Effects of Spatial and Temporal Variation in Snow Melt on Nitrate Ion and Sulfate Ion Pulses in Melt Waters Within an Alpine Basin

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Abstract
Source areas of snow-melt run-off vary spatially and temporally, with corresponding changes in chemistry of the snow-pack, and influence both timing and quality of snow-pack run-off. In the the alpine basin of Emerald Lake, located in the southern Sierra Nevada, California, U.S.A., we have found that nitrate ion and sulphate ion concentrations in streams were correlated with the amount of snow melt in each sub-basin. Inflows to Emerald Lake had elevated concentrations of , and , which corresponded temporally with the initiation of snow melt in each sub-basin. Concentrations of both anions then decreased as snow melt progressed. The onset of snow melt shifted temporally from sub-basins with a south-westerly aspect to basins with a progressively more northerly aspect. The and pulses also moved, with time, from the sub-basins with south-westerly aspects to those with more northerly aspects. The time span over which the basin experienced these anionic pulses was longer than that for any single sub-basin. Maximum concentrations of and in the lake outflow, which also occurred at the onset of snow melt, were elevated by 100 and 40%, respectively, above their January concentrations in line with increases in inflow, but were sustained for a longer period than that of any inflow increase.