[Review of dual stable isotope technique for nitrate source identification in surface- and groundwater in China]

Water nitrate (NO3-) contamination is a world-wide environmental problem under the effects of intensive human activities. Sources identification of NO3- contamination in water is important for better management of water quality. Dual stable isotope data of nitrate nitrogen (delta15N) and nitrate oxygen (delta18O) combined with other stable isotopes and chemical analysis data have been frequently used to identify NO3- sources, differentiate percentage of the different NO3- sources and assess the nitrification/denitrification processes of surface water, groundwater and precipitation, respectively. This review summarized the analysis technique of nitrate delta15N and delta18O in domestic and abroad, assessed typical values of delta15N, delta18O from different NO3- sources and evaluated the progress in application of dual stable isotope of delta15N and delta18O technique to trace NO3- sources in surface- and ground-water. Both ion exchange-AgNO3 and bacteria denitrifying methods have been successfully used in tracing water nitrate sources nationwide. The comprehensive metadata analysis of nitrate sources showed that the delta15N values of sewage and manure, soil, precipitation, fertilizer ranged from 3 per thousand to 17 per thousand, 3 per thousand to 8 per thousand, - 9 per thousand to 9 per thousand, -2 per thousand to 4 per thousand, respectively. And the delta15N values of ammonium fertilizer ranged from - 4 per thousand to 2 per thousand. According to the stable isotope technique, sewage and manure were identified as the major nitrate sources of surface- and ground-water in China. This indicated that municipal sewage and aquaculture exerted serious influence on the nitrate pollution of surface water. In the future, long-term monitoring, dual stable isotope fingerprinting and hydro-chemical analysis should be applied together to quantitatively differentiate contribution of nitrate sources, and to assess seasonal dynamic of nitrate sources. It will provide useful scientific basis for water environmental management of China.