Water chemistry and fish community responses to episodic stream acidification in Pennsylvania, USA

Five streams were studied on the Northern Appalachian Plateau of Pennsylvania from October 1988 through June 1989 to determine chemical changes that occur during episodic storm run-off and the responses of fish to these events. These second-order streams flowed through undisturbed, wooded, sandstone bedrock catchments with surface areas ranging from 500 to 1000 hectares. Median pH of precipitations was about 4·2, and among streams it ranged from 5·0 to 6·2. During storm events, pH declined by as much as 1·2 units and peak concentrations of total monomeric Al ranged from