Multi-pathway nutrient replenishment mechanisms sustaining the transboundary green tides region in the Southern...

Large-scale macroalgal blooms represent a critical environmental challenge for coastal regions worldwide, driven primarily by human-induced eutrophication. Since 2007, the Southern Yellow Sea (SYS) in China has experienced massive green tides of Ulva prolifera (U.prolifera) each summer, persistently impacting the coastal economies, ecosystems, and social well-being of Jiangsu and Shandong provinces. This study systematically quantified the contribution of different nutrient sources to the migration path of green tide in the outbreak area. The analysis was mainly based on field monitoring data from 2017, supplemented by historical datasets. Results show that atmospheric deposition acts as a key cross-regional driver, accounting for 70 %, 34 %, 54 %, 76 %, and 64 % of dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), dissolved silicon (DSi), dissolved organic nitrogen (DON), and dissolved organic phosphorus (DOP), respectively. Meanwhile, terrestrial inputs in the Subei Shoal-including river input and marine aquaculture-provide 25 % of DIN and 46 % of DIP, forming an essential nutrient base for the initial bloom development. As algal biomass drifted northward to the coastal waters of Shandong Peninsula, continuous atmospheric nutrient deposition became a key driver for the expansion of the green tide. This study quantitatively elucidates the transboundary effects of atmospheric and terrestrial nutrient inputs, offering scientific support for nutrient management strategies in coastal marine systems.