Study On The Mechanism Of Groundwater Salinization And Environmental Quality Evaluation Of Groundwater In The Yellow River Estuary

At present,the degradation of wetlands in the Yellow River Estuary National Park is severe,and the salinization of groundwater has become one of the most prominent ecological and environmental problems in the region.Identifying the sources of groundwater salt recharge in the Yellow River Estuary National Park,clarifying the internal mechanism of groundwater salinization,and evaluating the groundwater environment have become urgent requirements for improving the groundwater environment in the Yellow River Estuary National Park and curbing wetland degradation.In order to solve the above problems,with the support of the"Yellow River Estuary Ecogeological Environment Investigation and Evaluation（Wetland Ecosystem）"scientific and technological research project issued by the Shandong Provincial Bureau of Geology and Mineral Resources with Lu Dizi[2022]No.15（the notice of the Shandong Provincial Bureau of Geology and Mineral Resources Exploration and Development on the issuance of the 2022 Bureau of Geological Exploration Leading Demonstration and Scientific and Technological Research Project）,the geological data of the Yellow River Estuary National Park were collected,groundwater samples and surface water samples were collected on the spot at the Yellow River Estuary National Park,and sample data were obtained by isotope determination,indoor water analysis experiments and other means.The research methods of hydrogen-oxygen isotope relationship,water chemistry three-line diagram,and inter-ion relationship were used to analyze the salinity mechanism of groundwater and evaluate the environmental quality,and the results showed that:（1）According to the relationship between 8δ¹⁸O-δD relationship between groundwater,Yellow River water and atmospheric precipitation in the study area,it can be concluded that the diving in the Yellow River Delta mainly receives the replenishment of Yellow River water,seawater intrusion and modern atmospheric precipitation,in which the impact of seawater intrusion includes not only the mixing of modern seawater,but also the influence of the remaining ancient seawater.（2）Through water chemical analysis,it can be seen that Cl-is the main control ion of shallow groundwater quality in the study area.The Piper three-line diagram showed that the hydrochemical type of the northern coastal and paleochannel areas of the study area was mainly Cl^--Na⁺.In the south,from the upstream of the Yellow River Road to the estuary,the water chemistry type evolved from Cl^--Na⁺type water to SO₄^2--HCO₃^2--Na⁺-Ca²⁺-Mg²⁺type water,and finally evolved into Cl^--Na⁺type water.The key drivers for the formation of shallow groundwater chemistry in the region are lateral recharge and seawater intrusion in the Yellow River’s inflow path.The chemical composition of shallow groundwater is formed by mixing,evaporation concentration,dissolution filtration,and cation alternating adsorption under the influence of two major factors,and the strength of the above effects is significantly different in different regions.（3）The single-factor evaluation results show that the main pollutants of groundwater in the region are total hardness,TDS,chloride,manganese and sodium,which are extremely heavily polluted,among which chloride pollution is the most serious,and the chloride pollution index of 50%of the monitoring wells in the study area exceeds 10.The comprehensive evaluation results of Nemero showed that the shallow groundwater quality in the study area was relatively poor,and the water quality of 65%of the monitoring points was poor or very poor,but the excess factors were basically total hardness,TDS,chloride,etc.,which were related to the salinization background of the region,basically salty or brackish water,and were not suitable for drinking.The results of the causal analysis show that there are three main causes of groundwater pollution in the study area:the background of regional salinization,the interaction between geological background and human activities,and the influence of human activities on groundwater.Among them,the contribution rate of regional salinization background causes was 39.575%,which exceeded the sum of the contribution rates of the latter two causes,indicating that the characteristics of groundwater quality in the current study area were dominated by the regional salinization geological background and formed by human interference.