DETRITAL PROCESSING IN STREAMS EXPOSED TO ACIDIC PRECIPITATION IN THECENTRAL APPALACHIAN MOUNTAINS

Continuing high rates of acidic deposition in the eastern United State s may lead to long-term effects on stream communities, because sensiti ve catchments are continuing to lose anions and cations. We conducted a two-year study of the effects of pH and associated water chemistry v ariables on detrital processing in three streams with different bedroc k geology in the Monongahela National Forest, West Virginia. We compar ed leaf pack processing rates and macroinvertebrate colonization and m icrobial biomass (ATP concentration) on the packs in the three streams . Breakdown rates of red maple and white oak leaf packs were significa ntly lower in the most acidic stream. The acidic stream also had signi ficantly lower microbial and shredder biomass than two more circumneut ral streams. Shredder composition differed among streams; large-partic le detritivores dominated the shredder assemblages of the two circumne utral streams, and smaller shredders dominated in the acidic stream. W ithin streams, processing rates for three leaf species were not signif icantly different between the two years of the study even though inver tebrate and microbial communities were different in the two years. Thu s, macroinvertebrate and microbial communities differed both among str eams that differed in their capacity to buffer the effects of acidic p recipitation and among years in the same stream; these differences in biotic communities were not large enough to affect rates of leaf proce ssing between the two years of the study, but they did significantly a ffect processing rates between acidic and circumneutral streams.