Trophic status mapping for Changshou Lake from time series landsat images
ZHANG Chen1， XIA Jing2， MIN Tian3， LIANG Si3， TIAN Jingyi1
(1.State Key Laboratory of Information Engineering in Surveying， Mapping and Remote Sensing， Wuhan 430079， China；2.Changjiang Spatial Information Technology Engineering Co.Ltd， Wuhan 430010， China；3.Hubei Institute of Photogrammetry and Remote Sensing， Wuhan， 430074， China)
Abstract：Investigating the trophic status and changing trends of lakes is of great importance for understanding the evolution of lake water quality and managing lake ecosystems. The Forel-Ule Index (FUI)， an index of water color， is closely related to the trophic level of lakes and can be used to evaluate the trophic status and analyze its changing patterns. This study focused on Changshou Lake in Chongqing， using a series of Landsat 5/7/8 remote sensing data from 1986 to 2022 to calculate the FUI index， thereby assessing the lake's trophic status. Spatial and temporal changes in trophic levels over the past 40 years were analyzed using the coefficient of variation (CV)， Sen's slope estimator， and the Mann-Kendall (M-K) test for the whole lake and its functional zones. Results are shown as follows. 1) The trophic state of Changshou Lake has primarily been mesotrophic over the years， with significant improvements in water quality since 2002； the water quality in the western ecological aquaculture zone was the poorest. 2) The western ecological aquaculture zone showed the highest FUI CV of 0.17， with stable increase in trophic conditions after 2002， and the areas with notable water quality improvement were mainly distributed in the central and northwestern parts. 3) The central ecotourism zone had the lowest FUI CV at 0.10， indicating relatively stable trophic conditions over the years. The middle-western area in this zone showed a strong decreasing trend in FUI values with a significant reduction in eutrophication levels. 4) The eastern wetland protection zone exhibited a shift from mesotrophic to eutrophic conditions， with an increasing risk of eutrophication. These results play a crucial role in monitoring and assessing the water environment in Changshou Lake.
2025, Vol. 59 
