Research On Long-time Dynamic Process Of Tonle Sap Lake Water Environment Based On Multi-source Remote Sensing Data

Tonle Sap Lake(TSL)is the largest freshwater lake in Southeast Asia and is known as the "heart of the Mekong" because of its importance in ecosystem.In recent years,due to the impact of human activities and climate change,the inundation area of Tonle Sap Lake has shrunk severely,and the lake environment is facing great threats,which has seriously affected the local ecological environment and the production and lives of residents.In this paper,based on MODIS and Landsat(Landsat)data,we conducted a systematic study on the inundation area,Total suspended sediment concentration and eutrophication of Tonle Sap Lake.The research results provided a scientific basis for the settlement of the cross-border disputes on the control of inundation area and water turbidity of TSL.The MODIS satellite data was used to obtain information on the changes in the water range of Tonle Sap Lake from 2000 to 2018,and the change trend of lake inundation area was counted.Before 2000,the inundation area was basically stable.From 2000 to 2018,the annual maximum,minimum and annual average inundation area of the lake decreased significantly at a rate of 17.82 km2yr-1,5.93 km2yr-1 and 8.22 km2yr-1 respectively(P<0.05).The analysis of the driving factor for precipitation shows that the annual average inundation area of Tonle Sap Lake is significantly correlated with the precipitation in the upper Mekong(mostly outside the lake basin)during the same period(R2 = 0.67).At the same time,the regression results of Multivariable Linear Regression Model(MLRM)further indicate that precipitation change is the main contributor of the inter annual fluctuation of inundation area(76.1%).Based on the measured turbidity data and MODIS satellite data,an inversion model of total suspended sediment concentration in Tonle Sap Lake was established,and the spatial and temporal distribution pattern of suspended sediment concentration in the lake was explored based on the model.Since 2000,the total suspended sediment(TSS)of Tonle Sap Lake has increased significantly,with an annual rate of change of 7.92 mg·L-1,of which the total suspended sediment in the first,second and fourth quarters has shown an increased trend.The change in inundation area also showed a significant effect on the lake turbidity,and the shrinkage of the lake area may enhance the resuspension of the sediment at the bottom of the lake.Based on the surface reflectance data of MODIS from 2000 to 2018,FUI index was used to quantitatively analyze the change of hue angle of Tonle Sap Lake,and the water body of Tonle Sap Lake was evaluated according to the eutrophication assessment method.From 2000 to 2018,the hue angle of Tonle Sap Lake showed a decreased trend,during which the monthly difference of water color between 2014 and 2016 was significantly reduced.There was a significant positive correlation between the change of the hue angle and the inundation area of Tonle Sap Lake for 5 months.There was a significant negative correlation for 3 months,with the strongest positive/negative correlation in rainy June(R= 0.72)and dry December(R=-0.86).Tonle Sap Lake has been predominantly "eutrophic" in the past 19 years of which 99.97% of Tonle Sap Lake in June was in "eutrophic" state.However,in the years when the flood situation is prominent(2000,2001,2011 and 2013),the water eutrophication situation of Tonle Sap Lake will be improved.About 15% of the area is in the "medium nutrition" or "Poor nutrition" status during the dry season in December.