Soil erosion and carbon

The importance of soil in the carbon cycle

Soil play a significant environmental role in balancing the climate as it currently acts as a carbon sink, sequestering CO₂ from the atmosphere into soil organic carbon. On the other side, soil organic carbon is released to the atmosphere as a consequence of land use change, degradation processes and climate change. Soil erosion, which is likely to be exacerbated due to the more intense precipitation events expected as a result of climate change, leads to the displacement of soil and the organic carbon within it. The extent and consequences of this disruption to the terrestrial carbon stock is still uncertain.

Main findings of the article (Advanced Science)

Using a new biogeochemistry-erosion model to quantify the impact of future climate on the carbon cycle, the authors track the possible transformations of the organic carbon across the landscape. Taking into account all the additional feedbacks and C fluxes due to displacement by erosion, the authors of this study estimated a net source of 0.92 to 10.1 Tg C year⁻¹ from agricultural soils in the European Union to the atmosphere over the period 2016–2100. These ranges represented a weaker and stronger C source compared to a simulation without erosion (1.8 Tg C year⁻¹), respectively, and were dependent on the erosion-driven C loss parameterization, which is still very uncertain.

They estimate that accelerated soil erosion in EU agricultural land due to more intense precipitation will lead to a 35% increase in eroded carbon in the period 2016-2100.  This is likely to exacerbate carbon losses (as emissions of CO₂) from agricultural land to the atmosphere (up to 23% of the predicted losses under the RCP4.5 climate change scenario), thus increasing the effect of climate change.

Model Integration

The model framework was based on coupling the process-based biogeochemistry model CENTURY to the RUSLE2015 erosion model. The CENTURY model was ran at a resolution of 1 km² for the agricultural soil of the EU, using the soil erosion from RUSLE2015 model as input for CENTURY. Starting from 1900, the erosion process was implemented, keeping the climate, soil, and topographic factors (R, K, and LS, respectively) constant. While we considered K and LS factors quite invariable on a centennial scale, the C factor associated with the crop type was dynamically varied with crop rotations and land use changes. The simulated land use was based on the CORINE Land Cover 1990, 2000, and 2006, supplemented with Eurostat  statistics to build up crop rotations and implement consistent agronomic inputs (fertilization, irrigation, etc.).

The methodology for the estimation of the future rainfall erosivity was presented in a very recent study. Summarizing, this made use of the REDES (Rainfall Erosivity Database at European Scale) and a statistical approach (Gaussian process regression), used to spatially interpolate rainfall erosivity datawith climatic scenarios

Data:

The data on carbon budget in the EU agricultural soils including lateral C fluxes are available both for two different model configuration and for the current and accelerated erosion scenarios.

References:

Lugato, E., Smith, P., Borrelli, P., Panagos, P., Ballabio, C., Orgiazzi, A., Fernandez-Ugalde, O., Montanarella, L.,  Jones, A. 2018. Soil erosion is unlikely to drive a future carbon sink in Europe. Science Advances. 4, eaau3523.

The numbers in brackets [e; r] are the outcomes of the two model configurations: enhanced erosion-induced C sink (e), with the mineralization during transport set to 2%, the burial efficiency to 95%, and the enrichment factor to 2, and reduced erosion-induced C sink (r), where the same parameters were set to 10%, 20%, and 1, respectively. Dark arrows represent C displacements, while blue arrows represent C fluxes as C exchanges with the atmosphere (CO2-C). For the net soil flux, negative values represent a C source to the atmosphere, while positive values represent a C sink . The agricultural area simulated (arable crops, grassland, and permanent crops) covers 1.88 Mkm².