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

The idea of offsetting anthropogenic CO 2 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 CO 2 . To investigate this issue, we coupled soil erosion into a biogeochemistry model, running at 1 km 2 resolution across the agricultural soils of the European Union (EU). Based on data-driven assumptions, the simulation took into account also soil deposition within grid cells and the potential C export to riverine systems, in a way to be conservative in a mass balance. We estimated that 143 of 187 Mha have C erosion rates <0.05 Mg C ha −1 yr −1 , although some hot-spot areas showed eroded SOC >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 C loss or gain of −2.28 and +0.79 Tg yr −1 of CO 2 eq, respectively, depending on the value for the short-term enhancement of soil C mineralization due to soil disruption and displacement/transport with erosion. 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 CO 2 , strong agricultural policies are needed to prevent or reduce soil erosion, in order to maintain soil health and productivity.