Project at a Glance

Title: Aquatic biota in the Sierra Nevada: current status and potential effects of acid deposition on populations

Principal Investigator / Author(s): Jenkins, Tom

Contractor: UC Santa Barbara

Contract Number: a932-138

Research Program Area: Ecosystem & Multimedia Effects

Topic Areas: Acid Deposition, Chemistry & Reactivity, Ecosystem Impacts, Impacts


In the first part of this study we randomly selected 30 sample lakes from the subset of Sierra lakes above approximately 2,439 meter (8,000 foot) elevation, and qualitatively described the populations of fish and macroinvenebrates present in these lakes (and associated streams) relative to water chemistry. The lakes were selected with EPA's EMAP area-based sampling technique, which projected a total of 1,404 lakes > 1 ha in surface area (no actual count was attempted). We described the chemical and biological characteristics of five additional high-elevation lakes, including four that were part of a long-term CARB monitoring program. Although lakes in our survey were higher in elevation and smaller in surface area than lakes examined in EPA's Western Lakes Survey (WLS), water chemistry results were similar in these two surveys, showing a predominance of low ANC waters with no evidence of chronic changes caused by atmospheric deposition. This similarity is important because the EP A study has been the most comprehensive attempt to characterize the chemical sensitivity of Sierra Nevada waters in general. A few lakes at the southeastern border of Kings Canyon National Park were apparently acidic from natural basin sources, and had high sulfate and aluminum concentrations. Only 8% of the lakes in the study region had pHs < 6.0. Of the calculated total of 1,404 lakes meeting our selection criteria, we estimated that 881 contained one or two species of salmonid fish, 127 contained only yellow-legged frogs, 284 contained only invertebrates, and 112 contained no fish and almost no invertebrates. Golden trout (Oncorhynchus mykiss aguabonita) and rainbow trout (Oncorhynchus mykiss) were the most commonly collected fish species, with brook trout (Salvelinus fontinalis) ranking third and brown trout (Salmo trutta) fourth in frequency of occurrence. A few lakes contained cutthroat trout (Oncorhynchus clarki). Nearly all of the present high elevation fish populations were established by humans, and the vast majority (possibly all) of the lakes above 8000 feet in the Sierra Nevada were originally devoid of fish due to natural barriers. Fish and invertebrates were not collected in the two most acidic lakes (pHs 4.7 and 5.2). Aluminum concentrations tended to be lower where golden trout were present versus absent and pH tended to be higher where brook trout were present versus absent: however, these chemical factors were both correlated with elevation and relationships may have been confounded by patterns of stocking related to elevation. The taxon richness of macroinvertebrates in streams and lakes was positively related to pH, and in lakes it was negatively related to nitrate and elevation. Similarly, pH was higher and nitrate, sulfate, and elevation tended to be lower where common macroinvertebrates (e.g. Callibaetis, Pisidium) were present compared to where they were absent It was apparent, however, that all fish and most invertebrate species could live and reproduce in lakes and streams with pHs as low as 6. In the second part of this study, a dose response experiment was conducted during snow melt in channels lying next to the outlet stream (Mine Creek) of a representative high-altitude lake (Spuller Lake). Buried eggs of golden trout were exposed to a gradient of 6 pH levels ranging from 4.8 to 6.6, for a period of 40 hours, and the survivorship of eggs determined nine to ten days later. Survivorship of eggs was high at the low temperatures (5 degrees Celsius) encountered during the experiment, and there were no significant impacts of acid inputs on egg survival. When combined with literature data the results suggest that the eggs of trout species would not be affected by acid inputs until pH was lowered to less than or equal to 4.5. Literature data also show that later stages. such as sac and swim-up fry, are quite sensitive to high aluminum concentrations 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 (i.e. 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 substantial acid deposition in the High Sierra. 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.

For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753

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