Quantitative effects of stonedust sediment from a crushed limestone quarry on fish and macroinvertebrate populations of an Indiana stream were studied for four years. Light inputs increasing suspended solids loads less than 40 mg/l, resulted in a 25% reduction in macroinvertebrate density. Heavy inputs caused increases of more than 120 mg/l including some deposition of sediment resulted in a 60% reduction in macroinvertebrate population density. Since most taxa responded to the same degree, population diversity indices were unaffected by density changes. Experimental introductions of sediment caused immediate increases in rate of invertebrate drift proportional to the concentration of additional suspended solids. Standing crop of fish decreased drastically when heavy sediment input occurred in the spring but fish remained in pools during the summer when input was heavy and vacated pools only after sediment deposits accumulated. After winter floods removed sediment deposits, fish returned to pools during spring months achieving 50% normal levels by early June. Only spotted bass was resistant to sediment; however, its growth rate was lower below the quarry than above. Most fish were much reduced in standing crop below the quarry.

"18050 DWC 12/70." Includes bibliographical references (pages 108-113). Microfiche.