Project at a Glance
Title: Distribution of aquatic animals relative to naturally acidic waters in the Sierra Nevada
Principal Investigator / Author(s): Bradford, David
Contractor: UC Los Angeles
Contract Number: a132-173 & a132-192
Research Program Area: Ecosystem & Multimedia Effects
Topic Areas: Acid Deposition, Ecosystem Impacts, Impacts, Monitoring
We surveyed chemical conditions and the presence/absence of vertebrate populations in 104 lakes in the Bench Lake / Mt. Pinchot area of Kings Canyon National Park in early summer of 1992. These lakes ranged in pH from 5.0 to 9.3, and included 10 lakes with pH's < 6.0 (defined herein as acidic lakes). On the basis of this initial survey, 33 lakes were chosen for detailed analyses of their chemical and biological characteristics, including eight acidic lakes. Lake water composition data for 33 lakes in the detailed survey indicate that these lakes are all unusual in comparison to typical Sierra Nevada lakes sampled in previous surveys. Unlike typical Ca-Na-HCO, dominated Sierra lakes, SO, concentrations are high enough to classify 19 of these lakes with SO, as the dominant anion. Furthermore, 25% of the lakes surveyed had pH values less than six and essentially 0 ANC. The source of the acidity and SO, is sulfuric acid produced by the oxidation of pyrite found in metamorphic and granitic rocks in the area. Neutralization of acidity occurs downstream mostly by dilution with circumneutral water of lower ionic strength. This provides a chemical gradient along which various species of aquatic life may distribute themselves. This area appears to provide a good model for long-term acidification effects on aquatic ecosystems.
The faunal surveys revealed that mountain yellow-legged frog tadpoles (Rana muscosa), limnephilid caddis larvae (Hesperophylax) and large microcrustaceans (Daphnia, Diaptomus) were rare or absent in lakes having pH's < 6, but were commonly collected from lakes with pH's = 6. Trout belonging to four species were collected from or observed in a small proportion of the study lakes, and trout distributions appeared to be related to historical stocking patterns. The distribution of trout appeared to have large effects on the distributions and abundance of amphibian and invertebrate taxa, with large, mobile and conspicuous taxa being rare or absent in trout lakes, but relatively common in lakes lacking trout. The results suggest that increased acidification of High Sierra lakes will result in the elimination of larval amphibians, large microcrustaceans, and a few macro invertebrates from lakes, and a decline in micro crustacean species richness. Currently, however, the most profound human impacts on aquatic communities in the High Sierra appear to be related to historical and on-going stocking of exotic fish species into High Sierra waters.
For questions regarding research reports, contact: Heather Choi at (916) 322-3893
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