Assessment of groundwater contamination by nitrates associated with wastewater irrigation: A case study in Shijiazhuang region, China

In and and semi-arid regions there is usually a shortage of irrigation water; thus, wastewater water, as well as other low-quality water resources, may become an important source of water and nutrients. However, (pre)treated wastewater may contain elements and compounds that can damage the environment. It also has the potential to affect water quality adversely in an aquifer that may be the source of drinking water in the area. In order to assess the impacts of wastewater on the environment, groundwater samples were taken and analysed in typical croplands in the North China Plain, where urban wastewater or groundwater have been used for irrigation for several decades. Concentrations of nitrate (NO3-) in groundwater in the study area varied from 50 to 130 mg l(-1) in the croplands irrigated by wastewater, but in the croplands irrigated by pumping wells, away from the Dongming Canal, NO3- concentrations are less than 35 mg l(-1). It was found that values of delta(15)N ranged from +5 to +13parts per thousand, and dominantly from +7 to +11parts per thousand, and the NO3- concentration in most wells with depths of less than 40 m was higher than the drinking water standard set by the WHO. Cluster analysis was used to classify the spatial distribution of nitrates resulting from the wastewater. Identification of chemical patterns is found to be effective for the comprehensive assessment of the spatial distribution of groundwater quality. It is also emphasized that the wastewater in this area controls the NO3- distribution in the groundwater, and should be used carefully to protect both soil and groundwater from NO3- pollution. Copyright (C) 2004 John Wiley Sons, Ltd.