Reducing future nutrient inputs to the Black Sea.

Rivers export increasing amounts of dissolved inorganic (DIN, DIP) and organic (DON, DOP) nitrogen and phosphorus to the Black Sea causing coastal eutrophication. The aim of this study is to explore future trends in river export of these nutrients to the sea through a sensitivity analysis. We used the Global NEWS (Nutrient Export from WaterSheds) model to this end. We calculated that between 2000 and 2050 nutrient inputs to the Black Sea may increase or decrease, depending on the assumed environmental management. We analyzed the effects of agricultural and sewage management on nutrient inputs to the sea in 2050 relative to two Millennium Ecosystem Assessment (MEA) scenarios, Global Orchestration (GO) and Adaptive Mosaic (AM). In these baselines, total N and P inputs to the Black Sea decrease between 2000 and 2050, but not for all rivers and nutrient forms. Our results indicate that it is possible to reduce nutrient inputs to the sea further between 2000 and 2050 in particular for dissolved inorganic N and P and for many river basins, but not for all. For scenarios assuming combined agricultural and sewage management dissolved inorganic N and P inputs to the Black Sea are reduced by up to two-thirds between 2000 and 2050 and dissolved organic N and P inputs by one-third. River export of DIN is mainly affected by agricultural management and that of DIP by sewage management. On the other hand, in scenarios assuming increased fertilizer use for, for instance bioenergy crops, nutrient inputs to the sea increase. An increase in DIP inputs by southern rivers seems difficult to avoid because of the increasing number of people connected to sewage systems.