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Causes of Acidification of Four Streams on Laurel Hill in Southwestern Pennsylvania¹

ABSTRACT

Atmospheric deposition, soils developed from bedrock, a natural bog, gas wells, and a ski area were all investigated as possible sources of water quality degradation for four streams on Laurel Hill in southwestern Pennsylvania where fish kills have been reported since 1960. An intensive study of the chemistry of atmospheric deposition, soil leachate, and stream water and fish populations was conducted on these basins during 1980–1981 with emphasis on dormant season periods with runoff from snowmelt and rain. Although bedrock geology was found to control the natural buffering capacity of these streams, only acid precipitation could be linked to sharp drops in pH and increases in total Al concentrations observed during stormflows in the poorly buffered streams. Three poorly buffered streams exhibited drops to pH 4.4 to 4.5 and increases in total Al concentrations up to 1.5 mg/L during observed peak flows. Mineral soil leachate from the three major soil series on the basins during this time exhibited a low pH of 4.3 and mean total Al concentrations of 3.6 mg/L, indicating stream response during storms was closely linked to chemistry of soil leachate. Poorly buffered streams did not support reproducing populations of trout (Salmonidae sp.) or other fishes. In contrast, one well-buffered stream (20 mg/L CaCO₃) exhibited drops to pH 5.5 during peak flow and supported reproducing trout and sculpin (Cottus bairdi) populations. The acidification of the four streams studied was attributed to atmospheric deposition.

Key Words: atmospheric deposition • soil leachate • pH • bedrock geology • poorly buffered streams • fish populations • watershed • aluminum • hydrogeology

¹ The study which this report summarizes was conducted from 1979 through 1982 and was supported by the Office of Water Research and Technology, U.S. Dep. of Interior through matching grant B-117-PA, a grant from Richard King Mellon Foundation and with matching funds from The Pennsylvania State Univ.

² Authors are associate professor of forest resources extension, professor of forest hydrology, former graduate research assistant, former graduate research assistant all with the School of Forest Resources and Inst. for Research on Land and Water Resources, Pennsylvania State Univ.; professor of biological and environmental sciences, California Univ. of Pennsylvania, and executive director, Loyalhanna Watershed Assoc., Ligonier, PA.

Received for publication January 31, 1983.