ECOLOGICAL FINGERPRINTS IDENTIFY AQUIFER FLOWPATH OF SEWAGE CONTAMINANTS ENTERING ALEXANDER SPRINGS, FLORIDA

The primary flow component of Florida’s major spring systems is the Floridan aquifer system. The Floridan is a regional carbonate, karst aquifer. Eutrophication of the Floridan is increasing, due to aquifer-injection, induced-discharge, and seepage of sewage effluent, manure, and commercial fertilizers from urban and agricultural sources. The Florida Department of Environmental Protection (FDEP) recently evaluated Florida’s first magnitude springs (average flow > 100 cfs) as part of a multi-million dollar study of increasing groundwater eutrophication. Results of their single-point water quality sample event led to agency conclusions by that ground water discharging at the Alexander Springs Run system was low in nutrients.

Immediately downstream of the spring, the stream is clogged with a dense growth of macrophytes (nuisance and alien species of algae and vascular plants), and a thick dark layer of organic ooze blankets the bottom of the stream channel. These symptoms indicate chronic nutrient-loading and eutrophication of formerly pristine Alexander Springs Run. An independent study using stable nitrogen isotope (d 15N) analysis of these macrophytes revealed signatures indicative of sewage contamination.

The Ocala National Forest surrounds the site, minimizing contaminant introduction via the deeper, regional aquifer system tested by FDEP. Public toilets for the Forest Service’s Alexander Springs Recreational Area are located up-slope of the FDEP and independent study sites. The ecological fingerprints from this independent study are consistent with nutrient-loading of Alexander Springs Run via lateral flow and groundwater discharge of sewage introduced into the overlying sandy, surficial aquifer from the public toilets. This indicator-species analysis approach can reduce the time and expense of documenting ecologically-significant nutrient-loading from ground water, while identifying the contributing aquifer and the source of the nutrients.