Research On The Characteristics And Spatial Agglomeration Of Nitrogen And Phosphorus Non-point Source Emissions In The Upper Reaches Of Zhanghe River Basin

Zhanghe River is the most abundant branch of the Haihe River system in terms of water resources,and is one of the main water sources in the Beijing-Tianjin-Hebei Region.As an important tributary of the Haihe River Basin,the water resource security of the Zhanghe River is crucial for the healthy development of the Beijing-Tianjin-Hebei Region.Therefore,studying the characteristics of nitrogen and phosphorus non-point source emissions and their spatial agglomeration characteristics in the upper reaches of the Zhanghe River Basin is of great significance for controlling water environmental pollution in the basin.Therefore,this thesis uses the improved export coefficient model to estimate the nitrogen and phosphorus non-point source pollution load in the upper reaches of the Zhanghe River basin from 2007 to 2018,identify the key pollution sources of non-point source pollution in the basin,and use spatial autocorrelation methods to reveal the key pollution source areas of non-point source pollution in the basin.The main conclusions of this study are as follows:(1)Through research and analysis of land use data from 2007 to 2018 in the upper reaches of the Zhanghe River basin,the spatiotemporal dynamic characteristics of land use types in the basin were revealed.The research results show that due to the significant role of human activities in land use change,forest land and construction land continued to increase from 2007 to 2018,with cultivated land first decreasing and then increasing,and grassland first increasing and then decreasing.The comprehensive land use dynamics decreased from 0.65% to 0.45%,and the land pattern gradually stabilized.From 2007 to2018,cultivated land was mainly converted into grassland and construction land,while grassland was mainly converted into forest land.The transformation from agricultural land to no-tillage land was the main feature of the basin during this period.(2)The improved export coefficient model was used to estimate the nitrogen and phosphorus non-point source pollution loads in the upper reaches of the Zhanghe River basin from 2007 to 2018,revealing the temporal and spatial evolution of the non-point source pollution loads and the main pollution sources in the basin.The results show that there are significant temporal and spatial differences in non-point source pollution in the upper reaches of the Zhanghe River basin.From the time perspective,the nitrogen and phosphorus pollution load in the basin is consistent with precipitation,with minimum and maximum values appearing in 2008 and 2016;From the perspective of spatial distribution,there is a close relationship between nitrogen and phosphorus pollution load intensity and slope gradient,and non-point source pollution is more serious in flat terrain areas.The non-point source pollution load in the upper reaches of the Zhanghe River basin is influenced by factors such as rural life,livestock breeding,and land use.Cultivated land(47.2%)is the main source of TN pollution load in the basin,while rural life(59.9%)is the main source of TP pollution load in the basin.The contributions of each pollution source to the nitrogen and phosphorus pollution load in the basin show a small temporal variation and a large spatial variation.(3)The spatial autocorrelation method was used to reveal the spatial agglomeration characteristics of nitrogen and phosphorus non-point source pollution emissions in the upper reaches of the Zhanghe River basin from 2007 to 2018.The results show that nonpoint source pollution emissions have a significant spatial agglomeration effect,and weaken with the increase of distance;From 2007 to 2018,the Moran index of TN load in the upper reaches of the Zhanghe River varied from 0.37 to 0.42,and the Moran index of TP load ranged from 0.67 to 0.71.The spatial correlation of TP was higher than that of TN load,and there was a consistent temporal trend in the spatial autocorrelation of nitrogen and phosphorus pollution loads;From 2007 to 2018,the spatial concentration characteristics of non-point source pollution in the upper reaches of the Zhanghe River basin were basically consistent,with sub basins 1,2,and 3 being the main high value concentration areas,and sub basins 10,11 being the main low value concentration areas,with fewer discrete distribution anomalies.