Acid precipitation and lake susceptibility in the central Washington Cascades [USA]

Abstract

Bulk precipitation was monitored at five sampling sites across the Cascade mountains east and windward of the urban Puget Sound area January 1981 through July 1981. The volume weighted average pH over the collection period at the Cascade Crest (Snoqualmie Pass) was 4.71. Sulfate was the dominant anion. The average strong acid composition in terms of sulfate and nitrate over the five collector sites ranged from 57 to 62 equiv % sulfuric acid. The sulfate deposition for 1981 at the Cascade Crest is estimated to be 16.0kgha-1 year-1 of S04 (sea salt corrected). The strong acid content of the samples was observed to increase in the summer months. Twenty-nine watershed source lakes lying along the Cascade Crest 3-20 miles north of the precipitation collectors were sampled during the summer of 1981. All of the source lakes were found to be susceptible but not acid, with alkalinities ranging from 4 to 190 μequiv/L. (Median alkalinity was 57 μequiv/L.) The composition of the waters in terms of alkalinity and calcium concentration was similar to that of nonacidified waters of northwestern Norway and northwestern Ontario.