WOOD BREAKDOWN AND MICROBIAL BIOFILM RESPIRATION IN SOUTHERN APPALACHIAN STREAMS DRAINING WATERSHEDS WITH DIFFERENT LAND USE HISTORIES.

M.E. McTammany and E.F. Benfield. Department of Biology, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA 24061-0406

We investigated breakdown rate and surface biofilm activity of white oak wood veneer substrates in streams with different land use histories. Thirty second and third order streams in the Little Tennessee, French Broad, and New River basins (NC and VA) were selected based on land cover succession trajectories (agriculture to forest) over the last 50 years. Wood substrates were placed in each stream in fall 2000 and collected periodically to quantify mass loss over time. Surface microbial biofilm respiration was measured by CO₂ production in lab assays. Wood breakdown rates ranged from 0.0012-0.0076 /d and were generally faster in agricultural streams. Microbial biofilm respiration increased with incubation time in all streams and was higher in agricultural streams than in forested streams. Preliminary results did not show a relationship between stream nutrient concentration and either breakdown rate or biofilm respiration. However, streams with slow breakdown rates tended to have low biofilm respiration indicating the potential importance of microbial processes in wood breakdown. Reforesting streams had breakdown rates and biofilm respiration more similar to agricultural streams indicating persistence of historical agricultural impacts on stream ecosystem processes.