Remote Sensing Inversion And Eutrophication Evaluation Of Water Quality Parameters In Poyang Lake

Lakes have been an important freshwater resource for mankind since ancient times,and have played a vital role in all aspects of human life.At present,lakes nationwide are facing a crisis of deteriorating water quality,and Poyang Lake is no exception.Poyang Lake has a wide water area and complex hydrodynamic conditions.It is difficult for traditional water quality monitoring methods to accurately reflect the changes in lake water quality.Remote sensing has the advantages of economy and convenience.It can comprehensively and continuously monitor the temporal and spatial changes of the lake to provide water quality.Management provides important auxiliary data,which is currently a popular direction for water quality monitoring.Total nitrogen?TN?,total phosphorus?TP?,permanganate index(COD_Mn),nutritional status index are important parameters that reflect the status of water quality.Analysis of water quality parameter concentration,distribution,and eutrophication evaluation index is conducive to timely detection and control of pollution source.Based on the on-site acquisition of suspended sediment?SS?,chlorophyll a?Chl-a?,yellow substance?CDOM?,total nitrogen?TN?,total phosphorus?TP?,and permanganate index(COD_Mn)in August 2015 based on Poyang Lake.The concentration of TP and TN was found to be serious and exceeded the limit of occurrence of"bloom".The measured concentration of CODMn was basically in Class III water bodies and below.The calculation of the nitrogen-phosphorus ratio found that there are two types of waters in the Poyang Lake,namely phosphorus limitation and nitrogen limitation.The correlation coefficients of TN,TP and SS are 0.684 and 0.807,and the correlation between COD_Mn and SS,chl-a and CDOM is weak.The measured spectrum data shows that SS has a good response in the red-near infrared wavelength range.The reflectivity after the first-order differential processing is compared with the original remote sensing reflectivity.After the first-order differential processing,the highest correlation coefficient between TP and reflectance is increased to-0.773,the highest correlation coefficient between TN and remote sensing reflectance is increased to-0.749,COD_Mn and reflection The highest correlation coefficient increased to-0.755.By using the measured reflectance and referring to the band setting of Landsat 8OLI,the correlation between TN,TP,COD_Mn and the ratio of the two bands is higher than the correlation with other band combinations.Comparing direct and indirect inversion models,it is found that the accuracy of the TP direct model is slightly higher than that of the indirect model,and the direct model R₂ of TN is much lower than that of the indirect model.The indirect inversion model of TN selected in this paper,the mean relative errors of the three models of TP and COD_Mn direct inversion models are 29.4%,21.7%and 15.7%respectively.The model was applied to the Landsat 8 OLI image,and the inversion results showed that the spatial distribution of the three water quality parameters was roughly similar,with sand mining areas,estuaries,estuaries,and other eastern and southeastern waters as the main polluted areas.Concentrated in the summer,small lakes that enter the river channel lakes and the outer periphery of the lake body away from the main lake are also highly polluted.The lake as a whole is spatially distributed from south to north and from outside to inside.By comparing the adaptability of the five methods including comprehensive nutritional status index method,scoring method,and Nimelo index method in Poyang Lake,the scoring method was selected as the eutrophic evaluation method for Poyang Lake,and the inversion results showed that the eutrophication evaluation index range From 45.6 to 65.1,the nutritional level is between moderate to moderate eutrophication.The spatial distribution of the evaluation index is similar to the spatial distribution of water quality parameters.In the lake inlet,sand mining area,east,south,and small lakes away from the main lake The evaluation index of other waters is higher.Water quality parameters from external sources are important sources of TN,TP,and COD_Mn in Poyang Lake.Human activities such as river input,industrial sewage,agricultural sewage,and sand mining all have an impact on water quality,and targeted adjustments to corporate policies and strengthening Suggestions on environmental legislation,increased control of pollution of rivers and human activities,and implementation of information-based water environment monitoring.