Changes In Benthic Macroinvertebrate Communities Following Timber Harvest In Headwater Streams Of A Louisiana Low-Gradient Watershed

Abstract

Louisiana Department of Environmental Quality (LDEQ) currently uses only physicochemical parameters to assess surface water quality. Based on their methods, the Flat Creek watershed, a low-gradient, forest-dominated watershed located in northern Louisiana, was included on the 303(d) list as impaired due to low dissolved oxygen (DO). Macroinvertebrate sampling may create a surrogate for these physicochemical parameters to appropriately address natural conditions and anthropogenic stresses. or this study, macroinvertebrate samples were collected at 11 stream locations five times; spring of 2006, and 2008, and late summer 2006, 2007, and 2008. During the fall of 2007, trees were removed on both sides of three 1st-order streams. This study investigates how macroinvertebrate communities respond to timber harvest in a low-gradient watershed. Specifically, the objectives of this study were to determine (1) if timber harvest exacerbates low DO levels, (2) if there are any effects on the macroinvertebrate community structures, and (3) if biocriteria could be utilized for credible total maximum daily load (TMDL) development. Monthly water quality measurements including stream temperature and DO were taken from 2006 and continued following timber harvest through the present. Nine of the eleven sites decreased in monthly DO concentrations after harvest. Results also indicate that a change was evident in DO sensitive communities in the confluence of some of the harvested sites, but not in the immediate harvested plot areas. Macroinvertebrate communities may provide understanding to short term anthropogenic nonpoint disturbance to determine TMDL improvements. Continued monitoring is essential to understanding natural conditions and the impact of the timber harvest.