title: Tracing nitrate pollution sources and transformation in surface- and ground-waters using environmental isotopes.
abstract: Water pollution in the form of nitrate nitrogen (NO3(-)-N) contamination is a major concern in most agricultural areas in the world. Concentrations and nitrogen and oxygen isotopic compositions of nitrate, as well as oxygen and deuterium isotopic compositions of surface and groundwater from a typical irrigated region in the North China Plain (NCP) collected from May to October in 2012 were analyzed to examine the major nitrate sources and transformations. Concentrations of NO3(-)-N ranged from 0.2 to 29.6 mg/L (mean of 11.2 mg/L) in surface water, and from 0.1 to 19.4 mg/L (mean of 2.8 mg/L) in groundwater. Approximately 46.7% of the surface water samples and 10% of the groundwater samples exceeded the World Health Organization (WHO) drinking water standard for NO3(-)-N. Surface water samples that exceeded the standard were collected mainly in the dry season (May and October), while groundwater samples that exceeded the standard were collected in the wet season (June). Overall, the highest nitrate levels were observed in surface water in May and in groundwater in June, indicating that fertilizer application, precipitation, and irrigation strongly influence the NO3(-)-N concentrations. Analyses of isotopic compositions suggest that the main sources of nitrate are nitrification of fertilizer and sewage in surface water, in contrast, mineralization of soil organic N and sewage is the groundwater sources during the dry season. When fertilizers are applied, nitrate will be transported by precipitation through the soil layers to the groundwater in the wet season (June). Denitrification only occurred in surface water in the wet season. Attempts should be made to minimize overuse of nitrogen fertilizers and to improve nitrogen use efficiency in irrigated agricultural regions.
authors.affiliation: Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China; University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China. Electronic address: lifadong@igsnrr.ac.cn.
authors.forename: Fadong
authors.initials: F
authors.lastname: Li
authors.affiliation: Center for Agricultural Resources Research, Chinese Academy of Sciences, Shijiazhuang 050021, China.
authors.forename: Qiuying
authors.initials: Q
authors.lastname: Zhang
authors.affiliation: Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China.
authors.forename: Jing
authors.initials: J
authors.lastname: Li
authors.affiliation: Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China; University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Liu
mesh_terms: D000383:Agriculture; D002681:China; D004784:Environmental Monitoring / Q000379:methods*; D060587:Groundwater / Q000737:chemistry*; D009566:Nitrates / Q000032:analysis*; D009587:Nitrogen Isotopes / Q000032:analysis; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D009566:Nitrates; D009587:Nitrogen Isotopes; D014874:Water Pollutants, Chemical
keywords: Groundwater; Irrigated agricultural region; Isotope; Nitrate; Surface water