Spatiotemporal Characteristics And Controlling Factors Of Water Chemistry And Water Quality In The Main Rivers Of The Loess Plateau

The Loess Plateau is one of the regions with the most concentrated population-resource-environmental contradictions and the most fragile ecological environment in China.In recent years,with the economic development and the intensification of human activities,the water quantity and water quality have changed.Water chemistry is the premise for studying water quality,but the current research on the water chemistry characteristics and its influencing factors in the region is scattered,mostly for the monitoring of several sections of a single river or single sampling of multiple rivers,which is not conducive to the overall analysis of water chemistry and water quality of major rivers in the Loess Plateau.In view of this,this paper selects the Kuye River,Wuding River,Yan River,Jing River,Wei River,Fen River,Beiluo River and the middle reaches of the Yellow River in the Loess Plateau,and comprehensively analyzes the temporal and spatial distribution characteristics of water chemical parameters.The fuzzy membership function is used to analyze the water quality characteristics,and the correlation analysis,endmember analysis and forward model are used to qualitatively and quantitatively analyze the influencing factors.The main conclusions drawn are as follows:?1?The surface water and groundwater ion concentrations of the main rivers in the Loess Plateau show the same spatial and temporal variation characteristics.The main rivers in the Loess Plateau are weakly alkaline and belong to high salinity water.The water chemical types of the samples in the flood season and dry season are HCO₃^--Ca²⁺and HCO₃^--Na⁺respectively.HCO₃^-accounts for 48%and 63%of the dry and flood seasons respectively.The data of the main rivers in the Loess Plateau are larger than the historical monitoring data.The dry season is higher than the flood season,and the NO₃^-ion content is opposite.The ion concentration of the main rivers in the Loess Plateau shows the same change characteristics.The surface water and groundwater ions generally show a trend of decreasing from northwest to southeast,and surface water and groundwater have the same characteristics.?2?The temporal variation characteristics of water quality in the main rivers of the Loess Plateau showed a phenomenon in which the dry season was greater than that in the flood season,and the spatial distribution characteristics showed good in the north and northwest,and poor in the south and southeast.The fuzzy membership function analysis shows that the relative pollution of the Wei River,the Jing River,the Beiluo River and the Fen River is relatively serious,while the Kuye River,Yanhe River and Wuding River have relatively good water quality,TDS,SO₄^2-,Cl^-,Ca²⁺,NO₃^-has a trend of exceeding the standard.?3?Qualitative and quantitative analysis showed that evaporite dissolution is the main influencing factor in controlling water chemistry.The order of contribution of different sources to water chemistry is basically the same for evaporation salt rock>carbonate rock>silicate rock>atmospheric input>human activity,evaporation salt rock account for 37%and 42%of the different periods,followed by silicate rock salt and carbonate rock salt,human activities and atmospheric input contribute little to water chemistry,and cation alternate adsorption also affects water chemistry.