Solute Chemistry of Snowmelt and Runoff in an Alpine Basin, Sierra Nevada

Snowpack runoff contributions to the hydrochemistry of an alpine catchment in the Sierra Nevada were evaluated in 1986 and 1987 by analyzing snowpack, meltwater, and stream water samples for major inorganic ions, conductance, acid neutralizing capacity (ANC), and silicate. An ionic pulse in meltwater with initial concentrations twofold to twelvefold greater than the snowpack average, varying with site and with ion, was measured in lysimeters placed at the base of the snowpack. Maximum concentrations of ions in meltwater were inversely related to the rate of snowmelt; melt-freeze cycles increased the concentration of solutes in meltwater. Hydrogen concentration in meltwater was buff'ered by ANC produced in part by the dissolution of particulates. The anionic pulse in meltwater was observed in stream waters during the first 30 days of snowpack runoff, with NO•concentrations in stream waters at this time about 1.6-fold greater than the average NO•' concentration for the time period of snowpack runoff, CIabout 1.5-fold greater and SO42about 1.3-fold greater. Maximum H '• concentration during snowpack runoff (increase of 170% over winter concentrations) occurred near maximum discharge. ANC minima occurred at maximum discharge as a result of dilution, with a decrease from winter concentrations of 70% in 1986 and 60% in 1987. Interactions between snowpack runoff and soils were important to the chemistry of stream water. Eighty to ninety percent of the H * stored in the snowpack was consumed before it reached the base of the catchment. Soils were a sink for NH4 t' from snowpack meltwater, with less than I% of the NHd • released from snowpack storage xported i3⁄4om the basin as NH,i • . Sulfate concentrations i tream waters were less variable than N(•).• • or CIconcentrations' sorption processes in soils were a likely cause for the regulation ofS(),• ....... concentrations.