Spatial Variability And Simulation Of Phosphorus In River Sediment Of Upper Reaches Of Yuqiao Reservoir In Tianjin

The forms of phosphorus in the sediments of the standard test method SMT method for river sediments from upstream Yuqiao reservoir 33 sampling points of different forms of phosphorus were sequential extraction,and the content and spatial distribution of phosphorus in each form were statistically analyzed.The spatial heterogeneity of phosphorus and its relation to environmental factors in the surface sediments of the river basin were preliminarily understood.Then the quantitative relationship between phosphorus content in sediment and phosphorus concentration was analyzed.Based on the SWAT model,the spatial variation characteristics of sediment phosphorus in different situations were simulated.The influence of land use change on sediment phosphorus in the 30 years of flood season and dry season is discussed,providing reference for sustainable development of water environment in Yuqiao reservoir.The main conclusions of this study are as follows:(1)There is a large difference in the spatial distribution of phosphorus content in the surface sediments of the upstream Yuqiao reservoir.In total phosphorus(TP),the order of phosphorus content in each form was:Ca-P>OP>Fe/Al-P,where the variation coefficient of OP and Fe/Al-P was larger,respectively 71.90%and 100.49%,and the TP variation coefficient was small(39.63%).Global autocorrelation analysis showed that the phosphorus in the form of the five,only organophosphate(OP)and iron and aluminum phosphate(Fe/Al-P)are gathered in the spatial distribution of the model,the corresponding Moran,’I index were 0.27 and 0.19;The results of the correlation analysis show that the hot spots of organophosphorus(OP)and iron and aluminum phosphorus(Fe/Al-P)are located in the middle and lower reaches of the basin,and the cold spots are upstream of the basin.(2)The correlation analysis results show that the Fe/Al-P in surface sediments and OP content and water in overlying water correlation of TP and phosphate concentration in the best(P = 0.01),multiple correlation coefficients were 0.635 and 0.628;the content of Fe/Al-P and OP content in sediments were in a good linear regression relationship with the TP concentration,and the regression coefficient was 0.58 and 0.55,respectively.(3)From 1984 to 2015,the area and structure of various land use types in the basin have changed to varying degrees.The area of the garden and the construction of the town are increasing with the ground.The area of cultivated land and woodland decreased significantly.The main characteristics of the spatial variation of land use structure in the basin are the conversion of forestland to garden land,and the transformation of land to urban construction land in the middle and lower reaches.(4)The time variation of phosphorus load in the sediments of the basin was the same in the low water year and the year of abundant water.Watershed sediment iron and aluminum phosphorus and organic phosphorus load increases steadily.Among them,iron and aluminum phosphorus and organic load of farmland and woodland have changed with time in decreasing;The iron and aluminum phosphorus and organic phosphorus load generated by the town and the garden increased dramatically,and the urban gradually replaced the cultivated land as the dominant land use type affecting the phosphorus load of sediments at the present stage.(5)From the perspective of a single type,different land use methods have different effects on the load of nutrient elements in sediments.Urban construction land and arable land have positive effect on the increase of phosphorus load in sediment;woodland has a significant negative effect on phosphorus load of sediment;the garden plot has a certain promoting effect on the increase of phosphorus load in sediments.The effect of grassland on phosphorus load was not obvious.