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Wild Trout VII, Yellowstone National Park, October 2000
J.R. Webb, F.A. Deviney, Jr., B.J. Cosby, A.J. Bulger, J.N. Galloway
Department
of Environmental Sciences
University of Virginia
Charlottesville, Virginia 22903
Abstract
The Virginia Trout Stream Sensitivity Study (VTSSS) is an important part of the effort to insure that change in the acid-base chemistry of surface waters following enactment of the Clean Air Act Amendments of 1990 will be effectively evaluated for acid-sensitive watersheds. With other cooperators, we initiated VTSSS in the spring of 1987 to establish a baseline for a biologically defined class of streams against which to measure future effects of acidic deposition and air-pollution control measures. The initial survey measured the solute composition of 394 native brook trout streams in western Virginia. Results were reported at Wild Trout IV. Since the initial survey, a geographically distributed subset of the original survey sites (~60 sites) has been sampled on a quarterly basis to monitor long-term trends in solute concentrations. To assess how representative are trends based on the subsample of long-term monitoring sites, we resurveyed the 1987 sites and some additional sites (452 native brook trout streams) during the last week of April 2000.
Trend analyses based on 12 years of quarterly samples from the long-term monitoring sites provide little evidence for recovery from acidification. Although trends in sulfate concentrations have been variable, the predominant trend in acid neutralization capacity (ANC) has been downward, indicating continuing acidification. In contrast, the survey-resurvey data seem to provide more evidence for recovery, with sulfate concentrations predominantly decreasing and ANC concentrations predominantly increasing. However, changes in solute concentrations between the 1987 survey and the 2000 resurvey may reflect differences in stream flow ratherthan long-term trends in acid-base status. Given the larger number of points in time (48 versus 2), the analyses of trends based on quarterly sampling are less subject to effects of short-term variation. Therefore we accept trend analyses obtained for the long-term monitoring sites as the more reliable measure of change in the acid-base status of Virginia’s brook trout streams. These analyses indicate that biologically significant acidification is continuing.
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