A thirty-year Landsat study reveals changes to a river-lake junction ecosystem after implementation of the three Gorges dam

Abstract

Ecosystems at the junctions of large lakes and rivers are a significant resource which are yet susceptible to changes in the various water bodies. One of the most crucial river-lake junction points in China is the junction of Poyang Lake and the Yangtze River (JPLYR), with the Three Gorges Dam (TGD) upstream. Based on remote sensing images of the dry season from 1987 to 2018, landcover change of JPLYR was obtained using the random forest classification method. Linear regression, principal component analysis (PCA), and classification and regression tree (CART) were used to determine relationships between 16 hydrological variables regarding magnitude, duration, timing, variation, and vegetation area throughout different operational stages of the TGD. Results showed that the operation of the TGD has anticipated and elongated the dry seasons, with a consequential shortening of the flood seasons that now occur later in the year. The peak water level was significantly reduced (p < 0.05), while the minimum water level remained unchanged throughout the study period. There was a 344% increase in vegetation coverage across the JPLYR from 1987 (0.677 km2) to 2018 (3.005 km2). The earlier beginning of dry season (BDS) was found to be most significant in affecting the increased vegetation area before and after the operation of TGD. The results provide an essential reference for assessing the potential influence of newly proposed dams in river-lake junctions and for optimizing future operations.