Relations between large woody debris, physical habitat, and benthic macroinvertebrates in Appalachian mountain streams

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Virginia Tech


Large woody debris (LWD) was added to North Fork Stony Creek and North Prong Barbours Creek as an experimental stream enhancement technique. The purpose of this study was to determine the stream channel responses to LWD additions at the scale of the stream reach and around individual logs, to determine benthic macroinvertebrate relations to physical habitat, and to determine the potential effects of LWD created stream channel alterations on benthic macroinvertebrates.

Pool frequency and total surface area increased substantially at the expense of riffles in the random and controlled placement sections one year after LWD additions in Stony Creek. Although logs oriented as ramps produced more channel scouring, only log dams created pools. Results in Barbours Creek were similar but less pronounced.

Substratum detritus was greater in pools than riffles for both streams, but there was no difference between years, sections, or as a result of LWD additions. Most functional feeding groups and invertebrate orders were significantly more abundant in riffles than pools. The exception were collector gatherers which accounted for a large proportion of the benthic macroinvertebrate assemblage. Increased poor area at the expense of riffle area may decrease the overall relative abundances of functional feeding groups and result in a reduction of the stream's substratum detritus processing capabilities.

Decreased riffle area should result in an overall decrease in the abundance of potential food items for brook trout in Barbours Creek, but not in Stony Creek. However, average biomass was not significantly different between pools and riffles for either stream. Biomass may therefore compensate for a loss of prey items for brook trout because, although numbers may decrease, average individual weight increases with an increase in pool habitats.