| Nearly 2.4 million km2 of saline groundwater distribution area in the world is home to approximately 1.1 billion people.Groundwater salinization has become a global water environment and water resource issue.However,current research on saline groundwater is inadequate.The above issues manifest as an unclear saline groundwater formation mechanism,inaccurate identification and risk assessment of associated pollutants in saline grondwater,and ineffective saline groundwater prevention and control management.These research gaps not only have an impact on the prevention and control of water pollution and the efficient use of water resources,but they also exacerbate the problems of water resources and water environment,severely limiting society’s sustainable development.Weibei plain is a typical coastal area in northern China,as well as a strong land-sea interaction zone and a sensitive unit of human-natural environment interaction,with serious water pollution and water resource utilization.There is a large area of saline groundwater with frequent water pollution,and intensive human activities have put significant pressure on the fragile groundwater environment,making Weibei Plain an ideal location for saline groundwater research.In-depth research on groundwater salinization and its environmental consequences can provide critical theoretical and technical support for regional groundwater environment improvement,saline groundwater intrusion prevention and control,and coastal groundwater management.It has practical implications for the long-term development and utilization of water resources.Based on the research background described above,this paper focuses on the research goal of "groundwater salinization and its environmental effects," using Weibei’s saline groundwater as the research object and comprehensively employing research methods such as on-site monitoring,indoor experiments,theoretical analysis,and numerical simulation.The distribution of saline groundwater and groundwater runoff patterns are analyzed,and the main functional areas and associated hydrological processes in both shallow and deep groundwater are identified.The mechanism of brine formation and evolution is investigated,and the method of identifying hydraulic connections between brine reservoirs is summarized.The geochemical behavior of common pollutants in the saline-fresh water transitional zone is studied,and the water quality and potential health risks are quantified.The temporal and spatial evolution characteristics of flow field and saline groundwater intrusion under different mining schemes are simulated and predicted using a numerical model of regional saline groundwater migration.On this basis,a simulation-optimization model is built,revealing the synergistic response relationship between water resources,the environment,and economic benefits in a typical coastal zone.The main research results are as follow:1.Investigation of saline groundwater distribution and identification of groundwater circulation patterns.The distribution characteristics of groundwater in Weibei Plain and the main role of controlling groundwater formation are identified based on a review of previous studies.Six groundwater functional zones are divided:shallow groundwater flow zone,intense grondwater mixing zone,groundwater-seawater interaction zone,deep groundwater flow zone,deep groundwater mixing zone and brine storage zone.The effect of saline-fresh water mixing on shallow and deep groundwater is thoroughly examined,and the groundwater circulation evolution model in the Weibei Plain is summarized.2.Analysis of brine formation model and hydraulic connection between reservoirs.The response relationship between groundwater in different aquifers and climate change and sea level change is revealed using statistical analysis results of brine isotope data,and the brine formation model is summarized against the backdrop of paleoclimate change.Based on the analysis results of the preliminary investigation and field sampling of the brine reservoir,the hydrochemical composition,microbial community diversity and composition of the brine from Hanting saltworks and Changyi saltworks are all found to be significantly similar.Hanting saltworks’ brine exploitation horizon and the hydraulic connection between Hanting saltworks and Changyi saltworks are determined.3.Evaluation of typical pollutants’ geochemical behaviors and quantification of health risks in saline groundwater.Based on numerous field investigations,sampling and analysis,the distribution,sources,and main driving factors of typical pollutants in the transition zone between saline and fresh groundwater in Weibei Plain are revealed.The groundwater quality and potential health risks posed by groundwater pollutants are quantified.It is recognized that fluoride in groundwater poses greater health risks than nitrate,and drinking water consumption poses greater health risks than skin contact with pollutants,so special attention should be paid to reducing pollutant concentrations in drinking water and focusing on children’s health.The model of typical pollutant formation under seasonal fluctuation is summarized.Seasonal variations in groundwater environment control fluorine’s geochemical behaviors and cause seasonal enrichment of fluoride in groundwater.The seasonal variations in groundwater quality and the potential health risks of groundwater pollutants are revealed.The content of typical pollutants in groundwater obviously increases during the wet season,resulting in a decline in groundwater quality and a significant increase in health risks.4.Saline groundwater migration simulation and multi-objcctivc optimization management.Under the research background of saline groundwater intrusion in Weibei Plain,the temporal and spatial evolution characteristics of saline groundwater in more than ten years are investigated and analyzed,and the saline groundwater migration law is identified,in the regional scale,a three-dimensional numerical model of saline groundwater migration with variable density flow is established,which restores the dynamic evolution process of saline groundwater migration and predicts the temporal and spatial evolution law of saline groundwater migration under different mining schemes.Based on the surrogate model,a simulation-optimization model with three objectives constraints of regional groundwater exploitation,saline groundwater intrusion,and social economy,is developed to reveal the dynamic response relationship between water resources,water environment,and social economy.Taking into account the constraints of water resources,water environment,and social economy,the original groundwater exploitation in the three regions should be adjusted to decrease by 21.21%,decrease by 29.68%and increase by 24.94%,respectively,to ensure maximum groundwater exploitation,maximize economic benefits,and minimize the impact of saline groundwater intrusion. |
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