Search

In this paper, we assess and map the risk that atmospheric nitrogen (atN) pollution poses to biodiversity in Natura 2000 sites in mainland Portugal. We first review the ecological impacts of atN pollution on terrestrial ecosystems, focusing on the biodiversity of Natura 2000 sites. These nature protection sites, especially those located within the Mediterranean Basin, are under-characterized regarding the risk posed by atN pollution. We focus on ammonia (NH3) because this N form is mostly associated with agriculture, which co-occurs at or in the immediate vicinity of most areas of conservation interest in Portugal. We produce a risk map integrating NH3 emissions and the susceptibility of Natura 2000 sites to atN pollution, ranking habitat sensitivity to atN pollution using expert knowledge from a panel of Portuguese ecological and habitat experts. Peats, mires, bogs, and similar acidic and oligotrophic habitats within Natura 2000 sites (most located in the northern mountains) were assessed to have the highest relative risk of biodiversity change due to atN pollution, whereas Natura 2000 sites in the Atlantic and Mediterranean climate zone (coastal, tidal, and scrubland habitats) were deemed the least sensitive. Overall, results allowed us to rank all Natura 2000 sites in mainland Portugal in order of evaluated risk posed by atN pollution. The approach is of great relevance for stakeholders in different countries to help prioritize site protection and to define research priorities. This is especially relevant in countries with a lack of expertise to assess the impacts of nitrogen on biodiversity and can represent an important step up from current knowledge in such countries., Competing Interests: The authors have declared that no competing interests exist.

The increase of agricultural nitrogen (N) inputs since the 1960s is a key driver in surface- and groundwater nitrate pollution. The water abstracted from these sources can input substantial amounts of reactive nitrogen (N Irrig) if used for crop irrigation. This input is often not included in N related agricultural policies and studies, which are likely underestimating the magnitude of N pollution hotspots and overestimating the N use efficiency. In this study, we provided prima facie evidence that N Irrig is a neglected source of N in irrigated systems. The N Irrig was computed for 278 municipalities in mainland Portugal along the period 1995–2019 based on the gross irrigation requirements and nitrate concentration in ground- and surface water sources. The former was derived using two complementary approaches, using the AquaCrop and GlobWat models, while the latter were computed following spatially explicit approaches. N Irrig showed annual large fluctuations (6–11 Gg N yr-1), of which 91% was from groundwater sources. Results show that N Irrig averaged 14 (± 11) kg N ha-1 yr-1, which is equivalent to 3 (± 4) % of the N in synthetic fertilisers. This input was higher in the municipalities that simultaneously present high irrigation demand and the nitrate-contaminated groundwater as an irrigation source. In these cases, located in Nitrate Vulnerable Zones, N Irrig reached up to 95 kg N ha-1 yr-1 and more than 80% of the N in synthetic fertilizers. This study highlights the importance of linking water and nutrient policies to better gain insight on N Irrig , for which the current study provided for a simple modelling framework. • A framework to quantify the N input from irrigation water sources is developed. • Groundwater was the main source of N in irrigation water. • The N input from irrigation water sources can be comparable to synthetic fertilisers. • Results show the need to link water and N agricultural policies. [ABSTRACT FROM AUTHOR]