PHYSICAL AND ANTHROPOGENIC CONTROLS ON NUTRIENT CONCENTRATIONS ACROSS A MIXED-USE HEADWATER CATCHMENT

Streams and rivers are among the most important providers of goods and services (water for human use; habitat for economically-important species; regulation of flooding and soil erosion; recycling of pollutants; water quality control). Nutrient contamination of surface waters is a major concern worldwide. Nutrients (nitrogen and phosphorus) support the growth of algae and aquatic plants. In excess, they cause algae overgrowth, harming water quality, food resources, and habitats. Results from this project will improve our understanding of the relationship between land use, stream discharge, and nutrient concentrations in the Mohican River Watershed, a mixed-use catchment in north-central Ohio. Historical precipitation data from NOAA’s National Climatic Data Center was combined with nutrient analysis of stream water to evaluate the effects of discharge on nutrient transport. A GIS-based landscape model was used to examine relationships between streams and watersheds. Land use data from NLCD was used to select representative reach-catchment areas in one of four categories: forested, developed, cropland, and pasture. Nutrient concentrations were used for calculation of nutrient fluxes within the watershed. Sampling was undertaken during both baseflow and stormflow conditions. Results show that nutrient fluxes are highly controlled by land use and by precipitation events. In addition, there is a marked shift between local and external controls on biogeochemical processes under baseflow and stormflow conditions. During stormflow, nutrient input is primarily hydrologically controlled but during baseflow, biological processes dominate both the production and removal of nutrient ions from the stream. This short-term hydrological variability have a significant impact on the storage of nutrients in the study streams and on the amount of nutrients exported from the watershed to the Ohio River and the Gulf of Mexico. With Ohio becoming wetter, as a result of climate change, we should expect an increase in the supply of nutrients from similar headwater watersheds.