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Spatial Variation of Nutrient Concentrations (NH + 4 and Cl − ) in the Dudhkoshi River Basin, Sagarmatha National Park, Nepal

The Sagarmatha National Park (SNP) in Nepal is home to unique natural beauty and cultural significance. While the SNP has a relatively small local population, it has drawn thousands of visitors since Edmund Hillary and Tenzing Norgay reached the peak of Mt Everest in 1953. Importantly, the tourists and their concurrently generated refuse have caused massive anthropogenic pressure with serious environmental consequences for the unique SNP and SNP Buffer Zone ecosystems. This study aimed to understand the spatial variation of nutrient concentrations in stream water and drinking water (primarily shallow springs) using analyses of nitrogen as NH + 4 and chlorine (Cl − ) concentrations. Sampling occurred in April 2017 during the pre-monsoon dry season in the upper Dudhkoshi River Basin, SNP. Dissolved inorganic nitrogen (NH + 4 ) concentrations in both drinking water and stream water were low with average concentrations in drinking water of 0.016 mg/L (±0.010) and 0.033 mg/L (±0.031) in stream water. Similarly, Cl − concentrations were also low with average concentrations of 0.185 mg/L (±0.045) and 0.124 mg/L (±0.051) in stream and drinking water, respectively. Importantly, nitrogen in stream waters exhibits a decreasing trend with altitude whereas Cl − values decrease with altitude in improve understanding of the relationship between land use/land cover and water quality in the region.


Abstract
The Sagarmatha National Park (SNP) in Nepal is home to unique natural beauty and cultural significance. While the SNP has a relatively small local population, it has drawn thousands of visitors since Edmund Hillary and Tenzing Norgay reached the peak of Mt Everest in 1953. Importantly, the tourists and their concurrently generated refuse have caused massive anthropogenic pressure with serious environmental consequences for the unique SNP and SNP Buffer Zone ecosystems. This study aimed to understand the spatial variation of nutrient concentrations in stream water and drinking water (primarily shallow springs) using analyses of nitrogen as NH + 4 and chlorine (Cl − ) concentrations. Sampling occurred in April 2017 during the pre-monsoon dry season in the upper Dudhkoshi River Basin, SNP. Dissolved inorganic nitrogen (NH + 4 ) concentrations in both drinking water and stream water were low with average concentrations in drinking water of 0.016 mg/L (±0.010) and 0.033 mg/L (±0.031) in stream water. Similarly, Cl − concentrations were also low with average concentrations of 0.185 mg/L (±0.045) and 0.124 mg/L (±0.051) in stream and drinking water, respectively. Importantly, nitrogen in stream waters exhibits a decreasing trend with altitude whereas Cl − values decrease with altitude in both drinking water and streams. The observed spatial variations of nitrogen and chlorine concentrations are attributed primarily to the significant variations in land use/land cover from the highest portions of the drainage basin to the lowest elevations, which are outside of the SNP boundary and therefore allow more agricultural development. Our results demonstrated that although the quality of stream water in the upper reach of Dudhkoshi River Basin meets WHO standards for drinking water, there is significant surface water contamination in the form of agricultural run-off. These results will provide base-line data for further studies and will help to

Introduction
Headwater streams are important sources of nutrients for downstream use, particularly nitrogen, and can have a significant impact on both aquatic ecosystems and water quality in the downstream reaches [1] [2] [3] [4]. The concentrations of nitrogen and chlorine in river systems can be influenced by a variety of natural and anthropogenic factors, the relative influences of which vary spatially and temporally [5]. Recently, several major studies have shown that eutrophication has intensified in downstream systems [6] [7]. However, very little is known about the nutrient concentrations of headwater streams in the high elevation regions of the Nepal Himalaya where anthropogenic factors could have a significant impact downstream. In general, these streams have been considered indicative of a pristine environment; however, major changes in tourism and land use/land cover (LULC) over the past 70 years could be impacting water quality (land use refers to human activity on a piece of land, and land cover refers to its surface features, e.g. [8]).
The Nepal Himalaya region, including the Sagarmatha National Park (SNP) and in particular the Khumbu Valley, is considered a data-poor region, primarily due to the location's geographic remoteness and ruggedness; historically, it has been difficult and expensive to access [9]. Increasing tourism over the past few decades has boosted the local economy and infrastructure, making access to the region for scientific endeavors more feasible, and there has been a marked increase in published research of the region since the turn of the century [10]. In 1964, a total of 20 tourists visited the Khumbu region (what is now the SNP) whereas more than 32,000 tourists visited in 2010 [11]. In all, more than half a million trekkers have visited the Khumbu region since the first successful ascent of Mt. Everest by Tenzing Norgay and Edmund Hillary in 1953 [11]. Despite concerns since the 1970's regarding tourism-related pollution of the region, the first systematic study of drinking water quality in the Khumbu Valley was not undertaken until 2014. In that year, Nicholson et al. [12] sampled community water sources with a focus on fecal contamination of drinking water. The study concluded that there were higher counts of E. coli and other coliform bacteria associated with fecal contamination in samples collected from lower elevation, higher-population areas, and that surface water was more highly contaminated than springs fed by groundwater. Moving forward, an evaluation of the spatial variation of nitrogen, chlorine, physical parameters and LULC in the upper Dudhkoshi River Basin will establish baseline data and provide key information Journal of Water Resource and Protection for understanding the importance of LULC and park management practices in the region.

