Spatial-scale Effects Of Ju River Watershed Characteristics On Rainfall And Seasons Water Quality Changes

Good water quality is important for maintaining the stability of ecosystems,healthy human life and sustainable development.Surface water quality is determined by a combination of hydrological processes and biogeochemical cycles,so water quality indicators change under short periods of rainfall and long periods of seasonal variability.There is no clear answer as to whether these changes are related to watershed characteristics such as landscape patterns,topography and soils,and how these factors mediate water quality.Therefore,it is important to investigate the influence of watershed characteristics on river water quality,and then to propose targeted management recommendations.In this study,the water quality of the Ju River was studied under rainfall and seasonal conditions,and the spatial and temporal effects of watershed characteristics on water quality indicators were analyzed by taking the Ju River watershed(Danyang section),which is mainly agricultural,as the research object,and sampling was conducted several times between 2021 and 2022.The results of the study provide valuable insights for improving river water quality.The results of the study indicate that:(1)Ammonia nitrogen,total organic carbon,chloride ions and sulfate ions in the Ju River are correlated with rainfall intensity.From the results of the regression analysis,rainfall intensity and the number of dry days in the previous period have a positive interaction effect on several water quality indicators.(2)Spatially,changes in the concentrations of water quality indicators in tributaries were more sensitive to the response of rainfall.The results of the correlation analysis showed that rainfall has an important influence on water quality indicators,in which nitrogen is highly correlated with all other water quality indicators and has some homology with chloride ions and sulfate ions.The results of the principal component analysis showed that the variance contribution of PC1 before and after rainfall was larger and both were highly correlated with total nitrogen and conductivity,but the correlation with chloride ion weakened after rainfall.(3)In different seasons,the concentration of total organic carbon in the water bodies of Ju River increased more,the concentration of total nitrogen decreased,and the concentration of total phosphorus increased slightly.Biogeochemical cycles play an important role in regulating the ratio of carbon,nitrogen and phosphorus in the water bodies.Spatially,the tributary water quality indicators are more sensitive to seasonal changes,but the changes in the concentration of water quality indicators in the main stream are more obvious in seasonal changes compared with the small-scale rainfall.From the correlation point of view,the correlation between the water quality indicators will change in different seasons.From the results of principal component analysis,the cumulative variance contribution of the dry season is greater than that of the wet season,and PC1 is highly correlated with total nitrogen,conductivity and chloride ion in both seasons,while PC2 is highly correlated with total phosphorus,chemical oxygen consumption and total organic carbon in the dry season.(4)Before and after the rainfall,the sub-catchment scale was chosen to explore the influence of watershed characteristics on the water quality indexes of the Ju River;on different seasons,the 500 m circular buffer scale upstream of the sampling site was chosen to be more reasonable.(5)The contribution of topography is usually greater at small scales,and the contribution of soil factors before and after rainfall and in different seasons is low and the differences are not obvious enough.Before rainfall,the contribution of landscape pattern does not change significantly with the scale of the study;after rainfall,the contribution of land use composition is the largest at the medium scale,but the contribution of land use structure is the smallest at the medium scale.During the abundant water period,the contribution of land use composition is greater at the medium scale,and land use structure contributes at the sub-basin scale;during the dry water period,the contribution of land use structure is greater at the small scale,and the contribution of land use composition will be greater at the medium scale and large scale.(6)In order to improve or protect water quality in the watershed,management measures can be taken to optimize the spatial allocation of arable land,transform bare land in the watershed into forest land,and increase the diversity of land use types in the watershed,thereby better protecting water quality and building a sustainable ecological environment together.