Effects of EU policy and climate change on future delivery of nutrients to European freshwater and seas

Abstract In Europe, excessive nutrient pollution in freshwater and marine ecosystems poses a significant threat to human uses of water resources and disrupts aquatic ecosystems, compromising essential ecosystem services. The effectiveness of existing EU policies aimed at mitigating nutrient pollution will be influenced by the combined impact of climate variability and change. It remains uncertain whether current policies will suffice to reduce nutrient pollution to levels compatible with good environmental conditions in freshwaters and coastal waters. This study quantifies nitrogen and phosphorus fluxes in European freshwater systems and their delivery to the sea, considering the effects of existing EU policies and climate change up to 2050. Using the GREEN model, we simulated total nitrogen and phosphorus loads from 1990 to 2021 and projected future changes until 2050 using climate projections from 11 regional climate models (EURO-CORDEX) under the RCP 4.5 scenario. Our results indicate that implementing current EU policies—Common Agricultural Policy, Urban Waste Water Treatment Directive, FitFor55 package for climate neutrality—will reduce nutrient loads to European seas by 2050, with a 10% decrease in nitrogen and 8% decrease in phosphorus loads compared to 2020 values, albeit with significant uncertainty related to climate variability. Regional differences are also explored. Nutrient concentrations in the EU river network are expected to decrease slightly, as well as the potential risk for coastal eutrophication (ICEP index). However, further reductions of 10%–20% beyond existing policies may be necessary to achieve good conditions in large rivers. These reductions could come from improved agricultural practices, nature-based solutions and wetland restoration. Our study suggests that while current measures will lead to improvements by 2050, additional efforts will be required in some regions to achieve good environmental conditions, highlighting the need for integrated nutrient management to avoid imbalances between nitrogen and phosphorus in receiving waters.