Analysis Of Hydrochemical Characteristics And Influencing Factors In Typical Karst Small Watershed

The hydrochemical characteristics of the basin can reflect the impact of human activities and natural activities on the basin,and can also indirectly reflect the quality of the effluent environment,the source and migration and transformation of various elements.As the most direct way for human activities to affect the water environment in karst areas,land use can be controlled by human beings.Therefore,it is of great significance to study the impact of land use on karst water environment for improving karst water environment.Taking the Houzhai River basin in Puding County,Guizhou Province as the research object,this paper analyzes the space-time distribution characteristics and water quality of hydrochemistry,explores the impact of land use patterns,rock weathering,rainfall and other control factors on the hydrochemistry of the basin,and puts forward scientific suggestions on the protection of water resources in karst areas in combination with the impact of land use structure on water quality in recent years.The main conclusions are as follows:（1）Through analyzing the hydrochemical characteristics in dry season,we can see that the contents of carbon,nitrogen,phosphorus,Cl^-,NO₃^-,SO₄^2-,Na⁺in the water bodies in the construction area and farmland are higher than those in the natural vegetation areas.The content of various nutrients and ions increases from upstream to midstream,and decreases from midstream to downstream.The spatial distribution characteristics of carbon,nitrogen and phosphorus concentrations are closely related to the spatial distribution of soil thickness,the degree of karst development and the spatial differences of land use patterns in the basin.A variety of factors jointly control the hydrochemical characteristics and nitrogen pollution in the karst basin.（2）The hydrochemical type of the basin is HCO₃^--Ca²⁺type and is mainly affected by the weathering of carbonate rocks.Na⁺and SO₄^2-have a common source,such as the dissolution of gypsum and the discharge of domestic sewage,and K⁺also has a certain source of human activities.（3）During the dry season,the rivers in the basin are mainly limited by phosphorus,and there is a potential threat of water bloom.The total outlet of the downstream Houzhai River is limited by silicon,causing water quality problems.（4）In terms of time,the chemical concentration of water in the basin has seasonal variation characteristics,which is the result of the joint influence of dilution caused by seasonal rainfall and evaporation during dry season.The dissolution rate of rocks is faster in the wet season,and the salinity of water body is more affected in the dry season.H₂SO₄also participates in the weathering process of rocks,and the effect is more obvious in the dry season.Compared with farmland,the response of spring water in forest land to rainfall has a lag,but all of them are finally affected by the rain scouring,the pollutant content increases,and then decreases due to the rain dilution.（5）According to the analysis of the correlation between land use mode and water chemistry,compared with the dry season,the impact of the wet season on water quality is small.Farmland and construction land have obvious negative effects on water environment;Forest land has a negative correlation with nutrients,which has a positive effect on alleviating water pollution.（6）From the 1980s to present,the area of farmland and other land in Houzhai River Basin has decreased significantly,while the area of forest land and construction land has increased significantly.The content of the ions is generally high,and the nitrogen pollution in the basin has improved.Combined with the impact of land use structure change on water chemistry in recent years,effective land use optimization measures and sewage treatment facilities should be taken to treat karst water environment.