Satellite images reveal reduced lake chlorophyll concentration and eutrophication in China

Chlorophyll-a (Chl-a) concentration in lake water is an indicator of its trophic state and water quality. Although many anthropogenic drivers have increased lake trophic state, leading to severe negative consequences, many environmental policies and management were done towards improving water quality. Here, we analyzed the Chl-a concentration maps derived from Landsat images during 1990–2020 and assessed the changes of trophic states over > 1138 large lakes (surface water areas larger than 1 km 2 ), which together account for 60.1 % of total lake areas in China. The average Chl-a concentration over all the lakes declined more rapidly after 2010. Lake trophic states dropped in 180 light-eutrophic lakes (10 < Chl-a < 26, μg L -1 ), but rose in 14.29 % oligotrophic lakes (Chl-a < 1.6, μg L -1 ). We observed pronounced decreases in averaged Chl-a levels since 2010, accompanied by increased identified mesotrophic and oligotrophic states; however, this shift exhibited considerable variability across different provinces. The climate change (i.e., increased temperature, decreased precipitation) often lead to increases in Chl-a concentration, but the implementation of national environmental policies lead to decreases in lake Chl-a levels since 2010, particular in those provinces with large economy.