A Preliminary Study On The Origin Of Recharge And Salinity Of Shallow Groundwater Of Yellow River Delta

In development of exploiting Yellow River Delt（aYRD）,increasing water requirementand water scarcity have become major conflict. The implement of controlling qualityand sanity of groundwater is believed to further decrease the amounts of accumulatedsalts in the soil and prevent the deterioration of local farming and ecological system.In order to address the problem, in the support of100Talent Programme of TheChinese Academy of Sciences: The Mechanisms of Water, salinity Mobilization InThe North China Farmland Ecosystem，field investigation，along with gathering theinformation of fluctuation in water table and analysis of hydrochemistry and stableisotope were carried out，which calculate the results of major ions concentrations,δ18O and δ2H in the both of surface water and groundwater samples. On the basis ofthese results, this research aims to analyze the impact of transfer of irrigation waterfrom the Yellow River, in particular in relation to the recharge of groundwater and theorigin of salinity of shallow groundwater. The conclusions are as follows:1. According to hydrogeochemical analysis of water samples, the variation insurface water hydrochemistry is larger than that in groundwater hydrochemistry,which reflects surface water possibly recharges groundwater. Most chemicalcompositions of the groundwater samples are characterized by Na-SO4-Cl type,gradually becoming the more Na-Cl dominated with increasing salinity. The totaldissolved solids(TDS) of groundwater ranges from0.51g/L to63.91g/L, with greaterTDS values in areas of low topographic relief, while lower TDS values are located inthe areas where the water table fluctuations are higher or good permeability andinfiltration are located.(eg Yellow River palaeochannels).On the other hand, the ratiosof K/Cl, Ca/Cl, Na/Cl, and Mg/Cl decrease with increasing Cl concertrations,indicating hydrogeochemical evolution via minor water-rock interaction (feldsparweathering) and significant evaporation.2. According to the measured values of δ18O and δ2H,stable isotopiccompositions show a characteristic evaporation effect in the shallow groundwater and confirm that direct infiltration of precipitation is generally not a volumetric importantsource of recharge to the shallow aquifer. Preferential recharge of river water afterirrigation events and precipitation from rare heavy rain events is likely responsible forthe depleted δ18O and δ2H values, together with high values of deuterium excess insome of the groundwater samples. The negative relationship between deuteriumexcess and δ18O values indicates that even in groundwater with relatively depletedδ18O and δ2H values, evaporation has occurred to a significant degree.