Effects of sedimentation on the behavior and distribution of riffle insects in a laboratory stream1

Studies were conducted to determine the effects of 3 levels of sedimentation on the behavior and distribution of selected mayflies, stoneflies and caddisflies in artificial laboratory streams. Most species responded negatively to increased levels of sedimentation; all preferred unsedimented over heavily sedimented substrate. Sensitivity to sedimentation differed among species with size, morphology, and behavior accounting for much of the variation. As sediment levels increased, more of the test substrate became uninhabited. Density per cobble increased only slightly with greater quantities of fine sediment. Nonburrowing species were unsuccessful in gaining access beneath cobbles when the undersurfaces and sides were sealed in fine sediments.