MULTIPLE ENVIRONMENTAL STRESSES AFFECTING STREAM WATER QUALITY IN A MIXED-USE WATERSHED: THE COMBINED EFFECTS OF GEOLOGY AND LAND USE

Understanding the cumulative impact of a suite of simultaneously occurring environmental stresses on stream water quality is essential for developing effective management and restoration strategies at the watershed scale. Although it is well known that land use and geology are the most important factors regulating nutrient concentrations in streams ecosystems, most of the variation in stream chemistry cannot be explained by one of these factors alone, suggesting that these systems are influenced by multiple factors acting at multiple spatial and temporal scales. Furthermore, the combined effect of land use and geology on stream water quality produces more than simply additive impacts and such dynamic is still poorly understood. In order to explore the complex linkages among land use and geology at the watershed scale, we sampled 65 stream reaches monthly over a complete seasonal cycle (May to March). The stream reaches were carefully selected to provide a representative mix of the most common geological-land cover types in three major physiographic regions of North-Central Ohio. Land use classes selected for each stream reach include: Forested, Developed, Cropland, and Pastureland. To provide statistical robustness, at least three stream reaches from each combination of lithology and land use were sampled. We hypothesized that the use of catchment geology on watershed water quality management can improve predictive relationships by mediating stream response to land use change.