GROUNDWATER/SURFACE-WATER INTERACTIONS OF THE HISTORIC WETLAND PRAIRIES OF NORTHWEST OHIO

Historic Irwin Prairie is a wet prairie and as such its hydrology is in direct communication with the groundwater hydrology. Investigating the groundwater flow and storage within the Irwin Prairie unconfined aquifer involves investigating hydrologic interactions with the wet prairie as groundwater flows from areas of recharge to the wet prairie during the wet season. The groundwater/surface-water interactions of this system were monitored during the transition from active recharge into a dry period to observe the effects of changes in groundwater recharge and discharge. Hydraulic conductivity, specific yield, groundwater flow regimes and fluxes were quantified using fields of piezometers in the unconfined aquifer with pump tests and by monitoring the heads throughout the test period. Numerical modeling indicates that, during recharge, groundwater storage increases and much of the wet prairie is an effluent surface water body. This increase in storage, indicated by groundwater mounding and the presence of a groundwater divide, is slowly released to the wetland along the fringes by slow seepage through the wetland muck. Because human modification to drainage lowers the water table in the vicinity of the wet prairie, the groundwater mound dissipates, the groundwater divide migrates toward the wetland, and the wet prairie is converted to an influent surface water body. As a result, the historic wet prairies have been converted from predominantly groundwater discharge areas to wetlands that lose water by leakage through the bed of the wetland.