A NEW LOOK AT MAJOR KARST SPRINGS OF NORTH-CENTRAL OHIO

North-central Ohio exhibits a subtle, but extensive, karst terrain developed in Devonian age limestones. Caves, sinkholes, sinking streams and conduit springs which are characteristic of karst settings are present, but the area has been modified by glacial processes that have complicated the genesis of these features, and also obscured them through drift burial. Previous studies indicate that groundwater circulates deeply from recharge areas in the south, traverses northward through soluble beds in the Salina Group, and discharges in a series of highly mineralized springs near, and in, Lake Erie. In order to better understand the present hydrology, and genesis of this regional flow system, we have initiated high-resolution monitoring of the 2 major springs, Castalia Blue Hole (CBH) & Miller’s Blue Hole (MBH), as well as a flowing artesian well. For this initial characterization, temperature and conductivity were measured on a 15-minute interval. Diel variations in temperature are apparent in the MBH record (up to ~3 deg C), and to a lesser effect on the MBH record (~1 deg C). These are artifacts of deployment and water pool residence time. The flowing well temperature is invariant (instrument resolution ~0.1 deg C). CBH water was consistently about 1 deg C cooler (11 deg) than the artesian well water (12 deg). This may reflect a shallower/shorter residence time flowpath, or a more localized variation. During glaciation the area was overridden by ice, and groundwater flow was likely reversed from its present northward direction. Prior to ~12,200 BP this area was inundated by Lake Erie during a lake highstand, and both CBH and MBH would have been submerged. Beginning around 12,000 BP even the currently submerged springs in Sandusky Bay would have been sub-aerial. The complex hydrologic history, as well as highly soluble evaporite beds at depth, make for a unique genesis of this karst landscape and the regional flow system underlying it.