Response of Stream Macroinvertebrates to Agricultural Land Cover in a Small Watershed

Abstract

ABSTRACT We conducted a three-year study of the aquatic macroinvertebrate community of a rural, central-Pennsylvania, upland watershed (7.3 km2) with subwatersheds affected by a gradient of agricultural land use (87% forest to 96% managed agriculture). Macroinvertebrate samples were collected at 16 sites on first- to third-order streams within the watershed in May or June. Nitrate concentrations and habitat quality were also determined at these sites. The taxonomic richness of sensitive macroinvertebrates (mayflies and caddisflies) was lower in streams draining subwatersheds with high percentage agricultural land cover compared to low. Habitat quality decreased as percentage agricultural land cover increased. Nitrate concentration increased with percentage agricultural land cover for the three years of study but was only correlated with habitat quality in one year. Our data suggest that a high percentage of agricultural land cover reduced the number of sensitive macroinvertebrate taxa and produced a macroinvertebrate community composition that reflected altered stream habitat.