SOURCES AND FATE OF NITRATE IN THE AQUIFER SYSTEM UNDERLYING SOUTHERN BALDWIN COUNTY, ALABAMA

The contamination of groundwater with nitrate has become a major problem throughout the world. These related problems are often the result of anthropogenic activities, lack of management, and overdevelopment of water resources. A local to regional-scale study was conducted as part of a large-scale effort to assess the extent of nitrate contamination, identify source zones of nitrate to groundwater and surface water systems, determine the primary processes controlling the fate of nitrate/nutrients in groundwater, and determine primary contributions of nitrate/nitrogen input to coastal surface waters of southern Baldwin County, Alabama. Nitrogen and oxygen stable isotopes of groundwater nitrate, chloride/bromide ratios (Cl^-/Br^-), nitrate (NO₃^-), sulfate (SO₄^2-), and land-use/land-cover (LULC) data were used in order to assess sources of nitrate to the groundwater system and determine the primary processes controlling the fate of nitrate in groundwater and contributions to the coastal surface waters in the study area. Isotope analyses of groundwater nitrate (e.g., nitrogen-d¹⁵N_NO3 and oxygen-d¹⁸O_NO3) indicate that nitrate in groundwater is primarily derived from the nitrification of ammonium in soil. Isotope and geochemical data analyses reveal that the presence of nitrate was likely the result of mixed end-members with signatures ranging from fertilizer to sewer and/or manure. However, analyses of land-use/land-cover and geochemical data suggest that groundwater signature is mostly influenced by nitrate sources originated from fertilizer application. Furthermore, isotope data indicate that denitrification was not an important process in this aquifer system. In the absence of denitrification and the presence of a permanent source, it is expected that the elevated groundwater nitrate concentrations will not be readily attenuated posing a potential contamination and degradation problem of coastal discharge zones (i.e. wetlands, estuaries, lagoons, and coastal lakes) into the future.