Quantifying the erosion effect on current carbon budget of European agricultural soils at high spatial resolution

The idea of offsetting anthropogenic CO2 emissions by increasing global soil organic carbon (SOC), as recently proposed by French authorities ahead of COP21 in the ‘four per mil’ initiative, is notable. However, a high uncertainty still exits on land C balance components. In particular, the role of erosion in the global C cycle is not totally disentangled, leading to disagreement whether this process induces lands to be a source or sink of CO2. To investigate this issue, we coupled soil erosion into a biogeochemistry model, running at 1 km resolution in the agricultural soils of the European Union (EU). Based on data-driven assumptions, the simulation took into account also the deposition within the grid cells and the potential C export to riverine systems, in a way to be conservative in a mass balance. We estimated that 143 out of 187 Mha have C erosion rates 0.45 Mg C ha-1 yr-1. In comparison with a baseline without erosion, the model suggested an erosion-induced sink of atmospheric C consistent with previous empirical-based studies. Integrating all C fluxes for the EU agricultural soils, we estimated a net CO2 loss or gain of 2.6 and 0.54 Tg yr-1 of CO2eq, respectively, when a short-term enhanced C mineralization rate upon sediment transportation of 30 and 10% was implemented. We concluded that erosion fluxes were in the same order of current carbon gains from improved management. Even if erosion could potentially induce a sink for atmospheric CO2, strong agricultural policies are needed to prevent or reduce soil erosion, in order to maintain soil health and productivity.JRC.D.6-Knowledge for Sustainable Development and Food Securit