Using nitrogen isotope to identify the sources of Nitrate contamination in urban groundwater ——A case study in Zhuhai city

In order to assess the distribution,source of nitrate in groundwater system in South China,groundwater samples were collected during two different seasons and analyzed for NO-3、NH+4、NO-2、PO3-4、δ15N-NO-3 and EC、pH etc.The results show that nitrate is the dominant species of nitrogen in most samples.There are about is more than 40 percent of total samples whose nitrate concentration more than 10 mg/l（WHO drinking standard）.The values of δ15N-NO-3 ranged from 6.879‰ to 26.144‰.Nitrate in groundwater most originate from septic tanks and sewage water.Moreover,complexity of nitrate concentration in different season,higher values of δ15N in wet season suggest that denitrification probably occur in groundwater system as well as effects of dilution and mixing.