Hydrochemical Characteristics And Pollution Evaluation Of Groundwater In The Loess Plateau

The Loess Plateau is located in the arid and semi-arid regions of China,with serious soil erosion and serious shortage of surface water resources.Groundwater has become the only source of water supply in some areas.Therefore,exploring the source of groundwater solutes and evaluating groundwater quality are of great significance to the protection and utilization of groundwater resources in arid areas.In recent years,a few scholars have conducted researches on groundwater chemistry in the Loess Plateau,but most of them was limited to small-scale research areas,or ignored the influence of seasonal changes for groundwater chemistry and water quality.There was a lack of comprehensive research on groundwater in the Loess Plateau at the spatial and temporal scales.Therefore,this study uses the Loess Plateau as the study area,based on the groundwater collected at two different periods in the dry and flood seasons,expounds the basic characteristics of groundwater chemistry and seasonal differences in the Loess Plateau,and evaluates the groundwater quality of the Loess Plateau and its impact on residents’health.,And analyze groundwater solute control factors and pollution sources from qualitative and quantitative perspectives.The main research conclusions are as follows:（1）There are significant temporal and spatial differences in the chemical composition of groundwater in the Loess Plateau.The main reasons for the temporal differences are the leaching effect of seasonal rainfall and the hysteresis of rainwater replenishment.The Groundwater is slightly alkaline with 6.7-8.1 of p H.The TDS value is high in the northwest and low in the southeast,and individual high-concentration prominent points in the middle may be affected by geological background or human factors.The average TDS concentration in the flood season is 445 mg·L^-1,which is higher than the average TDS value of 400 mg·L^-1in the dry season.The water chemistry type is mainly HCO₃-Ca and HCO₃-Ca·Ma type in the flood season,and HCO₃-Na type in the dry season.Ca²⁺,K⁺,Cl^-,As,Cr,Cu,Fe,Mn,Pb and Zn have significant differences in dry and flood seasons.（2）The quality of most groundwater is excellent,and there are seasonal and regional differences in water quality.High-quality drinking water sources in flood season and dry season accounted for 78.4%and 88.9%,respectively.The dry season is better than the flood season,and the southeast region is better than the northwest region.89%of the sample points are suitable for irrigation.The suitability of irrigation is greatly affected by the annual precipitation.The semi-arid area of the northwest has a high salinity of groundwater.Depending on the situation,some salt-tolerant and alkali-resistant crops can be irrigated.All heavy metal pollutants with HI<1 have no non-carcinogenic risk,but As and Cr have carcinogenic risks,and the risk levels are medium risk and low risk respectively.Therefore,monitoring plans for arsenic and other potential elements and effective health education on arsenic pollution are necessary.At the same time,in the treatment of regional non-point source pollution,we must also pay attention to sudden pollution incidents caused by seasonal changes.（3）The source of groundwater solutes in the Loess Plateau is mainly controlled by the weathering of evaporite,carbonate and silicate rocks.The Forward model results show that there is a slight seasonal difference in the contribution rate of rock weathering.During the flood season,the order of the contribution of different sources to the solute is:silicate weathering（42.8%）>carbonate weathering（30.6%）>evaporite weathering（19.3%）>anthropogenic input（5.0%）>atmospheric input（2.3%）,and in the dry season:silicate weathering（56.6%）>evaporite weathering（20.3%）>carbonate weathering（10.7%）>atmospheric input（9.1%）>anthropogenic input（3.4%）.The PCA and APCS-MLR models show that the contribution rate of natural sources during the flood season is 35.24%,and that of man-made sources is 16.96%.In addition,the solid waste generated by human activities will be affected by the rainwater during the flood season and will cause secondary pollution to the groundwater in the form of landfill leachate,contributing about 12.72%.During the dry season,the contribution rate of natural sources reached 51.21%,and the man-made sources accounted for 17.96%.This study conducts research on groundwater in the Loess Plateau,aiming to grasp the state of groundwater pollution,assess the damage to human health caused by groundwater pollution,and explore the sources of pollutants,to provide guarantees for the safety of groundwater resources and residents’drinking water in arid areas,and also to protect the ecology of the Yellow River Basin.The quality development strategy provides a scientific basis.It is suggested that relevant units should pay attention to sudden pollution incidents caused by seasonal changes when carrying out the treatment of regional non-point source pollution.At the same time,attention should be paid to the potential hazards of arsenic and other elements in groundwater.