Satellite images reveal reduced lake chlorophyll concentration and eutrophication in China

Lake trophic state is the sentinel of water quality. Improvement of lake trophic state is at the core of various aquatic sustainable development goals for China. Although trophic state regime shifts have been well documented in some lakes, a national-scale assessment on spatiotemporal variation of trophic state has not been done. Here, we analyze Chl-a maps derived from Landsat images during 1990-2020 and assess the changes of trophic states over >1138 large lakes (surface areas larger than 1 km2), which account for 60.1% of total lake areas in China. On the average, these lakes in China had the most pronounced decreases of Chl-a levels since 2010. 180 light-eutrophic lakes (10<1.6, μg L-1) showed increases. At province-scale, the climate variations such as precipitation, temperature and wind speed could positively drive Chl-a’s increases, the increased GDP (3.16%) dominated their reduces. Further, the national protected policies promulgated and implemented significantly decrease lake Chl-a levels and alleviate trophic state since 2010. The patent policies implemented have a greater role in promoting water qualities, particular in relatively rich provinces/municipality as Beijing, Zhengjiang and Shanghai, following by central and east regions. Increased conservation and restoration efforts offset the success of climate change to increase eutrophication.