Influence of short-term transfers on nitrogen fluxes

Biogeosciences Discussions This discussion paper is/has been under review for the journal Biogeosciences (BG). Please refer to the corresponding final paper in BG if available. Abstract Spatial interactions at short-term may lead to large inputs of reactive nitrogen (N r) to oligotrophic ecosystems and induce environmental threats such as additional N 2 O emissions and global warming. The paper presents a new methodology to estimate N r fluxes, especially additional N 2 O emissions, at the landscape scale by taking into 5 account spatial interactions between landscape elements. We used the NitroScape model which integrates processes of N r transformation and short-term transfer in a dynamic and spatially distributed way to simulate N r fluxes and budgets at the landscape scale. Four configurations of NitroScape were implemented by taking into account or not the atmospheric, hydrological or both pathways of N r transfer. We simulated N r 10 fluxes, especially direct and indirect N 2 O emissions, within a test landscape including pig farms, croplands and unmanaged ecosystems. Simulation results showed the ability of NitroScape to simulate patterns of N r losses and recapture for each landscape element and the whole landscape. They made it possible to quantify the contribution of both atmospheric and hydrological transfers in N r fluxes and budgets. Indirect N 2 O 15 emissions were estimated at almost 25 % of the total N 2 O emissions. They varied within the landscape according to land use, meteorological and soil conditions as well as topography. This first attempt has proved that the NitroScape model is a useful tool to estimate the effect of spatial interactions on N r fluxes and budgets as well as indirect N 2 O emissions within landscapes. Our approach needs to be further tested by apply-20 ing NitroScape to several spatial distributions of ecosystems within the landscape and to real and larger landscapes.