SEASONAL CHLORIDE BEHAVIOR IN THE GREAT MIAMI RIVER, OHIO

Chloride is delivered to rivers by road salts, sewage treatment, and agricultural runoff throughout the year, but primarily by road salt during the winter months. This study examines precipitation, flow, and seasonal chloride behavior in the Great Miami River watershed at Miamisburg (6954 km²) and Fairfield (10,220 km²), Ohio. For the Miamisburg site, seasonal total yields were calculated from sixteen years of high-resolution chloride data (n>7000) from the Heidelberg University National Center for Water Quality Research (NCWQR). These were compared with flow and precipitation record compiled by the USGS and the Miami Conservancy District (MCD). At Fairfield, instantaneous samples were collected by the MCD and filtered and analyzed for median seasonal chloride trends at Wittenberg University between December 2013 and February 2014. Throughout the entire collection period, Miamisburg samples had its greatest median concentrations during fall months (79.7 mg/l) associated with low median discharge (28.0 m³/s). However, the 16 year average chloride yield was lowest in fall months (26,152 kg/km²) most distal from winter road salt applications. The greatest seasonal chloride yields occurred in both winter and spring months with both seasons increasing through time. Increased spring yields are associated with increased precipitation and discharge, whereas winter increases also reflect increases in salt applications. Like Miamisburg, the Fairfield site experienced greatest median chloride loading (2.0 kg/hr/km²) during winter months. Groundwater samples collected from an EPA site in Miamisburg, Ohio within the last 10 years suggest that Cl sources are seasonally dynamic. Molar Cl/Br values range from (476) in to (834) in the spring suggesting a shift from agricultural to urban deliveries.