Evaluation Of Lake Eutrophication By Remote Sensing In Wuhan Area

Eutrophication is the main problem of lake pollution in China. It is quite necessary for the protection of the lakes' environment to evaluate and monitor efficiently the lakes' status of eutrophication in time.Through the analysis of the Thematic Mapper (TM) images in September,1999,and reliable monitoring data for many years of each parts of Donghu Lake in Wuhan area,the author has established a good regression relation between the values of grey degree abstracted from TM several images and eutrophication indices of the lakes. According to the models,the author investigated and evaluated all the main lakes in Wuhan area. At the same time,based on the in-situ monitoring data they also evaluated the eutrophication degree of lakes in Wuhan area by another method "Modified Trophic State Index"(TSlM) which was brought forward by Japanese scholar Morikiro Aizaki.The evaluating results by both methods show that most lakes are meso-eutrophic,and some of them have neared or even reached hypereutrophic states. Among the results of eight lakes that have been evaluated simultaneously by linear regression model and the TSlM method,results of six lakes are identical and that of Houhu Lake's evaluating values is very near,only but that of Moshuihu Lake is very different. Among the results of eight lakes that have been evaluated simultaneously by multi regression model and the TSlM method,results of six lakes are identical and that of the other two lakes' (Liangzihu Lake and Moshuihu Lake) are very different.There are three possible reasons that lead to the bigger difference of the evaluating results among few lakes. First,remote sensing technology reflects the average value of a certain area corresponded with TM images in a certain period,but "Modified Trophic State Index" reflects the annual average values of the monitoring points. Second,the time of TM images is later than that of in-situ monitoring data. And third,parts of the TM images are affected by cloud,water depth,suspension such as sand,hyper-hydrophytes,etc.In a word,the result by remote sensing is almost agreed with the monitoring data. It means that remote sensing technology is feasible and effective to monitor and evaluate the eutrophication of lakes in Wuhan area and the method developed in this thesis can also be used to investigate and evaluate lake eutrophication in a larger area,for example,in the plain area of middle and down reach of Yangtze River Basin.