,2011:article/125088 2019-11-01T09:53:39Z 2019-11-01T09:53:39Z River deltas are 'drowning', threatening hundreds of millions of people

The Ganges delta spans India and Bangladesh and is home to more than 100m people. Elena11 / shutterstock

The world's river deltas take up less than 0.5% of the global land area, but they are home to hundreds of millions of people. Many live in major fast-growing cities such as Kolkata in the Ganges delta, Bangkok in the Chao Phraya delta, or Shanghai, one of dozens of large cities in the Yangtze delta region.

With fertile soils and easy access to the coast, deltas are critical hotspots of food production. Vietnam's Mekong delta alone supplies almost 20% of the world's rice. They also host unique ecosystems such as the Sundarbans in Bangladesh and India, the largest mangrove forest in the world.

But many of the world's deltas are now facing an existential crisis. Sea levels are rising as a result of climate change, while deltas are themselves sinking, and together this means the relative sea level is rising extra fast.

Deltas are built from sediments that are carried downstream by rivers and eventually deposited where the river meets the sea. As these sediments compact under their own weight, deltas naturally sink. Where left undisturbed, the supply of new river sediment can compensate for the subsidence and help to maintain the delta surface above sea level.

But deltas are now subsiding much faster than they would do naturally. That's thanks to groundwater being pumped (or "mined") from aquifers underneath them and used to irrigate crops and provide water for rapidly growing cities.

In these circumstances, only the continued deposition of sediment on deltas can keep them from "drowning". We therefore wanted to find out whether supplies of river sediments would be affected by future environmental changes.

To address this question, we used a computer model to project changes in the flows of sediment to almost 50 major deltas worldwide. We used the model to explore the impact of various environmental changes, including climate change, population growth, increases in wealth and the construction of dams. Our results are published in the journal Environmental Research Letters.

 <img alt="" src="https://images.theconversation.com/files/299461/original/file-20191030-17924-jr9bnl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/299461/original/file-20191030-17924-jr9bnl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=380&fit=crop&dpr=1 600w, https://images.theconversation.com/files/299461/original/file-20191030-17924-jr9bnl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=380&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/299461/original/file-20191030-17924-jr9bnl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=380&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/299461/original/file-20191030-17924-jr9bnl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=478&fit=crop&dpr=1 754w, https://images.theconversation.com/files/299461/original/file-20191030-17924-jr9bnl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=478&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/299461/original/file-20191030-17924-jr9bnl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=478&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 Rice farmers in the Mekong Delta, Vietnam. Phuong D. Nguyen / shutterstock

We found that most of the world's major deltas will receive less river sediment by the end of the century, regardless of the environmental change scenario. On average, we projected a 38% decrease. Our results suggest that many deltas – already significantly stressed – will become sediment starved, further compounding the risks of rising relative sea levels.

Some of the most severe reductions will be found in major Asian deltas such as the Ganges (81% less sediment) and the Mekong (77%). This is particularly concerning because these deltas are among the largest and most densely populated in the world.

We found that climate change will generally drive a small increase in the flows of sediments as, among other factors, warmer temperatures lead to increased precipitation and more soil is washed into rivers. But in many deltas this modest uptick will be more than offset by dams (which trap river sediments) and improved soil conservation practices as societies become wealthier. The Aswan Dam on the River Nile in Egypt or the Hoover Dam on the Colorado River in the US are among the dams that have already starved their downstream deltas of sediment.

 <img alt="" src="https://images.theconversation.com/files/299459/original/file-20191030-17893-18jv875.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/299459/original/file-20191030-17893-18jv875.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/299459/original/file-20191030-17893-18jv875.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/299459/original/file-20191030-17893-18jv875.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/299459/original/file-20191030-17893-18jv875.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/299459/original/file-20191030-17893-18jv875.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/299459/original/file-20191030-17893-18jv875.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 Bad news for a river delta. Tupungato / shutterstock

Better management of river sediment is vital to improve the outlook for the world's deltas. International cooperation will be essential in deltas such as the Mekong and Ganges which are supplied by large rivers that drain many countries. For dams specifically, comprehensive environmental risk assessments that fully cost the consequences for downstream regions are required so that plans can be changed or scrapped. For those dams that are to be built in the coming decades, their design must accommodate transport of sediment downstream.

For authorities within deltas, faced with managing a dwindling supply of river sediment, new approaches are needed to better manage this precious declining resource. Flood embankments prevent sediment reaching delta plains and may need to be breached, as is being explored in the Ganges delta. Additionally, the removal of sand from rivers for construction materials, which is pervasive in many deltas around the world, must be better managed.

Ultimately, difficult decisions need to be made about development priorities between countries upstream of deltas and those including the deltas themselves, and there will be trade-offs to be made between hydropower, agricultural practices and delta sustainability.

Frances Eleanor Dunn received funding from the Southampton Marine and Maritime Institute.

Stephen Darby receives funding from the United Kingdom Natural Environment Research Council
 Sea levels are rising, while deltas are being starved of sediment by upstream dams. Frances Eleanor Dunn, Researcher in Earth Sciences, Utrecht University Stephen Darby, Professor of Physical Geography, University of Southampton Licensed as Creative Commons – attribution, no derivatives. tag:theconversation.com,2011:article/124845 2019-10-15T15:24:54Z 2019-10-15T15:24:54Z How tiny creatures are reshaping the very rivers they live in

Caddisfly larvae rearrange pebbles on the river bed to build themselves a shelter. FJAH / shutterstock

What shapes a river? People typically imagine large-scale processes such as storms and floods or human modifications like dams or fortified banks. But the shape of our rivers today is also a result of the cumulative impact of millions of tiny invertebrates, often small enough that most people don't even notice them.

"Zoogeomorphology" is the study of how animals effect their physical environment, such as by moving sediment or modifying the habitat. The zoogeomorphic effects of larger organisms are easily seen. For example, when a beaver builds a dam it retains water, creating diverse wetlands upstream and sometimes helping to reduce flooding downstream. Fish also alter the river, turning over gravels while feeding and spawning.

The individual impacts of invertebrates are much smaller but, collectively, they can make a big difference. Charles Darwin recognised this as early as 1881 in his snappy-titled "The Formation of Vegetable Mould through the Action of Worms, with Observations on their Habits", and the same is true in rivers. This army of small engineers is changing river environments, and we are part of a research group that is working out exactly how.

Here are three small creatures we already know are having a big impact:

1) Crayfish – burrowing banks

Signal crayfish are freshwater crustaceans, similar in shape to lobsters but only about the size of an iPhone. Signal crayfish were introduced to the UK in the 1970s to be farmed for food. But after a series of escapes, the species is now widespread, with no known methods for eradication. Signal crayfish are having detrimental impacts on the ecology of rivers. They feed largely on aquatic plants and native invertebrates, consequently modifying the species of native fauna and flora present. Furthermore, via competition and spreading crayfish plague, signal crayfish are destroying populations of native white-clawed crayfish.

 <img alt="" src="https://images.theconversation.com/files/297090/original/file-20191015-98678-11u4saw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/297090/original/file-20191015-98678-11u4saw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=528&fit=crop&dpr=1 600w, https://images.theconversation.com/files/297090/original/file-20191015-98678-11u4saw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=528&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/297090/original/file-20191015-98678-11u4saw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=528&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/297090/original/file-20191015-98678-11u4saw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=663&fit=crop&dpr=1 754w, https://images.theconversation.com/files/297090/original/file-20191015-98678-11u4saw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=663&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/297090/original/file-20191015-98678-11u4saw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=663&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 An invasive signal crayfish hiding in its burrow in Leicestershire, England. Harry Sanders, Author provided

Signal crayfish are also dramatically changing the river environment. In the UK, they burrow into clay banks, causing bank failure, bringing down buildings and infrastructure. For example, the burrowing into earth dams at Prior Park Landscape Gardens in Bath has necessitated repairs costing millions of pounds. Crayfish burrowing also adds vast quantities of clay into the river which clogs gravel-beds and is bad news for fish who like to spawn in gravel.

2) Mussels – gluing gravels

Mussels filter the water they live in, removing sediment and organic detritus. Native freshwater mussels are keystone species, facilitating higher populations of other invertebrates. However, invasive mussels are causing problems.

 <img alt="" src="https://images.theconversation.com/files/297089/original/file-20191015-98670-ezbed2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/297089/original/file-20191015-98670-ezbed2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=802&fit=crop&dpr=1 600w, https://images.theconversation.com/files/297089/original/file-20191015-98670-ezbed2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=802&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/297089/original/file-20191015-98670-ezbed2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=802&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/297089/original/file-20191015-98670-ezbed2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1008&fit=crop&dpr=1 754w, https://images.theconversation.com/files/297089/original/file-20191015-98670-ezbed2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1008&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/297089/original/file-20191015-98670-ezbed2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1008&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 Quagga mussels attach themselves to river gravels and each other. River Wraysbury, England. Harry Sanders, Author provided

Zebra mussels, originally from Russia and the Ukraine, are prolific breeders and have now spread across Europe and into the Great Lakes of the US and Canada, where they are blocking pipes and costing American water and electric companies an estimated $17.8m each year.

The zebra mussel was first found in the UK in 1825 but has seen a recent rapid expansion, and lately its larger cousin, the quagga mussel has arrived. These mussels attach themselves to river gravels, native mussels, and each other, creating a dense mesh of mussels. This effectively solidifies the river bed, reducing the quality of the habitat for other animals.

3) Caddisfly – sticking stones

Caddisflies are an incredibly diverse group of aquatic insects, with nearly 200 species in the UK alone. Their larvae produce silk, similar to spiders, except it is sticky underwater, and many species use it to construct silk nets much like spider webs. Caddisflies string these nets between stones in order to catch particles of food moving down the river.

 <img alt="" src="https://images.theconversation.com/files/297092/original/file-20191015-98632-1ral7gd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/297092/original/file-20191015-98632-1ral7gd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/297092/original/file-20191015-98632-1ral7gd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/297092/original/file-20191015-98632-1ral7gd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/297092/original/file-20191015-98632-1ral7gd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/297092/original/file-20191015-98632-1ral7gd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/297092/original/file-20191015-98632-1ral7gd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 Caddisfly nets. Matthew Johnson, Author provided

These nets also act to tie river gravels together. This results in more stable patches of gravel, reducing erosion and possibly providing a safe refuge for other invertebrates in floods. Caddisfly larvae are smaller than a thumbnail, however they are often found in extremely high numbers with many thousands of individuals per square metre of river bed. This abundance, coupled with their extraordinary use of silk, means they can affect the geomorphology of rivers.

In addition to building nets, many species of caddisfly larvae construct "cases" to protect them from predator fish, both as larvae and when pupating (transforming into flies). To build these cases, larvae use silk to stick together everything from gravel to very fine sand and bits of plants. By transporting this sand around the river bed, tiny caddisflies may impact much larger physical processes, such as the transport of sand downstream.

 <img alt="" src="https://images.theconversation.com/files/297196/original/file-20191015-98670-mgc088.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/297196/original/file-20191015-98670-mgc088.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=393&fit=crop&dpr=1 600w, https://images.theconversation.com/files/297196/original/file-20191015-98670-mgc088.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=393&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/297196/original/file-20191015-98670-mgc088.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=393&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/297196/original/file-20191015-98670-mgc088.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=494&fit=crop&dpr=1 754w, https://images.theconversation.com/files/297196/original/file-20191015-98670-mgc088.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=494&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/297196/original/file-20191015-98670-mgc088.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=494&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 Caddisfly 'cases' on algae covered stones in a laboratory flume (indoor river) at Loughborough University River Science laboratory. Richard Mason, Author provided

Aquatic invertebrates, such as the three considered above, may be small but they can shape the landscape around them. We need to better understand these zoogeomorphic effects because without them we cannot predict how rivers will change over time, including in response to climate change.

In the case of invasive creatures such as signal crayfish and zebra mussels, it is important to prevent their spread not only to protect native species, but to prevent the invaders changing their habitat for the worse. However, native species may be key to the restoration of rivers.

Richard Mason receives funding from the Natural Environment Research Council (NERC) to conduct his PhD research on caddisfly.

Harry Sanders does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
 Rivers are shaped by storms, floods, humans and... aquatic invertebrates. Richard Mason, PhD Researcher, River Zoogeomorphology, Loughborough University Harry Sanders, PhD Researcher, Zoogeomorphology, Loughborough University Licensed as Creative Commons – attribution, no derivatives. tag:theconversation.com,2011:article/124743 2019-10-09T12:51:02Z 2019-10-09T12:51:02Z Curious Kids: why is the sea salty?

  Grant Elliott/Unsplash., FAL

Why is the sea salty? – Torben, aged nine, Sussex, UK.

Two-thirds of the Earth's surface is covered in water, and 97% of that is salty seawater. Only 3% of our planet's water is fresh, and 2% is trapped, frozen in ice caps, glaciers and soils. That leaves less than 1% as fresh, liquid water in rivers, lakes and streams – and this fresh water plays a big role in explaining why the sea is salty.

Water moves around our planet in a cycle powered by the sun: from the sea, to the sky, to the land and then back to the sea. When the sun heats the water in the sea, it changes into a gas called "water vapour" and rises into the air, through a process called "evaporation".

