Impact of land-use types on nitrate concentration and δ15N in unconfined groundwater in rural areas of Korea

An understanding of the long-term changes in the nitrate contamination pattern of unconfined groundwater is critical to conservation of drinking water in rural areas supporting mixed land-use activities such as cropping, livestock farming, and residence. To examine the effect of different land-use activities on nitrate contamination, groundwater samples were collected monthly for 3 years (1997-1999) from 12 wells in rural areas with different land-use activities and analyzed for the concentrations and N isotopic ratios (delta N-15) of nitrate. The characteristics of nitrate contamination clearly differed with land-use activities. The percentages of samples that had a nitrate concentration exceeding the national standard for drinking water (10 mg N L-1) were 0, 23, 43, and 67% for the uncontaminated natural area, cropping area, cropping-livestock farming complex area, and residential area, respectively. The range of delta N-15 values was between +1.4 and +4.5 parts per thousand for groundwater nitrate from the uncontaminated natural area. In the cropping area, the delta N-15 values were slightly different with the type of fertilizer applied to fields in the vicinity of the well, and the values ranged between +8.7 and +14.4 parts per thousand for the compost-applied area and between +4.5 and +8.5 parts per thousand for the area where urea was applied with compost. The delta N-15 values of the cropping-livestock farming complex area ranged from +1.0 to +17.7 parts per thousand, probably resulting from mixed contamination sources (inorganic fertilizer and livestock manure). The well located closest to the livestock feedlot had relatively higher delta N-15 values, with a range between +8.7 and +17.6 parts per thousand. In the residential area, a higher delta N-15 (most frequently above +10 parts per thousand) of nitrate suggested that the major source of contamination was effluent from leaky septic tanks. Our data showed that unconfined groundwater is susceptible to land-use activities above the aquifers, and the impacts of the activities could be more precisely inferred from long-term data on the concentration and delta N-15 of nitrate. By determining the impacts, more effective (specific to contamination sources) measures for preventing groundwater quality could be implemented. (c) 2006 Elsevier B.V. All rights reserved.