Hydrogeochemical and isotopic study of the origins of groundwater salinization in the deep confined aquifer of northern Yangtze River

Qi Zhao,Yiqun Gan,Xiaosi Su,O Chudaev,R Millot,Y Kharaka,O Shouakar-Stash,R Harmon

doi:10.1051/e3sconf/20199807034

Abstract

The deep confined water of coastal plain of northern Yangtze River suffers salinization. That results from overexploitation. This work aims to investigate the geochemical processes that lead to the salinization for this aquifer. Multiple environmental tracers of major ions, minor ions and isotopes (18O, 87Sr, 13C) were used to yield reasonable conclusions. The TDS of the aquifer ranges from 387 to 2600 mg/L. The aquifer is mainly composed of fresh water. Brackish water is distributed in the eastern and southern coastal areas, and is scattered in some inland areas. The water chemical type evolves from HCO3-Na to Cl-Na as TDS increases. Groundwater salinization is caused by mixing with saline water of marine origin. The aquifer is also affected by other hydrochemical processes. Silicate weathering and carbonate dissolution add Na+, K+, Ca2+, Mg2+ and HCO3- to groundwater. Sulfate reduction makes sulfate be deficient and HCO3- be enriched. Carbonate minerals equilibrium limits the increase in the concentrations of Ca2+, Mg2+ and HCO3-. Cation exchange reduces the concentration of Ca2++Mg2+ and increases the concentration of Na++K+. The aforementioned processes have a combined influence on the formation of fresh water with HCO3-Na type.

Highlights

Most of the coastal areas are economically developed with dense population and large water demand
The DCW in the study area is mainly composed of fresh water
The nitrate concentration of the DCW samples is

Summary

Introduction

Most of the coastal areas are economically developed with dense population and large water demand. Groundwater has become the main source of fresh water in coastal areas because of its good water quality and convenient for exploitation. With the rapid development of society and economy in coastal areas, the demand for freshwater resources has increased tremendously. Coastal groundwater in many areas suffers overexploitation, which induces some environmental problems. Salinization is the most common problem and limits the sustainable utilization of groundwater [1,2,3,4]. In order to prevent further deterioration of groundwater quality, it is of significant importance to fully understand the spatial distribution of salinity and its origin in this aquifer

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