 <img alt="" src="https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/282267/original/file-20190702-126345-1np1y7m.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">

Curious Kids is a series by The Conversation, which gives children the chance to have their questions about the world answered by experts. If you have a question you'd like an expert to answer, send it to firstname.lastname@example.com. We won't be able to answer every question, but we'll do our very best.

While floating in the air, the water vapour cools off and turns back into liquid water, forming clouds (through a process called "condensation"). This water eventually falls from the clouds in the sky as rain, sleet, hail or snow (that's called "precipitation").

 <img alt="" src="https://images.theconversation.com/files/296200/original/file-20191009-3887-1r501t4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/296200/original/file-20191009-3887-1r501t4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/296200/original/file-20191009-3887-1r501t4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/296200/original/file-20191009-3887-1r501t4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/296200/original/file-20191009-3887-1r501t4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/296200/original/file-20191009-3887-1r501t4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/296200/original/file-20191009-3887-1r501t4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 The water cycle in action. Vikas Anand Dev/Unsplash., FAL

When precipitation falls on land, the water flows into streams and rivers, and eventually makes its way back out to the sea. Then the sun heats the sea water and the cycle starts all over again.

(Slightly) acid rain

You're probably still wondering where the salt comes in. Well, the rain that falls from the sky is not just pure water – it actually contains small amounts of chemicals called carbon dioxide and sulphur dioxide, which are absorbed by the water while it is still in the air.

This means that rain is actually very slightly acidic (but not enough to do you any harm). When the rain falls on the ground, this weak acid can dissolve small amounts of mineral salts from the rocks, including sodium and chloride, which then enter the water.

 <img alt="" src="https://images.theconversation.com/files/296199/original/file-20191009-3872-1bof5jj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/296199/original/file-20191009-3872-1bof5jj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=429&fit=crop&dpr=1 600w, https://images.theconversation.com/files/296199/original/file-20191009-3872-1bof5jj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=429&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/296199/original/file-20191009-3872-1bof5jj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=429&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/296199/original/file-20191009-3872-1bof5jj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=539&fit=crop&dpr=1 754w, https://images.theconversation.com/files/296199/original/file-20191009-3872-1bof5jj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=539&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/296199/original/file-20191009-3872-1bof5jj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=539&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 Run, river, run. Matt Heaton/Unsplash., FAL

Sodium chloride is the main salt in seawater, and the same one you might have on your table at home. The rain water flows off the land and into the rivers and streams that lead all the way to the sea – carrying the dissolved salts along with it.

Salinity in streams?

But if the rivers and streams are carrying these dissolved salts, then why aren't they as salty as the sea? In fact, they're only carrying very low levels of these salts. The salts in the seas have built up over billions of years, and seawater contains about 300 times more dissolved salts than average river water.

To put it another way, every one litre of seawater has 35 grams of salts dissolved in it, while a litre of freshwater would only have 0.5 grams. That's why we say that seawater has a much higher concentration of salt – or "salinity" – than the freshwater flowing through rivers and streams.

Some salts can also enter the seas from hot vents on the deep ocean floor and from volcanoes on the land and in the sea. Some salts (particularly chloride) are also moved around as part of the water cycle – these are known as "cyclic salts" and originally came from volcanoes.

Tipping the balance

Since salt is always flowing from the land to the sea, you might think the sea is getting saltier. But actually, some of this salt is removed by algae and animals that live in the sea, and some is deposited as sediment on the bottom of the ocean. So the salt going into the sea keeps a balance with the salt being deposited or removed.

The salinity of the sea isn't the same everywhere. In warmer, tropical areas, more evaporation occurs, so the water is saltier. Towards the north and south poles, the seawater is diluted by melting ice, so the water is not so salty. This is natural.

 <img alt="" src="https://images.theconversation.com/files/296205/original/file-20191009-3856-1r1vi0u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/296205/original/file-20191009-3856-1r1vi0u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/296205/original/file-20191009-3856-1r1vi0u.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/296205/original/file-20191009-3856-1r1vi0u.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/296205/original/file-20191009-3856-1r1vi0u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/296205/original/file-20191009-3856-1r1vi0u.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/296205/original/file-20191009-3856-1r1vi0u.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 Melting sea ice. Roxanne Desgagnés/Unsplash., FAL

But these differences in salinity might get bigger in the future, because of climate change. Warmer climates may lead to more rain and melting ice in the northern hemisphere, and more evaporation in the southern hemisphere, which could change the saltiness of our seas.

The saltier that water is, the more dense (or heavier) it becomes. Along with warmer temperatures, this could affect how water moves around in the oceans, which could affect all life on our planet – not just the creatures living in the sea.

This article has been updated to reflect the fact that sodium and chloride ions separate out when dissolved in water.

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Sally Little does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
 The salt in the sea has built up over billions of years – but it wouldn't have got there without freshwater rivers and streams. Sally Little, Senior Lecturer in Ecology, Nottingham Trent University Licensed as Creative Commons – attribution, no derivatives. tag:theconversation.com,2011:article/120801 2019-09-17T12:49:30Z 2019-09-17T12:49:30Z Caribbean fish love catastrophic hurricanes
Hurricanes like Dorian and Maria may be disastrous for humans and their property, but some fish have actually evolved to thrive in severe weather.

Our team of scientists studied how extreme weather events affect river fish in Puerto Rico. The island is ideal for examining the environmental and human impacts on freshwater fish because Puerto Rico has only nine native species and, unlike smaller Caribbean islands, many inland rivers – 46, to be exact.

Numerous exotic fish, introduced by humans over the past century, compete for limited food and habitat with Puerto Rican species like the waterfall-climbing sirajo goby, the streamlined mountain mullet and the bigmouth sleeper, a top river predator.

 <img alt="" src="https://images.theconversation.com/files/285728/original/file-20190725-136744-15oadbf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/285728/original/file-20190725-136744-15oadbf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=544&fit=crop&dpr=1 600w, https://images.theconversation.com/files/285728/original/file-20190725-136744-15oadbf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=544&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/285728/original/file-20190725-136744-15oadbf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=544&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/285728/original/file-20190725-136744-15oadbf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=683&fit=crop&dpr=1 754w, https://images.theconversation.com/files/285728/original/file-20190725-136744-15oadbf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=683&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/285728/original/file-20190725-136744-15oadbf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=683&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 The native Caribbean mountain mullet (top) has evolved to survive floods. The sedentary red devil cichlid, a fish native to Nicaragua but now present in Puerto Rico's lakes and rivers, is better suited to drought. Tom Kwak, Author provided

Because these same native fish are found throughout the Caribbean, their conservation is an important environmental priority for the region. Native fishes are perfectly adapted to their environment and provide services to humans, such as food and nutrient transport. Their presence indicates a healthy ecosystem and clean drinking water.

After Hurricane Maria hit the island in 2017, we discovered that nonnative species – and only the nonnative species – had been decimated by the storm.

Thousands of exotic fish, which are physically adapted to survive drought – not extremely high river flows and flooding – were flushed far downriver during Hurricane Maria, even into the ocean. Many died from blunt force trauma or exposure to salt water.

 <img alt="" src="https://images.theconversation.com/files/285729/original/file-20190725-136759-1lw6zjf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/285729/original/file-20190725-136759-1lw6zjf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=803&fit=crop&dpr=1 600w, https://images.theconversation.com/files/285729/original/file-20190725-136759-1lw6zjf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=803&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/285729/original/file-20190725-136759-1lw6zjf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=803&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/285729/original/file-20190725-136759-1lw6zjf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1010&fit=crop&dpr=1 754w, https://images.theconversation.com/files/285729/original/file-20190725-136759-1lw6zjf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1010&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/285729/original/file-20190725-136759-1lw6zjf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1010&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 The Espíritu Santo River after 2017's Hurricane Maria (top) and 18 months after. P. Gutierrez-Fonseca, Author provided

Native river fish, in contrast, were unaffected by the hurricane. Their body shape and behavior are designed to survive high, fast waters. Puerto Rican fish are actually hit hardest by drought, since they struggle to migrate for reproduction and to find food when waters are low.

Big hurricanes, in short, reset the balance in Puerto Rico's rivers, favoring native fish over imported species. The same would hold true in rivers across the Caribbean.

So which fish will win the battle for resources in Caribbean waters? The answer may change with the weather.

Climate predictions indicate that the Caribbean will experience both more catastrophic hurricanes and increased drought in the future.

With help from staff and graduate assistants Gus Engman, Bonnie Myers and Ámbar Torres, we are now conducting experiments to better understand the dynamics between native and exotic fishes in Puerto Rico. We plan to model the future balance between these species – and, hopefully, help keep the Caribbean's native fish swimming.

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Thomas J. Kwak is an employee of the U.S. Geological Survey and receives funding from the U.S. Geological Survey, U.S. Fish and Wildlife Service and the Puerto Rico Department of Natural and Environmental Resources.

Alonso Ramirez receives research funding from the National Science Foundation.
 Big storms with lots of flooding, like hurricanes Dorian and Maria, actually restore the Caribbean's delicate balance between native and nonnative fish species, new research finds. Thomas J. Kwak, Professor, Unit Leader, North Carolina State University Alonso Ramirez, Professor, North Carolina State University Licensed as Creative Commons – attribution, no derivatives. tag:theconversation.com,2011:article/118326 2019-07-16T11:41:58Z 2019-07-16T11:41:58Z As flood risks increase across the US, it's time to recognize the limits of levees

Water rushes through a breached levee on the Arkansas River in Dardanelle, Ark., May 31, 2019. Yell County Sheriff's Department via AP

New Orleans averted disaster this month when tropical storm Barry delivered less rain in the Crescent City than forecasters originally feared. But Barry's slog through Louisiana, Arkansas, Tennessee and Missouri is just the latest event in a year that has tested levees across the central U.S.

Many U.S. cities rely on levees for protection from floods. There are more than 100,000 miles of levees nationwide, in all 50 states and one of every five counties. Most of them seriously need repair: Levees received a D on the American Society of Civil Engineers' 2018 national infrastructure report card.

Levees shield farms and towns from flooding, but they also create risk. When rivers rise, they can't naturally spread out in the floodplain as they did in the pre-flood control era. Instead, they flow harder and faster and send more water downstream.

And climate models show that flood risks are increasing. During this year's unusually wet winter and spring, dozens of levees on the Missouri, Mississippi and Arkansas rivers were overtopped or breached by floodwaters. Across the central U.S., rivers are becoming increasingly hard to control.

 <img alt="" src="https://images.theconversation.com/files/284158/original/file-20190715-173366-2aosna.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/284158/original/file-20190715-173366-2aosna.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=232&fit=crop&dpr=1 600w, https://images.theconversation.com/files/284158/original/file-20190715-173366-2aosna.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=232&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/284158/original/file-20190715-173366-2aosna.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=232&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/284158/original/file-20190715-173366-2aosna.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=291&fit=crop&dpr=1 754w, https://images.theconversation.com/files/284158/original/file-20190715-173366-2aosna.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=291&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/284158/original/file-20190715-173366-2aosna.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=291&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 Levees exist in one out of every five U.S. counties. USACE

Remaking the Missouri

In my book, "A River in the City of Fountains," I describe the complexities of flood control in Kansas City, which sits at the junction of the Missouri and Kansas rivers.

The Missouri, the larger of these two, is America's longest river, rising in Montana's Rocky Mountains and flowing east and south for 2,341 miles until it joins the Mississippi River north of St. Louis. Historically it was wide and shallow, full of sand bars and snags that created challenges for steamboats.

In the late 19th and early 20th centuries, Kansas City business leaders began lobbying for federal navigation subsidies to counter the influence of the railroads. Until the river could be narrowed and deepened, navigation was unreliable. And without levees, industry in the floodplain was at risk.

 <img alt="" src="https://images.theconversation.com/files/279628/original/file-20190615-158925-1m47g6s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/279628/original/file-20190615-158925-1m47g6s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=632&fit=crop&dpr=1 600w, https://images.theconversation.com/files/279628/original/file-20190615-158925-1m47g6s.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=632&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/279628/original/file-20190615-158925-1m47g6s.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=632&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/279628/original/file-20190615-158925-1m47g6s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=794&fit=crop&dpr=1 754w, https://images.theconversation.com/files/279628/original/file-20190615-158925-1m47g6s.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=794&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/279628/original/file-20190615-158925-1m47g6s.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=794&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 Flooding in Kansas City's industrial West Bottoms in 1903. Library of Congress

Major floods inundated Kansas City in 1903, 1908, 1943 and 1951, leaving thousands homeless and causing heavy economic damage. These disasters convinced civic leaders that more than piecemeal navigation and flood control projects along the lower Missouri were needed.

In 1944 they got their wish when Congress passed the Flood Control Act, which authorized construction of dozens of dams nationwide. One section of the bill, the Missouri Basin Plan, sought to convert the entire Missouri into what historian Donald Worster calls an "ornate hydraulic regime," with five upstream dams for hydroelectric power, irrigation and recreation, as well as levees and a navigable barge channel from Sioux City to St. Louis.

Over the next decade engineers built levees and straightened and dredged the river channel. Upstream dams curbed the Missouri's spring rise. In August 1955, Life Magazine reported that "U.S. engineers have finally clinched their victory over the rampaging Missouri River. Flood control … is already bringing prosperity to the valley it drains."

