INTER-HABITAT VARIATION IN BENTHIC COMMUNITY STRUCTURE, FUNCTION, ANDORGANIC-MATTER STORAGE IN 3 APPALACHIAN HEADWATER STREAMS

Inter-habitat variation in benthic community structure and function wa s investigated in 3 headwater streams in West Virginia, USA. Abundance and biomass of benthic macroinvertebrates and salamanders together wi th standing crop of benthic organic matter were estimated for riffles, rock faces, plunge pools, debris-dam pools, and leaf packs. In 1 stre am, installation of log dams for fish habitat (K-dams) created artific ial plunge pools and debris-dam pools. Standing crop of benthic organi c 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 deb ris-dam pools (>2 kg ash-free dry mass/m(2)), and was dominated by coa rse particles and wood. Mean animal density (macroinvertebrates and sa lamander larvae) was highest in debris-dam pools and on rock faces (>1 0,000/m(2)) and lowest in riffles and plunge pools (<5000/m(2)). Stand ing 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 macroinverteb rate taxa showed that community structure was more similar among habit ats than among streams. Functional organization differed among habitat s. In riffles, all functional groups were well represented. Scrapers, filterers, and gatherers predominated on rock faces. In pools, shredde rs and predators dominated biomass, although gatherers were the most a bundant group. In plunge pools, crayfish (Cambarus) were relatively mo re abundant than in debris dam pools; the opposite was true for macroi nvertebrate predators. Overall, inter-habitat variation in taxonomic s tructure, animal abundance, biomass, functional organization, and bent hic organic matter exceeded among-stream variation. Comparison with pu blished data for a North Carolina headwater stream revealed common pat terns of inter-habitat variation in functional organization. Installat ion of K-dams in a headwater stream influenced the abundance, biomass, and functional organization of the benthos by providing habitat for t axa able to exploit debris-dam pools formed upstream of K-dams, which retain abundant organic matter.