Natural and human-induced factors controlling the phreatic groundwater geochemistry of the Longgang River basin, South China

Wei Li,Linshen Xie,Xiaohong Chen,Shuping Yi,Gong Cheng,Zhao Liu

doi:10.1515/geo-2020-0039

Abstract

Abstract Groundwater chemical evolution is the key to ensuring the sustainability of local society and economy development. In this study, four river sections and 59 groundwater wells are investigated in the Longgang River (L.R.) basin in South China. Comprehensive hydrochemical analysis methods are adopted to determine the dominant factors controlling the chemical evolution of the local phreatic groundwater and the potential impact of human activities on groundwater quality. The results indicate that the ionic composition of the local phreatic groundwater is dominated by Ca2+ (0.9–93.8 mg/L), HCO3 − (4.4–280.0 mg/L), and SO4 2− (1.0–91.0 mg/L). Ca–Mg–HCO3, Ca–Na–HCO3, and Na–Ca–HCO3 are the major groundwater hydrochemical facies. Water–rock interactions, such as the dissolution of calcite and dolomite, are the primary source of the major ions in the local groundwater. Cation-exchange reaction has its effects on the contents of Ca2+, Mg2+, and Na+. Ammonia concentration of the sampling sections in the L.R. increases from 0.03 to 2.01 mg/L along the flow direction. Groundwater nitrate in the regions of the farmland is attributed to the lowest level of the groundwater quality standards of China, while the same test results are obtained for heavy metals in the industrial park and landfill, suggesting a negative impact of the anthropogenic activities on the local phreatic groundwater quality.

Highlights

Groundwater is the most important source of freshwater throughout the world, and one-third of the world’s population relies on groundwater supply [1,2,3]
Studies focused on the anthropogenic activities resulting in groundwater pollution of nitrate/heavy metals [15,16,17,18,19,20,21]; groundwater geochemical assessment using geostatistical and geographic information system approaches [22,23,24]; and groundwater salinization related to pumping and irrigation [25,26]
In the context of current needs, geochemical survey was conducted in the L.R. basin in Shenzhen, South China, and the specific objectives of this study were to (1) investigate the geochemical evolution of groundwater in the L.R. basin using the hydrochemical analysis methods; (2) evaluate the local water quality status and the predominant factors of natural and anthropogenic activities on the groundwater chemistry; and (3) identify the impact of the potential pollution sources on the groundwater quality

Summary

Introduction

Groundwater is the most important source of freshwater throughout the world, and one-third of the world’s population relies on groundwater supply [1,2,3]. Rapid urbanization and increasing population have accelerated the consumption of groundwater resources and caused deterioration in groundwater quality [4,5,6], which raises concern about the drinking water safety worldwide, especially in the developing countries such as India, Pakistan, and China [7,8,9]. Groundwater chemical evolution is largely dominated by the natural factors (topography and landforms, stratum, lithology, meteorological conditions, water– rock interaction, etc.) and the anthropogenic activities (agricultural irrigation, exploitation for domestic water supply and industrial manufacturing, etc.) [12,13,14]. A significant number of studies have been conducted on this topic owing to the importance of the domestic water supply. The regions with highly developed river net (such as the South China) generally consider the surface

Objectives

Methods

Results