Chemical effects of snowmelt on an alpine lake in the Wind River Range, WY

Nitrogen deposition from air pollution is increasingly reaching alpine
lakes where the addition of nitrate and ammonium to sensitive surface
waters can cause acidification and or eutrophication. Thirty years of
sampling in the Wind River Range, WY have shown some lakes increasing in
nitrogen. We sought to determine (1) if nutrient concentrations in Deep
Lake increase during snowmelt when atmospheric deposition is released from
the snowpack and (2) assess if the sampling season, location,
meteorological factors, and time of day samples are collected influence
lake chemistry metrics, to inform monitoring. We analyzed water samples
from the outlet of Deep Lake in peak snowmelt (June) and from the inlet,
outlet, and middle of Deep Lake when the basin was snow free (August). In
June, outlet samples were more acidic, and nitrogen content was three
times August levels. Acid neutralizing capacity (ANC) declined with
snowmelt. August inlet samples were higher in nutrients than outlet and
mid-lake samples. Our results indicate that atmospheric pollution in the
snowpack enters the lake with snowmelt. Although Deep Lake has not
acidified, ANC levels indicate a risk of episodic acidification if
nitrogen deposition continues to increase. When monitoring lakes at risk
for episodic acidification, sampling during the late snowmelt pulse should
be prioritized. Simplified sampling protocols may be used in some lakes,
as epilimnion and outlet samples were nearly identical. The time of day
and cloud cover did not affect lake chemistry, while wind speed and
precipitation weakly increased August ANC and June pH, respectively.