Researchers warn of climate change ‘roulette’ for European nitrate pollution. Climate change could significantly increase nitrogen pollution risks in freshwater systems across parts of Europe unless nutrient management practices adapt to changing environmental conditions, new research has found.
The use of both synthetic and organic fertilisers increases nitrate pollution risk by allowing surplus nitrogen to leach into rivers, groundwater, and other freshwater systems.
The research, from the University of Aberdeen and the Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB) in Berlin, reveals that climate-driven changes can strongly influence both the pattern and speed at which nitrogen from fertilisers is transported into freshwater.
Published in Science, the study demonstrated how climate-induced changes such as rainfall patterns, snowmelt and drought frequency, all influence how water moves through landscapes and that both extremes – too wet or too dry – can increase nitrate pollution risk.
Nitrogen pollution is a growing global environmental challenge – contributing to the growth of harmful algae blooms, threatening drinking water supplies, damaging ecosystems, and affecting food production.
The research team developed a new isotope-enabled biogeochemical model to track water and nitrogen movement across more than 3,800 European river basins. Using stable water isotopes, the model mapped the velocities of water cycling and assessed how shifts in wetter and drier climatic conditions have influenced nitrogen pollution since the 1980s. The study also projected how these patterns may evolve by the end of the 21st century.
The findings show that landscape water velocities are a major but previously underappreciated control on nitrogen pollution. Faster-moving water, often found in mountainous areas and along Europe’s north-west coast, can rapidly flush nitrogen into groundwater and streams before plants and microorganisms have time to remove it. In contrast, slower-moving water in lowland regions generally allows more time for natural nitrogen processing and retention.
Professor Chris Soulsby from the University of Aberdeen said:
“Previously nitrogen pollution was mainly attributed to excess fertiliser application. Here we demonstrated that landscape hydrology and water velocities are also critical controls on leaching.”
The study found that moderate climate-driven hydrological changes can sometimes reduce nitrogen pollution risk, but more extreme changes tend to increase it. Very wet conditions can accelerate water movement and rapidly transport nitrogen into freshwater systems, while prolonged drying can suppress plant and microbial uptake, allowing nitrogen to build up in soils before being flushed out during heavy rainfall events.
To explain these patterns, the researchers introduce the concept of ‘wetness boundaries’, thresholds within which landscapes are more resilient to hydrological change. Crossing these boundaries, either through excessive drying or wetting, increases the likelihood of nitrogen leaching and freshwater pollution.
Professor Dörthe Tetzlaff of Humboldt University zu Berlin said:
“The wetness boundaries can help define a safe operating space resilient to hydrological change and can be used to identify potential increased risk in nitrogen leaching.”
Looking ahead, the study projects contrasting futures for Europe depending on greenhouse gas emissions. Under a low-emissions scenario, hydrological changes are expected to remain within these wetness boundaries across much of Europe, reducing nitrogen leaching risk in more than 70 percent of the continent.
Under high-emissions scenarios, however, continued drying in parts of Eastern and Southern Europe could suppress vegetation and microbial activity, increasing nitrogen accumulation in soils and raising the risk of pollution during extreme rainfall events.
The researchers say the findings highlight the need to adapt nutrient management practices, including fertilizer application strategies, to future climatic conditions. They also suggest that reducing anthropogenic nitrogen inputs could help landscapes remain within safer hydrological boundaries and reduce future pollution risks.
The research was supported by the German Research Council and the Leibniz Association. Professor Chris Soulsby is also a Visiting Research Fellow at the Leibniz Institute of Freshwater Ecology and Inland Fisheries in Berlin.
Image: Professor Chris Soulsby from the University of Aberdeen