Study Site
The Sagarmatha National Park was established in 1976 and designated a World Heritage Site in 1979 [13]. The park and its associated Buffer Zone (here within referred to as the SNP) covers an area of ~1425 km 2 and includes the majority of the Khumbu Valley and Mt. Everest [14]. The region is characteristically high altitude; with 31% of the total land area at elevations of 4000 -5000 m, and 52% of the total land area at elevations 5000 -6000 m. This study focuses on the Dudhkosi River Basin ( Figure 1). The Dudhkosi River is one the highest-elevation river systems in the world [15] and one of the seven tributaries of the Saptakoshi River, which is part of the greater Ganges River System. Within the study area, the Dudhkosi River flows from the Gokyo Lakes region, is joined by the tributaries Imja Khola and Lobuche Rivers, downward to Lukla and then out of the study area.
The Khumbu Valley has a temperate climate characterized by clear seasonality with dry winters as cold at −17˚C and summers as warm as 37˚C [12]. More

Land Use/Land Cover (LULC)
The Khumbu region was first inhabited 500 years ago by the Sherpa people, who emigrated from Eastern Tibet [10] and are still the majority of the permanent residents in the region. Accurate census data for the region are scarce, and estimates place the population of the Khumbu Valley between 3500 m and 6000 m (e.g. [10] [14]). The economy of the Khumbu Valley is based upon tourism and agriculture. Local farmers grow potatoes, barley, and buckwheat, as well as raising yaks and zopkios (a cattle-yak hybrid), for dairy, meat, and as beasts of burden [10]. Throughout the entire SNP, areas with relatively gentle slopes tend to be extensively cultivated whereas areas with steep topography are generally left as forest and grassland. However, the steady increase in and dependence on tourism has resulted in many changes, for example: the number of lodges grew from 56 in 1989 to over 300 in 2012 [22]. The issue of changes to LULC has been the subject of several recent studies, e.g. [23] [24] [25] [26] [27]. The studies of Humagain [24] and Garrard et al. [27] both combined stakeholder perceptions and interviews with remote sensing data. Their results suggest a substantial decrease in the land area covered by snow and ice since 1992 (>24%), with decreases in forests and farmland (>20%) and increases (>40%) in the land area covered by rock and soil [24] [27]. Humagain [24] also found an increase in grazing, settlement and shrubland. Both studies conclude that the lower elevations LULC changes are a direct result of anthropogenic factors (specifically related to increasing tourism and park management) whereas at higher elevations the melting snow and glacial ice are attributed to climate change [24] [27].

Methods
Sampling and field analysis occurred between April 21 and May 05, 2017, during the dry, pre-monsoon spring season. Sampling was conducted within the Khumbu Valley along the main Everest Base Camp Trekking Route between the town of Journal of Water Resource and Protection Lukla and Everest Base Camp. Sampling locations included large rivers, small streams, natural springs, and numerous community standpipes. Locations were selected to reflect community drinking water sources (primarily standpipes; n = 19) and the waterways that supply them (rivers, tributaries, and springs; n = 9).
A study site map with sampling locations is provided in Figure 1.
Samples for ion analysis were collected with a sterile syringe, then passed through a 0.45-μm filter into pre-washed 60-mL or 125-mL high-density polyethylene bottles with screw-on polypropylene caps. Bottles were then sealed with paraffin sealing film. Temperature, pH, conductivity, and total dissolved solids (TDS) were measured in the field via Fisher Scientific Accumet AP85 portable waterproof meter. When possible, the instrument probes were inserted directly in the uncollected water for measurements. In case of insufficient flow it was necessary to insert probes into water collected in a plastic 1-L bottle.
For bacteria analyses, samples were collected in a sterile 60 mL syringe and passed through a 0.45 µm filter at the sample site. After filtration, the filter paper was placed in a sterile test card (manufactured by Micrology Labs®) containing a medium which uses two color producing chemicals, one for the detection of the enzyme glucuronidase (produced by E. coli strains but not by general coliforms) and one for the detection of galactosidase (produced by all coliforms, including E. coli). The samples were then placed into a portable field incubator and kept as close to 35˚C as possible for ~24 hours. Sample counts were done using a magnifying glass and a 10x geological hand lens. E. coli colonies are royal blue/purple and coliform bacteria colonies appear to be light green.

Physical Parameters E. Coli and Coliform Bacteria
The overall trend for all samples is decreasing in the case of temperature, total dissolved solids (TDS) and conductivity, and increasing pH with altitude ( Figure 2, see [28] [29] for complete analyses including household use water). In 2017 average drinking water temperatures were 9.14 (±3.79)˚C: stream water 8.53 (±3.87)˚C, spring water 9.42 (±3.83)˚C. Stream and spring water temperatures consistently decrease with increasing altitude (Figure 2(b)). pH (Figure 2  The correlation between bacterial content and physical parameters is weak; however, there is a correlation between bacterial content and altitude and, hence, temperature (Figure 2(c), Figure 2(f)).

