EVALUATING THE ADVECTIVE CAPACITY OF REGIONAL FLOW REGIMES TO TRANSPORT LEGACY PHOSPHORUS IN A TILED FARM FIELD, NORTHWEST OHIO

Harmful and nuisance algal blooms resulting from excess phosphorus is an issue of increasing importance for the water quality of the western Lake Erie basin. Dissolved reactive phosphorus (DRP) is delivered to Lake Erie from the Maumee River watershed which is dominated by agricultural land use. After decades of farmers adopting conservation land and crop management practices in the Maumee watershed many fields still test above recommended soil phosphorus levels due to the presence of legacy phosphorus in the near surface soil profile. Legacy phosphorus sources are currently exacerbating DRP loading in the Maumee watershed. A demonstration farm field operated by the Lucas County Soil and Water Conservancy located in the Maumee watershed was selected as a study area to evaluate the contributions of regional groundwater flow regimes and flow paths to the advective transport of legacy phosphorus. Phosphorus fertilizers have not been applied to the study area since 1995 yet soil phosphorus concentrations tested at 101ppm, exceeding tr-state agronomy soil recommendations. Fifteen piezometers were installed throughout the farm field to monitor the regional potentiometric surface and to allow for groundwater sampling. A modified current flow meter and datalogger were placed on the tile effluent outlet to record discharge velocities and volumes. Preliminary results indicate elevated concentrations of DRP present in piezometers (0.142mg/L) and in tile drain effluent (0.200mg/L) during a baseflow recession period. A positive correlation between elevated DRP concentrations in discharge effluent and discharge hydrograph frequency indicate groundwater transport of legacy DRP. These preliminary data sets highlight the importance groundwater flow regimes play in transporting legacy phosphorus off tiled farm fields characteristic of the Maumee watershed.