Terrestrial nutrient exports and environmental changes explain eutrophication trends in fifty large lakes of Yangtze Plain, China

Over the past two decades, lakes in Yangtze Plain have suffered from serious eutrophication, in some regions with increased frequency of cyanobacteria blooms over years. In this study, we investigated the underlying causes of eutrophication using a combination of process-based ecosystem modelling and statistical data analysis. We found that terrestrial nutrient exports with runoff have significantly increased from 1979 to 2018 in Yangtze Plain, directly linked to the enhanced usage of chemical fertilizer for crops. Based on statistical analyses of environmental variables, terrestrial nutrient exports and satellite-observed probability of eutrophication occurrence (PEO), we separated the studied fifty lakes into five classes with similarities in environmental and nutrient variations, and attributed key factors in controlling the temporal changes of PEO. The results showed that the satellite-observed PEO trends in five classes could be largely linked to the terrestrial nutrient exports and environmental changes. Specifically, we found agricultural activities can explain the observed eutrophication trends in western lakes where lake catchments are dominated with arable and natural land, and the reduced discharge of industrial wastewater was found to be linked to the declining trends in eutrophication for eastern lakes where the green growth of industrialization were promoted from 2003 to 2011. These findings highlight the importance of sustainable management of agriculture and industrialization to overcome eutrophication issues in this region.