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

Abstract

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. This work assesses the potential impacts of anthropogenic activities on the Horn Hollow Valley (HHV) in Carter County Kentucky. HHV 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 (NO 3-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 NO 3-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 NO 3-N and chloride. Waters from Mammoth Cave and the Missouri Ozarks tended to have higher NO 3-N concentrations and similar chloride concentrations. Waters from southwestern Illinois had higher NO 3-N concentrations and chloride concentrations. Overall, the karst aquifer of HHV appears to be a relatively pristine system, with minor human impacts.

Differentiation of Surface Water and Groundwater in a Karst System Using Anthropogenic Signatures

“…With Na/Cl ratios near or above 1 (Figure 6), dissolution of halite was inferred for all of the stream waters and the waters of Cora Spring and Holesinger. The Na-Cl relationship for the streams suggested that halite was the source of the ions, which could be indicative of road salts contamination [3,5,26,27,45,58]. While Cl − concentrations above the 13 mg/L may indicate impacts of road salt, typical chloride concentrations of streams impacted by road salt exceed 100 mg/L, especially in the winter months [27,45].…”

“…Waters with chloride concentrations above 13 mg/L have been linked to the influence of anthropogenic practices [26]. Road salt, animal manure, septic effluent, and synthetic fertilizer have been documented to contribute Cl − to surface water and groundwater in karst areas [5,26,45,58]. Fertilizers used in the area include urea, anhydrous ammonia, diammonium phosphate, potash, and, on a more local basis, hog and dairy manure [38].…”

“…Nitrate is a common groundwater pollutant symptomatic of anthropogenic sources, i.e. agricultural, domestic sewages, and animal manure [61,62] and elevated concentrations are common in karst aquifers [5,7,22,63,64]. In karst areas of Illinois, elevated NO 3 -N concentrations have been reported in areas impacted by animal manure or domestic sewage [6,12,16,17,59,65].…”

“…In karst areas of Illinois, elevated NO 3 -N concentrations have been reported in areas impacted by animal manure or domestic sewage [6,12,16,17,59,65]. Background NO 3 -N concentrations reported for karst aquifers of southwest Illinois are typically equal to or less than 2.5 mg/L [5,6,16], with concentrations above that level indicative of anthropogenic influences [26]. All of the springs and streams had NO 3 -N concentrations above the background NO 3 -N concentration.…”

“…Numerous studies have examined the impact that humans have on karst areas (e.g., [4][5][6][7][8][9][10][11][12]). These studies highlight possible sources of pollutants, including the application of fertilizers and pesticides to fields [6,13,14], road salt [15], leaky septic systems [16,17], and wastewater [10,18,19].…”