The source-sink landscape pattern change and its effect on phosphorus pollution in Yuqiao watershed
流域"源-汇"景观格局变化及其对磷污染负荷的影响——以天津于桥水库流域为例

The relationship between source-sink landscape pattern and phosphorus pollution in Yuqiao watershed(Tianjin) was revealed by use of digital elevation model and phosphorus pollution spatial simulation model on the basis of remote sensing(RS) images interpretation.DEM data at the scale of 1∶50000 were used to extract surface features,identify flow direction,calculate flow accumulation and extract river network in the whole basin using the hydrology module in the ArcGIS spatial analyst tool.Maximum like hood classification algorithm was used to extract land cover information for Yuqiao watershed from the TM images of 1999 and 2009 on which basis landscape change from 1999 to 2009 was statistically analyzed.Spatial distribution of phosphorus pollution in Yuqiao watershed under different landscape patterns were simulated by scenario approach.It is found that the area ratio of sink landscape types of forest,shrub and grass decreased 18.44% whereas that of source landscape types of cultivated land,orchard,built-up increased 12.34%.For the main sub-basins in Yuqiao watershed,namely,Li River,Sha River and Lin River,the area ratio of source landscape types to sink landscape types were 2.81∶1,1.82∶1 and 0.85∶1,respectively in 2009.The total phosphorus pollution of Yuqiao watershed increased significantly from 1.00(kg/km2) up to 1.12(kg/km2) from 1999 to 2009 when the total phosphorus pollution of source landscape has increased 51.5% from 0.98(kg/km2) to 1.49(kg/km2).Significant spatial heterogeneity of phosphorus pollution existed among the three sub-basins with the total phosphorus load in Lin River,Sha River and Li River being 1.26(kg/km2),1.14(kg/km2) and 1.10(kg/km2),respectively.In sum,there were significant temporal and spatial heterogeneity between source-sink landscape pattern and phosphorus pollution in Yuqiao watershed.