Unusual Chemistry and Anthropogenic Contaminants in Upper Floridan Aquifer Groundwater Underneath the Chickasawhatchee Swamp
Opsahl, Stephen P.
Happell, James D.
Chanton, Jeffrey P.
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In the karst landscape of the lower Flint River basin, there are large exchanges of water between wetland depressions such as the Chickasawhatchee Swamp and the Upper Floridan aquifer (UFA). At times, the creeks and wetlands within the swamp are a source of water to the aquifer, and at other times the aquifer is a source of water to creeks and wetlands. Groundwater chemistry was examined between January 2002 and December 2004 as part of a preliminary assessment of the role of the Chickasawhatchee Swamp in regional hydrology. Evidence for the influx of water from the overlying wetland was provided by the presence of high methane concentrations and anoxia in some areas of the aquifer. Large temporal variations in groundwater chemistry underneath the swamp were also attributed to the dynamic mixing between surface water and ground water in this area. The average apparent recharge age of the water underneath the swamp varied between 24 and 57 years when determined using the 3H/3 He method. Chlorofluorocarbon (CFC) supersaturation was evident in both surface water and many ground water samples indicating an unidentified local source of CFC contamination. A large pulse of nitrate was observed in two wells that were down-gradient of an adjacent agricultural area. The nitrate pulse was much higher in concentration than other groundwater wells within the swamp, but similar to other parts of the UFA that have been contaminated by nitrate.