Dual-quantification of the different contributions of climate change and anthropogenic activities to eutrophication of rivers and lakes in Asia's largest river basin (Yangtze River)

The impact of anthropogenic activities and climate change on surface water eutrophication has been of great concern. However, the contribution proportions of anthropogenic activities and climate change to the lakes and rivers’ eutrophication in large basins has not been clearly revealed. This study employed Geographically Weighted Regression (GWR) and Structural Equation Modeling (SEM) to conduct a dual quantification of the differential contributions of anthropogenic activities and climate change to the eutrophication of rivers and lakes in the Yangtze River Basin (YRB). Regression coefficients of GWR variables demonstrated the spatial heterogeneity of eutrophication drivers. Shapley additive explanations showed that nutrients and land use intensity were the main drivers during wet seasons. Combining the direct and indirect path results from SEM, the relative contribution of anthropogenic activities and climate change was 92.1 % and 7.9 % to river eutrophication, respectively, and was 67.1 % and 32.9 % to lake eutrophication, respectively. Anthropogenic activities consistently exacerbate eutrophication in both rivers and lakes, whereas climate change intensifies lake eutrophication but exerts seasonally variable effects on rivers. These findings revealed that intensive anthropogenic activities continue to dominate the eutrophication of the YRB. This study can provide a scientific reference for the integrated management of aquatic ecosystems in large basins.