Isotope Hydrology and Stream Nutrient Chemistry of the Cuyahoga River in Northeast Ohio, USA

Recent increasing occurrence of disruptive eutrophic conditions in Lake Erie highlights a shortcoming of our understanding on the dynamics of nutrients in aquatic ecosystems. In spite of significant reduction in point- source nutrient discharge, the loadings of bioavailable nutrients such as ammonia (NH4+), nitrate (NO3-), and soluble reactive phosphorus (SRP) from tributaries continue to sustain such harmful events. But little is known about how much and how the structure of nutrients changes along the Cuyahoga River, a major nutrient contributor to Lake Erie. To better understand the stream hydrology and nutrient dynamics in this impaired river, we proposed to 1) examine the stream hydrology through stable isotopic analysis, 2) determine the concentrations of various nutrient variables, and 3) evaluate the bioavailability of P in river bed sediments by chemical extraction tests. River waters and sediments were collected in a dozen locations from the Cuyahoga River and its major tributary five times from July 2007 to May 2008. As a result, we found that 1) river water becomes isotopically heavier from upstream to downstream, 2) nutrient concentrations increase stepwise downstream, and 3) changes in water soluble phosphorus (WSP) of river bed sediments are consistent with those of nutrient concentrations in river waters. The results of this study further attest that the majority of nutrient inputs are from point sources like effluents of municipal wastewater treatment plants.