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The biota of over a thousand lakes and streams at high elevations in the Sierra Nevada could be affected by an increase in acid deposition. This study was conducted to determine the distributions of fish and invertebrate populations at high elevations. The results will provide baseline information for detecting changes in the distributions of organisms. In addition, the sensitivity of golden trout eggs to simulated acid pulses was investigated. These studies were conducted under the Atmospheric Acidity Protection Program. Studies in this program provide information to guide the Board in considering a deposition standard to protect sensitive ecosystems in the Sierra Nevada. |
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Thirty lakes, each with a surface area greater than 1 hectare, were randomly selected from the approximately 1400 lakes above 8000 ft in California's Sierra Nevada. Fish were sampled from the 30 lakes by gill net, angling, and an electrofishing unit. Macroinvertebrates were sampled by netting. For each of the 30 lakes, one unfiltered water sample was measured for pH, acid neutralizing capacity, and conductivity. Major ions and aluminum were measured from one filtered water sample per lake.
During snowmelt, a dose-response experiment was conducted on golden trout eggs in channels lying next to the outlet stream (Mine Creek) of Spuller Lake in the Inyo National Forest. Buried eggs were exposed to six pH gradients from 4.8 to 6.6 for a period of 40 hours. Survival of eggs was determined nine to ten days later. |
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Although lakes in this survey were higher in elevation and smaller in surface area than lakes examined in the Western Lake Survey conducted in the mid-1980s by the U.S. Environmental Protection Agency, water chemistry results were similar. The water in the majority of the lakes has low acid neutralizing capacity (
Of the 1400 lakes above 8000 feet, 63 percent were estimated to contain one or two species of salmonid fish, 20 percent only invertebrates, 8 percent no fish and almost no invertebrates, and 9 percent only yellow-legged frogs. Golden and rainbow trout were the most commonly collected fish species, with brook trout ranking third and brown trout fourth. A few lakes contained cutthroat trout. Nearly all of the current fish populations resulted from stocking. The vast majority (possibly all) of the lakes were originally devoid of fish because of natural barriers.
The taxon richness of macroinvertebrates in streams and lakes was positively related to pH and in lakes negatively related to nitrate and elevation. It was apparent, however, that all fish and invertebrate species could live and reproduce in lakes and streams with pH as low as 6.
Survival of golden trout eggs in the dose-response experiment was high at the low temperature (< 5° C) encountered. No significant impacts of acidity on egg survival were detected. |
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Combined with literature data, the results suggest that the eggs of trout species would not be affected by acid inputs until pH of the water environment reached 4.5. Literature data also show that later developmental stages are sensitive to aluminum and would be negatively affected by pH depressions to 5.0-5.5 if accompanied by high aluminum levels. Trout belonging to the genus Oncorhynchus (golden, rainbow, and cutthroat trout) are more sensitive to acid inputs than trout belonging to the genera Salvelinus (brook trout) or Salmo (brown trout), and would be the first fish to respond to acid deposition. Because early life stages of trout are most susceptible to acid inputs, the timing of acid pulses relative to the timing of trout reproduction, egg development and hatching, and emergence of fry from substrates is particularly important in evaluating the effects of acid deposition on trout populations. |
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The Air Resources Board has also funded these related projects (ARB contract numbers are given in parentheses): Aquatic Amphibians in the Sierra Nevada: Current Status and Potential Effects of Acidic Deposition on Populations (A932-139) and Distribution of Aquatic Animals Relative to Naturally Acidic Waters in the Sierra Nevada (A132-173). |
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