| Abstract/Description or Keywords |
I investigated the immediate effects of clear-cut logging on the export of invertebrates and organic matter from headwater streams by using a Before, After, Control, Impact, Paired series approach (BACIP). Seventeen high elevation streams within two study areas (Horsefly River and Eagle Lake) in the southern interior of British Columbia, Canada were sampled for drifting macro-invertebrates, fine particulate organic matter (FPOM), and dissolved organic carbon (DOC). Invertebrate drift was collected by diverting the entire stream flow through a 250 Ķm mesh drift net over a 24 hour period (in triplicate for a total of 72 hours), directly before and one year after logging. I compared differences between 10 clear-cut treatment and 7 control streams in terms of invertebrate drift biomass/abundance flux (mg 24 hrs-1and invertebrates 24 hrs__), invertebrate drift biomass/abundance density (mg m__ and invertebrates m__), and FPOM and DOC concentration and flux (mg L__ and mg 24 hrs__). In addition to total invertebrate export, biotic metrics in the form of composition measures, taxa richness and diversity were calculated to determine changes in the invertebrate drift community. In the pre-impact phase of this study, I found that headwater streams were productive exporters of invertebrates (18-5382 invertebrates 24hrs__) and organic matter (FPOM: 3-516 g 24hrs__, DOC: 105-1579 g 24hrs__). In the post-impact analysis, significant increases in total drifting invertebrate biomass and abundance flux were detected in clear-cut streams at Horsefly River. Additionally, community analysis of the drift composition showed significant changes in flux and density of Ephemeroptera (E), Plecoptera (P), Trichoptera (T) and Diptera (D). %EPT (ratio of EPT/total invertebrate abundance) was the only measure to indicate reduced abundance of sensitive taxa as a result of logging at both study areas. Significant changes in diversity were also observed at Eagle Lake. Overall, no significant responses in total flux or concentrations of FPOM and DOC were revealed. It is possible that seasonal and longer term annual monitoring may further define trends that were observed in the short term. |
