Reducing future coastal eutrophication under global change in Europe

Agricultural production and sewer systems have been the main contributors to nutrient losses to surface waters. A high load of nutrients by rivers causes coastal eutrophication and leads to harmful algal blooms. Several negative environmental impacts of eutrophication include the production of toxins by cyanobacteria, fish kills, increased production of algae, and reduction in coral reef communities and aquatic vegetation. Despite the environmental policies and targets in Europe, rivers transport large amounts of nutrients to coastal waters and thus, coastal eutrophication is still an issue. Half of the nitrogen (N) exports by the European rivers to coastal waters is from agricultural production. The losses can increase if effective actions are not taken to improve agricultural management. As a result, the risks of coastal eutrophication will likely increase in the future coupled with global change including socio-economic development and climate change.

This study aims to assess the future river export of N and phosphorous (P) and explore options to reduce associated coastal eutrophication in Europe under global change with a focus on sustainable agriculture and urbanization. We use the MARINA-Nutrients (Model to Assess River Inputs of Nutrients to seAs) model for 601 European basins to quantify river exports of N and P in the 21^st century, and calculate an indicator for coastal eutrophication potential (ICEP) to evaluate their impacts on coastal waters. We develop scenarios based on existing storylines (e.g., Shared Socio-economic Pathways, Representative Concentration Pathways) to quantify the impacts of socio-economic and climate changes on future coastal pollution in Europe. In our scenarios, we reflect on environmental policies (e.g., Green Deal, reduced waste, and improved wastewater treatment) from optimistic views.

Model results show that under the current practice approximately one-third of the European basin area, including 59% of the total population, is responsible for over half of nutrient losses to European rivers. Over one-fourth of river exports of N and P ended up in the Atlantic Ocean and the Mediterranean Sea around 2017-2020, respectively. On the other hand, intensive agriculture and technological development will increase nutrient pollution in coastal waters. For example, river exports of N and P to coastal waters are projected to increase by approximately 20-30% by 2050 under a scenario with high global warming and high urbanization rates. The Atlantic Ocean is projected to receive the largest portion of nutrient losses in the future compared to other European seas in 2050. In our scenarios, we analyze optimistic options to reduce future coastal eutrophication in European coastal waters. during the presentation, we will show the effects of several optimistic options (e.g., recycling of organic waste) on reducing coastal eutrophication. We will discuss the possible implications of the Green Deal and European environmental policies for coastal water quality in Europe.