Modelling the contribution of short-range atmospheric and hydrological transfers to nitrogen fluxes, budgets and indirect emissions in rural landscapes
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 N 2O emissions were estimated at around 21% of the total N 2O 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.