Solute chemistry of snowmelt and runoff in an Alpine Basin, Sierra Nevada

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Abstract
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 buffered 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 NO3− concentrations in stream waters at this time about 1.6‐fold greater than the average NO3− concentration for the time period of snowpack runoff, Cl− about 1.5‐fold greater and SO42− about 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+ from snowpack meltwater, with less than 1% of the NH4+ released from snowpack storage exported from the basin as NH4+. Sulfate concentrations in stream waters were less variable than NO3− or Cl− concentrations; sorption processes in soils were a likely cause for the regulation of SO42− concentrations.