Nitrates in karst systems: a comparison of a relatively unimpacted system to impacted systems

Karst aquifers are highly susceptible to contamination because of the connection with surface water. Nitrate contamination is common; with most karst aquifers exhibiting some degree of impact. Horn Hollow Valley (HHV) in Carter County Kentucky is a karst aquifer system that appears to be minimally impacted by nitrate and chloride contamination. Sampling of the HHV area was conducted from June 2005 to November 2006. Nitrate as nitrogen (NO3-N) concentrations were between 0.13 to 1.54 mg/L; chloride concentrations ranged from 1.43 to 66.3 mg/L. Impact from anthropogenic sources are observed at 1 mg/L for NO3-N and 13 mg/L for chloride. Sources of nitrate are primarily soil organic matter and mineralized fertilizers. In addition to mineralized fertilizers, chloride appears to be contributed from road salts. Compared to waters from three other systems: the Mammoth Cave area, the southwestern Illinois sinkhole plain, and the Missouri Ozarks-Salem Plateau; waters from HHV exhibited lower concentrations of both NO3-Nand chloride. Waters from Mammoth Cave and the Missouri Ozarks tended to have higher NO3-N concentrations and similar chloride concentrations. Waters from southwestern Illinois had higher NO3-N concentrations and chloride concentrations. Overall, the karst aquifer of HHV appears to be a relatively pristine system, with minor human impacts.