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

Abstract

The human-driven production of reactive nitrogen to stimulate agricultural productivity and its unintended formation in combustion processes both have major impacts on the global environment. Effects of excess reactive nitrogen include reductions in air quality, water quality, soil quality and 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 reactive nitrogen on the global radiative balance is currently far from clear. To better quantity these relationships requires measurement data and modelling that 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 each of the reactive nitrogen components and greenhouse gases, as well as the fixation and denitrification of di-nitrogen. 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 of the 6th Framework Programme of the European Commission European has developed a strategy to quantifying these different terms on multiple scales. This presentation reports some of the emerging results. It highlights the first estimates of net greenhouse gas exchange for a series of 13 flux ‘supersites’, complemented by the emerging results of reactive nitrogen concentrations a large network of 58 ‘inferential sites’, which are being used to estimate nitrogen inputs. In addition to these, new low cost methods to measure nitrogen fluxes will be reported, which are being tested at the ‘supersites’ and a network of regional sites, which extend the European representativity of the results. Results from this 3-tier flux network will be complemented by emerging findings from an extensive Manipulation Network, and by modelling at plot, landscape and European scales. Finally the paper 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