Influences Of Landscape On Nitrogen Export On Multi-scales In Zhongtian River Watershed

To explore the regulation mechanism of landscape composition and landscape pattern characteristics of river nutrient transportation is a hot spot in the watershed ecology concerned.Nutrient loading into rivers is generally changed by human-induced land use changes and can lead to surface water quality changes.Understanding the extent to which landscape characteristics influence nutrient loading is critical to the development of best-management practices aimed at water-quality improvement.With the economic development of Taihu Lake region in recent years,the water environment problem is outstanding in the last few years,therefore,the study of the influence of landscape of Taihu Lake region on nutrient output is significant for water pollution.This study selects Zhongtian River watershed which is a typical small watershed of hilly region in Taihu Lake as the study area,Considering the nested relationship of watershed unit,applying correlation analysis,principal component analysis,stepwise regression analysis and redundancy analysis and other methods in the sub-watershed scale,riparian buffers area scale and coastal scale to study the effect of landscape on the nitrogen output.The main conclusions are as following:(1)Landscape features has an important impact on the total nitrogen output in sub-watershed scale,nitrogen output is closely related with landscape composition and landscape pattern.Total nitrogen concentration is affected by the surrounding land use in Zhongtian River sub-watershed,with strong spatial variability.It shows that construction land and grasslands have a significant impact on total nitrogen concentration,construction land will increase the output of nitrogen,as the grasslands can reduce the output of nitrogen.Landscape area pattern index and landscape composition are the key factors that affect the output of nitrogen,and increase the area of land use patch has a significant effect on nitrogen output.The degree of polymerization and complexity of land-use patch shape is closely related with nitrogen output,manifested as increased the patch shape complexity and irregularity can reduce the output of nitrogen and can improve its quality condition.(2)Landscape pattern in different width of the riparian buffers have different effects on nitrogen output.The landscape characteristics in 100m width of the riparian buffer effect water environment were the most significant,landscape pattern variables can explain 99.6%of the variation of river nitrogen output.Grassland,wetland and construction land have the strongest interpretation ability to river nitrogen output spatial differentiation.In all widths of the riparian zone buffer,the broken degrees of grassland,forest land,cultivated land,construction land and wetland have significant influence on spatial differentiation of river nitrogen output.Through the analysis of the relationship between the sampling points and the landscape pattern variables,we found Zhongtian River watershed upstream area is mainly affected by the construction land,the downstream area mainly affected by the grassland and wetland.Within the 100m,250m,500m and 1000m width of the riparian buffer zone,landscape composition variables on the ability to explain the spatial differentiation of river nitrogen output is better than the landscape spatial pattern of the variables.Landscape of variable within the buffer for the interpretation of the spatial differentiation rate of river nitrogen output was 55.4%,29.5%,14.7%and 55.4%respectively.With the increase of the width of buffer,the landscape of the variable for the interpretation of river nitrogen output spatial differentiation ability decreases.(3)The study about Zhongtian River watershed on near shore scale indicated that grassland,forest and wetlands are good to decrease nitrogen output,and the distribution of farm land and construction land near Zhongtian River watershed can increase nitrogen output.From the point of landscape level,the more abundant of landscape diversity and the more complex of the spatial adjacency distribution of various patches,the lower the pollutants concentration in river and the better of the water quality.In the landscape type level,increase the grassland and wetland broken degree can reduce the nitrogen output,and farm land and construction land are the opposite;forest land,farm land and construction with the patch area larger and connectivity is stronger,higher nitrogen output,grasslands and wetlands are on the contrary;garden,grassland and wetland patch shape are more complex,nitrogen output is lower.Relative to the sub-watershed scale,Relative to the sub-watershed scale,the effect of landscape composition on the nitrogen output was more significant in the riparian buffer.On the whole,the key control areas of the non-point source pollution in the watershed is inshore scale.So the water environment management of Zhongtian River watershed need to further optimize the regional landscape pattern,and according to the different scales,the sustainable development of the river basin need to choose the appropriate optimization scheme to reduce nitrogen pollution of the river water quality from the source and improve water quality.