Sediment and Macroinvertebrate Responses to Forest Harvest. Results from a Paired-Watershed Study from the Pacific Northwest

Land-use changes related to forest harvest have the potential to increase delivery of sediments to streams affecting the physiology and distribution of benthic organisms. Although the amount of sediments delivered to streams have been reduced because of Best management practices (BMPs), there is still concern about potential effects on the aquatic community. Here we present results from the Trask Watershed Study, a multi-disciplinary research project located in the Coast Range of Oregon, designed to evaluate the effectiveness of BMPs in protecting water quality and aquatic species during forest management in headwater basins. We examined the macroinvertebrate community and stream sediments during eight years (six before and two after forest harvest) in five headwater basins subjected to different treatments (existence of a riparian buffer/ no buffer/ no harvest) and at three downstream sites to assess whether responses in fishless headwaters are transferred downstream to fish-bearing reaches. Although suspended sediments increased during the winter following harvest, this did not reflect on the amount of fine sediments deposited in the stream measured in summer. Post-harvest macroinvertebrate biomass was similar to pre-harvest, except at one site, and sediment-sensitive macroinvertebrates index scores did not show changes post-harvest.