Chemical Characteristics And Formation Process Of Pore Water In Pingtan Island

As the largest island in Fujian Province,the Pingtan Island is located in the eastern part of the economic zone on the west side of the Straits.It is enriched in resources and has contributed to the economic development of Fuzhou and its surrounding areas for a long time.However,the artificial exploitation of groundwater caused the continuous decreases in groundwater levels,which changed the interface between salt and fresh water,destroyed the equilibrium between freshwater and seawater,and resulted in the seawater intrbusion into the freshwater aquifer.On the other hand,long-term transitional mining,unreasonable tidal flat development,and high water level marine aquaculture caused seawater intrusion.Taking the Quaternary pore water of Pingtan Island as the research object,the paper investigated groundwater chemistry,formation process and seawater intrusion characteristics,which has certain theoretical and practical significance.The groundwater chemical type of Pingtan Island is dominated by HCO₃·Cl-Na·Ca or Cl·HCO₃-Na·Ca,while groundwater affected by seawater intrusion is of Cl-Na type.Groundwater chemicals originated from rock weathering and seawater.Groundwater components are mainly controlled by hydrogeochemical processes of rock weathering,evaporative crystallization,leaching filtration and cation exchange adsorption.Seawater intrusion caused changes in groundwater components,and increased in concentrations Cl^-,Br^-,SO₄^2-and salinity.According to concentrations of Cl^-,Br^-,SO₄^2-,salinity,and?Na/?Cl,?Mg/?Ca and Cl/Br and other delineated seawater delineated the range of seawater intrusion.The seawater intrusion mainly occurred in the western part of Pingtan Island-the Hengyu-Guoyu-Jiyu-Dongyu area in the central part,the southern salt-salt salt field,the Shamaqi-Nanyu field,the eastern part of the eastern part of the Bay,and the Pingtan Island.The seawater intrusion in the western-central Hengyu-Guoyu-Jiyu-Dongyu area and the southern salt-salt salt field was relatively serious,while the east was relatively slight.The seawater intrusion in Pingtan Island was evaluated by using The Nemero index method and fuzzy mathematics comprehensive evaluation method with Cl^-,SO₄^2-,salinity?TDS?,?Cl/?HCO₃^-and sodium adsorption ratio SAR indicators as water parameters.Results showed that 53.52%of groundwater was unaffected?Class I?;26.76%of groundwater was classified as mild invasion?Class II?;8.45%as moderate invasion?Class??;11.27%as serious invasions?Class IV?.The main reasons included unreasonable mining of groundwater resources,high water level marine aquaculture and climate change.