 <img alt="" src="https://images.theconversation.com/files/283907/original/file-20190712-173360-o8i4dw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/283907/original/file-20190712-173360-o8i4dw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=134&fit=crop&dpr=1 600w, https://images.theconversation.com/files/283907/original/file-20190712-173360-o8i4dw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=134&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/283907/original/file-20190712-173360-o8i4dw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=134&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/283907/original/file-20190712-173360-o8i4dw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=168&fit=crop&dpr=1 754w, https://images.theconversation.com/files/283907/original/file-20190712-173360-o8i4dw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=168&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/283907/original/file-20190712-173360-o8i4dw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=168&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 'Achelous and Hercules,' painted by Thomas Hart Benton in 1947, evokes a struggle between Hercules and Achelous, the Greek river god. Benton, a Kansas City native, saw the legend as a parable for efforts to tame the Missouri River. Smithsonian American Art Museum, CC BY-ND

The limits of levees

Today Kansas City and many other U.S. river towns are fortified behind levees and floodwalls, but faith in the idea of engineered flood control is starting to erode.

Disastrous Midwest flooding in the summer of 1993, which killed 50 people and caused US$15 billion in damages, showed the limitations of this strategy. Floodwaters rose to unprecedented levels, eventually breaching or overtopping more than 1,000 levees.

After the waters ebbed, federal and state officials paid to move some homes and communities off floodplains to higher ground. However, this trend quickly reversed. By 2008, Missouri had authorized more than $2 billion of new development in zones that were flooded in 1993.

Many Kansas City residents still believe that higher, stronger levees will hold back future floods, and Congress has authorized millions of dollars to build them. But experienced engineers like retired Army Brigadier General Gerald Galloway, who coauthored a federal government assessment of the 1993 floods, warn that "there's no such thing as absolute protection."

For their part, many scientists and engineers have found that levees can exacerbate floods by pushing river waters to new heights. One 2018 study estimated that about 75% of increases in the magnitude of 100-year floods on the lower Mississippi River over the past 500 years could be attributed to river engineering.

What about commercial benefits from channeling rivers? Kansas City is still an economic hub, but railroads and highways have been more important than barges. The Missouri carries only a fraction of the tonnage shipped on other navigable rivers, such as the Mississippi, even though its channel has been expensively built and maintained for over 100 years.

High levees come at a high cost, often pushing water into communities that can't afford similar protection.

Rethinking river control

Levees also constrain cities' relationships with rivers, walling off any connections for purposes other than commerce. Author William Least Heat-Moon captured this paradox when he traveled across the U.S. by boat in the late 1990s and observed that "Kansas City, born of the Missouri, has turned away from its great genetrix more than almost any other river city in America."

More recently, however, Kansas City has begun to remember its interest and love for the Missouri. Riverside development and public spaces are fostering new physical and cultural interfaces with the river.

In my view, this year's floods should lead to more of this kind of rethinking. River towns can start by restricting floodplain development so that people and property will not be in harm's way. This will create space for rivers to spill over in flood season, reducing risks downstream. Proposals to raise and improve levees should be required to take climate change and related flooding risks into account.

Davenport, Iowa has embraced this approach. With a population of over 102,000, it is the largest U.S. river city without levees or a permanent floodwall. Instead Davenport has emphasized adapting to flooding by increasing public green spaces in the flood zone and elevating buildings that flank the Mississippi River.

Kansas City and other towns could advance this discussion by moving beyond strictly commercial visions of their waterways and considering this question: What does a healthy river of the future look like?

Amahia Mallea does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
 At a time when storms are becoming more frequent and severe, relying on levees for flood control can create as many problems as it solves. Amahia Mallea, Associate Professor of History, Drake University Licensed as Creative Commons – attribution, no derivatives. tag:theconversation.com,2011:article/119448 2019-07-10T12:09:30Z 2019-07-10T12:09:30Z Western states buy time with a 7-year Colorado River drought plan, but face a hotter, drier future

The white "bathtub ring" around Arizona's Lake Mead (shown on May 31, 2018), which indicates falling water levels, is about 140 feet high. AP Photo/Ross D. Franklin

As Midwest states struggled with record spring flooding this year, the Southwest was wrestling with the opposite problem: not enough water. On May 20, 2019, federal officials and leaders from seven states signed the Colorado River Drought Contingency Plan, a sweeping new water management agreement for this arid region.

The plan is historic: It acknowledges that southwestern states need to make deep water use reductions – including a large share from agriculture, which uses over 70% of the supply – to prevent Colorado River reservoirs from declining to critically low levels.

But it also has serious shortcomings. It runs for less than a decade, through 2026. And its name – "Drought Contingency Plan" – suggests a response to a temporary problem.

As scholars who have spent years researching water issues in the West, we know the Colorado River's problems are anything but temporary. Its waters have already been over-allocated, based on a century of false optimism about available supply. In other words, states have been allowed to take out more than nature puts back in.

Now the river is being further depleted by climate change-driven aridification. The next steps, post-2026, require a recognition that Arizona, Nevada and California will likely have to come to terms with permanent reductions in their Colorado River supply. For their part, Wyoming, Utah, Colorado and New Mexico must abandon dreams of taking ever-larger gulps from the Colorado River to support future growth.

 <img alt="" src="https://images.theconversation.com/files/283586/original/file-20190710-44505-23d60g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/283586/original/file-20190710-44505-23d60g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=776&fit=crop&dpr=1 600w, https://images.theconversation.com/files/283586/original/file-20190710-44505-23d60g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=776&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/283586/original/file-20190710-44505-23d60g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=776&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/283586/original/file-20190710-44505-23d60g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=976&fit=crop&dpr=1 754w, https://images.theconversation.com/files/283586/original/file-20190710-44505-23d60g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=976&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/283586/original/file-20190710-44505-23d60g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=976&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 The Colorado River historically flowed 1,450 miles from Colorado south into Mexico and then into the Gulf of California. For over 50 years it has failed to reach the ocean due to upstream diversions. USBR

Draining western reservoirs

The Drought Contingency Plan is an important step in that direction. By creating a new layer of rules that temporarily reduces water allocations, it significantly reduces the chance of emptying Lake Mead, the massive reservoir on the Arizona-Nevada border that supports residents of Arizona, Nevada, California and Mexico. Without the plan, the lake conceivably could have been sucked dry – a devastating prospect for 40 million people who live in the Colorado River Basin.

As a seven-year stopgap, the plan comes just in time. After 19 years of unprecedented low flows, the nation's two largest reservoirs – Lakes Mead and Powell – collectively contain only 40% as much water as they held in 2000. And while the winter of 2018-2019 was a big snow year, it merely balances the previous year, when record-setting warm and dry weather in large parts of the basin lowered water levels in Lake Powell by over 40 feet.

Dry years like 2018 are the far more likely future. From 2000 through 2004, annual runoff totaled only 65% of the 20th-century average. And in 2012-2013, it was just 60% of the 20th century average. More episodes like these would seriously compromise the system's ability to provide water to the seven Colorado River Basin states and Mexico.

Farmer Dan Thelander talks about how the Colorado River drought plan will affect farms in Pinal County, Ariz.

A hotter, drier future

Climate change is and will remain a significant issue. Since 2000, Colorado river flows have been 16% below the 20th-century average. Temperatures across the Colorado River Basin are now over 2 degrees Fahrenheit warmer than the 20th-century average, and are certain to continue rising.

Scientists have begun using the term "aridification" to describe the hotter, drier climate in the basin, rather than "drought," which implies a temporary condition.

Studies show that higher 21st-century temperatures have been reducing runoff. Warmer temperatures increase evaporation from soils and water bodies, and increase sublimation from snowpacks – direct conversion of snow and ice into fog or steam, without melting first. And they increase plant water use, due to a longer growing season and more warmth on any given day.

In a 2017 study, one of us (Brad Udall) and Jonathan Overpeck found that higher temperatures due to climate change had reduced the flow of the Colorado River by approximately 6%. The study projected that additional warming could reduce flows by approximately 20% in 2050 and up to 35% by 2100 if precipitation levels did not change. A 2018 modeling study estimated the flow losses due to higher temperatures at about 10%.

Overuse in the Lower Basin states of Arizona, Nevada and California is the second major problem. This problem is officially known as the "Structural Deficit" – a 1.2 million acre-foot gap, representing 8% of the river's flow, between allocations made in the early 20th century and the amount of water the river can provide.

Cities from Las Vegas on the north to Tucson and Phoenix on the south and west to San Diego and Los Angeles all have come to depend on that water. Meanwhile, agriculture – including important areas like Yuma and the Imperial Valley, where much of the nation's valuable winter produce is grown – uses 70% of the river's water.

 <img alt="" src="https://images.theconversation.com/files/283370/original/file-20190709-44479-k3gdf.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/283370/original/file-20190709-44479-k3gdf.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/283370/original/file-20190709-44479-k3gdf.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/283370/original/file-20190709-44479-k3gdf.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/283370/original/file-20190709-44479-k3gdf.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/283370/original/file-20190709-44479-k3gdf.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/283370/original/file-20190709-44479-k3gdf.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 The All American Canal diverts water from the Lower Colorado River to irrigate crops in California's Imperial Valley and supply 9 cities. Although the Colorado River is depicted here as reaching the ocean, it no longer does so due to upstream diversions. USGS

Looking past 2026

With the contingency plan only running until 2026, Basin leaders are already discussing the framework of a new planning effort. In our view, the process should be open and inclusive, given the huge number of competing interests in the region, including municipalities, agriculture, tribes and the environment.

An effective long-term plan should solve the overuse problem in the Lower Basin, while preparing for extended and unprecedented low flows. It should revisit a number of long-standing assumptions about how the river is managed, including the Upper Basin's so-called "delivery obligation" to the Lower Basin, which leaves the upper states – Wyoming, Utah, Colorado and New Mexico - bearing the burden of climate change, while the Lower Basin states remain free to overuse. And it will have to address the reality that there is not enough water for users in the Upper Basin to continue exporting ever more water to growing cities like St. George, Utah, and Colorado's Front Range.

Solving the twin problems of climate change and overuse will not be easy. The good news is that water users in the basin have found ways to work together for everyone's benefit, first in a set of water management guidelines negotiated in 2007, and then with the Drought Contingency Plan.

Now, after staving off worry that system reservoirs could drop to calamitous levels, water users and managers can focus on these pressing longer-term issues. It is time to step back, look at the big picture and design a water management system that works for all stakeholders in the basin for the next several decades.

This study has been updated with a more detailed map of the Colorado River Basin.

Brad Udall has received funding from NOAA, the Department of Interior, the State of Colorado, and the Walton Family Foundation for Colorado River related work. He is affiliated with the Colorado River Research Group.

Douglas Kenney receives funding from the Walton Family Foundation. He is a member (and chairman) of the Colorado River Research Group.

John Fleck has received research support funding from the Colorado River Water Conservation District and the Albuquerque Bernalillo County Water Utility Authority.
 Western states adopted a 7-year plan in May 2019 to manage low water levels in the Colorado River. Now they need to look farther ahead and accept that there will be less water far into the future. Brad Udall, Senior Research Scientist, Colorado Water Institute, Colorado State University Douglas Kenney, Senior Research Associate and Director, Western Water Policy Program, University of Colorado Boulder John Fleck, Professor of Practice in Water Policy and Governance and Director, Water Resources Program, University of New Mexico Licensed as Creative Commons – attribution, no derivatives. tag:theconversation.com,2011:article/119400 2019-06-27T13:19:53Z 2019-06-27T13:19:53Z Microplastic pollution and wet wipe 'reefs' are changing the River Thames ecosystem

London - June 19 2018: Volunteers cleaning the southern shores of the Thames from waste during low tide. Daniel Lange/Shutterstock

Ever since the issue was highlighted in shows like "Blue Planet 2", plastic pollution in the world's oceans has generated a wave of concern among the public. It might surprise people to learn that despite comparably less attention, many of the world's rivers are just as polluted, if not more so.

Around 80% of marine litter starts on land and rivers help transport it out to sea. In this way, plastic pollution is not just a problem for the distant open ocean – it's an issue on our doorstep. For this reason, I chose to focus on the River Thames and the impact that plastics are having close to home.

There are currently no estimates for the amount of plastic in the Thames, but the world's rivers are estimated to carry up to 4,000 kg of plastic out to sea every day. Despite much of the plastic in the Thames making it to the North Sea, a portion is permanently accumulating in the catchment.

 <img alt="" src="https://images.theconversation.com/files/281381/original/file-20190626-76730-94j7pr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/281381/original/file-20190626-76730-94j7pr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281381/original/file-20190626-76730-94j7pr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281381/original/file-20190626-76730-94j7pr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281381/original/file-20190626-76730-94j7pr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281381/original/file-20190626-76730-94j7pr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281381/original/file-20190626-76730-94j7pr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 A large wet wipe reef on the south bank just upstream of Hammersmith Bridge. Katy McCoy, Author provided

Researchers recovered nearly 8,500 items from the Thames riverbed over three months in 2012. After 20 river cleans on the foreshore of the Thames in 2019, nearly 9,000 plastic items were recovered, almost all of which were single-use.

