CHEMICAL AND FLOW CHARACTERISTICS OF MAJOR KARST SPRINGS OF NORTH-CENTRAL OHIO

In north central Ohio, numerous large springs in and near Sandusky Bay discharge regional groundwater flow from recharge areas in the south. During the last ice age, the Laurentide icesheet likely reversed regional groundwater flow to southward. The current flow system is a confined carbonate/evaporite bedrock aquifer overlain by a surficial aquifer made of glacial drift. The springwater is highly mineralized (>10,000 ppm) and under artesian pressure. This research aimed to identify groundwater recharge zones, characterize flow, and examine major and minor chemical variations. The study has potential importance to drinking water quality because groundwater can supply nutrients to Sandusky Bay that encourage cyanobacteria to form Harmful Algae Blooms. Terrain and geological data provide spatial analysis for possible recharge zones. Groundwater flows from potentiometric highs in Logan and Morrow Counties to Sandusky Bay. Data loggers deployed at Castalia Blue Hole, Miller’s Blue Hole, and a flowing artesian well examined variations of temperature and specific conductance in 15-minute intervals. Analysis shows differences in physical properties in the groundwater at each site. Quarterly sampling of major ion and nutrient chemistry analysis of the groundwater shows slight seasonal variations in chemistry. Castalia Blue Hole temperature averages 11.3°C, and ranges from 10.9 to 11.9°C with specific conductance from 1750 to 1870 µS/cm. Miller’s Blue Hole temperature ranges from 8 to 13°C year-round and a higher specific conductance around 2,300 µS/cm. Groundwater from the Stidham well ranges from 11.5 to 12.12°C and specific conductance from 2430 to 2440 µS/cm. The Stidham well best represents groundwater since it directly samples the aquifer. Specific Conductance is similar between Miller’s Blue Hole and the Stidham Well, but they have different temperature ranges year-round. The limited variations in specific conductance and temperature suggest diffuse flow, even though the orifices appear to be conduit-type. Agriculturally related organic chemicals were not detected over the sampling period. However, nutrient chemistry may show the presence of fertilizers in groundwater based on nitrate concentrations.