In order to understand the distribution and trace the sources of nitrate contamination in shallow karst aquifer in Jinfo Mountain area, hydrochemical concentrations and stable nitrogen isotopic compositions of dissolved nitrate in water samples collected from 19 epikarst springs were tested. The hydrochemical characteristics of these springs were measured in 1977, 2004-2009, and 2011. The data show that the hydrochemistry type of springs in different areas, and for different years, is Ca-HCO3 and Ca-HCO3-SO4, whereas the concentrations of NO3– is very sensitive to changes in human activities. All the springs with the highest NO3– concentrations in the study area showed minimum concentrations in 1977 and an upward trend in concentrations from 2004 to 2008, followed by a period of lower concentrations. Springs with low NO3– concentrations were distributed solely at the top of Jinfo Mountain in the National Nature Reserve. The hydrochemical variations observed in springs on Jinfo Mountain demonstrate that the implementation of environmental policy measures and industrial restructuring have successfully contributed to environmental protection of the springs. Furthermore, the nitrate concentration of samples range from 0.99 to 91.79 mg/L. According to the national drinking water reference dose of China (NO3—N≤10 mg/L), 7 water samples are of nitrate concentration(c:10.5 ~ 46.18mh/L) over the threshold. The isotope compositions of nitrate (δ15N-NO3) in the samples range from -5.1 ‰ ~ +12.2 ‰, and two main distribution intervals ranging from 0‰ ~ +5‰ and +10‰ ~ +12.5‰. Correlation between isotopic composition of nitrogen in nitrate (δ15N–NO3-) and nitrate concentration indicate that there are two main sources of anthropogenic nitrate contaminants, including animal/sewage and synthetic nitrogen fertilizer. springs inside of the National Nature Reserve with low nitrate concentrations (not over the water dring line) and δ15N–NO3- values consist with δ15N values of natural nitrate sources are interpreted as unpolluted waters becase thers is only forest inside National Nature Reserve in Mt. Jinfo.
Key words: shallow karst aquifer, nitrate contamination, nitrogen isotope, Mt. Jinfo area.