Functional structure and production of the benthic community in a Piedmont river: 1956‐1957 and 1991‐1992

Abstract

Taxonomic composition and functional group abundance, biomass, and annual production were measured in 1991–1992 for the macroinvertebrate community in a Piedmont river. Abundances and biomass values were influenced by standing crops of Podostemum ceratophyllum, a hydrophyte which covered bedrock substratum. Collector‐filterers, collector‐gatherers, and scrapers dominated functional‐group abundance; scrapers and collector‐filterers dominated biomass. Benthic production was 181.9 g ash‐free dry mass m−2 yr−1; 57% was attributable to collector‐filterer hydropsychid caddisflies and 13% to a scraper snail. Results were compared to a previous study conducted at the same site in 1956–1957. Physical parameters of temperature and discharge regimes, P. ceratophyllum standing crops, and riparian vegetation were similar between studies, but marked changes in land use had occurred within the catchment. Benthic community structure was dominated by small, multivoltine collector‐gatherers and microfilterers in 1956–1957; in 1991–1992 dominant taxa consisted of larger, longer lived macrofilterers and scrapers. Changes in community structure and indices of biotic integrity indicate stream condition improved in 1991–1992 relative to 1956–1957; changing land‐use practices are implicated as the key factor for improvement.