Pore-Water And Groundwater Hydrochemical Characteristics And Hydrogeochemical Processes In Baiyangdian Lake Basin

Baiyangdian is the largest freshwater lake type wetland in the North China Plain?NCP?,which serves as a supplement to the groundwater regulating regional climate.In recent years,due to the over-exploited water resources and the arid climate,the lake is surferring fromdrying and shrinking,ecological deterioration,the biodiversity destruction and function degradation.The recharge,runoff and discharge conditions of groundwater has changedgreatly,which lead to a series of resources and environment problems,and became the hot spot in our country and international hydrogeology.This paper comprehensively utilizes the hydrochemistry and isotopes of pore-water and groundwater to study the chemical characteristics and hydrogeochemical processes in different aquifers of the Baiyangdian lake basin,and evaluates effects of palaeoclimatic evolution oxygen isotopes and hydrochemica lcomponents of pore-water in sediments,which has therotical and practical significance.Major conclusions are shown as follows.?1?The major components of aquicludesedimentswere higher than thosein the aquifersediments.As the depths increased,the contents of most elements decreased gradually due to the removal of the elements.However,Fe,Mn and Ti were gradually enrichedin the aquicludesediments due to the input of terrestrial products.The trace elements gradually increased with depth in aquicludesediments,and decreased in aquifer sediments,which weremainly controlled by Fe and Ti.?2?The pore-water in the study area was neutral to weak alkalinity.Compared with the porewater in aquifer,the porewater in aquiclude had higher EC value.The main anion was HCO₃^-,and Na⁺was the main cation.With the increase of depths,the concentrations of Na⁺,HCO₃^-and pH increased,while concentrations of Ca²⁺,Mg²⁺decreased.Environment conditions gradually became reducing.The hydrochemistry type changed from a mixed type to HCO3·SO4-Na type.Results of hydrogen and oxygen isotopes of porewater indicated that the source of pore-water in aquifers was the atmospheric precipitation under the influence of evaporation,while the porewater in aquiclude showed the characteristics of ancient atmospheric water.?3?Groundwater components were similar topore-waters of sandy sediments.Results of stable hydrogen and oxygen isotopes showed that groundwaterbelongedto the precipitation under the influence of evaporation,and deep groundwater in aquifers was recharged from higher altitudes under or colderclimate.?4?Themainhydrochemicalprocessesinaquiferswere evaporation-crystallization,rockweathering,cationexchange,and oxidation-reduction.The similar components and hydrochemical processes of groundwater and pore-water showed the possibilities of the applications of pore-water on the hydrogeochemical study,which could get precise results of the hydrogeochemical components and processes in specific depthsof the different aquifers.?5?Sediments ages were measured by using ¹⁴C,OSL and paleomagnetism.Palaeo-vegetationand palaeo-climate evolutionshad been reconstructed by the analysis of the sediment palynology:the warm and humid climate during Tertiary;the cold and dry climateduring the Quaternary,with three warm distinct interglacial periods of climate in the middle;the warm climate duringthe Holocene.The climate changes would affect oxygen isotopes and Fe,Al,K concentrations of porewater.With the warmer climate,the values of the oxygen isotopes of porewater werepositive,and the hydrolysis of clay minerals increased.