Origin Of Shallow Salt(Brine) Water Salinity In The Coast Of Laizhou Bay

Underground fresh water is a very valuable water resource in the coastal areas of the southern Laizhou Bay.With the rapid urbanization of the coastal cities,the problem of groundwater salinization is now becoming more and more severe in this area,especially in the past twenty years.Previous studies on this issue mostly focused on the mixture of fresh water and seawater or brine.In this study,water samples analyzed include the Bailang River water and the estuarine seawater,groundwater in the southern plain,as well as the brine from the local brine production area,totaling 46 pieces.In terms of methodology,relationships between solvent?stable isotopes of water molecules?and solute?Cl-?are used to identify the properties of water molecules?i.e.,atmospheric water molecules vs.seawater molecules?and the salinization mechanism?s?,with the latter generally falling into three categories,namely,evaporation,dissolution,and mixing.The mixture of freshwater and seawater?cf.seawater intrusion?is actually a special case of mixing.And then the main components(K⁺,Na⁺,Ca²⁺,Mg²⁺,HCO₃^-,SO₄^2-),halogen elements?F^-,Cl^-,Br^-,I^-?,trace elements(Li⁺,Sr²⁺,Ca²⁺)and piper diagram are analyzed to determine the origin?s?of salt.On basis of our results,the following conclusions are drawn on river water,groundwater and brine,respectively.?1?Isotope values of 5 river water samples collected from the Bailang River suggest that the river water originate from the Bailang River reservoir in the upstream.In addition to the input from precipitation,the high salinity of rive water samples is attributed to the dissolution of evaporites debris,which is carried by the wind from the brine salterns into the river.The 7seawater samples collected at the Bailang River estuary show characteristics of a mixture of Bailang River water and standard seawater?undiluted seawater?to varied proportions.Due to the seasonal variations in river water,the chemical composition of coastal seawater varies with time and space.?2?Stable isotope values of the 6 groundwater samples collected in Laizhou are considered as a reference for our isotopic analyses.Comparatively,the 10 groundwater samples in Longkou reveal that the groundwater is directly recharged from precipitation,and the Cl-contents are derived from dissolved evaporites which are mostly halite crystals.Analysis of the 9groundwater samples in Shouguang indicates that the groundwater in Shouguang is mostly recharged from the precipitation of the southern mountain,but via the ancient Judian Lake that are infiltrated by rivers passing through this area.The salinity in Shouguang is mainly resulted from dissolution of transgressive strata salt and hydrolysis with diagenetic mineral in the soil layer.?3?The Cl-contents of the 9 brine samples collected in Laizhou Bay range from 58100mg/ L to 101000 mg/ L.??Measured values of ?D and ?¹⁸O were therefore corre cted based on isotope salt effect.Using five independent methods,analyses of the brine samples show that the molecules of the brine water originate from atmospheric water,an d that the salinity increase is associated with the dissolved marine evaporite,excluding th e possibility of residual water evaporated by seawater.Comprehensively,our results indicated that when carrying on a salt source study,the minor source can be easily neglected since it is weightily much less than the major one?s?.Specifically,1)since river water only exists in reservoirs and rivers,the chemical inputs are mainly through atmospheric precipitation?i.e.atmospheric gases and marine aerosols inputs?and wind blowing which could carry salt debris from the local brine salterns.Both of these two sources come from air and belongs to the regional impact factors.2)Likewise,the salt of groundwater,particularly in the coastal areas,is mainly from the salt dissolution of the transgressive formations and the hydrolysis with the diagenetic minerals in the soil layer.In this case,the two sources addressed above?atmospheric precipitation and salt debris from the local brine salterns?can be easily ignored.3)For the brine in the coastal area,the source of salt is usually referred to the marine salt and all other sources can be neglected.In this study,following the sequence from river water,via groundwater,to brine water,we are able to analyze the salt sources step-by-step.The result show that all these three parts,from air,aquifer and marine,respectively,indeed make the regional salt sources.Finally,we highlight that the wind blowing debris from the brine salterns can be much more important than the previously recognized.We infer it is an important factors giving rise to the salinization of shallow groundwater in the study area.