EFFECTS OF LARGE WOODY DEBRIS PLACEMENT ON STREAM CHANNELS AND BENTHIC MACROINVERTEBRATES

Large woody debris (LWD) was added as an experimental stream restorati on technique in two streams in southwest Virginia. Additions were desi gned to compare human judgement in log placements against a randomized design and an unmanipulated reach, and also to compare effectiveness in a low- and a high-gradient stream. Pool area increased 146% in the systematic placement and 32% in the random placement sections of the l ow-gradient stream, lending support to the notion that human judgement can be more effective than placing logs at random in low-gradient str eams. Conversely, the high-gradient stream changed very little after L WD additions, suggesting that other hydraulic controls such as boulder s and bedrock override LWD influences in high-gradient streams. Logs o riented as dams were responsible for all pools created by additions re gardless of stream or method of placement. Multiple log combinations c reated only two pools, while the other seven pools were created by sin gle LWD pieces. Total benthic macroinvertebrate abundance did not chan ge as a result of LWD additions in either stream, but net abundances o f Plecoptera, Coleoptera, Trichoptera, and Oligochaeta decreased, whil e Ephemeroptera increased significantly with the proportional increase in pool area in the low-gradient stream.