Modelling long-term soil organic carbon dynamics under the impact of land cover change and soil redistribution

- Landscape evolution model linking land cover, soil landscape and SOC turnover
- Good prediction of both sediment fluxes the SOC profiles for each land cover
- Modeled SOC profiles are each geomorphic position are in line with observations.
- C uptake balances the initial loss due to land cover change over centuries.
- Need to consider and accurately quantify past erosion rates to assess the SOC budget

During the last millennia, anthropogenic land cover change has caused a significant release of carbon from soils while also accelerating rates of soil erosion by one to two orders of magnitude. However, mechanistic frameworks that explicitly link land cover change, erosion and soil organic carbon (SOC) cycling and, in addition, can be applied to longer timescales are currently lacking. This study presents a 4D soil-landscape model coupling sediment fluxes and carbon dynamics in response to continuous land cover change over a period of 1000 years. We applied the model to a well-studied catchment of 591 km2 in Central Belgium. The model evaluation showed that the simulated magnitude and spatial patterns of soil redistribution and SOC stocks are in good agreement with field observations. At the catchment scale, land cover change over the last 1000 years decreased the SOC stock of the top 1 m of soil by 33.1 tC·ha− 1 (32% loss compared to the initial SOC stock) while in contrast, erosion resulted in an uptake of 31.9 tC·ha− 1 from the atmosphere (29% gain compared to the initial SOC stock). As a result, the combined effect is a small source of c. 1.2 tC·ha− 1 over the last 1000 years. While the SOC released from the soil to the atmosphere quickly responded to land conversion, the erosion induced sink operated at a much lower intensity but with a longer duration. These transient simulations show that the soil carbon budget is highly variable in both space and time.