These were most often wet wipes, sanitary products and food packaging, which accumulate in the sediment or are deposited on the inside of bends in the river. Several members of our lab group helped with a cleanup with local environment charity Thames21. On the Thames foreshore at Hammersmith in early 2019, 23,000 wipes were collected, averaging 201 wipes per square metre. You may have heard of wet wipes forming "fatbergs" in sewers, but on the banks of the Thames there are wet wipe reefs that are slowly changing the shape of the river itself.

 <img alt="" src="https://images.theconversation.com/files/281378/original/file-20190626-76713-1cw667g.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281378/original/file-20190626-76713-1cw667g.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=610&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281378/original/file-20190626-76713-1cw667g.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=610&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281378/original/file-20190626-76713-1cw667g.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=610&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281378/original/file-20190626-76713-1cw667g.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=766&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281378/original/file-20190626-76713-1cw667g.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=766&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281378/original/file-20190626-76713-1cw667g.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=766&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 3 mm microplastic particle recovered from the stomach of a fish compared to a 7 mm grain of rice. Alex McGoran, Author provided

As plastics move through the aquatic environment they break up. Eventually, these particles reach a microscopic scale. I have been researching microplastics, which are items smaller than 5 mm – roughly the size of a grain of rice – since 2015 and every study I have undertaken has found plastic. I have studied two UK rivers, the Thames and the Clyde, and fish in both estuaries have ingested plastic.

A river of plastic

As part of my PhD, I'm researching the accumulation of microplastics in the Thames food web. When I trawl in the Thames for fish the nets are full of plastic, especially tangles of wet wipes. It's extremely rare that we bring in a net with no litter at all.

Despite its murky appearance, the Thames is a diverse ecosystem that's full of life. It supports over 120 species of fish as well as many marine mammals, such as grey seals, common seals, dolphins and porpoises. Even a beluga whale was once spotted. Microplastics in the river can be ingested by all animals in the food web. Negative impacts on one part of this system can potentially cause a cascade which affects other species.

 <img alt="" src="https://images.theconversation.com/files/281383/original/file-20190626-76730-birsrv.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/281383/original/file-20190626-76730-birsrv.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=417&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281383/original/file-20190626-76730-birsrv.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=417&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281383/original/file-20190626-76730-birsrv.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=417&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281383/original/file-20190626-76730-birsrv.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=525&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281383/original/file-20190626-76730-birsrv.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=525&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281383/original/file-20190626-76730-birsrv.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=525&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 Microplastics accumulate in greater quantities in organisms feeding nearer the top of food webs, like seals. Alex McGoran, Author provided

Microplastics contain chemical additives which are released as they degrade and can act as harmful pollutants in water. These toxic chemicals can be transferred to organisms if they ingest them. This forces the animal to use their energy to treat the problem, rather than growing, feeding or reproducing.

The amount of plastic in an animal's gut is likely to increase higher up the food web that the animal feeds. If amphipods near the base of the foodweb ingest a few pieces of plastic then fish eating large numbers of amphipods – each likely to contain small amounts of plastic – would gradually accumulate more as they feed. Then seals at the top of the foodweb, which ingest lots of fish, would be exposed to a greater concentration still.

Though plastic straws and other single-use items have taken much of the blame, the plastic most commonly eaten by flatfish – a species often caught by fishers – are fibres. These are long threads of plastic which originate in our fabrics. Straws may flow out to sea quicker but during my research in the Thames, I found that 80% of all plastic extracted from animals there were fibres.

 <img alt="" src="https://images.theconversation.com/files/281382/original/file-20190626-76730-9tl1dz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/281382/original/file-20190626-76730-9tl1dz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=405&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281382/original/file-20190626-76730-9tl1dz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=405&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281382/original/file-20190626-76730-9tl1dz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=405&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281382/original/file-20190626-76730-9tl1dz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=509&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281382/original/file-20190626-76730-9tl1dz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=509&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281382/original/file-20190626-76730-9tl1dz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=509&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 Example of some of the plastic found in UK fish – here a plaice is shown with a tangle of fibres. Alex McGoran, Author provided

Hundreds of thousands of these tiny plastic fibres can drain into rivers with every use of our washing machines. Wastewater treatment plants catch the majority of these fibres, but with so many people washing their clothes in the Thames catchment area, a vast number of fibres are still entering the river and making their way out to sea.

Washing clothes less often and using products designed to capture fibres in the wash can prevent them getting to rivers or the sea, such as the guppy friend bag and coraball. We may rightly fret about the impact of our plastic on life in the ocean, but it's time we realised that the plastic pollution crisis is a lot closer to home than we care to think.

Alex McGoran receives funding from NERC through the London NERC DTP in the form of a research grant and stipend to support her research at the Natural History Museum, London and Royal Holloway, University of London. She also receives additional funding through a CASE partnership, organised with the London NERC DTP, with The Fishmonger's Company.
 It's not just the ocean we need to worry about – plastic is accumulating in the world's rivers, too. Alex McGoran, PhD Researcher in Aquatic Pollution, Royal Holloway Licensed as Creative Commons – attribution, no derivatives. tag:theconversation.com,2011:article/119089 2019-06-20T05:35:14Z 2019-06-20T05:35:14Z Memo to the environment minister: a river does need all its water
Given her new role as federal environment minister, one of Sussan Ley's comments in an interview with Nine Newspapers was eyebrow-raising, to put it mildly. She said:

Sometimes the environment doesn't need all its water but farmers desperately do need water.

This is inaccurate and concerning, but not all that surprising, given the attitude to water and rivers of some in the community and federal government.

In this age of water sharing and trading, and storing water in dams, it is easy to lose sight of what water is to a river, and how every drop of water that enters (or should enter) a river defines the character and function of that river.

Ultimately, the community – not scientists or even river managers – decides how much water a river should get. But it's essential to be honest about the effects these decisions have on rivers and the ecosystems they support. This is vital for long-term environmental sustainability, upon which all our industry, agriculture and indeed our society are based.

Crises and concerns

Recently the Murray-Darling river system has suffered several crises, including fish kills, hypoxic water, acid-sulfate soils, and algal blooms. These are all wake-up calls that the way we manage rivers are not working.

   Read more: Damning royal commission report leaves no doubt that we all lose if the Murray-Darling Basin Plan fails

But besides these disastrous incidents, there are many other ways in which river ecosystems are changing, that are not as obvious to the general public.

Contraction of native species' ranges, local extinctions, success of invasive species and the "need" to stock native recreational fish species are just a few of the insidious symptoms of a general malaise.

Water to a river is like air to a balloon. Let out a little air and the balloon is still balloon-shaped, albeit less taut than before. But let out more air and there comes a point, which is hard to predict exactly, when the balloon suddenly collapses. By this analogy, the Murray-Darling Basin is very deflated indeed.

The point is that if we take water out of a river, or change the patterns of its flow, we inevitably change the nature of that river. Irrigators undoubtedly need water. But we shouldn't kid ourselves that we're not altering the river and its ecosystems by allowing them to take it.

Do we want healthy rivers?

Our job as river scientists is not to say what type of river the community wants. Our job is to inform people on what the actions of changing river management will do to a river and its life.

We already have seriously degraded river ecosystems. Restoring them is exceedingly unlikely under current demands and management. But if we take even more of a river's water away, we need to acknowledge that the river will become yet a different river, and in some cases, one that we hardly recognise.

The public backlash following the fish kills earlier this year suggests that the community has decided that further degradation of our rivers is not acceptable.

   Read more: 5 ways the government can clean up the Murray-Darling Basin Plan

Paul Humphries has received funding from the Murray-Darling Basin Authority and the Murray-Darling Basin Environmental Water Knowledge and Research Program.

R. Keller Kopf receives funding from the Commonwealth Environmental Water Holder and is affiliated with the Australian Society for Fish Biology.
 Federal environment minister Sussan Ley said the environment doesn't necessarily need all its water, whereas farmers do. But denying rivers even part of their water can harm their health in many ways. Paul Humphries, Senior lecturer in Ecology, Charles Sturt University R. Keller Kopf, Research fellow, Charles Sturt University Licensed as Creative Commons – attribution, no derivatives. tag:theconversation.com,2011:article/118710 2019-06-12T12:17:14Z 2019-06-12T12:17:14Z Britain is in the middle of a drought – so how come there's flooding?

A commuter train passes the swollen River Taff, near Cardiff. Ceri Breeze/Shutterstock

Parts of the UK had more than a month's rain in one day on Monday June 10. More rain on the following Tuesday, particularly in the north of England and Midlands, created localised flooding. Sinkholes appearing on the M25 – one of Europe's busiest motorways – and closed train lines have created expensive travel chaos. The flooding of hospitals and other essential services has even put lives at risk.

In the middle of all this, groundwater levels across the country are much lower than normal. There's been little rain between 2018 and 2019 – the winter was drier than normal and it wasn't so long ago that Britain was basking in one of the warmest Easter weekends on record. Still yellowing lawns suggest that hardly any rain has fallen since.

This isn't an usual pattern of weather and it isn't specifically linked to climate change. Slow-moving, intense bands of rainfall can emerge in the summer, though wetter Junes can possibly be linked to climate change as the jet stream – which is responsible for steering much of the weather systems we get over Britain – changes due to a warming atmosphere.

You might expect the dry ground to soak up all the water, but it hasn't for several reasons.

Dry earth meets torrential rain

The rainfall has been so intense that the ground can't soak it up fast enough. So many of the surfaces in urban areas of the UK are paved over and don't allow water to soak through naturally, causing huge amounts of run-off.

Smaller rivers respond very quickly to heavy rainfall, which is why we have seen many smaller rivers and tributaries bursting their banks and causing localised flooding. Many of the flood warnings in place in the north of England and Midlands are for tributaries and smaller rivers with names that many people have never heard of before, but these often flow through urban areas and close to homes and businesses. Whatever the river is called, it's not much fun when it's flowing through your kitchen.

The bigger rivers on the other hand, such as the Thames and Severn take much longer to respond to heavy rain and will only flood when water tables are much higher than they are at present. Lower groundwater levels mean that larger rivers are able to swallow up extra water without too much trouble. If rain keeps up for another month or two, we could be in trouble. This is what happened during the winter of 2013-14, when months of rain meant the Thames flooded towns like Oxford, Staines and Wraysbury, and low-lying parts of Somerset resembled a lake.

What does this mean? It's a reminder that floods are pretty simple – lots of rain very often equals flooding, no matter what has happened with the weather in previous weeks and months. It also shows that floods are made worse by the way people have changed the landscape – paving over areas so that water runs off the ground too quickly, creating floods that are essentially human-made.

Climate change is here

Floods are only a problem when people are in the way of them. Britain needs to build more homes, but where and how many will affect the risk of more floods in future. There are still plans to build homes on floodplains, which we should avoid. The construction of sustainable drainage systems – ditches and ponds that hold back water where it falls and prevent heavy rain from rushing into rivers too quickly – hasn't gone far enough.

Dealing with flooding is a team effort – it requires collaboration between flood authorities, landowners, homeowners, community groups, and local and national government. Only by working together can effective action be taken. People very often have good local knowledge about flooding. They know when and where it will flood, and can sometimes be perplexed when "experts" tell them otherwise. Much of the political fallout during the 2013-14 flooding was not due to the damage itself, but anger from communities who felt abandoned or ignored.

As the UK commits to limit future climate change by setting emissions targets, people must consider the costs of the climate change people are already experiencing. This means changing how we live our lives, not just to prevent future floods but to deal with floods when they next occur. We must prepare better for floods, not just for the next decade, but for those next week.

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Hannah Cloke advises the Environment Agency on flood risk and flood forecasting. She works with local flood groups and advises local and national government on flood emergencies. Her flood research is funded by the Natural Environment Research Council, the European Commission's Horizon 2020 programme.
 The UK has seen drought conditions since 2018, but the flooding of June 2019 shouldn't come as a surprise. Hannah Cloke, Professor of Hydrology, University of Reading Licensed as Creative Commons – attribution, no derivatives. tag:theconversation.com,2011:article/114171 2019-05-17T10:45:16Z 2019-05-17T10:45:16Z Hydropower dams can harm coastal areas far downstream

The San Pedro Mezquital River is the last free-flowing river in Mexico's western Sierra Madre. Octavio Aburto, CC BY-ND

Thousands of hydroelectric dams are under construction around the world, mainly in developing countries. These enormous structures are one of the world's largest sources of renewable energy, but they also cause environmental problems.

Hydropower dams degrade water quality along rivers. Water that flows downstream from the dams is depleted of oxygen, which harms many aquatic animals. The reservoirs above dams are susceptible to harmful algal blooms, and can leach toxic metals such as mercury from submerged soil.

We wanted to know whether dams also impact river systems farther away, at the coastlines where rivers flow into the sea. So we performed a natural experiment comparing four rivers along Mexico's Pacific coast – two that are dammed and two that remain free-flowing. We found that damming rivers has measurable negative ecologic and economic effects on coastal regions more than 60 miles (100 kilometers) downstream.

