Effects of increased bedload on algal and detrital based stream foodwebs: experimental manipulation of sediment and macro-consumers.
Abstract: 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 to benthic communities.  To examine how increased bedload affects algal and detrital-based stream communities, we simultaneously manipulated sediment and top-down effects of macroconsumers (fishes and crayfish) in tow factorial experiments, one using tiles and one using leaf packs as sampling substrates.  We elevated bedload approximately 60% over normal transport rates, via daily sediment addition to localized areas (0.25 m^2) of an otherwise unaltered low-order stream.  Sediment addition directly affected both algal and detrital resources:  algal species composition was altered in the tile experiment, and fungal biomass was negatively correlated with sediment mass in the leaf pack experiment.  Sediment addition also had indirect effects, via alteration of macroconsumer impacts.  In the tile experiment, macroconsumers reduced total insect biomass and abundance and/or biomass of several dominant insect taxa under ambient sediment conditions.  Sediment addition eliminated these macroconsumer effects; the only effect of macroconsumers that was not influenced by sediment addition was their reduction of chironomid biomass.  Macroconsumer effects on fungal accumulation rates and dipteran predator abundance were eliminated by sediment addition in the leaf pack experiment.  Small, environmentally realistic increases in bedload directly and indirectly affected biota in both algal and detrital-based food webs.  Indirect effects of sedimentation have been examined less frequently than direct biotic responses, but this study demonstrates the importance of sediment regime in determining the outcome of fish- and crayfish-mediated species interactions.
Schofield, L., C. M. Pringle and J. L. Meyer. 2004. Effects of increased bedload on algal and detrital based stream foodwebs: experimental manipulationof sediment and macro-consumers.Ý Limnology and Oceanography 49: 900-909

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