[Using stable isotope to trace the sources of nitrate in groundwater in Shijiazhuang]

A dual isotope method of measuring both the delta 15N and delta 18O in NO3- was used to discriminate the origin of nitrate and its denitrification in groundwater in Shijiazhuang. Furthermore, the contaminated depth was discussed by tritium. The results show that the ratio of delta 15N/delta 18O in NO3- is close to 2:1, indicating that some denitrification is occurring in this area; The value of delta 15N and delta 18O in NO3- after denitrification are 4.6 per thousand-13.9 per thousand and 1.9 per thousand-7.8 per thousand respectively, which indicates that the main source of nitrate in groundwater are local fertilizer and Animal Waste/Septic Systems. The relationship between NO3- concentration and the depth also shows that the pollution depth is less than 150 m, which is corresponding to the depth of active rechargezone indicated by tritium content. This implies the shallow aquifer above 150m is vulnerable to pollution.