Elucidating the Pollution Sources and Groundwater Evolution in Typical Seawater Intrusion Areas Using Hydrochemical and Environmental Stable Isotope Technique: A Case Study for Shandong Province, China

Guangquan Chen,Hongjun Yu,Xingyong Xu,Wenquan Liu,Qiao Su,Jin Lin,Guiyao Xiong,Tengfei Fu,Changsheng Peng,Yancheng Wang,Yunfeng Dai,Xilai Zheng,Imran Ali,Zhi Dou

doi:10.2113/2021/4227303

Abstract

Abstract Seawater intrusion has a serious impact on industry, agriculture, and people’s daily life. Thus, the present study was designed to elucidate the pollution sources and groundwater evolution in typical intrusion areas of Shandong Province by hydrochemistry and environmental isotope techniques. The water samples were collected to analyze the groundwater evolution under different intrusion, and groundwater evolution in the south of Laizhou Bay from 2005 to 2019. The findings indicated that the groundwater level dropping funnel caused by overexploitation was the direct causation of seawater intrusion in the three typical intruded areas. The groundwater evolution paths demonstrated that the groundwater in the south of Laizhou Bay had the fastest evolution rate and the highest degree of evolution, followed by the Dagu River Basin. The groundwater evolution extent and fitting of mixing lines indicated that the groundwater in the south of Laizhou Bay, Longkou, and Dagu River Basin was dominated by palaeosaltwater intrusion, modern seawater intrusion, and sea-saltwater mixed intrusion, respectively. Palaeosaltwater mixing produces a more severe salinization effect compared to seawater mixing. Meanwhile, the isotopes are gradually enriched with the deepening of intrusion, while the decrease of isotopes is delayed compared with the saltwater retreat. This is caused by that the stable isotopes enriched in the aquiclude due to the chemical permeation effect will be released into the aquifer after the salinity attenuates in the aquifer. The palaeosaltwater intrusion caused by anthropogenic activities has promoted serious fluorine pollution in the south of Laizhou Bay, while the groundwater nitrate pollution in Longkou was the most serious, followed by the Dagu River Basin due to high-density agricultural and domestic activity.

Highlights

About 40% population of the world live within 100 km in coastal zones [1], and freshwater stored in coastal aquifers has become a vital resource for sustaining the economy of coastal communities around the world [2]
The groundwater evolution speed and extent in Laizhou Bay are the highest in the three study areas, the groundwater samples are scattered close to the mixing line of brine and freshwater, and the brine as the initial groundwater distributed in a stripe shape on the south of Laizhou Bay
These findings confirm that the groundwater in Laizhou Bay is dominated by palaeosaltwater intrusion

Summary

Introduction

About 40% population of the world live within 100 km in coastal zones [1], and freshwater stored in coastal aquifers has become a vital resource for sustaining the economy of coastal communities around the world [2]. With the increase in water demands, groundwater pollution caused by seawater intrusion [3,4,5,6,7], waste disposal of urban residents, and industrial and agricultural production [8,9,10] have caused severe threats to freshwater resource. Seawater intrusion is widely regarded as a common environmental problem affecting groundwater in coastal areas [11,12,13]. Seawater intrusion changes the pore medium by changing the cohesion between particles and the microbial community in the aquifer, which affects the flow of groundwater in different natural conditions [15,16,17,18]. It is important to identify the types and evolution of seawater intrusion for proper management actions

Methods

Results

Conclusion