Source characterization of nitrate in groundwater using hydrogeochemical and multivariate statistical analysis in the Muling-Xingkai Plain, Northeast China

The source characterization of nitrate (NO3−) in groundwater of Muling-Xingkai Plain (MXP) and the influence of NO3− on the water environment were studied by hydrogeochemical and multivariate statistical analysis. A total of 164 groundwater samples were collected, and the samples were classified into three clusters by using hierarchical cluster analysis. Cluster 1 (C1), accounting for 13% of total samples, was mainly located in local residential zones where the top soils were the medium-textured sediments. Cluster 2 (C2) and cluster 3 (C3) were mainly located in farmlands and residential zones where the clay sediments were overlaying the aquifers. The soil media covering the aquifers was an important factor controlling the concentration of NO3− in groundwater, which determined the infiltration rate of wastewater and the redox environment of aquifers. Only the samples in C1 exceeded the WTO standards for NO3− (50 mg/L), and the samples in C2 and C3 had low NO3− concentration (less than 10 mg/L). The excessive NO3− in groundwater was observed in the shallow groundwater under local residential zones, and it was closely related to the anthropogenic activities since the 1950s. The domestic sewage was responsible for the elevated NO3− contents in the MXP. Then, it was still necessary to construct the sewage disposal system in rural areas to further protect the groundwater resource to avoid the formation of extensive nitrogen pollution. At present, NO3− in the groundwater mainly shows a fertilizer and natural rainwater origin and is not demonstrating the significant deterioration of groundwater qualities and water environment.