Droughts and heavy rain drive nitrate into groundwater

Extremes Make It Worse

This is exactly where climate change comes into play. Heavy rainfall accelerates water flow and washes nitrate out of the soil. Droughts slow it down dramatically. Plants and microorganisms can barely function, causing the substance to accumulate. When rain finally does come, everything is washed away all at once.

To describe these relationships, the researchers introduce the concept of so-called moisture thresholds. As long as the water balance remains within these limits, nitrate levels stay relatively stable. If the limits are exceeded due to extreme wetness or extreme dryness, the risk of nitrate leaching increases significantly.

Project leader Prof. Doerthe Tetzlaff of the IGB and Humboldt University of Berlin explains that the moisture limits could “help define a safe margin of action that is resilient to hydrological changes.”

The researchers have calculated two future scenarios for Europe. With low greenhouse gas emissions, nitrate pollution would decrease in more than 70 percent of Europe by 2100. With high emissions, however, the opposite is likely, particularly in Eastern and Southern Europe: persistent drought, higher nitrate levels, and poorer water quality.

The study shows that nitrate pollution can only be understood within the “complex interplay of transport and retention in the landscape,” summarizes UFZ hydrogeologist Dr. Andreas Musolff. The projections highlight where Europe is particularly at risk.

To reduce nitrate pollution in soils and water bodies, more targeted fertilization and improved wastewater treatment are needed. At the same time, climate change also plays a role, as droughts and heavy rainfall can increase the leaching of nitrate.


Original publication:
Songjun Wu, Chris Soulsby, Yi Zheng, Andreas Musolff, Doerthe Tetzlaff: Divergent Evolution of Nitrogen Cycling Along Gradients of Landscape Water Velocities; Science, 2026.