Land use influences and ecotoxicological ratings for upper clinch river tributaries in virginia.

The Clinch River system of southwestern Virginia and northeastern Tennessee is among the most biodiverse aquatic ecosystems of the United States, but its fauna are in decline. Unionidae (freshwater mussel) species are a major component of the Clinch's aquatic community, and their decline is well documented. Point-source discharges within the Clinch drainage are few, and primary stressors on the biota are believed to originate from non-point sources that are transported into the mainstem by tributaries. Currently, the relative influences of tributaries as stressors on aquatic biota are unclear. We studied 19 major tributaries of the free-flowing Upper Clinch River, developed an Ecotoxicological Rating (ETR) utilizing eight parameters, and assessed stream quality among land use categories using the ETR rating system. Biological, toxicological, habitat, and chemical variables were measured in each tributary, near its confluence with the Clinch. Geographic Information System software was used to quantify land use within each tributary watershed; all tributary watersheds are predominately forested, but agricultural, mining, and developed land uses (urban, transportation) are also present. ETRs indicated that the tributaries draining mining-influenced watersheds had greater potential impact on the mainstem than those draining agricultural or forested watersheds, because of poor benthic macroinvertebrate scores. ETRs ranged from 44 to 63, on a 100-point scale, for mining-influenced tributaries compared to agricultural (57-86) and forested tributaries (64-91). Mean ETRs for the mining-influenced tributaries (51) were significantly different than ETRs from agricultural and forested streams (75 and 80, respectively), and the presence of developed land uses had no significant relationship with ETRs.