Effect Of Landscape Pattern Of Yuqiao Reservoir Watershed On Temporal And Spatial Differentiation Of Nitrogen And Phosphorus In River

Tianjin Yuqiao reservoir watershed as the research object,from 1984 to 2018were analyzed spatial landscape pattern characteristics of river basin,and used the geographical detector model and geographically weighted regression model analysis of landscape pattern on river the influence of the nitrogen and phosphorus segregation,and built the SWAT model in the watershed,nitrogen and phosphorus load change,and analyzed the landscape pattern change under different situation of rivers,the effect of nitrogen and phosphorus load.The main conclusions of this study are as follows:(1)The landscape pattern of the river basin had significant spatial and temporal heterogeneity.The areas with large urban land use were concentrated in the middle and lower reaches of the city.The distribution of cultivated land type was also concentrated in the middle and lower reaches of the city due to human factors.The area of various landscape types in the basin changed to different degrees in 34 years.From 1984 to 2018,the total area of forest land and cultivated land decreased by 23.3%and 8.7%respectively,and the area of town and garden land increased by 13.8%and 18.9%respectively,while the area of grassland and water body fluctuated to some extent.(2)The analysis of geographical detector showed that the landscape index can reflect the degree of influence on the output of nitrogen and phosphorus,and the location-weighted landscape contrast index(LWLI),Urban percentage(Urban%)and forest percentage(For%)had significant influence on the water quality index(p<0.05).Among them,LWLI index had the highest interpretation of TN and TP(q>0.57)by integrating multiple indexes,which can better explain the output state of nitrogen and phosphorus.In addition,there was a strong interaction between different landscape indexes.(3)The analysis of the geographical weighted regression model showed that LWLI,Urban%and For%have different influences on TN and TP,and the t-value has great differences in spatial distribution.The spatial difference was related to the interaction of other landscape indexes,and the diversity, fragmentation,shape complexity and connectivity of landscape patches(SHDI,LSI,LPI,CONTAG)had an impact on the output of N and P.(4)SWAT model had a good simulation effect on surface runoff and nitrogen and phosphorus pollution load of the watershed,and the correlation coefficient(R~2)and Nash-Sutcliffe(NS)of surface runoff,TN and TP simulation results at regular and validation periods were all greater than 0.7.The R~2and NS coefficients of surface runoff in the model validation period were 0.76 and 0.75,respectively.The R~2and NS coefficients in the verification period of total nitrogen load were0.79 and 0.76,respectively.The R~2and NS coefficients in the verification period of total phosphorus load were 0.80 and 0.75,respectively.(5)From 1984 to 2018,the total nitrogen and phosphorus loads in the basin increased steadily in both the wet year and the dry year.TN increased by 220.8t in the dry year and 575.6t in the wet year.The TN and TP loads generated by urban land and farmland were larger than other landscape types.From 1984 to 2018,TN and TP loads generated by urban land and garden land increased year by year.TN and TP loads generated by urban land and garden land were greater than those generated by garden land,and TN and TP generated by farmland and forest land decreased year by year.This indicated that the influence of the urban expansion on the nitrogen and phosphorus load in the basin is continuously strengthened and gradually became the main factor affecting the nitrogen and phosphorus output in the basin.