 <img alt="" src="https://images.theconversation.com/files/274975/original/file-20190516-69213-tibbnr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/274975/original/file-20190516-69213-tibbnr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/274975/original/file-20190516-69213-tibbnr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/274975/original/file-20190516-69213-tibbnr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/274975/original/file-20190516-69213-tibbnr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/274975/original/file-20190516-69213-tibbnr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/274975/original/file-20190516-69213-tibbnr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 Shrimp fishing along the coast of Nayarit, Mexico. Tomas Castelazo/Wikimedia, CC BY-SA

Feeding or starving coastlines

We studied four river outflows along the Pacific Coast of Mexico in the states of Sinaloa and Nayarit. Two of these were from the San Pedro and Acaponeta rivers, which are relatively unrestricted, with over 75% of their flow unobstructed.

The other two outflows came from the nearby Santiago and Fuerte rivers, which have over 95% of their flow retained in reservoirs. In addition to restricting water flow, these reservoirs trap sediments – over 1 million tons per year along the two rivers combined.

In unobstructed rivers, sediment flows downstream and is eventually deposited along the coast, helping to stabilize the shoreline and sometimes even to build it up. We found that this was happening along the free-flowing Acaponeta and San Pedro rivers.

However, because the sediment from the dammed Santiago and Fuerte rivers is no longer carried downstream, wave action takes over at the coast. At the mouths of these two rivers, we found that waves were eroding up to 33 hectares of combined land – equivalent to about 62 football fields – each year, with widespread ecologic and economic effects on the surrounding regions.

 <img alt="" src="https://images.theconversation.com/files/274971/original/file-20190516-69178-1l35y9j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/274971/original/file-20190516-69178-1l35y9j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=580&fit=crop&dpr=1 600w, https://images.theconversation.com/files/274971/original/file-20190516-69178-1l35y9j.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=580&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/274971/original/file-20190516-69178-1l35y9j.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=580&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/274971/original/file-20190516-69178-1l35y9j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=729&fit=crop&dpr=1 754w, https://images.theconversation.com/files/274971/original/file-20190516-69178-1l35y9j.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=729&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/274971/original/file-20190516-69178-1l35y9j.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=729&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 The dammed Fuerto and Santiago Rivers show greater erosion where they reach the Pacific coast than the free-flowing San Pedro and Acaponeta rivers. Images at right show coastline changes during the two periods: blue indicates land accretion, red indicates erosion. Ezcurra et al., 2019., CC BY-NC

The ecology of healthy coasts

Our field research clearly showed that coastal instability resulting from sediment loss at the mouths of the dammed rivers was harming ecosystems along the shore. For example, we found that coastal regions downstream of free-flowing rivers had significantly more plant diversity. Many of these plants were found only in coastal areas, and therefore had high conservation value.

Coastal erosion due to lack of sediment input from the rivers also reduces critical nursery habitat, such as mangrove forest, where many commercially important fish species spend their juvenile stage. We found that fishing activity at the mouth of the free-flowing San Pedro River was much higher than around the mouth of the dammed Fuerte River. This loss of fishing potential comes at a cost of around US$1.3 million every year.

Reduced sediment flow also deprives coastal estuaries of nutrients. Lucrative shrimp and oyster fisheries in the region we studied rely heavily on nutrient inputs from rivers. In the San Pedro River region, these fisheries generate around $5.8 million yearly; near the dammed rivers, they have been all but abandoned.

Coastal mangrove wetlands also protect shorelines from hurricanes and tropical storms, and serve as recreational areas and conservation habitat for wildlife. Knowing this, we calculated that the loss of these ecosystem services around the dammed rivers totals $3.9 million annually.

 <img alt="" src="https://images.theconversation.com/files/274972/original/file-20190516-69189-1c74q1k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/274972/original/file-20190516-69189-1c74q1k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=404&fit=crop&dpr=1 600w, https://images.theconversation.com/files/274972/original/file-20190516-69189-1c74q1k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=404&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/274972/original/file-20190516-69189-1c74q1k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=404&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/274972/original/file-20190516-69189-1c74q1k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=507&fit=crop&dpr=1 754w, https://images.theconversation.com/files/274972/original/file-20190516-69189-1c74q1k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=507&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/274972/original/file-20190516-69189-1c74q1k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=507&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 Vegetation profile of sandbars of the free-flowing San Pedro River (A) and dammed Santiago River (B), where receding black mangrove forest is being eroded away into the advancing coastline. Ezcurra et al., 2019, CC BY-NC

Still another valuable function that mangrove wetlands perform is storing "blue carbon" in plant tissue and soils, reducing the effects of climate change. But when coastlines recede and mangroves are destroyed, this carbon is released. We calculated that mangrove loss in our study region represented a loss of around $130,000 in annual carbon trading potential for this region.

Adding up all of the ecological services that coastal ecosystems provide, we estimate that the economic consequences of shoreline loss around the Santiago and Fuerte rivers related to hydroelectric damming totaled well over $10 million yearly.

Letting more sediment flow

Because sediments are so essential to areas around river mouths, reducing sediment trapping behind dams could mitigate some harmful impacts on coastal areas. There are several ways to do this – notably, sediment bypassing, or diverting a portion of the sediments flowing from upriver around dams and allowing it to rejoin the river downstream.

This strategy can be included in new construction or incorporated into existing dams. In addition to reducing dams' environmental impacts, it also increases dams' service lives by reducing the rate at which their reservoirs fill up with silt.

To date, environmental impact assessments of large inland dams have often failed to properly analyze the impacts that these dams will have downriver on coastlines, estuaries, deltas and lagoons. Our study shows how important it is to fully account for dams' environmental and economic impacts along coasts and basins.

Critics are challenging a proposed dam on the San Pedro River at Las Cruces.

Mexico may be at a juncture in its approach to hydropower. The Mexican government recently contracted with Hydro-Quebec, the world's largest hydroelectric power producer, to revamp existing dams across the country. And a recent study by a Mexican nongovernment organization, SuMar-Voces por la Naturaleza, reported that a long-disputed proposal to build a new hydroelectric dam at Las Cruces is neither financially feasible nor needed to meet energy demand for the region, prompting national groups to call for the final cancellation of the project.

We believe that Mexico and all nations working to develop efficient, low-impact energy sources should take a holistic approach to future dam-related projects, so they can weigh their potentially harmful consequences. The coastal effects that we documented should be part of those reviews.

Octavio Aburto receives funding from the David and Lucile Packard Foundation, UC MEXUS and the Leona M. and Harry B. Helmsley Charitable Trust.

Paula Ezcurra does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
 Thousands of hydropower dams are under construction around the world. New research shows that by cutting off sediment flow, these dams can have big ecological effects on far-off bays and deltas. Paula Ezcurra, Digital Communications Specialist, Gulf of California Marine Program, University of California San Diego Octavio Aburto, Assistant Professor of Marine Biology, Scripps Institute of Oceanography, University of California San Diego Licensed as Creative Commons – attribution, no derivatives. tag:theconversation.com,2011:article/109048 2019-02-13T11:50:06Z 2019-02-13T11:50:06Z Satellites reveal a new view of Earth's water from space

Zambezi river delta, snapped by Landsat 8 in March 2018. NASA

In 1889, near the remote border town of Embudo, New Mexico, John Wesley Powell, the famous explorer of the Grand Canyon and second head of the U.S. Geological Survey, started a quiet scientific revolution.

He knew that water would be increasingly important to the American West, but no one had developed a way to figure out how much was available. Powell set up a field camp with 14 students, three instructors, two laborers and a cook, and tasked them with developing the first gauge to measure how much water flows through a U.S. river.

With their success, it was possible to know how much water could be taken out of the Rio Grande for irrigation without it becoming unnavigable or, worse, drying up entirely.

More than a century later, the USGS operates more than 10,000 stream gauges around the country. They're remarkably similar to that first Embudo gauge. Other countries operate thousands more.

Today, hydrologists like me use the stream gauge network, along with similarly vast networks of sensors measuring rainfall, soil moisture, snow depth and other parts of the water cycle. These tools help show how much water is available to people and ecosystems and how that water moves from place to place.

 <img alt="" src="https://images.theconversation.com/files/258322/original/file-20190211-174873-agabk4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/258322/original/file-20190211-174873-agabk4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=759&fit=crop&dpr=1 600w, https://images.theconversation.com/files/258322/original/file-20190211-174873-agabk4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=759&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/258322/original/file-20190211-174873-agabk4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=759&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/258322/original/file-20190211-174873-agabk4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=953&fit=crop&dpr=1 754w, https://images.theconversation.com/files/258322/original/file-20190211-174873-agabk4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=953&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/258322/original/file-20190211-174873-agabk4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=953&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 A team member working on the Embudo stream gauge project in 1889. USGS

Moving to space

In the last 30 years, hydrology has run into a sticky problem. There are simply not enough sensors for the questions hydrologists want to answer.

 <img alt="" src="https://images.theconversation.com/files/258385/original/file-20190211-174873-1ddyvll.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/258385/original/file-20190211-174873-1ddyvll.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/258385/original/file-20190211-174873-1ddyvll.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/258385/original/file-20190211-174873-1ddyvll.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/258385/original/file-20190211-174873-1ddyvll.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/258385/original/file-20190211-174873-1ddyvll.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/258385/original/file-20190211-174873-1ddyvll.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 A snow pillow. USDA Natural Resources Conservation Service

Try, for example, to measure how much snow is stored in a mountain range like California's Sierra Nevada. This water is a critical resource for the state. The Sierra Nevada contains about 130 "snow pillows" that measure the amount of water stored in the snow directly above them. But the area measured by the sensors is something like 2 millionths of a percent of the total area of the Sierra.

If you try to figure out the total water stored in the Sierras, you run into a methodological wall. There's no good way to get there directly.

This kind of problem crops up all over hydrology, from snow to soil moisture and rivers to reservoirs. Although putting out more sensors is an option, they are expensive to maintain, and it's impossible to put out enough to measure an entire mountain range. A better option would be to measure large areas all at once.

Starting about two decades ago, a small group of scientists suggested a new solution: What if they could measure the water cycle from space?

The University of Saskatchewan's Jay Famiglietti was one of these scientists. Much of Famiglietti's work has used the Gravity Recovery and Climate Experiment (GRACE) mission, a pair of satellites launched in 2002. The satellites, nicknamed Tom and Jerry, chase each other around the planet and use tiny variations in the the distance between them to measure changes in Earth's gravity. Many of these variations come from water moving around. GRACE tracks changes in total water storage across groundwater, the surface and the atmosphere.

"[GRACE] paints a compelling picture, because it allows us to see the human fingerprint on water availability, and the climate change impact on water availability," Famiglietti told me. Some of his work with GRACE has shown deep losses of groundwater in northern India, the Middle East and other places that could be vulnerable to future water shortages. The original pair of GRACE satellites went offline in 2017, but a new pair launched the following year.

 <img alt="" src="https://images.theconversation.com/files/258273/original/file-20190211-174883-823q09.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/258273/original/file-20190211-174883-823q09.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=427&fit=crop&dpr=1 600w, https://images.theconversation.com/files/258273/original/file-20190211-174883-823q09.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=427&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/258273/original/file-20190211-174883-823q09.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=427&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/258273/original/file-20190211-174883-823q09.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=536&fit=crop&dpr=1 754w, https://images.theconversation.com/files/258273/original/file-20190211-174883-823q09.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=536&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/258273/original/file-20190211-174883-823q09.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=536&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 Artist's rendition of the GRACE follow-on mission. NASA

A golden age

Other satellites designed to measure specific parts of the water cycle came online at around the same time as GRACE, though they had some limitations.

IceSAT, active from 2003 to 2009, measured the changing shape of glaciers and ice sheets, but its lasers had some technical problems that limited its lifetime. The Tropical Rainfall Measurement Mission provided data on precipitation at low latitudes, but it worked poorly for snow and regions with strong thunderstorms. Scientists came up with improved ways to use data from passive microwave sensors, some of which were already in orbit, to estimate soil moisture, but they provided data only at relatively coarse scales.

Starting in 2014, a new generation of satellites has offered improvements. The Global Precipitation Mission, a constellation of satellites, has substantially improved on TRMM. IceSAT-2, which NASA launched in 2018, has much better lasers than its forerunner. Dedicated soil moisture missions launched by the European Space Agency and NASA offer more finely tuned measurements than past sensors could.

I am part of an international team that will launch the first project dedicated to measuring Earth's most readily accessible water resources: rivers and lakes. The Surface Water and Ocean Topography (SWOT) mission is an active sensor that, starting in 2021, will send radar pulses down to Earth and measure how long they take to return to the satellite. Through finely tuned algorithms, SWOT will measure changes in the amount of water stored in millions of lakes and reservoirs around the world and estimate, from space, the amount of water flowing through most of the world's major rivers.

This NASA animation shows how SWOT will collect data over ocean and freshwater areas.

With all these satellites, hydrologists will be able to track many individual parts of the water cycle using observations from space. The next challenge will be putting all of those measurements together in a coherent way. Each satellite has its own idiosyncrasies. Scientists are working to integrate all of their past and present data with computer simulations of Earth's water cycle.

Together, these observations can help better predict drought, track floods and inform the world about how climate change is altering access to water resources. For example, a suite of satellites showed that the world's landlocked basins, already among the driest places on Earth, most notably the Aral Sea in Central Asia, are rapidly losing water.

