The Critical Role of Wetland Conservation and Restoration in Mitigating Nitrogen Pollution Across European River Basins

Excessive nitrogen (N) inputs from agricultural intensification, wastewater, and atmospheric deposition pose a severe threat to European ecosystems and public health, with N levels in over 57% of freshwater monitoring stations exceeding thresholds for good ecological status. While traditional management practices focus on reducing inputs, nature-based solutions (NBSs) like wetlands offer powerful, cost-effective filtration by facilitating denitrification in their carbon-rich, anoxic soils. This study presents a novel, pan-European modeling framework that combines high-resolution N surplus data, historical wetland distribution, and projected land-use changes to quantify the current and potential N-removal capacity of wetlands across the EU27 and neighboring countries.

The analysis estimates that existing European wetlands currently remove approximately 1,000 kt of nitrogen per year, a service that prevents riverine N loads to the sea from being 25% higher than they are today. Despite this contribution, Europe remains a hotspot for wetland loss, having drained roughly 70% (~78 Mha) of its historical wetland area, primarily for agricultural expansion.

To address current pollution gaps, the study evaluates three restoration scenarios designed to meet water quality targets while balancing agricultural productivity. The most ambitious Restoration scenario - restoring 27% of wetlands historically drained for agriculture (3.2% of total land area) - could reduce N loads to the sea by 36%. However, the study identifies a more efficient strategy, which targets restoration on lands projected to be abandoned by 2040. This approach yields a 22% reduction in total N loads and enables major rivers like the Rhine, Elbe, and Vistula to meet water quality targets with minimal impact on agricultural output.

Cost-benefit analysis indicates that while restoration costs are significant - ranging from €55-358 billion per year for the full scenario - the co-benefits of ecosystem services, such as carbon sequestration and flood regulation, often outweigh these expenses. Ultimately, the findings highlight that spatially targeted wetland restoration is a vital, policy-relevant tool for achieving the European Green Deal’s goals for water quality, biodiversity, and climate sustainability. However, the study concludes that in the most heavily polluted basins, wetland restoration must be paired with continued reductions in diffuse N sources to reach good ecological status.