FUNCTIONAL STRUCTURE AND PRODUCTION OF THE BENTHIC COMMUNITY IN A PIEDMONT RIVER - 1956-1957 AND 1991-1992

Taxonomic composition and functional group abundance, biomass, and ann ual production were measured in 1991-1992 for the macroinvertebrate co mmunity in a Piedmont river. Abundances and biomass values were influe nced by standing crops of Podostemum ceratophyllum, a hydrophyte which covered bedrock substratum. Collector-filterers, collector-gatherers, and scrapers dominated functional-group abundance; scrapers and colle ctor-filterers dominated biomass. Benthic production was 181.9 g ash-f ree dry mass m(-2) yr(-1); 57% was attributable to collector-filterer hydropsychid caddisflies and 13% to a scraper snail. Results were comp ared to a previous study conducted at the same site in 1956-1957. Phys ical 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. Ben thic community structure was dominated by small, multivoltine collecto r-gatherers and microfilterers in 1956-1957; in 1991-1992 dominant tax a consisted of larger, longer lived macrofilterers and scrapers. Chang es in community structure and indices of biotic integrity indicate str eam condition improved in 1991-1992 relative to 1956-1957; changing la nd-use practices are implicated as the key factor for improvement.