Acidic deposits and snowpack chemistry at a Sierra Nevada site

Snowpack chemistry studies evaluated the fractionation model of rapid release of acidic pollutants from the snowpack near Donner Summit, California. Event samples of precipitation and snowpack basal outflow, and weekly samples of snowpit layers and stream water were analyzed for pH, alkalinity, and sulfate and nitrate solute concentrations. Chemical signatures from specific precipitation events identified subsequent changes in the chemistry of the snowpack and outflow waters. Acidification was not apparent in either stream or snowpack basal outflow waters during the main spring melt period. The lowest seasonal pH's for stream and basal outflow waters were, however, recorded synchronously with rain or mixed rain and snowfall precipitation events during early- and mid-winter when both basal outflows and stream discharges rose. Fractionation may bave caused these pH minima. Snowfall was slightly acidic at the test site, and mean pH for rainfall, hail, and graupel was below 5.0. Snowpack layer pH remained generally constant through time.