Scale-specific effects of sediment burial on benthic macroinvertebrate communities

The structure and composition of stream benthic macroinvertebrate communiti es are thought to be at least partially controlled by small and large scale disturbances. We deposited 6.6L of silt at each of ten sites along a 30m s tretch of a 4(th) Order stream to experimentally disturb small (800 cm(2)) patches of stream bottom. We saw little effect of such a disturbance, after either a three hour (short-term) or three day (long-term) deposition perio d, on summary community descriptors including taxon richness and Simpson's diversity and equitability. At both time scales, the disturbed patch had ab out 36% fewer invertebrates than an adjacent control patch, and showed a gr eater abundance of oligochaetes relative to chironomids. The heterogeneity of community structure at the scale of meters on a stream bottom represents the results of a mosaic of interacting patches with varying disturbance hi stories.