Effects Of Landscape Pattern Of "Source-Sink" On The Nitrogen And Phosphorus In Rivers

The composition and spatial pattern of watershed landscape affected the process of river pollutants.The change of landscape pattern had a significant impact on the water environment.With the development of watershed urbanization,With the acceleration of urbanization,human activities were increasing,resulting in a significant increase in nitrogen and phosphorus pollutants in rivers,water quality continues to deteriorate.In this paper,the urbanization of Tianjin Yuqiao watershed,"source sink" landscape features index based on combining the water quality data of Yuqiao Reservoir Watershed in 2013,2014 and 2015 33 sub basins,Spatial analysis,correlation analysis and redundancy analysis were used to investigate the quantitative relationship between the landscape characteristics index and water quality index in the Yuqiao reservoir watershed.Based on the data of land use from 1984 to 2013,the SWAT model was used to simulate the change of nitrogen and phosphorus load in the past 30 years.Finally,the CLUE-S model model was used to simulate the future land use change and the SWAT model was used to simulate the effect of the change of landscape pattern on the nitrogen and phosphorus load in the future.The results showed that(1)the "sink" landscape reduced,while the "source" landscape increased in the whole basin from the upstream to the downstream.The area proportion of residential construction land averagely reached 34.6%in the middle and lower sub-basin,and the forest area accounted for 33.5%of "sink" landscape.(2)LWLI's Moran's I of the Yuqiao Reservoir watershed was 0.637(P<0.01),and tended to cluster in spatial scale.LWLI and spatial patterns of nitrogen and phosphorus were significantly correlation.The coefficient of determination(R2)between the LWLI and total nitrogen(TN)was 0.811 during normal-water period,and the R2 was 0.741 during high-water period.(3)A11 water quality parameters of sub-basins:NH4+-N,TN,NO3--N,TP and LWLI gathered in the fourth quadrant.Compared with other indices of landscape patterns,LWLI had the greatest impact on nitrogen and phosphorus in the river.It had widely distributing and apparently aggregating characteristics in the urban residential land.(4)1984 to 2013 from upstream to downstream Stream Landscape increased,sink landscape decreased.Urban construction land increased from 11.66%in 1984 to about 18.10%in 2013.(5)The semi-distributed SWAT model and associated water quality module could be calibrated to adequately simulate runoff,N and P loads in peri-urban watershed,with the NSEs and R2 over 0.70 and the PBIAS under 12 for both the calibration and validation period.(6)The amount of TN and TP released from the source landscape increased continuously,and the TN and TP of the cultivated land decreased,while the TN and TP in the urban areas increased.In the process of urbanization,the effect of cultivated land on total phosphorus and total nitrogen decreased,while the trend of total nitrogen and total phosphorus increased.