Space agencies are also designing new missions to cover parts of the water cycle that current satellites can't yet adequately observe, like the snowpack in the Sierra Nevada. Estimating evaporation also remains a real challenge. Current methods produce very different global patterns, and the path toward new solutions for reliably estimating evaporation from space remains uncertain.

Satellites have gone from curios on the sidelines of hydrology to central players in understanding the global water cycle. When John Wesley Powell sent 20-odd members of the new USGS to the banks of the Rio Grande, he likely couldn't have imagined that, 130 years later, water scientists like me would be following in his footsteps using satellites orbiting hundreds of miles overhead.

Tamlin M. Pavelsky receives funding from NASA related to the SWOT mission and measuring the water cycle from space.
 Satellites hundreds of miles overheard are helping scientists to predict drought, track floods and see how climate change is changing access to water resources. Tamlin M. Pavelsky, Associate Professor of Global Hydrology, University of North Carolina at Chapel Hill Licensed as Creative Commons – attribution, no derivatives. tag:theconversation.com,2011:article/111345 2019-02-10T19:14:11Z 2019-02-10T19:14:11Z Melting Himalayan glaciers: a big drop in a bucket that's already full
A new report has warned that even if global warming is held at 1.5℃, we will still lose a third of the glaciers in the Hindu Kush-Himalaya (HKH) region. What does that mean for rivers that flow down these mountains, and the people who depend on them?

The HKH region is home to the tallest mountains on Earth, and also to the source of rivers that sustain close to 2 billion people. These rivers supply agriculture with water and with sediments that fertilise soils in valleys and the floodplain.

Some of these rivers are hugely culturally significant. The Ganges (or Ganga), for instance, which flows for more than 2,525km from the western Himalayas into the Bay of Bengal, is personified in Hinduism as the goddess Gaṅgā.

 <img alt="" src="https://images.theconversation.com/files/257843/original/file-20190207-174857-jk1rf2.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/257843/original/file-20190207-174857-jk1rf2.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/257843/original/file-20190207-174857-jk1rf2.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/257843/original/file-20190207-174857-jk1rf2.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/257843/original/file-20190207-174857-jk1rf2.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/257843/original/file-20190207-174857-jk1rf2.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/257843/original/file-20190207-174857-jk1rf2.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 The Ganga River at Rishikesh, as it exits the Himalayas. Anthony Dosseto

   Read more: Warm ice in Mount Everest's glaciers makes them more sensitive to climate change – new research

When it rains, it pours… literally

Before we get to the effect of melting glaciers on Himalayan rivers, we need to understand where they get their water.

For much of Himalayas, rain falls mostly during the monsoon active between June and September. The monsoon brings heavy rain and often causes devastating floods, such as in northern India in 2013, which forced the evacuation of more than 110,000 people.

2013 floods in Uttarakhand, India.

But the summer monsoon is not the only culprit for devastating floods. Landslides can dam the river, and when this dam bursts it can cause dramatic, unpredictable flooding. Some of those events have been linked to folk stories of floods in many cultures around the world. In the Himalayas, a study tracking the 1,000-year history of large floods showed that heavy rainfall and landslide-dam burst are the main causes.

When they melt, glaciers can also create natural dams, which can then burst and send floods down the valley. In this way, the newly forecast melting poses an acute threat.

The potential problem is worsened still further by the Intergovernmental Panel on Climate Change's prediction that the frequency of extreme rainfall events will also increase.

Come hell or high water

What will happen to Himalayan rivers when the taps are turned to high in this way? To answer this, we need to look into the past.

For tens of thousands of years, rivers have polished rocks and laid down sediments in the lower valleys of the mountain range. These sediments and rocks tell us the story of how the river behaves when the tap opens or closes.

 <img alt="" src="https://images.theconversation.com/files/257845/original/file-20190207-174894-ksaduy.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/257845/original/file-20190207-174894-ksaduy.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/257845/original/file-20190207-174894-ksaduy.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/257845/original/file-20190207-174894-ksaduy.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/257845/original/file-20190207-174894-ksaduy.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/257845/original/file-20190207-174894-ksaduy.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/257845/original/file-20190207-174894-ksaduy.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 Rock surfaces tell us where the river was carving into its bed. Anthony Dosseto

Some experts propose that intense rain tends to trigger landslides, choking the river with sediments which are then dumped in the valleys. Others suggest that the supply of sediments to the river generally doesn't change much even in extreme rainfall events, and that the main effect of the extra flow is that the river erodes further into its bed.

The most recent work supports the latter theory. It found that 25,000-35,000 years ago, when the monsoon was much weaker than today, sediments were filling up Himalayan valleys. But more recently (3,000-6,000 years ago), rock surfaces were exposed during a period of strong monsoon, illustrating how the river carved into its bed in response to higher rainfall.

 <img alt="" src="https://images.theconversation.com/files/257846/original/file-20190207-174870-3o7iha.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/257846/original/file-20190207-174870-3o7iha.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/257846/original/file-20190207-174870-3o7iha.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/257846/original/file-20190207-174870-3o7iha.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/257846/original/file-20190207-174870-3o7iha.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/257846/original/file-20190207-174870-3o7iha.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/257846/original/file-20190207-174870-3o7iha.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 Sediments laid down in Himalayan valleys support agriculture, but also tell us the ancient story of rivers that carried them. Anthony Dosseto

So what does the past tell us about the future of Himalayan rivers? More frequent extreme rainfall events mean more floods, of course. But a stronger monsoon also means rivers will cut deeper into their beds, instead of fertilising Himalayan valleys and the Indo-Gangetic plain with sediments.

   Read more: Devastating Himalayan floods are made worse by an international blame game

What about glaciers melting? For as long as there are glaciers, this will increase the amount of meltwater in the rivers each spring (until 2060, according the report, after which there won't be any meltwater to talk about). So this too will contribute to rivers carving into their beds instead of distributing sediments. It will also increase the risk of flooding from outburst of glacial lake dams.

So what is at stake? The melting glaciers? No. Given thousands or millions of years, it seems likely that they will one day return. But on a more meaningful human timescale, what is really at stake is us – our own survival. Global warming is reducing our resources, and making life more perilous along the way. The rivers of the Himalayas are just one more example.

Anthony Dosseto receives funding from the Australian Research Council.
 A new report predicts that one-third of the ice in the Himalayas will melt, even if we contain global warming to 1.5C. So what does that mean for the flood-prone valleys below? Anthony Dosseto, Associate Professor, University of Wollongong Licensed as Creative Commons – attribution, no derivatives. tag:theconversation.com,2011:article/109781 2019-02-03T17:55:49Z 2019-02-03T17:55:49Z How drought affects freshwater fish

A dry river bed in south Australia.  (Shutterstock)

When we think of a river, dark, cool rushing water — full of energy and life — comes to mind. Yet, in the face of climate change we are frequently witnessing almost entirely dry river beds with barely enough water to support fish and other aquatic life.

Dry conditions and water removal are leaving little space for the animals that depend on these freshwater systems. Australia recently witnessed the consequences of this in several massive fish kills on the Darling River.

Throughout history, some years have been hotter and drier, and under these conditions drought occurs. Droughts are natural ecological phenomena in response to climatic variation. Soaring temperatures accelerate water loss and dry conditions deprive freshwater systems of their natural water cycle. Droughts can naturally occur seasonally or for multiple years, such as Australia's Millennium drought.

Some ecosystems are used to droughts, which have shaped the behaviour of animals that migrate or disperse to find water and long term droughts shape ecosystems so that tolerant species thrive. But in an era of rapid global change, droughts are becoming more common and severe.

As researchers, we noticed more and more media attention being given to the impact of droughts on local fish habitat and fisheries. We realized science needed a better understanding of how freshwater fish will respond to an increasingly drought-stricken world.

Healthy freshwater ecosystems

Fresh water is one of humanity's greatest natural resources, although this is only slowly becoming truly appreciated. Humans are drawn to water not just for drinking, but also its aesthetic.

Freshwater provides many services whose value we struggle to quantify. Rivers, creeks, and lakes provide great recreational value in cities and the countryside. They give us places to play volleyball on a warm, sandy beach, take a dip in a cool river, paddleboard or kayak, wade along the bank in search of fish, or pick up stones to skip or look for insects and crayfish.

 <img alt="" src="https://images.theconversation.com/files/256542/original/file-20190131-127151-1s5cwft.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/256542/original/file-20190131-127151-1s5cwft.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/256542/original/file-20190131-127151-1s5cwft.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/256542/original/file-20190131-127151-1s5cwft.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/256542/original/file-20190131-127151-1s5cwft.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=565&fit=crop&dpr=1 754w, https://images.theconversation.com/files/256542/original/file-20190131-127151-1s5cwft.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=565&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/256542/original/file-20190131-127151-1s5cwft.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=565&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 Kids enjoy a dip into a river in Ukraine. (Shutterstock)

Can we put a price on healthy habitat and thriving animals that live there? There are thousands of species of freshwater fish beneath the surface of lakes and rivers around the world, and these species are hit hard by human activities and the consequences of climate change.

Our actions are now having a noticeable impact on temperatures and water flows, which accelerate drought. Receding water levels mean a fish will have less and less access to different types of habitat. Some fish are adapted to live in fast flowing water, others in slow moving pools. But during drought, they all must share the same shallow, sluggish water, an unfair competition that disfavour fish used to flowing water.

Large, mobile fish such as trout or salmon may anticipate drought as water levels begin to dwindle, and leave for large lakes or seas. If they're unable to complete the journey before parts of the river dry up, the fish can get stuck in remnant pools and become disconnected from their spawning or feeding areas.

   Read more: Freshwater wildlife face an uncertain future

Rising temperatures and declining oxygen puts the stranded fish under stress. As they cluster in refuge areas to try to outlast the drought, these fish are vulnerable to predators, diseases spread readily and many die.

When the water returns after weeks, months or even years, recolonization can be slow and there may be fewer species than before for many years to come. There may also be new species if the drought facilitated the survival and expansion of an invasive species better adapted to the harsh conditions.

A new reality

As more frequent and severe droughts become the new reality for freshwater ecosystems, we believe it's critical to manage freshwater with fish conservation in mind. But a closer look at the science showed that researchers are only beginning to understand how fish respond to drought.

   Read more: Cotton and rice have an important place in the Murray Darling Basin

The impacts of drought can be very different in different regions. In places like California where infrequent or more mild droughts have always occurred, many of the fish have adapted to cope with drought. Tolerant species have long lifespans and can spawn whenever conditions are right.

In other regions, where drought has not guided the evolution of the freshwater species, native species may die out and invasive species could take over. In Puerto Rico, for example, researchers found that droughts allowed invasive fishes to expand and dominate over the native species.

Hundreds of thousands of fish have died in Australia's Darling River. Water mismanagement has enhanced the effects of the drought for the worse.

The ongoing drought in Australia highlights the social impacts of drought. Prolonged hot weather combined with diverting water to agriculture stripped the river of its flows, promoted algal blooms and yielded a catastrophic fish kill that has had broad effects on the local people, many of whom have a close connection with the river and its fish.

Turbulent times

We still don't know what the long-term effects of this newly drought-stricken world will be. If fish are repeatedly challenged by droughts, how will they respond? In many places we need to start studying the fish communities now to establish a starting point so that we can make effective comparisons when drought does come.

But by the time we have the information, it may be too late to change the way we manage our rivers, streams and lakes. Agencies and people that manage these bodies of freshwater must be proactive to protect flows and water levels. Protecting fish means protecting livelihoods and food security for the many people that rely on fisheries.

Climate change will challenge our ability to maintain healthy freshwater ecosystems, but it must be one of our most ardent priorities. Managing flows in rivers with the goal of maintaining ecological flows is critical to mitigating the impacts of drought. Researching drought and maintaining healthy freshwater fish communities will go a long way towards ensuring that we are protecting this resource even through this turbulent new era.

Robert Lennox received funding from the Natural Sciences and Engineering Research Council of Canada during his PhD at Carleton University. He is a member of Ocean Tracking Network Canada and is presently a senior researcher at NORCE Norwegian Research Centre in Bergen, Norway researching fish habitat and fish ecology.

Steven J Cooke receives funding from the Natural Sciences and Engineering Research Council of Canada, the Canada Research Chairs Program and a variety of other sources. He is employed by Carleton University (as a Professor) and is affiliated with InFish. He is also a member of the College of the Royal Society of Canada.
 Freshwater fish are suffering as drought becomes more common and severe. Whether they survive will depend on how governments manage rivers and lakes, and on taking action against climate change. Robert Lennox, PhD Candidate, Carleton University Steven J Cooke, Canada Research Chair & Professor, Carleton University Licensed as Creative Commons – attribution, no derivatives. tag:theconversation.com,2011:article/110735 2019-02-03T09:18:29Z 2019-02-03T09:18:29Z What we learned when our map of southern Africa's rivers went viral

The map that went viral. Sukhmani Mantel

Can you name the river closest to where you live? Have you ever seen that river on a map? How would you react if you saw that river, and others near you, in a map unlike others you have seen before?

We have spent a lot of time considering these questions and others related particularly to maps since a map of southern Africa's rivers that one of us, Sukhmani, created and posted on Facebook. The post went viral.

