Analysis Of Source,distribution And Influencing Factors Of Sulfate In Karst Basin Based On Sulfur And Oxygen Isotope Tracing

Water environment is one of the important ecological environments,and water quality safety is an important support for national security and economic development.The study found that the qualified rate of urban drinking water was85.51%,much higher than the qualified rate of rural drinking water 51.12%,in addition,the areas with low qualified rate of water quality are mainly distributed in Yunnan,Guizhou and other southern regions.The existing status of sulfate can not be ignored in water quality security.The origin,migration and transformation characteristics of sulfate can reflect the quality of water environment and the influence of natural and human factors on water environment.Based on this,the Gaoping River Basin,located in Zunyi City,Guizhou Province,is a typical karst basin.The water resources in the karst basin are the main source of drinking water in the world.The ecological environment of the karst basin is fragile and vulnerable to pollution,so we can understand the chemical characteristics of water bodies.The use of isotopes to trace the source,migration and transformation of sulfate in water can provide a basis for the protection and management of karst water.Based on this,the surface water and groundwater in the Gaoping River Basin were routinely sampled in the abundance,drought and normal water periods in 2022,and the main ions in the water body were measured and analyzed.Combined with the water quality parameters measured on site,the water chemical characteristics,spatial and temporal distribution characteristics and main control factors in the Gaoping River Basin were discussed by comprehensive use of mathematical statistics.The source,migration and transformation of sulfate in karst basin were analyzed by using sulfate sulfur and oxygen isotope composition,which is of great significance to the protection of water environment in karst basin.The main results are as follows:（1）From the upper reaches to the lower reaches,the SO₄^2-concentration in surface water basically increased during the period of abundance,drought and normal water,while the SO₄^2-concentration in groundwater showed seasonal changes.The results of hydrochemical analysis show that Ca²⁺and Mg²⁺are the main cations,HCO₃^-and SO₄^2-are the main anions,and the chemical types of surface water and groundwater are HCO₃·SO₄-Ca type.The equivalent relationship between ions indicates that the concentration of SO₄^2-in water samples is significantly affected by rock weathering,and in this process,sulfuric acid is involved in rock weathering.（2）From upstream to downstream,δ³⁴S_SO4 andδ¹8O_SO4 in surface water and groundwater have little fluctuation in time,and the source factors affecting sulfate are relatively stable.There are seasonal variations in space.There is a certain homology betweenδ³⁴S_SO4 andδ¹⁸O_SO4in the Gaoping River Basin.The sources of sulfate in surface water and groundwater are soil sulfate,gypsum dissolution and atmospheric rainfall.（3）According to the results of equilibrium mass model,the difference of monthly cumulative rainfall has an obvious effect on the source of SO₄^2-in groundwater of Gaoping River Basin.After rainfall,the groundwater level in the recharge area rises,and the water head difference between the water level and the dewpoint of the spring becomes larger,so that the deep groundwater is discharged.The SO₄^2-concentration in the deep groundwater is relatively high,and the source of SO₄^2-in the recharge process of the deep groundwater to the surface water is affected by atmospheric rainfall.Compared with atmospheric rainfall,the source of sulfate in the basin is significantly affected by rock weathering and soil sulfate,while the source of sulfate in the Gaoping River is not significantly affected by seasons.