Impact of changing agricultural management on the exceedance of empirical critical loads of nitrogen in terrestrial habitats of southwestern Europe

Abstract

Ammonia (NH₃) emissions from agricultural activities are one of the main sources of air pollution, a challenge for EU emission targets, and contribute significantly to nitrogen (N) deposition and eutrophication of sensitive ecosystems. This study used modelling to evaluate the mitigation of this eutrophication by improved fertilizer management techniques in the EU Interreg “SUDOE” region (Spain, Portugal, and southwestern France), comparing it with the current situation. The results showed that the implementation of improved fertilizer management -removing urea-based fertilizers and optimizing manure application- led to a 36% reduction in NH₃ emissions and a 20% decrease in total N deposition. Consequently, the area of habitats exceeding their critical nitrogen load dropped from 39% to 22%, representing a 43% reduction in area at risk of eutrophication. However, spatial heterogeneity was considerable, driven by atmospheric transport, deposition patterns, and distribution of sensitive habitats. The majority of the most sensitive habitats experienced a reduction of their area at risk, particularly natural and semi-natural grasslands, and most of shrublands. However, some others, such as coastal dunes and certain Mediterranean shrublands, experienced smaller improvements. The Alpine region remained the most threatened region. This study highlights the importance of improved fertilizer management in achieving strategic environmental goals, and confirms that spatially explicit modelling and precautionary assessments using critical loads are useful tools to inform regionally adapted environmental policies, considering sensitivity of the ecosystems, deposition magnitude and pollution sources as key factors.