Using Long-term Chemical and Biological Indicators to Assess Stream Health in the Upper Oconee River Watershed

Macroinvertebrates are commonly used as biological indicators of stream habitat and water quality. Chemical variables, such as dissolved oxygen (DO), specific conductance (SC), and turbidity are used to measure stream water quality. Many aquatic macroinvertebrates are sensitive to changes in water chemistry, and streams with degraded water quality are often characterized by low macroinvertebrate diversity. Chemical (DO, SC, turbidity) and biological (macroinvertebrates) data from multiple tributaries of the North and Middle Oconee Rivers in Clarke County, Georgia, USA were collected seasonally from 2000 – 2006. Macroinvertebrates were identified, and communities were scored using the Georgia Adopt-AStream biotic index. Significant differences in biotic index scores were identified across sites and time using a two-way ANOVA. A general linear model relating chemical variables to biological score was more parsimonious than a model without chemical variables. These relationships varied by sample site, but they were consistent across seasons and years. Macroinvertebrate communities became degraded with increasing specific conductance, but associations with the other chemical variables were unclear. Results suggest the importance of using long-term chemical and biological indices in assessing stream health. INTRODUCTION AND BACKGROUND The Upper Oconee Watershed Network (UOWN) is a community-based, volunteer watershed monitoring group that collects quarterly biological and chemical samples from multiple tributaries of the North and Middle Oconee Rivers, Athens-Clarke County, Georgia, USA. Since 2000, we have routinely sampled both macroinvertebrates and water chemistry to assess water and habitat quality in seven tributaries. Land-use change in riparian areas due to urbanization is impacting stream ecosystems (Paul and Meyer 2001, Roy et al. 2003). Accompanying changes include: loss of riparian forests, increased transport of nutrients and sediment, alterations to the thermal and hydrologic regimes of impacted streams, and negative impacts on stream biota. The presence of wastewater treatment plant effluent and non-point source organic pollutants (Lenat 1988, Lenat and Crawford 1994) along with changes in bed sediment particle size in urbanized streams have been shown to reduce overall aquatic macroinvertebrate diversity and increase the relative abundances of tolerant taxa (Paul and Meyer 2001, Roy et al. 2003). Sedimentation and solute transport have been of specific concern, as these variables often correlate with low dissolved oxygen and negative impacts on macroinvertebrate communities, which are often used to as biotic indicators of stream habitat and water quality. Macroinvertebrates are widely used as bioindicators of stream water and habitat quality because they are relatively long-lived and immobile, easy to capture, and integrate effects of disturbance (Rosenberg and Resh 1993). Although comprehensive assessments of macroinvertebrate diversity and abundances are often limited by taxonomic knowledge and time (Engel and Voshell 2002), standardized qualitative biomonitoring is effective to assess stream water quality (Lenat 1988). Here we present a long-term chemical and biological assessment of seven streams in the Upper Oconee River Watershed from 2000-2006. Our objectives were to: 1) measure long-term temporal trends in chemical and biological variables across multiple streams in the watershed; and 2) determine how well chemical variables explain the variation in macroinvertebrate biological scores across sites and across years.