Future Scenarios for River Exports of Multiple Pollutants by Sources and Sub-Basins Worldwide: Rising Pollution for the Indian Ocean.

In the future, rivers may export more pollutants to coastal waters, driven by socio-economic development, increased material consumption, and climate change. However, existing scenarios often ignore multi-pollutant problems. Here, we aim to explore future trends in annual river exports of nutrients (nitrogen and phosphorus), plastics (macro and micro), and emerging contaminants (triclosan and diclofenac) at the sub-basin scale worldwide. For this, we implement into the process-based MARINA-Multi model (Model to Assess River Inputs of pollutaNts to the seAs) two new multi-pollutant scenarios: "Sustainability-driven Future" (SD) and "Economy-driven Future" (ED). In ED, river exports of nutrients and microplastics will double by 2100, globally. In SD, a decrease of up to 83% is projected for river export of all studied pollutants by 2100, globally. Diffuse sources such as fertilizers are largely responsible for increasing nutrient pollution in the two scenarios. Point sources, namely sewage systems, are largely responsible for increasing microplastic pollution in the ED scenario. In both scenarios, the coastal waters of the Indian Ocean will receive up to 400% more pollutants from rivers by 2100 because of growing population, urbanization, and poor waste management in the African and Asian sub-basins. The situation differs for sub-basins draining into the Mediterranean Sea and the Pacific Ocean (mainly less future pollution) and the Atlantic Ocean and Arctic Ocean (more or less future pollution depending on sub-basins and scenarios). From 56% to 78% of the global population are expected to live in more polluted river basins in the future, challenging sustainable development goals for clean waters.