NUTRIENTS AND ISOTOPES AS TRACERS IN UNDERSTANDING SURFACE WATER AND GROUNDWATER INTERACTIONS AT A RETIRED AGRICULTURAL SITE

Analyses of oxygen and hydrogen isotopes can be used to understand groundwater and surface water interactions in streams, especially during periods of baseflow. These data can be coupled with nutrient analysis to determine the extent of groundwater influence on surface water in streams. The purpose of this study was to quantify surface water and groundwater interactions at Andalusia Farm in Milledgeville, Georgia. Andalusia is a retired farm, which is now in recovery and has been agriculturally inactive for over 30 years. This work is part of a larger project to understand the influence of internal loading (caused by past agricultural activities) on the water quality of a creek running through the farm. The creek is listed as impaired by the EPA. Nutrient concentrations were monitored in groundwater and a nearby pond. Average nitrate concentrations were highest in the groundwater (3.2 mg/L) during the monitoring period while phosphate concentrations were highest in both the pond and groundwater (0.72 mg/L). The creek had the lowest concentrations of nutrients despite having high nutrients sorbed on its sediments. Preliminary O¹⁸/O¹⁶ and H²/H isotope data show that the pond and the groundwater had a strong influence on the stream. Combining isotope and nutrient data will provide the most detailed insight into surface water and groundwater interactions at the site.