And though it didn't start out strictly as "science" – it was created on a whim after seeing a map of US rivers – the map has provided us with valuable insights into how scientists and researchers can use maps to engage with broad audiences beyond the usual journals and conferences.

The map was shared thousands of times in the months after it was posted on Facebook. A high-resolution version was accessed more than 2000 times in five months by people from 48 countries, many of them outside southern Africa.

These figures may not sound high in a world of viral online content. But, as researchers who are not necessarily used to such abundant public engagement, we were so surprised by the response that we asked those interested in downloading the map to complete a survey so that we could begin to better understand what it was about the map that sparked their interest.

Our initial findings echo those emerging from a growing field of study, viral cartography. The rise of open data and mapping platforms like Google Earth and QGIS is turning maps and other spatial information into powerful tools for advancing knowledge.

Essentially, maps can show "the big picture" to a great many people. They can tell people an enormous amount in an engaging and often colourful way, revealing everything from real and hypothetical voting patterns to the layout of a region's rivers.

Our hope is that other researchers who want to share knowledge, source information and engage with the public can learn from – and build on – this story of a river map gone viral.

Why maps matter

Maps have fascinated people for centuries. In recent years, research has shown that they can elicit emotional responses. After all, maps are inherently political. What we see on a map either aligns with our view of the world, or doesn't. When it does, we share the map because it confirms our beliefs. When it doesn't, we hit "share" because we want others to see what we're criticising.

Maps are also inherently incorrect, and can be misleading. This is because they depict three-dimensional earth on a two-dimensional space. We cannot (yet) capture all the detail of earth's surface in a single map.

It's also important to remember that maps aren't perfect. They can contain errors, or leave out information that would help people understand what they're seeing.

So, how did these factors play out in relation to the rivers map?

Going viral

Through an initial review of responses to our questionnaire we identified several themes related to why people might have been interested in downloading the rivers map. These also linked to broad characteristics that were previously shown to give particular internet memes a competitive advantage, and to spread.

Broadly speaking, the characteristics of internet content with a competitive advantage are that it: 1) is genuinely useful to people; 2) is aesthetically pleasing or easily imitated by the human brain; and 3) answers a question of interest to a diverse group of people.

Respondents identified the rivers map as being genuinely useful to them. They appreciated that the map was freely accessible and that they could download it to share with family members and friends.

Second, respondents found the river map as aesthetically pleasing. One person noted that, had such a map been available when they were in school, it would have made learning geography more memorable. This is another reminder that art, in many forms, can bring "unseen" elements of science and nature to diverse audiences.

   Read more: An artist's lens on the wonders of the world brings science to life

This response also chimes with research that suggests that colours in an image can influence how it spreads in social media. Red, purple and pink have been found to be particularly useful when promoting an image on social media.

Third, respondents indicated that the map helped them understand the distribution of the rivers and the land over which water flows in southern Africa. This group was interested in how the map visualised boundaries and connections between rivers and land and sea. One person wrote: "Correlation between the mountain ranges and watersheds is easily observed on this map, even without the topographic information."

In this way, the rivers map offered the landscape in a new or interesting perspective. It provided information in a way that seems to have addressed questions held by diverse groups of people.

Finally, people were able to engage with the map and point out errors, which could then be fixed.

Of course, not all content that ticks these boxes will go viral. But, as public engagement becomes more and more important to society, it's useful for scientists to know what can work.

Sukhmani Mantel receives funding from Water Research Commission, a government funding body. The data I used for the map is from the Department of Water and Sanitation.

Stephanie Januchowski-Hartley receives funding from Welsh European Funding Office and European Regional Development Fund under project no. 80761-SU-140 (West).
 Maps can show "the big picture" to lots and lots of people in an engaging and colourful way. Sukhmani Mantel, Senior Research Officer Institute for water research, Rhodes University Stephanie Januchowski-Hartley, Sêr Cymru Research Fellow, Swansea University Licensed as Creative Commons – attribution, no derivatives. tag:theconversation.com,2011:article/109948 2019-01-31T19:10:57Z 2019-01-31T19:10:57Z Australia's spike in summer drownings: what the media misses

Media reports tend to focus on people who drown at the beach. But almost as many people drown in rivers and lakes. Where are the safety messages for them? from www.shutterstock.com

You'd be hard pressed to have missed the news that there's been a big spike in the number of drowning deaths this summer – up about 50% since last year. The media's been full of stories of migrants and tourists losing their lives on our beaches.

But our unpublished analysis of the coverage of drowning deaths this summer reveals many news outlets don't present the true picture of what's happening in our waterways. And that's putting people most at risk of drowning in even greater danger.

   Read more: Monday's medical myth: wait 30 minutes after eating before you swim

What the media is not quite getting right

Are foreigners and migrants more at risk than Australian-born swimmers?

We found that almost half of all stories reported on drownings of migrants and people from overseas. For example, the deaths of three migrants at Moonee Beach in NSW was the most covered incident across stories analysed. Many of these articles suggested solutions such as ensuring tourists are informed of water risks and providing new migrants swimming classes.

Again, these suggestions are useful, but the idea that more drowning victims are foreign-born is misleading. Only two articles we read pointed out the truth – that only a third of deaths this summer involved people born overseas. This is about the same proportion of the Australian population born overseas at 28.2%. Although overseas tourists are more at risk of drowning, migrants are not.

All swimmers need to be made aware they are at risk, foreign-born or not. In fact, Australians raised on home soil may actually be overconfident of their water safety knowledge and swimming ability, and the media needs to be more explicit about this.

 <img alt="" src="https://images.theconversation.com/files/255521/original/file-20190125-108370-q9axaw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/255521/original/file-20190125-108370-q9axaw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/255521/original/file-20190125-108370-q9axaw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/255521/original/file-20190125-108370-q9axaw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/255521/original/file-20190125-108370-q9axaw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/255521/original/file-20190125-108370-q9axaw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/255521/original/file-20190125-108370-q9axaw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 Australian and foreign-born swimmers are both at risk of drowning. Photo by zayzayem on Foter.com / CC BY-SA

Are beaches really more dangerous than rivers?

Our analysis showed a clear preference for reporting beach-related drowning deaths over deaths occurring inland, such as in rivers and lakes. This bias perpetuates the idea that beaches are more risky than inland water.

However, this summer, almost as many deaths occurred in inland waterways than beaches (43% v 47% at the time this was written), and in 2017/18 more drowning deaths occurred in natural inland waterways.

So most stories emphasise providing beach-related safety tips, emphasising the importance of visiting patrolled beaches and learning how to spot rips. Although this is important advice, it doesn't apply to inland bodies of water. Where advice is provided, there are statements such as "respect the river", which provides little practical guidance.

By focusing on beaches, the media may also be missing an opportunity to warn Australians of the dangers of rivers and lakes, which are being greatly underestimated.

 <img alt="" src="https://images.theconversation.com/files/255278/original/file-20190124-135142-ccqhqg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/255278/original/file-20190124-135142-ccqhqg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/255278/original/file-20190124-135142-ccqhqg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/255278/original/file-20190124-135142-ccqhqg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/255278/original/file-20190124-135142-ccqhqg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/255278/original/file-20190124-135142-ccqhqg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/255278/original/file-20190124-135142-ccqhqg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 Rivers may seem safe, but deep water and fast flowing currents can be dangerous. Mr.TinDC on Foter.com / CC BY-ND

Vague advice

In many stories, safety spokespeople talk about the "think and plan" approach to water safety. This guidance encourages swimmers to choose swimming areas that suit their abilities, assess the risks and consider possible rescue methods. However, little guidance is given on how to assess environments for dangers. And few Australians know what to do when someone is drowning.

How can we reduce drownings?

What should governments do?

Governments need to provide education that reflects real risks. This includes identifying dangerous river and lake conditions, and learning what to do if you get stuck in a current. Communication around water safety after storms and heavy rains can also help, such as during news weather reports.

Although many water bodies have safety warning signs, there is limited evidence they work to prevent unsafe behaviours.

What is well documented is that people follow what other people are doing, especially when they are young, so may ignore signs if others are acting dangerously. As well as signs, more strict enforcement at particularly dangerous spots may be needed, such as random patrolling of rangers and building fences.

A last important action is providing rescue equipment at beaches and popular inland swimming spots, including emergency phones, floatation devices and rope.

What should I do?

Check out these tips on how to stay safe around rivers. Tips include checking the depth of the water before swimming, something many Australians don't do.

You can do this by looking for reeds breaking the surface or using a stick. You can also test current speed by throwing a leaf in the water and seeing how fast it flows. If you get stuck in a current, lie on your back, feet forward, until you reach a shallower area.

It's also important to be aware of when you need to wear life jackets. Most Australians would be aware that we should wear them on smaller motor boats, but what if you are rock fishing? Or being towed in a tube? Different states have slightly different guidelines.

Don't swim if you've been drinking. Even a small amount of alcohol can impair your ability to swim and respond to hazards.

 <img alt="" src="https://images.theconversation.com/files/255282/original/file-20190124-135154-14cyrjl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/255282/original/file-20190124-135154-14cyrjl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/255282/original/file-20190124-135154-14cyrjl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/255282/original/file-20190124-135154-14cyrjl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/255282/original/file-20190124-135154-14cyrjl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/255282/original/file-20190124-135154-14cyrjl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/255282/original/file-20190124-135154-14cyrjl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 Use a floating object to rescue. christophercjensen on Foter.com / CC BY-ND

If someone is drowning, the safest way to save them is to throw a floating object, such as a life ring or life jacket, or the end of a rope or stick. If the person is too far or you have nothing available, don't try to saving the victim if you have not received proper training or you are not a confident swimmer. Call emergency services and ask others for help.

Lastly, look out for friends and children. Active supervision isn't about sitting nearby on your phone – it can take as little as 20 seconds for a child to go under. Signs of a person drowning include their head tilted back and mouth at water level, hair over the forehead or eyes, their body in a vertical position, and gasping.

 <img alt="" src="https://images.theconversation.com/files/255277/original/file-20190124-135151-15h3y9i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/255277/original/file-20190124-135151-15h3y9i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/255277/original/file-20190124-135151-15h3y9i.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/255277/original/file-20190124-135151-15h3y9i.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/255277/original/file-20190124-135151-15h3y9i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/255277/original/file-20190124-135151-15h3y9i.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/255277/original/file-20190124-135151-15h3y9i.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 Actively supervise children at all times. dickdotcom on Foter.com / CC BY-SA

With the right action from governments and individuals, we can save tens of lives from drowning in our waterways. This action can't just wait until next summer – staying safe is an all-year round endeavour. So, campaign for better safety measures at your local waterways, get yourself educated and trained, and help make sure that Australia's favourite summer pastime only leaves happy memories.

The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.
 Migrants are no more at risk of drowning than Australian-born swimmers but you'd never know from media reports. Medhavi Gupta, PhD Candidate, George Institute for Global Health Jagnoor Jagnoor, Senior research fellow, George Institute for Global Health Licensed as Creative Commons – attribution, no derivatives. tag:theconversation.com,2011:article/110849 2019-01-31T11:43:09Z 2019-01-31T11:43:09Z What good are wetlands? 5 essential reads

Wetlands are feeding, nesting and breeding sites for migratory birds, such as these sandhill cranes in Minnesota. USFWS/Kris Spaeth, CC BY

World Wetlands Day on Feb. 2 marks the date when 18 nations signed the Convention on Wetlands in 1971, in the Iranian city of Ramsar on the shores of the Caspian Sea. Since that time, scientists have shown that wetlands provide many valuable services, from buffering coasts against floods to filtering water and storing carbon. As the Trump administration moves to strip legal protection from many U.S. streams and wetlands, we offer five articles from our archives describing the many benefits these water bodies provide.

1. Soaking up floodwaters

Wetlands line coasts in many parts of the world. They act as natural sponges that soak up floodwaters and absorb force from storm surges, protecting communities farther inland.

Working with Lloyds of London, researchers Siddharth Narayan and Michael Beck sought to quantify the value of these functions. Using insurance industry storm-surge models, they calculated that during Hurricane Sandy in 2012, wetlands along the U.S. Atlantic coast prevented more than US$625 million in direct property damage by reducing storm surge. They also estimated that marshes in Barnegat Bay, New Jersey reduced annual losses from flooding during smaller storms by an average of 16%, and up to 70% in some locations.

Narayan and Beck see restoring wetlands as an effective way to make coastal communities more resilient against storms and flooding:

"Across the United States, the Caribbean and Southeast Asia, coastal communities face a crucial question: Can they rebuild in ways that make them better prepared for the next storm, while also conserving the natural resources that make these locations so valuable? Our work shows that the answer is yes."

 <img alt="" src="https://images.theconversation.com/files/256460/original/file-20190130-110834-g5zogz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/256460/original/file-20190130-110834-g5zogz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=588&fit=crop&dpr=1 600w, https://images.theconversation.com/files/256460/original/file-20190130-110834-g5zogz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=588&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/256460/original/file-20190130-110834-g5zogz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=588&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/256460/original/file-20190130-110834-g5zogz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=739&fit=crop&dpr=1 754w, https://images.theconversation.com/files/256460/original/file-20190130-110834-g5zogz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=739&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/256460/original/file-20190130-110834-g5zogz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=739&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 Coastal wetlands can extend well inland, transitioning from saltwater to brackish and freshwater. EPA

2. Carbon-rich mud

Wetlands store large quantities of carbon in plant tissue and soils. But as climate expert William Moomaw and wetland scientists Gillian Davies and Max Finlayson point out, no global climate change agreement calls for protecting wetlands as a way to slow climate change. And around the globe, wetlands are constantly being drained, diked and paved over.

