Abstract
Physicochemical parameters and fish and benthic macroinvertebrate community structure were studied in a small mountain stream in western Pennsylvania. Sampling stations were located upstream and downstream of coal mine drainage in an otherwise unpolluted stream. Due to an alkaline discharge and significant upstream alkalinity the pH below the mine discharges remained between 6·5 and 8. The major factor affecting the benthic community and fish population appeared to be ferric hydroxide deposition. Rates of deposition during dry-weather conditions ranged from 3 g/m
2/day near the discharges to 0·01 g/m
2/day at the downstream end of the study site. The biomass of macroinvertebrates decreased from approximately 14 g wet wt/m
2 above the discharges to 0·1–1·5 g wet wt/m
2 within the area of iron deposition. Invertebrate diversity decreased significantly at the discharge but recovered to 75% of upstream values. The low but constant-temperature discharge from the mine may have enhanced the diversity recovery. The standing crop of fish decreased from approximately 228 to 11 kg/ha. Benthic fishes such as sculpin and suckers were the groups most affected.