Simulation of fluxes of greenhouse gases from European grasslands using the DNDC model

Agricultural management of grasslands results in sequestration and emission of greenhouse gases (GHGs, particularly CO2, N2O and CH4). Here, we used a process-based model (DNDC) to estimate the fluxes of the major GHGs from grasslands at 0.5° resolution across Europe, and combined these to produce a spatially explicit estimate of the total global warming potential (GWP, expressed in CO2 equivalents). The DNDC model [Li, C., Frolking, S., Crocker, G.J., Grace, P.R., Klir, J., Korchens, M., Poulton, P.R., 1997. Simulating trends in soil organic carbon in long-term experiments using the DNDC model. Geoderma 81, 45–60] simulates carbon and nitrogen cycling in agro-ecosystems at a sub-daily time step and consists of four interacting submodels: soil and climate (including water flow and leaching), plant growth, decomposition, and denitrification. Input data sets for grassland area, climate, nitrogen deposition, and soil properties were collated. The typical current grassland management regime was established for ten biogeographical regions on the basis of questionnaires sent to national experts, and used to derive model input data. A 20-year simulation was carried out using DNDC for each site. Simple estimates of methane emissions from grazing livestock were made according to the IPCC Tier 1 method. Most grassland areas are net sources for GHGs in terms of total global warming potential—the beneficial effect of sequestering carbon in soil is outweighed by the emissions of N2O from soil and (predominantly) CH4 emissions from livestock. The net effect of European grasslands on GWP (emission of 23 Tg C year−1) corresponds to a 2.5% increase on the EU-15 fossil fuel CO2 emissions (907 Tg C year−1).