SULFATE CONCENTRATIONS AND DYNAMICS IN THE MAUMEE AND GREAT MIAMI RIVER

Nutrient concentrations and behavior have been researched immensely in Maumee and Great Miami watersheds, as they are noted sources of agricultural runoff to Lake Erie and the Gulf of Mexico, respectively. However, not much research has been done to understand sulfate concentrations and behavior in these or other agriculturally-influenced watersheds. The Maumee River at Waterville (16,395 km²) is located in northwestern Ohio, while the Great Miami, Fairfield (7,032 km²) watershed is located in the southwestern part of the state. Both watersheds are used primarily for agriculture (90% for the Maumee and 83% for the Great Miami); however the Great Miami also drains major cities with 12% urban area compared to less than 2% in the Maumee. The total flow of both of these rivers is increasing over time, though the Maumee River has a higher mean baseflow than the Great Miami River. Samples collected from 2013 to 2015 during the same sample months suggest that the Maumee watershed has median sulfate concentrations that are >20% higher than the Great Miami. That being said, the concentration of sulfate in the Maumee watershed has decreased significantly between 1975 and the present as interpreted from high resolution monitoring by the National Center for Water Quality Research Center. While longer-term trends may result from decreased emissions, dynamics in rising and falling flow have also shifted. Maumee watershed sulfate concentrations are higher in rising flow than in falling flow but trends are beginning to converge. These trends and seasonal concentrations and flow behaviors from both the Maumee and Great Miami are explored to better understand flow delivery dynamics in association with agricultural and agro-urban land use. Seasonally, median sulfate concentrations are the highest in the fall for both watersheds (62 mg/L for the Maumee and 40 mg/L for the Great Miami).