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Hydrogen Ion Concentration and Alkalinity of Reservoir Water in the Sierra Nevada, California, and Correlations with Air Pollutants

Department of Plant and Soil Biology, Univ. of California, 108 Hilgard Hall, Berkeley, CA 94720.

^* Corresponding author.

ABSTRACT

Pardee reservoir supplies water for the east San Francisco Bay Area from a large forested drainage basin located in the Sierra Nevada foothills, extending east to the crest of the mountain range. Analyses of weekly data of reservoir discharge water indicate that [H⁺] has been increasing (1954–1985 data) and alkalinity decreasing (1944–1985 data). Hydrogen ion concentration and alkalinity of reservoir water are correlated with NO_x (and SO₂ to a lesser extent) emissions from the San Francisco Bay Area. Emissions of NO_x are about four times greater than those of SO₂. A lag-time of 3 to 4 yr improves the correlations, especially those of SO₂. Greatest increases in [H⁺] occur in spring when the snowpack is melting. In the 1950s, spring melt had a dilution effect on [H⁺], but now [H⁺] increases during spring melt. The following is an explanation for the seasonal variations observed: Atmospheric NO_x and SO₂ appear to have their greatest effect on [H⁺] of water when there is little contact of runoff with soils and rocks. There is no correlation between acidity and alkalinity during the winter when water penetrates the soil profile, resulting in proton exchange with soil "base cations." During summer, when runoff is minimal, other processes within the reservoir appear to control [H⁺] and alkalinity. Alternative hypotheses are discussed, which may help explain the observed trends in [H⁺] and alkalinity over seasons and years. These hypotheses largely involve processes within the reservoir, but without historical data their importance remains unclear.

Contribution from the Dep. of Plant and Soil Biology, Univ. of California, Berkeley, CA 94720.

Funded by Hatch Project CA-B-PSB-3664-H.

Received for publication May 19, 1987.