Impacts Of Landscape Pattern Changes On Runoff And Sediment And Water Quality In Danhan River Basin At Different Scales

The Dan-Han River Basin is the main water conservation area of China's South-to-North Water Diversion Project,and it is of great significance to the social development of Shaanxi and Hubei provinces.The runoff,sediment transport,and water quality of the basin were affected by landscape patterns and vegetation changes.Different degrees of influence on different spatial and time scales.This study takes the Danhan River basin in Shaanxi Province as the research object,based on the monitoring data from 2000-2015,mainly through geographic information technology(GIS),landscape pattern change analysis,gray correlation analysis and The least square regression model and other methods are used to analyze the basic characteristics of water and sediment changes,land use patterns,vegetation changes and water quality changes in local areas during the study period.Establish vegetation-topographic landscape factors,Explore the differences in the impacts of watershed and landscape patterns on water and sediment at different spatial scales,and the effects of different spatio-temporal scales on changes of water quality in typical small watersheds.The main results obtained in this study are as follows:(1)During the study period,the Danhan River Basin had an average annual precipitation of 789.2 mm and a ratio of 73.9%during the flood season;an average annual runoff of 143.03 billion m3 and an annual ratio of 75.7%durin g the flood season;and an average annual sediment transport of 2.141 million tons,and the percentage of sediment transport in the flood season is 92.5%;the average runoff shows an increasing trend with a smal l degree of variation;the sediment transport shows a decreasing trend with a large degree of variation;the water quality of the main stream basically belongs to medium and weak variation,which is in line with National Class ? Surface water quality standards;(2)Grassland and forest land in Danhan River Basin are the main landscape matrix.The proportions of grassland,forest land and cultivated land are 40.9%,33.6%and 24.5%Class II Surface water quality standards;(2)Grassland and forest land in Danhan River Basin are the main landscape matrix.The proportions of grassland,forest land and cultivated land are 40.9%,33.6%and 24.5%respectively;there is a clear urbanization trend during the study period.Unused land has the largest degree of change;the land use pattern in the study area is characterized by a decrease in landscape fragmentation,increased connectivity,and increased landscape diversity;(3)The area of the Danhan River Basin where vegetation significantly increased spatially accounted for 82.6%,and the area that decreased significantly was less than 1%;the spatial mutation of vegetation was mainly concentrated in 2006-2009;combined with the MK trend test,it can be seen that the area with increased vegetation during the study period will also show a trend of continuous increase in the future;(4)With the increase of the land use buffer,the indexes such as PD,LSI,COHESION,and SHID have obvious scale effects;the average correlation between the runoff and sediment with the land use landscape of the buffer zone with a width of 1000m is the highest,achieved 0.802 and 0.795;on the landscape scale,the correlation between vegetation-topography landscape index with runoff and sediment is 0.816 and 0.841,respectively.The coupling relationship between vegetation-topography index with runoff and sediment in Danhan River Basin is better;(5)The coupling relationship between water quality and landscape in the typical watershed of Danhan River is obviously different in dry and wet seasons;the interpretation of vegetation-topographic landscape for dry and wet season water quality is higher than that of land use landscape,reaching 50.45%and 37.10%respectively;Nitrate and total nitrogen are spatially strong variations,while ammonia and total phosphorus are moderately variable.In the OLS model of Danjiang water quality and vegetation-topography landscape,R2 is basically less than 0.6,while in the GWR model,the effectiveness of factor information extraction is significant,and the increase is greater than 60%,which indicates that the GWR model has a better fit for spatial water quality-landscape fitting.