Variations in Phytoplankton Blooms in the Yangtze River Estuary and Its Adjacent Waters Induced by Climate and Human Activities

The long-term characteristics of phytoplankton blooms and the relative importance of driving factors in the Yangtze River Estuary (YRE) and its adjacent waters remains unclear. This study explored the temporal and spatial patterns of blooms and their driving factors in the YRE and its adjacent waters using MODIS bloom data from 2003 to 2020. Bloom intensity varied along both longitudinal and latitudinal gradients, with very few blooms occurring near the shore and in the open sea. Temporally, blooms exhibited seasonal variations, peaking during the summer and being weakest during the winter. Sea surface temperature was the primary driving factor behind the seasonal variations in algal blooms. The implementation of controlling the pace of urban land development, returning farmland to forest, and initiating marine pollution prevention programs have contributed to a downward trend in the bloom intensity. Additionally, the operation of the Three Gorges Dam altered the Yangtze River's diluted water during the summer months, thereby reducing the bloom intensity. Conversely, the Taiwan Warm Current promoted an increase in the bloom intensity. Elucidation of the spatiotemporal patterns and the driving factors of blooms in the YRE and its adjacent waters provide crucial support for the prediction and management of algal blooms.