Study On The Long-time Change Of Lacustrine Water Color In The Inner Mongolia Based On Landsat Datasets

Inner Mongolia Autonomous Region is an important ecological security barrier in northern China.It mainly belongs to arid and semi-arid climate area.It has large regional span,significant regional differentiation and fragile ecosystem background.Under the dual influence of global temperature rise and human factors,the ecological environment is becoming more and more fragile.As an important part of the surface hydrosphere,lakes have also been seriously damaged.Water color is an important index to reflect the comprehensive state of lake and reservoir water quality,but there is still a lack of large-scale spatio-temporal research on lake water color in Inner Mongolia.Based on Landsat-5/8 satellite data,this paper extracts Hue-Angle（HA）and Fore-ule index（FUI）from May to October of 1986-2021,studies the long-term dynamic change of lake water color,and discusses its main driving factors;Taking Daihai as the key research lake,a linear regression model is constructed based on the measured Nutritional state index and HA.The nutritional state index of Daihai Lake from 1986 to 2021 is inversed,and its temporal and spatial variation characteristics are analyzed.The main conclusions are as follows:（1）Among the five typical lakes,Wuliangsuhai has the highest FUI and Hongjiannao is low on the whole.The change trend of water color index of each lake is different.Hulun Lake shows a slow growth trend,Hongjiannao shows an obvious downward trend,and other lakes show a slow downward trend;The spatial difference of Fore-ule index in Wuliangsuhai Lake is large,and the spatial distribution of other lakes is relatively uniform.（2）Analysis on the external driving factors of lake FUI:the monthly mean of HA of five lakes is negatively correlated with NDVI and Precipitation,and positively and negatively correlated with Wind speed respectively;Different land use types in the basin are correlated with lake water color change,among which construction land and cultivated land have a greater impact on lake water color change than other types.（3）Analysis of internal driving factors of lake water color index change:there is no correlation between Daihai Lake area and water color change,but there is a significant correlation between Hongjiannao area and water color change trend;The area of marine vegetation in Wuliangsu is correlated with the change of water color,and the correlation of emergent vegetation is the highest;The depth,Transparency（SD）,Suspended Particulate Matter（SPM）and Chromophoric Dissolved Organic Matter（CDOM）of Daihai Lake all play a role in the change of water color.（4）Evaluation of nutritional status of Daihai water body:the nutritional status inversion model based on Modified Trophic Status Index（TSI_M）is the best,with R~2of 0.65,MAPE=4.54%and RMSE=3.22;The nutritional status of Daihai from 1986 to2021 was evaluated by using the model based on Tsim index.It was found that Daihai Lake has been in eutrophication for 35 years and showed the characteristics of inter monthly variation.The degree of eutrophication in May and October was higher than that in other months.In space,the degree of eutrophication in the center of the lake was low,and the closer it was to the lake shore,the higher the level of eutrophication.