Friday, August 10, 2018

In the Weeds

For you biologists out there: yup, this particular clump isn't milfoil. But
the removal process is the same
From the Rideau Canal to the Champlain Canal, our passage has been plagued by Eurasian watermilfoil.

This fast-growing water plant wraps around your propeller shaft in such thick clots that it stops the boat.

Then Cap has to go swimming, to yank the stuff off. (Oh for a "weed hatch," like the English narrowboats have. Lets you remove weed from the prop without a dunk in the canal. (See a weed hatch in action.)

Evil Weed

Nonnative watermilfoil is more than an annoyance for boaters and people who want clear swimming areas, more than an economic issue for municipalities that want tourists to keep coming and waterfront property to stay valuable.

It's an ecological assault weapon that's wrecking vast ecosystems. And it's almost impossible to stop.

Bad for the Natives--But Why?

Sometimes you can remove weed from your prop
by putting it in reverse.
If you read the educational signs at nearly every marina and boat ramp, they tell you milfoil replaces beneficial water plants.

How does that work? This stuff grows FAST, strands can be 20 feet long, and stands of the weed are THICK. Where milfoil takes root, it shades out other water plants, the way trees in a forest can shade out other trees.

Milfoil grows so thick, it creates lots of hiding places where small fish can avoid being eaten by bigger fish.  That sounds like a good thing, right?

But naturally occurring food webs have a balance. The big fish can't get to their prey, so they starve, and then all the little fish out-eat their food supply (plankton and the like) and then THEY starve.  Not good.

How Did Milfoil Get Here?

I remember buying my first  goldfish at the pet store. The store owner threw in a sprig of something green to keep the water oxygenated and make the bowl look pretty. That was Eurasian milfoil, first brought to the United States in 1942 as an aquarium plant. (As the name suggests, it's native to Europe and Asia.)

Soon after, someone dumped their aquarium contents in a pond or stream somewhere. And now the evil weed is in 45 out of the 48 lower states.

A two-inch sprig from a frond cut up by a propeller can root and grow into a massive infestation.

Out of Control

Weed removal on the Champlain Canal
States have spent a boatload of money trying to understand milfoil biology and find effective control measures.

The watermilfoil weevil, an insect native to North America, actually likes Eurasian milfoil BETTER than native northern milfoil.

But so far, studies don't find that it eats enough to control the invader.

Mowing machines work like hay combines, cutting swathes to keep channels open. But they don't eradicate the weeds.

Rotavating machines that are more like tillers can yank the plants up by the roots. You push the plants on shore so they don't float away and just make more weed.  This approach can be effective but isn't practical for anything beyond small infestations.

No Happy Ending Yet

It's kind of mind-boggling to see the extent of this problem and how difficult it is to address.

And milfoil is just one of 122 invasive species now living in the Hudson River (where we are currently boating) and one of 49 invasives in beautiful Lake Champlain. It's a little harder to enjoy the scenery knowing what lurks under the water.

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