Benthic community organization in replicate stream channels colonized through drift

Benthic community organization is the product of numerous factors.  This project investigated the role of drift in community organization. Four artificial gravel-filled, stream channels (60m long, 8m wide, 1.3m deep) at the Oregon Hatchery Research Center, near Alsea, Oregon, were supplied with water from Fall Creek starting in late fall 2005.  The benthic community then was sampled from the upper, middle and lower riffles in each channel and in similarly-spaced riffles from Fall Creek in May 2006.  A biological cline was evident in each channel, with large-bodied stoneflies, mayflies and caddisflies most abundant in the upper riffle of each channel and declining downstream, while small-bodied chironomids were least abundant in the upper riffle and increased downstream.  Meanwhile periphyton abundance and organic matter concentration increased along the length of each channel.  This biological cline was completely absent along the sampled length of Fall Creek.  Furthermore, the macroinvertebrate composition in the channel riffles did not match that in Fall Creek, even when non-drifting macroinvertebrates such as stone-cased caddis, snails and crustaceans were ignored.  Despite the short-term length of this experiment (about 7 months), results suggest that colonization pathways other than drift are likely important contributing factors to benthic community organization.