In contrast, forest protection gets a special section in the Paris climate agreement, which offers developing countries incentives to protect and expand tropical forests as carbon sinks. Moomaw, Davies and Finlayson believe wetlands deserve equal attention:

"In our view, instead of draining swamps and weakening protections, governments at all levels should take action immediately to conserve and restore wetlands as a climate strategy. Protecting the climate and avoiding climate-associated damage from storms, flooding and drought is a much higher use for wetlands than altering them for short-term economic gains."

3. 'Blue carbon' banks

Mangrove forests, which grow in saltwater in tropical regions, are especially effective at locking up "blue carbon" – so called to distinguish it from "green" carbon storage on land. Louisiana State University scientists Robert Twilley and Andre Rovai estimate that "the wood and soil of mangrove forests along the world's coastlines hold 3 billion metric tons of carbon – more than tropical forests."

 <img alt="" src="https://images.theconversation.com/files/256461/original/file-20190130-108338-1pab6mx.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/256461/original/file-20190130-108338-1pab6mx.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/256461/original/file-20190130-108338-1pab6mx.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/256461/original/file-20190130-108338-1pab6mx.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/256461/original/file-20190130-108338-1pab6mx.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/256461/original/file-20190130-108338-1pab6mx.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/256461/original/file-20190130-108338-1pab6mx.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 Mangrove forest in wetlands of Lebak, Sultan Kudarat, Philippines. Bonvallite/Wikimedia, CC BY-SA

Coastal development is an enormous threat to mangroves, whether for vacation homes in Florida or aquaculture farms in Asia. Twilley and Rovai wanted to pinpoint what type of mangroves were the most effective at storing carbon. By comparing conditions in different settings where mangroves flourish, they determined that river deltas and estuaries offer the best conditions for mangrove growth and carbon uptake:

"Overall, mangroves in deltaic coasts such as the Mississippi River delta, the Amazon in Brazil and the Sundarbans in India and Bangladesh can sequester more carbon yearly than any other aquatic or terrestrial ecosystem on the globe. These are the world's blue carbon hot spots."

4. Mangroves versus marshes

Mangroves are actually benefiting from climate change in some regions, such as Florida and the Gulf of Mexico. Villanova University biologist Samantha Chapman has found that mangroves are becoming more abundant in these areas, moving into zones formerly dominated by salt marshes, which typically are found in cooler zones.

Mangroves protect coasts more effectively against large waves, so this change isn't necessarily harmful. However, as Chapman says,

"It is important to note that marsh plants provide important habitats for numerous species of birds and fish. We don't yet know how these animals will fare as mangroves replace marshes, nor do we yet understand other downsides of plant range shifts due to climate change."

Moreover, she notes, mangroves are not building new shoreline quickly enough to keep up with sea level rise in all locations. As her findings show, there is still much to learn about how climate change will affect different types of wetlands in various locations.

The Trump administration's changes will limit protection to large bodies of water, rivers that drain into them and some nearby wetlands, leaving many other waters unprotected from pollution or development.

5. Small streams, big roles

Wetlands aren't just found along the coasts. Many major rivers, such as the Colorado and the Mississippi, start as networks of small streams, some of which may flow only during certain seasons or when it rains. But as Colorado State University geoscientist Ellen Wohl explains, a lot happens in these small tributaries and isolated wetlands that affects the larger rivers downstream:

"Marvelously adapted organisms in dry streams wait for periods when life-giving water flows in. When the water comes, these creatures burst into action. … Amphibians move down from forests to temporarily flooded vernal wetlands to breed. Tiny fish, such as brassy minnows … speed through breeding and laying eggs that then grow into mature fish in a short period of time."

 <img alt="" src="https://images.theconversation.com/files/256463/original/file-20190130-75085-zq6jxi.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/256463/original/file-20190130-75085-zq6jxi.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/256463/original/file-20190130-75085-zq6jxi.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/256463/original/file-20190130-75085-zq6jxi.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/256463/original/file-20190130-75085-zq6jxi.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/256463/original/file-20190130-75085-zq6jxi.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/256463/original/file-20190130-75085-zq6jxi.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 Brassy minnows, found throughout the northern U.S. and Canada, live in cool, slow-moving streams, creeks, overflow ponds near rivers, boggy lakes and ditches. Ellen Wohl, CC BY-ND

Small channels in river networks also harbor microbes that are very good at removing contaminants from the water. And these channels slow down heavy rainfalls, allowing water to soak into the ground and reducing the risk of flooding downstream.

Eliminating federal protection for many of these small streams and wetlands, Wohl contends, "will strip rivers of their ability to provide water clean enough to support life, and will enhance the spiral of increasingly damaging floods that is already occurring nationwide."

Editor's note: This story is a roundup of articles from The Conversation's archives.
 The Trump administration is sharply reducing environmental protection for wetlands and streams across the US. This roundup of stories spotlights the many benefits that such water bodies provide. Jennifer Weeks, Environment + Energy Editor, The Conversation Licensed as Creative Commons – attribution, no derivatives. tag:theconversation.com,2011:article/110342 2019-01-30T11:52:06Z 2019-01-30T11:52:06Z Small streams and wetlands are key parts of river networks – here's why they need protection

Biscuit Brook, a popular fly fishing spot in New York's Catskill Mountains. Ellen Wohl, CC BY-ND

The Trump administration is proposing to redefine a key term in the Clean Water Act: "Waters of the United States." This deceptively simple phrase describes which streams, lakes, wetlands and other water bodies qualify for federal protection under the law.

Government regulators, landowners, conservationists and other groups have struggled to agree on what it means for more than 30 years. Those who support a broad definition believe the federal government has a broad role in protecting waters – even if they are small, isolated, or present only during wet seasons. Others say that approach infringes on private property rights, and want to limit which waters count.

I study rivers, and served on a committee that reviewed the science supporting the Obama administration's 2015 Clean Water Rule. This measure, which defined waters of the United States broadly, is what the Trump administration wants to rewrite.

The Trump proposal goes completely against scientists' understanding of how rivers work. In my view, the proposed changes will strip rivers of their ability to provide water clean enough to support life, and will enhance the spiral of increasingly damaging floods that is already occurring nationwide. To understand why, it's worth looking closely at how connected smaller bodies of waters act as both buffers and filters for larger rivers and streams.

 <img alt="" src="https://images.theconversation.com/files/255951/original/file-20190128-39344-2abi7o.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/255951/original/file-20190128-39344-2abi7o.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/255951/original/file-20190128-39344-2abi7o.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/255951/original/file-20190128-39344-2abi7o.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/255951/original/file-20190128-39344-2abi7o.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/255951/original/file-20190128-39344-2abi7o.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/255951/original/file-20190128-39344-2abi7o.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 Ephemeral channels like upper Antelope Creek in Arizona flow only after rain or snowfall, but are important parts of larger river systems. Ellen Wohl, CC BY-ND

Parts of a whole

The fact that something is unseen does not make it unimportant. Think of your own circulatory system. You can see some veins in your hands and arms, and feel the pulse in your carotid artery with your finger. But you can't see the capillaries – tiny channels that support vital processes. Nutrients, oxygen and carbon dioxide move between your blood and the fluids surrounding the cells of your body, passing through the capillaries.

And just because something is abundant does not reduce each single unit's value. For example, when we look at a tree we tend to see a mass of leaves. The tree won't suffer much if some leaves are damaged, especially if they can regrow. But if it loses all of its leaves, the tree will likely die.

These systems resemble maps of river networks, like the small tributary rivers that feed into great rivers such as the Mississippi or the Columbia. Capillaries feed small veins that flow into larger veins in the human body, and leaves feed twigs that sprout from larger branches and the trunk.

A conservation biologist explains how the wetlands and backwaters of Oregon's Willamette River system were critical to rescuing the Oregon chub, one of this valley's most endangered fishes, from near extinction.

Microbes at work

Comparing these analogs to rivers also is apt in another way. A river is an ecosystem, and some of its most important components can't be seen.

Small channels in a river network are points of entry for most of the materials that move through it, and also sites where potentially harmful materials can be biologically processed. The unseen portions of a river below the streambed function like a human's liver by filtering out these harmful materials. In fact, this metaphor applies to headwater streams in general. Without the liver, toxins would accumulate until the organism dies.

As an illustration, consider how rivers process nutrients such as nitrogen and phosphorus, which are essential for plant and animal life but also have become widespread pollutants. Fossil fuel combustion and agricultural fertilizers have increased the amount of nitrogen and phosphorus circulating in air, water and soil. When they accumulate in rivers, lakes and bays, excess nutrients can cause algal blooms that deplete oxygen from the water, killing fish and other aquatic animals and creating "dead zones." Excess nitrogen in drinking water is also a serious human health threat.

River ecosystems are full of microbes in unseen places, such as under the roots of trees growing along the channel; in sediments immediately beneath the streambed; and in the mucky ooze of silt, clay, and decomposing leaves trapped upstream from logs in the channel. Microbes can efficiently remove nutrients from water, taking them up in their tissues and in turn serving as food for insects, and then fish, birds, otters and so on. They are found mainly in and around smaller channels that make up an estimated 70 to 80 percent of the total length of any river network.

 <img alt="" src="https://images.theconversation.com/files/255956/original/file-20190128-108370-1hplf1t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/255956/original/file-20190128-108370-1hplf1t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=476&fit=crop&dpr=1 600w, https://images.theconversation.com/files/255956/original/file-20190128-108370-1hplf1t.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=476&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/255956/original/file-20190128-108370-1hplf1t.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=476&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/255956/original/file-20190128-108370-1hplf1t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=598&fit=crop&dpr=1 754w, https://images.theconversation.com/files/255956/original/file-20190128-108370-1hplf1t.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=598&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/255956/original/file-20190128-108370-1hplf1t.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=598&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 Map of the Missouri River basin showing its network of tributaries. Missouri River Water Trail, CC BY-ND

Water does not necessarily move very efficiently through these small channels. It may pond temporarily above a small logjam, or linger in an eddy. Where a large boulder obstructs the stream flow, some of the water is forced down into the streambed, where it moves slowly through sediments before welling back up into the channel. But that's good. Microbes thrive in these slower zones, and where the movement of dissolved nutrients slows for even a matter of minutes, they can remove nutrients from the water.

Flood control and habitat

Other critical processes, such as flood control, take place in small upstream river channels. When rain concentrates in a river fed by numerous small streams, and surrounded by bottomland forests and floodplain wetlands, it moves more slowly across the landscape than if it were running off over land. This process reduces flood peaks and allows more water to percolate down into the ground. Disconnect the small streams from their floodplains, or pave and plow the small channels, and rain will move quickly from uplands into the larger channels, causing damaging floods.

These networks also provide critical habitat for many species. Streams that are dry much of the year, and wetlands with no surface flow into or out of them, are just as important to the health of a river network as streams that flow year-round.

Marvelously adapted organisms in dry streams wait for periods when life-giving water flows in. When the water comes, these creatures burst into action, with microbes removing nitrate just as in perennially flowing streams. Amphibians move down from forests to temporarily flooded vernal wetlands to breed. Tiny fish, such as brassy minnows, have waited out the dry season in pools that hold water year-round. When flowing water connects the pools, the minnows speed through breeding and laying eggs that then grow into mature fish in a short period of time.

 <img alt="" src="https://images.theconversation.com/files/255946/original/file-20190128-42594-1600m8o.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/255946/original/file-20190128-42594-1600m8o.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/255946/original/file-20190128-42594-1600m8o.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/255946/original/file-20190128-42594-1600m8o.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/255946/original/file-20190128-42594-1600m8o.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/255946/original/file-20190128-42594-1600m8o.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/255946/original/file-20190128-42594-1600m8o.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
 The Arikaree River in eastern Colorado is an intermittent stream that supports brassy minnow, a species of concern in the state. Ellen Wohl, CC BY-NC

Scientific sleuthing with chemical tracers has shown that wetlands with no visible surface connection to other water bodies are in fact connected via unseen subterranean pathways used by water and microbes. A river network is not simply a gutter. It is an ecosystem, and all the parts, unseen or seen, matter. I believe the current proposal to alter the Clean Water Act will fundamentally damage rivers' ability to support all life – including us.

Ellen Wohl receives (or has received) funding from the National Science Foundation, the USDA Forest Service, the US National Park Service, the US Army Corps of Engineers, the US Environmental Protection Agency, the Colorado Water Conservation Board, the Colorado Division of Wildlife, the US Bureau of Reclamation, the US Bureau of Land Management, Trout Unlimited, and The Nature Conservancy. She is a life-member of The Nature Conservancy and the Sierra Club.
 The Trump administration wants to end federal protection under the Clean Water Act for many small streams and wetlands. But as a geoscientist explains, these are critical parts of large river systems. Ellen Wohl, Professor of Geosciences, Colorado State University Licensed as Creative Commons – attribution, no derivatives.