Objective In recent years, the groundwater of drinking water sources in Zhanjiang City has been polluted to varying degrees, such as nitrogen pollution, but its water quality status and nitrogen pollution sources are not clear. The purpose of this paper is to explore the hydrochemical characteristics and nitrogen sources of groundwater in drinking water sources in Zhanjiang City.

Methods Through various means such as hydrogeological, hydrogeochemical combined with environmental isotope analysis, the hydrochemical characteristics of shallow, middle and deep aquifers in Zhanjiang urban area and the main natural and human factors and nitrogen sources are clearly affected.

Results There are hydraulic connections and exchange phenomena in the recharge sources of shallow, middle and deep aquifers in Zhanjiang City. The seasonal variation of the hydrochemical types of each aquifer is not large, and the hydrochemical types of the shallow aquifer are more complex, which are affected and interfered by many factors. The water−rock interaction of shallow water in the study area is dominated by silicate weathering and evaporite dissolution, the middle water is dominated by silicate weathering, and the water−rock interaction of deep water is dominated by silicate weathering and evaporite dissolution. Rainfall and evaporation have a weak impact on the groundwater quality of each aquifer in the study area. Nitrate is the main inorganic nitrogen form in shallow and middle aquifers. Shallow groundwater has nitrogen pollution in both dry and rainy seasons. The main sources are septic tank leachate and domestic sewage. However, the overall concentration of inorganic nitrogen is not large and the pollution is light.

Conclusions The hydrochemical types of groundwater in drinking water sources in Zhanjiang City are complex, mainly controlled by silicate weathering and evaporite dissolution, and also affected by some human activities. Groundwater ammonia nitrogen and nitrate factors exceed the standard. Strengthening the supervision and prevention of domestic sewage, agricultural fertilizer and industrial pollution sources around the site can effectively ensure the quality and sustainable use of groundwater.