Disaster avoided: current state of the Baltic Sea without human intervention to reduce nutrient loads

Abstract

Excessive nutrient inputs have caused eutrophication of coastal ecosystems worldwide, triggering extensive algal blooms, oxygen‐depletion, and collapse of local fisheries. In the Baltic Sea, inputs of nitrogen (N) and phosphorus (P) have been significantly reduced since the 1980s, but the environmental state shows little to no signs of recovery. However, a simulation with continued high loads from the mid‐1980s demonstrates that while the state has not improved yet, it would be considerably worse today without the load reductions (e.g., 82% larger oxygen‐free bottom areas and 104% and 58% higher wintertime concentrations of inorganic N and P, respectively, in the Baltic Proper). Additional simulations with current nutrient loads continuing into the future indicate that conditions will likely improve in the coming decades. This study underscores the significance of acting on early warning signs of eutrophication, and furthermore how sustained efforts to decrease nutrient loads can mitigate the severity of eutrophication.