The Evolution Of Ground-Saline Water And Process Mechanism Of Saline Water Intrusion In Southern Laizhou Bay

Saline water?brine?resource with high concentration is distributing widely in coast of Bohai Sea,and which is the typical saline water intrusion area.The study of evolution of ground-saline water and processing mechanism of saline water intrusion is useful for the reasonable configuration of groundwater resource and environmental science management.This essay is based on the sedimentary characteristics and groundwater distribution characteristics in coast of Bohai Sea.Sourthern Laizhou Bay is the study area and ground-saline water formed from Late Pleistocene is the main study object.The typical hydrogeological section of the middle and lower reaches of Bailang River in the souther Laizhou Bay is chosen as the example.Groundwater monitoring methods,hydrogeochemistry,isotopic geochemistry and groundwater numerical simulation methods are used to discuss the evolution of ground-saline water and the peocessing mechanism of saline water intrusion in Southern Laizhou Bay,and the responses of submarine ground-saline water under the reclamation.The main work and achievements gained are as follows:?1?According to groundwater distribution characteristics and factor analysis,the structure of the sedimentary layer is the dominant controlling factor of groundwater distribution and the evolution of sedimentary environment is the key factor of ground-saline water formation.Hydrochemical data show that saline water and brine are not the result of evaporation or the concentration of seawater.Brackish water and saline water with low mineralization in Holocene groundwater are formed by the mixing of fresh water and highly mineralized saline water,dissolution of evaporates by meteoric water,and water-rock interaction.And the saline water formed through dissolution of evaporates in Holocene and Late Pleistocene groundwater.There were many processes of transgression and regression in the coasts of Bohai Sea.The alternation of marine and terrestrial environment was constant.Especially since the quaternary period,the geographical environment and paleoclimate of the Bohai Sea have changed dramatically,and the coastal environment is constantly changing.At the same time,it has experienced several large-scale regressive processes of transgression?Cangzhou transgression,Xianxian transgression and Huanghua transgression?,and the influence scale of Xianxian transgression was the most widely.Because of the alternation of marine and terrestrial environment,a large amount of sea water was left in the land area and loose sediments.Under the evaporation,the moisture of stranded seawater entered into atmospheric environment and evaporate was left in sediments which became the source of formation of saline water and brine.Since the Holocene,the river began to develop and many deltas were formed.It is the main storage area and supply source of groundwater in the coasts of Bohai Sea.Besides,buried ancient channels have formed and provided a good channel for local groundwater movement.Isotopic results reveal that the main recharge of saline water in Holocene groundwater and Late Pleistocene groundwater is a combination of the meteoric water and lateral recharge from rivers.?2?The groundwater monitoring data has revealed that the groundwater levels show seasonal changing characteristics which are determined by meteoric water and artificial groundwater exploitation.Two large-scale groundwater depression zones have formed due to groundwater exploitation.Monitoring data revealed the formation of two clear groundwater depression zones in ZK04?fresh water zone,Gudi?and ZK05?brine zone,north of Yangzi?.The lowest groundwater levels were-8.78 m in ZK04 and-44.60 m in ZK05.The distribution pattern of EC value is“low–high–low”from south?land?to north?sea?at the same groundwater level.And the vertical distribution pattern of EC was“low–high–low”and“low–high”.The saline water intrusion occurs in a-10–-25 m section of ZK04 and a-10–-40 m section of ZK09.Saline water intrusion was found to follow a wedge-shaped intrusion pattern.Significant variations in Cl^-and Na⁺indicate saline intrusion in the southern area.The degree of saline water intrusion in Holocene groundwater was found to be more serious than that in Late Pleistocene groundwater.According to the saturation index in saline water intrusion area,anhydrous gypsum and gypsum are not saturated.And there is a reprecipition phenomenon of calcite and dolomite.Combined of HFE-Diagram,the exchange of Ca and Na is obviously in the groundwater mixing process.Groundwater numerical simulation is used to predict the groundwater quality and the migration of saline-fresh water interface.Under the conditions of reasonable exploitation of underground fresh water and full use of the ground-saline water?near to saline-fresh water interface?,the underground fresh water begins move to saline water area.The saline-fresh water interface moves to north and the saline water intrusion is relieved.If the underground fresh water resource is still in the state of overexploitation,the groundwater depression zone is expanding which can lead the saline-fresh water move to south.The phenomenon of saline water intrusion will be more and more serious.?3?The filling layer,added in the coastal reclamation project,is comprised of clayey silt and fine sand,and its high porosity means that it is suitable for water storage.After the reclamation,the groundwater system has been changed on the northern study area.The conditions of recharge,discharge and flow have been changed.Meteoric water was stored in the filling layer that became the stable recharge resource.The recharge resource and the filling layer can improve the properties of the confined aquifer to increase the groundwater level.They may also influence the groundwater quantity and the flow direction.The groundwater in the Holocene strata is clearly influenced by recharge and the previously saline water aquifers receive freshwater on an on-going basis,such that the water is now becoming fresh.Freshwater is the major recharge source in the upper section of the Holocene strata,between the surface and8.00 m depth,and the hydrochemical type has changed from Cl-Na to Cl·HCO₃-Na.In the lower section of Holocene strata?8.00²3.00 m?and upper section of late Late Pleistocene strata?23.00³8.00 m?,groundwater is influenced by seawater and groundwater of upper aquifer.The freshwater,seawater,and groundwater recharge in the upper aquifer has no influence on the groundwater in the section below the late Late Pleistocene?between 38.00 and 49.15 m?and the early Late Pleistocene strata?between 49.15 and 75.00 m?.