Effects Of Groundwater And Replenishment Water On Water Salinity For Lake In Arid Areas

As an important water carrier in arid and semi-arid regions,lakes play an important role in maintaining regional water cycle and ecosystem health.Due to the scarcity of precipitation,strong evaporation and shortage of surface water resources in dry areas,groundwater plays an important role in maintaining the water balance of lakes in dry areas.In recent years,affected by climate change and human activities,the water environment problems such as shrinking lake surface,accelerated salinization and serious water pollution in dryland lakes have become increasingly prominent.Ningxia Shahu Lake is a typical artifical replenishment water lake in the dry zone.Artificial recharge has greatly alleviated the water shortage of the lake and has become an important means to maintain the water balance of the lake.However,the impact of artifical replenishment water（water quantity and quality）and the resulting changes in the interaction between lake water and groundwater on the salinity evolution of the lake is still lacking in in-depth systematic research,which is difficult to support the scientific management and protection of the lake.In this paper,through a combination of field investigation,indoor experiment and theoretical analysis,the effects of different mixing ratios,different temperature and humidity and different artificial water quality on the chemical characteristics of lake water were considered,and a total of 51 static mixing experiments and 5 groups of mixed dynamic monitoring experiments were carried out,and the effects of groundwater and artificial water recharge on the salinity evolution of lakes in arid areas were studied,and the main conclusions are as follows:（1）Under different mixing ratios,different temperature and humidity,and different artificial recharge water quality conditions,compared with the initial moment,the lake water at the end of the experiment all showed an increase in K⁺,Na⁺,Cl^-and SO₄^2-concentrations,a decrease in Ca²⁺,Mg²⁺,HCO₃^-and CO₃^2-concentrations,a significant increase in TDS,and a change in the water chemistry type to Cl-SO₄-Na type.The hydrogeochemical simulation results show that the salinity of lake water at the end moment is closely related to the hydrogeochemical effects of rock salt dissolution,gypsum dissolution,soda clay dissolution,calcite precipitation,dolomite precipitation and alternating cation adsorption,in addition to the effects of recharge water quantity,recharge water quality and evaporation.（2）Under different mixing ratios and different temperature and humidity conditions,the salinity of lake water at the end moment did not increase monotonically with the increase of groundwater recharge ratio and drainage ditch water ratio.Influenced by the proportion of Yellow River water,groundwater and evaporation,TDS was highest at the end of M6（Groundwater:Yellow River water=6:4）and lowest at the end of M1（Groundwater:Yellow River water=1:9）.p H values in M1～M5 were higher than those of water samples at the beginning,mainly influenced by the non-allosteric dissolution of calcite,which consumed H⁺in the water column and made the p H values rise rapidly;calcite precipitation and dolomite precipitation occurred in M6～M9,and p H values did not change significantly.With the increasing proportion of drainage ditch water,the TDS of the lake water at the end moment showed a trend of first decreasing and then increasing.When the drainage ditch water accounted for 60%of the artificially recharged water,the TDS of the lake water was the lowest;when the proportion of drainage ditch water was 90%,the TDS of the water body at the end of the experiment was the highest.（3）Under different temperature and humidity conditions,when the humidity is the same,with the increase of temperature,the evaporation of lake water becomes larger,at this time,the dissolved amount of rock salt and gypsum shows a trend of first decreasing and then increasing,and the precipitation of calcite and dolomite at 25℃is smaller.When the temperature is the same,the evaporation decreases with the increase of humidity,the dissolved amount of rock salt and gypsum decreases,and the precipitation amount of dolomite and calcite increases.（4）Comparing the salt accumulation in the lake under different conditions,it can be seen that the influence of environmental factors on the salinity evolution of artificially recharged lakes in dry areas is:temperature and humidity factor>artificially recharged water quality factor>groundwater-yellow river water mixing ratio factor.Meanwhile,based on the hydrogen-oxygen stable isotope characteristics of the lake water at the end moment of the experiment,comparing the evaporation ratios obtained by the Rayleigh fractionation method and the weighing method,the reliability of the Rayleigh fractionation estimation results decreases when the temperature is lower than 15℃.