Quantifying nitrogen fluxes and their influence on the greenhouse gas balance - recent findings of the NitroEurope Integrated Project

The generation of reactive nitrogen (Nr) by human activities to stimulate agricultural productivity and the unintended formation of Nr in combustion processes both have major impacts on the global environment. Effects of excess Nr include the deterioration of air quality, water quality, soil quality and a decline in biodiversity. One of the most controversial impacts of nitrogen, however, is on the greenhouse gas balance. While recent papers have highlighted a possible benefit of nitrogen in enhancing rates of carbon sequestration, there remain many trade-offs between nitrogen and greenhouse gas exchange. The result is that the net effect of Nr on the global radiative balance has yet to be fully quantified. To better understand these relationships requires intense measurement and modelling of Nr fluxes at various temporal and spatial scales in order to make the link between different nitrogen forms and their fate in the environment. It is essential to measure fluxes for a wide range of ecosystems considering the biosphere-atmosphere exchange of the Nr components and greenhouse gases, as well as the fixation of di-nitrogen and its creation by denitrification. Long-term observations are needed for representative ecosystems, together with results from experiments addressing the responses of the key nitrogen and greenhouse gas fluxes to different global change drivers. The NitroEurope Integrated Project (in short NEU IP), funded under the 6th Framework Programme of the European Commission, has developed and applied a strategy for quantifying these different terms on multiple scales. With the project nearing completion, this presentation reports selected preliminary findings. It highlights the first estimates of Nr inputs and net green-house gas exchange for a series of 13 flux ‘supersites’, complemented by the emerging results of Nr concentrations and related N inputs at a network of 58 ‘inferential sites’, which extend the European representativity of the results. In addition, new low cost methods to measure nitrogen fluxes will be reported, which have been extensively tested at those sites. Results from this 3-tier flux network are underpinned by emerging findings from an extensive network of manipulation sites. A combination of modelling at plot, landscape and European scales is used to upscale the results. Finally the talk will illustrate how nitrogen mitigation techniques are being considered at the European scale, including an estimation of the scale of costs involved in simultaneously mitigating nitrous oxide, ammonia and nitrate losses.