Effects of the Upper Floridan Aquifer on Water Chemistry and Oxygen Metabolism in the Lower Flint River During Drought

Abstract

The lower Flint River in southwestern Georgia flows through the limestone formation of the Upper Floridan aquifer, and large exchanges of water occur through natural spring conduits between the river and the aquifer. Our studies center on how exchanges of river and aquifer water affect these aquatic ecosystems, particularly during periods of drought when both the aquifer and river are heavily stressed due to the combined effects of climatic conditions and human use. Large increases in nitrate and calcium concentrations in the lower Flint River between Albany and Bainbridge are attributed to an increase in the proportion of aquifer water that comes in from springs. Conversely, decreases in phosphate and ammonium result from dilution by groundwater. Measurements of microbial metabolism based on oxygen consumption indicate very low rates of bacterial activity and a strong dependency on bioavailable dissolved organic carbon during drought conditions. Groundwater inputs from the Upper Floridan aquifer play a critical role in maintaining the health of the river and should be sustained to ensure the ecological integrity of the lower Flint River ecosystem.