Direct and indirect effects of increased bedload on algal and detrital-based stream food webs at the Coweeta Hydrologic Laboratory from 1997 to 1999: Tile/ sediment addition experiment, Summer 1997; Chlorophyll, AFDM, inorganics (days 5-40)

Anthropogenic sedimentation poses a significant threat to stream ecosystems throughout the world. Increases in bedload (sediment transported and deposited on the stream bottom) can be especially detrimental for benthic communities. To examine how increased bedload directly and indirectly affects stream communities, we simultaneously manipulated sediment and top-down effects of macroconsumers (fishes and crayfish) in situ in two factorial experiments, one using tiles and one using leaf packs as sampling substrates. Bedload was increased by adding small amounts of sediment (2.5 x normal levels) to localized areas (0.25 m2) of an otherwise unimpacted stream. This increase in bedload had direct effects on basal resources in both the tile and leaf pack experiments. In the tile experiment algal composition was altered by sediment addition, while in the leaf pack experiment fungal biomass declined with sediment.