| Phosphorus is a nutrient element necessary for the crops growth and a major nutrient component in lakes.Monitoring the migration of phosphorus in basins through remote sensing technology can provide a scientific basis for the management and control of lake water environment safety.The Hongze lake basin is selected as the research area.According to the DEM data and the main rivers into the lake,three natural basins are divided by the SWAT model.To determine the pattern of land use in different watershed by the change of land use quantity and structure,and the landscape pattern index.The comprehensive utilization of plot test and satellite remote sensing method.Based on the SEDD model,the spatial-temporal variation characteristics of non-point source phosphorus load in each basin were estimated,and the spatial-temporal variation characteristics of phosphorus content in Hongze Lake under long time series were estimated by MODIS image data.The corresponding relationships between land use change,non-point source phosphorus load and lake phosphorus concentration in long time series were constructed,to study the effects of non-point source phosphorus output in lakes phosphorus content under different land use changes.The results showed:(1)The area of construction land changed significantly in Gaosong River Basin.The type of land use showed a trend of fragmentation and integration,and the spatial distribution of various land types appeared to be homogenized.The area of water area changes drastically in Bian River Basin,and the fragmented land shows an overall trend,but the shape of the land shows an irregular trend.There is less disturbance of human activities in Weiqiao River Basin,and the most significant trend is the uniform distribution of land use.(2)The non-point source phosphorus loads in all three watersheds showed an upward-downward-upward trend over time,and reached the maximum in 2005,reaching the minimum in 2010.In spatial distribution,although the non-point source phosphorus load intensity was the highest in Weiqiao River Basin,reaching 1.261 kg·ha-1·a-1 in 2010,the loss of non-point source phosphorus was the highest in Gaosong River Basin,reaching 28.268 t in 2005.The non-point source load is positively correlated with PD and forestland can effectively alleviate the increasing trend of non-point source phosphorus load intensity.(3)Using MODIS image data,the algorithm of phosphorus concentration in Hongze Lake body was constructed by 645/555.R2 was over 0.8,RMSE was only 0.02 mg/L,MRE was 13%,and the model accuracy was good.According to this algorithm,the spatial-temporal reconstruction of phosphorus content in Hongze lake was completed,the concentration of phosphorus in the north and the western lake bay in Hongze is low,and the concentration of phosphorus in the middle and southern parts is high.The phosphorus concentration in Hongze Lake decreased slowly before 2011.In 2012,due to the illegal sand mining activities in Hongze lake,resulting in the release of large amounts of phosphorus in the sediments.The phosphorus concentration in the lake increased 0.042mg/L in 2012,reaching 0.101 mg/L.(4)Under natural condition,Huai River is the main source of phosphorus in Hongze lake.The Gaosong River Basin and Bian River Basin near the outlet phosphorus concentration was lower than lake phosphorus concentration,therefore,two rivers have the effect of reducing phosphorus concentration.The change of land use will affect the source and migration process of phosphorus.The interception effect of wetland on phosphorus is very significant.The increase of construction land area will increase the output of point source,resulting in the reduction of non-point phosphorus in the outlet. |
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