2024

Wåhlström, Iréne; Almroth-Rosell, Elin; Edman, Moa; Olofsson, Malin; Eilola, Kari; Fleming, Vivi; Gröger, Matthias; Arneborg, Lars; Meier, H.E. Markus

Highlights • Climate change and nutrient load changes may affect the future coastal zone. • Future filter efficiency of nutrients may increase in the coastal zone. • Cyanobacteria biomass may increase 5-fold in a worst-case scenario. • Higher phytoplankton biomass may increase the risk of bottom anoxia. • Sustainable nutrient management may counteract future coastal blooms of cyanobacteria. Abstract Climate change and coastal management directly affect the magnitude of nutrient loads and the functioning of the coastal zones. In this novel approach, a coastal-zone-model was used to study future retention capacity of nitrogen and phosphorus loads and changes in cyanobacterial blooms in an archipelago in a eutrophied coastal sea. By conducting projections under the combined impact of changing climate and nutrient loads we demonstrate that i) future filter efficiency of the archipelago increases compared to present day regardless of the nutrient load projection, ii) the cyanobacteria biomass increased 5-fold in a worst-case nutrient load projection and iii) resulting in an increased spread of bottom anoxia and hypoxia. However, the phytoplankton biomass and hypoxia/anoxia will remain stable if the planned mitigation is successfully implemented. This study highlights the importance of nutrient load management and the need to understand more about the complex interactions taking place in the coastal systems.