Modelling the contribution of short-range atmospheric and hydrological transfers to nitrogen fluxes, budgets and indirect emissions in rural landscapes

Abstract. Spatial interactions within a landscape may lead to large inputs of reactive nitrogen (N_r) transferred from cultivated areas and farms to oligotrophic ecosystems and induce environmental threats such as acidification, nitric pollution or eutrophication of protected areas. The paper presents a new methodology to estimate N_r fluxes at the landscape scale by taking into account spatial interactions between landscape elements. This methodology includes estimates of indirect N_r emissions due to short-range atmospheric and hydrological transfers. We used the NitroScape model which integrates processes of N_r transformation and short-range 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 fluxes, especially direct and indirect N_r 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 emissions and recapture for each landscape element and the whole landscape. NitroScape made it possible to quantify the contribution of both atmospheric and hydrological transfers to N_r fluxes, budgets and indirect N_r emissions. For instance, indirect N₂O emissions were estimated at around 21% of the total N₂O emissions. They varied within the landscape according to land use, meteorological and soil conditions as well as topography. This first attempt 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_r emissions within landscapes. Our approach needs to be further tested by applying NitroScape to several spatial arrangements of agro-ecosystems within the landscape and to real and larger landscapes.