Authors: Albert Nkwasa, Maria Theresa Nakkazi, Celray James Chawanda, Ting Tang, Keerthana Suresh, Arthur H W Beusen, Ilaria Micella, Maryna Strokal, Taher Kahil and AnnvanGriensven
Abstract
Riverine exports of total nitrogen (TN) and total phosphorus (TP) are major drivers of coastal eutrophication. However, few studies have quantified the reductions required to mitigate future eutrophication risks under changing socio-economic and climatic conditions. Here, we use three global water quality models (Integrated Model to Assess the Global Environment-Dynamic Global Nutrient Model, CoSWAT-WQ, and MARINA-Multi) to project TN and TP export loads from twenty four of the world’s largest river basins under a high-emission and high socio-economic growth scenario (SSP5-Representative Concentration Pathways 8.5). Our multi-model mean projections indicate that TN and TP exports from these basins could increase by 18% and 21%, respectively, by 2050 relative to 2010 export levels. To avoid the risk of future coastal eutrophication, we estimate reductions in TN and TP riverine exports to coastal waters of approximately 67% and 64%, respectively by 2050. In particular, major river basins such as the Nile, Niger, Yangtze, Ganges, Danube, S˜ ao Francisco, and Zhujiang will require nutrient load reductions exceeding 50% for both TN and TP. Ultimately, achieving the necessary nutrient reductions will require coordinated, targeted interventions to protect our global coastal ecosystems. Meanwhile, the variability among model simulations underscores the need to advance global water quality modeling frameworks to reduce uncertainties and better support science-based policy making.
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