Water Types, NH + 4 and Cl − Values
Ion analysis revealed domestic water resources in the study area are primarily of Journal of Water Resource and Protection the calcium bicarbonate water-type. All samples were undersaturated with respect to any mineral. Ionic strength ranged from 0.14 -0.91 mM/L with an average of 0.50 mM/L. Both Balestrini et al. [21] and Wood et al. [30] report ion concentrations for samples within the study area, and both report that the samples are enriched in all species except NH + 4 compared with precipitation samples from the same study.
On average, NH   Trendlines and R 2 values were calculated using Excel. Of significance is the difference similarity between trends in surface water and in springs and stand pipes, as opposed to the trends observed in Figure 3.

Trends
NH + 4 and Cl − , particularly in stream water, show distinct correlations with physical parameters and bacterial content (Figure 3, Figure 4). Notably both NH 4 + and Cl − in stream water decreases with altitude, pH, conductivity and TDS but shows only a weak relationship with temperature ( Figure 3, Figure 4). Conversely, NH 4 + and Cl − concentrations in stream water both show a positive correlation with bacterial content, particularly Total Coliforms. For stream water samples NH 4 + and Cl − themselves correlated positively (Figure 3, Figure 4).
Trends in the spring water samples show that NH 4 + concentrations are essentially independent of altitude, physical parameters, bacterial content and Cl − ( Figure 3). Cl − concentrations in spring water, however, do show negative correlation between altitude and physical parameters, with Cl − decreasing with pH, temperature, conductivity and TDS ( Figure 4). Additionally, Cl − shows a strong positive correlation with Total Coliforms (Figure 4).

Discussion
LULC change is one of the most important forms of environmental change occurring in many of the world's mountain regions [31].  [21] concluded that Cl − in precipitation samples were derived from the long-range transport of sea salt from the Indian Ocean, especially given that the regional precipi- with altitude is a result of depletion of the precipitation as it moves further from the ocean and upward [21]. The major difference between spring and stream water is the relationship Cl − /NH + 4 , whereby stream water shows increasing Cl − with increasing NH + 4 , whereas spring water does not. A similar relationship is seen between Cl − and bacteria, whereby the stream water appears to correlate better with increasing bacteria (both E. coli and Total Coliforms) than spring water.
These trends suggest that surface water in the region derives a small amount of Cl − from animal waste (including human), whereas spring water does not.
Concentrations of NH + 4 show very different trends to those observed in Cl − . NH + 4 in spring samples are independent of altitude, physical parameters and bacteria. Given that the primary source of NH + 4 in the region is from human and/or animal waste this suggests that springs contain relatively little (or no) surface water contamination during the pre-monsoon dry season. These results agree with the conclusions of Nicholson et al. [28] who suggest that during the premonsoon dry season, most village water sources are relatively uncontaminated. The stream samples were collected from the border of the SNP buffer zone and extend, along the main trekking route and the Dudhkoshi River, into the park itself and uphill towards Mt Everest based camp (Figure 1). The buffer zone (below ~2900 m) has a higher population [10], more agriculture and few restrictions on land use. As altitude increases, the population decreases, the number of tourists decreases, and the type of agriculture shifts toward more grazing and less cultivation. Although there does not appear to be a significant relationship between population, LULC and Cl − concentrations in either spring or stream water samples, there does appear to be a relationship with NH + 4 concentration in surface water. At lower altitudes there is more NH + 4 in the streams which is likely a direct result of contamination by human and/or animal waste. Above ~4000 m there appears to be little difference between NH + 4 in spring and stream water samples, supporting the idea that the impact of cultivation and/or population at the lower altitudes is important. Given that waste is typically used as fertilizer and that open defecation is a problem within the region [10], these conclusions seem reasonable. What remains to be investigated is how changing LULC in the region will impact water quality.
Work by Humagain [24] and Garrard et al. [27] show significant changes in LULC in the SNP since 1992. Of particular interest to this study is the fact that there has been an increase in grazing, settlement, and shrubland throughout the region [24], and that the lower elevations LULC changes are a direct result of anthropogenic factors [24] [27]. These changes are bound to impact water quality, particularly surface water, hence a better understanding of the impacts of LULC on spring and stream water is important to park management. Resource and park management strategies must take these factors into account, especially considering the impact of climate change continues, glacial retreat and changing monsoon patters.

Conclusion
This study provides an evaluation of the spatial variation of nitrogen, chlorine, physical parameters and LULC in the upper Dudhkoshi River Basin to establish baseline data and provide key information for understanding the importance of LULC and park management practices in the region. Stream samples indicate direct contamination by human and/or animal waste. Higher altitude stream and spring samples support the idea that cultivation and/or population at the lower altitudes is significant. Given that waste is typically used as fertilizer and there is a problem with open defecation in the region, these conclusions seem reasonable.
What remains to be investigated is how changing LULC in the region will impact water quality, but this study implies that proper waste management is key to protecting vital water resources.