Effects of land use on groundwater chemistry in springsheds of the Upper Floridan aquifer, southwest Georgia

Background/Question/Methods

Widespread contamination of groundwater is an emerging global problem with consequences for both human and ecosystem health.  In Southwest Georgia, groundwater in the Upper Floridan aquifer is susceptible to chemical alteration, the extent of which may vary depending on land use within recharge areas. Springs along the lower Flint River (Georgia, USA) discharge large quantities of water from the aquifer directly into the river providing baseflow for most of the year.  We examined groundwater chemistry over a seven year period beginning in June 2001 to December 2007 in Radium (urban), Riverview (rowcrop), Bovine (pasture), and Hog Pen (pasture) Springs that discharge into the lower Flint River between Albany and Bainbridge, Georgia.  The Radium Spring springshed includes substantial urbanized land cover; whereas, the other three springs are recharged in areas dominated by agriculture.

Results/Conclusions Significantly lower nitrate concentrations in Radium Spring were attributed to differences in land use and lower rates of fertilizer application.  Positive correlations between groundwater levels and nitrate concentrations at Radium (r²=0.4486; p=0.0289) and Riverview (r²=0.3522; p=0.0013) Springs suggest that recharge water coming into the aquifer may contain higher concentrations of dissolved nitrate than groundwater already present in the system within these two springsheds.  Although a portion of the nitrate variability can be explained by water table fluctuations, long-term trends demonstrated a statistically significant increase in groundwater nitrate concentrations for Radium (r²=0.5016; p<0.0001), Riverview (r²=0.9105; p<0.0001), Bovine (r²=0.4507; p<0.0051), and Hog Pen (r²=0.8845; p<0.0001) Springs with net increases ranging from 0.4 to 1.3 mg/L. Similar to nitrate, there was a statistically significant increase in chloride concentrations for Riverview (r²=0.6929; p=0.0064), Bovine (r²=0.3482; p=0.0198),  and Hog Pen (r²=0.6446; p=0.0032) Springs.  In addition, nitrate concentrations were positively correlated with chloride concentrations at Riverview (r²=0.4481; p=0.0415), Bovine (r²=0.461; p=0.0064), and Hog Pen (r²=0.6778; p=0.0021) Springs suggesting that elevated nitrate and chloride concentrations may originate from a similar source within these rural springsheds.  This study demonstrates the importance of long-term datasets for evaluating the effects of anthropogenic activities on regional groundwater quality.