Spatial-temporal Variation And Control Factors Of Surface And Groundwater Chemical Composition And Water Quality In The Wei River

The special hydrological and geological conditions of the Wei River Basin have created a unique hydrochemical weathering process in the region.In recent years,human activities and environmental changes have caused significant changes in the hydro-chemical characteristics of the Wei River and the groundwater along the coast.In order to ascertain the characteristics and causes of spatio-temporal changes of hydro-chemical and water quality in the area,this study takes the Wei River Basin as the study area,adopts various methods such as statistical analysis,water chemistry and isotope tracing technology,and mass balance method,from qualitative and Quantitatively discussing the influencing factors of solute sources,which is of great significance to the safety management of the surface and groundwater environment of the Wei River Basin.The main conclusions are as follows:?1?Analyze the spatiotemporal characteristics of hydro-chemicaland water quality.The dominant anions and cations in the surface water and groundwater of the from Ca-Mg-HCO₃ in the dry season to Ca-Mg-SO₄-Cl in the wet season.The main ion concentration in the upstream is higher than that in the middle and lower reaches.The spatial variability of the main ion concentration in the dry season is less than that in the wet season.In particular,the NO₃^-concentration of surface water in the wet season is significantly higher than that in the dry season.Regarding water quality,the surface water and groundwater quality of the Wei River is characterized by weak alkalinity and high salinity,and the water quality classification is mainly micro-hard/hard freshwater.The spatial and temporal characteristics of water quality are mainly as follows:the water quality in the wet season is worse than that in the dry season,and the proportion of surface water and groundwater in the upstream area of the wet season accounts for 22%and 26%,respectively.In terms of inter-annual changes,the quality of surface water in the 2018 wet season has improved compared with 2017,and category V water has dropped from 28%to 3%,but the quality of groundwater in the downstream areas of the wet season has shown a deteriorating trend,and category V water has increased by 19%.?2?Clarified the control mechanism and influencing factors of solute sources in water.The main control mechanism of the surface water and groundwater solute sources in the Wei River is mainly rock weathering.Evaporative concentration has a certain impact on some water samples,and human activities mainly have a relatively large impact on the surface water in the wet season.The results of the forward deduction model show that there is no obvious seasonal difference in silicate rock weathering,and its contribution to solute sources in surface water and groundwater is33±4%,but carbonate weathering and evaporite dissolution show significant seasonal changes.The former contributes 51±21%to the source of groundwater solute in dry season,and the latter contributes 46±5%of the total ion contribution rate to the source of groundwater solute in wet season.During the wet season,the contribution rate of human activities to the source of surface water solutes is 10±5%.The water body is simultaneously polluted by agricultural activities and urban wastewater,and the main pollution is agricultural activities.Among them,compound fertilizers in chemical fertilizers,such as NH₄HCO₃ and KNO₃,and manure sewage The average contribution rate to nitrate in water is 42.7%and 26.1%,respectively,which deserves everyone's attention.?3?Clarified the causes of spatiotemporal variation of hydro-chemicaland water quality.The results of factor analysis show that,compared with the dry season,the dissolution of evaporite and fluoride and the large amount of application of manure and chemical fertilizer are the main reasons for the increase of the main ion content and the deterioration of water quality in the wet season.In terms of inter-annual changes,due to the effects of evaporative concentration and agricultural activities,the quality of groundwater in the downstream area of the 2018 wet season has deteriorated compared with 2017.In terms of spatial variation,according to the analysis results of the end element map and the Cl^--NO₃^-ratio map,it can be seen that compared with the middle and lower reaches,except for a few source waters,the water samples in the upstream area are greatly affected by chemical fertilizers;The effect of rain erosion brings a large amount of solute into the river,which greatly increases the ion content in its water body,and the problem of water pollution is more prominent.To sum up,it can be seen that the seasonal differences in weathering of rocks and human activities,especially agricultural activities,play an important role in changing hydro-chemical and water quality.Therefore,they should be the focus of improving water quality,especially by increasing the utilization rate of fertilizers.And measures to strengthen the safety management of high-quality drinking water fluoride.