Inter-habitat variation in benthic community structure, function, and organic matter storage in 3 Appalachian headwater streams

Inter-habitat variation in benthic community structure and function was investigated in 3 headwater streams in West Virginia, USA. Abundance and biomass of benthic macroinvertebrates and salamanders together with standing crop of benthic organic matter were estimated for riffles, rock faces, plunge pools, debris-dam pools, and leaf packs. In 1 stream, installation of log dams for fish habitat (K-dams) created artificial plunge pools and debris-dam pools. Standing crop of benthic organic matter was lowest in riffles and rock faces (approximate to 50 g ash-free dry mass/m(2)) and was dominated by coarse (1-10 mm) and fine (0.25-1 mm) particles. Mass of benthic organic matter was highest in debris-dam pools (>2 kg ash-free dry mass/m(2)), and was dominated by coarse particles and wood. Mean animal density (macroinvertebrates and salamander larvae) was highest in debris-dam pools and on rock faces (>10,000/m(2)) and lowest in riffles and plunge pools (<5000/m(2)). Standing biomass of animals was highest in pools (3-8 g dry mass/m(2)) and lowest in riffles and on rock faces (<2 g dry mass/m(2)). Chironomids and the stonefly Leuctra were the most abundant taxa in most habitats; co-dominant taxa differed among habitats. Ordination of macroinvertebrate taxa showed that community structure was more similar among habitats than among streams. Functional organization differed among habitats. In riffles, all functional groups were well represented. Scrapers, filterers, and gatherers predominated on rock faces. In pools, shredders and predators dominated biomass, although gatherers were the most abundant group. In plunge pools, crayfish (Cambarus) were relatively more abundant than in debris dam pools; the opposite was true for macroinvertebrate predators. Overall, inter-habitat variation in taxonomic structure, animal abundance, biomass, functional organization, and benthic organic matter exceeded among-stream variation. Comparison with published data for a North Carolina headwater stream revealed common patterns of inter-habitat variation in functional organization. Installation of K-dams in a headwater stream influenced the abundance, biomass, and functional organization of the benthos by providing habitat for taxa able to exploit debris-dam pools formed upstream of K-dams, which retain abundant organic matter.