Beyond nitrogen critical loads – is there a role for the‘Ecosystem Services’ approach?

This paper considers the extent to which indicators of critical load exceedance capture the potential impacts of changes in nitrogen deposition on ecosystem services. It shows that there are significant links between nitrogen deposition and a large range of ecosystem services. There is potential for indicators to be adapted to provide more specific qualitative information for Natura 2000 sites of the implications of critical load exceedance for ecosystem services. For the provision of ecosystems goods (e.g. food, fuel, fibre) and water quality and erosion regulation, it is likely that quite specific information can be provided on the effects of nitrogen deposition. For others, such as pollination and cultural services, the implications for ecosystem services are likely to depend on the specific changes in species composition that are found in specific habitats and sites. The issue of climate regulation has been identified as a critical ecosystem service, but this effect is not currently considered explicitly in setting critical loads, and given the complexity of the potential effects of nitrogen deposition on different greenhouse gas fluxes, it seems impractical to include this in any simple assessment of effects of critical load exceedance. There are ecosystem services where exceedance of the established empirical critical load for nitrogen input can be a positive outcome, for example, increases in more nitrophilous species increasing productivity in certain grassland types and increased grass growth stabilising coastal dunes, and hence enhancing erosion regulation. An ecosystems approach would therefore have value in informing the prioritization of conservation management practices in areas with high nitrogen deposition, depending on the ecosystem service that is most valued at any particular site. However, given that the cause and effect relationships underlying important ecosystem services are often complex and not sufficiently understood, more data and research is needed to provide specific guidance on potential conservation priorities.