The Chaobai River (CBR) basin in northern China is experiencing an unprecedented continuous inflow of external water via the South–North Water Diversion Project, which has channeled water from the southern part of the country to the north. Consequently, the steady rise of groundwater table in recent years is threatening soil salinity regulation. The purpose of this study was to describe the status of salinity of the surface soil in the CBR basin and to evaluate the impact of environmental factors including groundwater table on the spatial distribution of soil salinity using multivariate analysis (MVA) technique. In this study, 10 chemical variables of soil samples collected in 204 sites along CBR were analyzed, considering their interaction with three environmental factors: the density of irrigation canals, groundwater depth and topography. Statistical analysis mainly consisted of principal component analysis (PCA), redundancy analysis (RDA) and clustering analysis (CA). The results allow defining the surface soil in the CBR basin as a slightly saline and moderately alkaline media. The first two axes of multivariate model approximately explains 51% of the observed variability and allows distinguishing two main domains: the saline and the alkaline. The variability of the saline domain, defined by major cations and anions, is obviously controlled by macro environmental factors, of which the density of irrigation canals and groundwater depth contributes 71% and 28%, respectively, while that of the alkaline domain, related to pH and bicarbonate, mainly manifests as singular behaviors of soil groups like rice cultivation or sewage irrigation. The results suggests that more attention should be paid to the ongoing water table rise to help inform future land management decisions and to prevent a double threat of both groundwater and surface water on soil salinization. Meanwhile, this study shows the enormous potential of MVA technique, specifically the complementary duo of RDA and CA, for integrating both global and local information of soil salinity and environmental factors.

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Background：Groundwater serves as the drinking water source, which chemical components directly affect human health. Different regions own their groundwater hydro-chemical characteristics based on various geological, hydro-geological conditions, human activities. From the perspective of human health, it is necessary to select groundwater quality health risk assessment (GQHR) factors combined with 2 hydro-chemical characteristics of different regions. Methods：In this paper, taking Tongzhou of Beijing,China as the study area, according to the groundwater hydro-chemical characteristics, NO3 -, NO2 -, NH4 + and Fwere extracted as assessment factors to evaluate the GQHR. Based on GQHR results, the formation and concentration characteristics of health risk factors and the prominent controlling role of influencing risk distribution were explored from natural and human factors. Furthermore, the targeted measures to prevent the increase of groundwater health risk were put forward. Results：Assessment factors: NO3 -, NO2and NH4 + are derived by human factors, such as sewage irrigation, fertilization, and Fstems from irrigation of geogenic high fluoride groundwater and fertilizer use. Still, their distribution is affected by natural factors (geology, geomorphology, and climate). The GQHR follows the order: children > adult females > adult males. The low and medium risk regions are located in upper groundwater, which are mainly controlled by natural factors (groundwater depth, aquifer medium, hydraulic conductivity coefficient, etc.) The measures to prevent the increase of groundwater health risk are to control the pollution sources and reduce the change of groundwater hydrodynamic conditions. The high-risk regions are located in eastern part of the study area, which are affected by both natural and human factors. The preventative measures are to reduce pollution caused by human factors and scientific groundwater resource exploitation and management.

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