A millennium of arable land use – the long-term impact of water and tillage erosion on landscape-scale carbon dynamics

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In the last decades, soils and their agricultural management have received great scientific and political attention due to their associated potential to act as sink of atmospheric carbon dioxide (CO2). It is questioned if soil redistribution processes affect this potential CO2 sink function, as agricultural management has a strong potential to accelerate soil redistribution. Most studies analysing the effect of soil redistribution upon soil organic carbon (SOC) dynamics focus on water erosion, analyse only relatively small catchments and relatively short timespans of several years to decades. The aim of this study is to widen the perspective by including tillage erosion as another important driver of soil redistribution and performing a model-based analysis in a 200 km2-sized arable region of north-eastern Germany for the period since the conversion from forest to arable land (approx. 1000 years ago). Therefore, a modified version of the spatially explicit soil redistribution and carbon (C) turnover model SPEROS-C was applied to simulate lateral soil and SOC redistribution and SOC turnover (spatial resolution 5 m x 5 m). The model parameterisation uncertainty was estimated by simulating different realisations of the development of agricultural management over the past millennium. The results indicate that in young moraine areas, which are relatively dry but intensively used for agriculture for centuries, SOC patterns and SOC dynamics are substantially affected by tillage-induced soil redistribution processes. To understand the landscape scale effect of these redistribution processes on SOC dynamics it is essential to account for long-term changes following land conversion, as typical soil-erosion induced processes, e.g. dynamic replacement, only take place after former forest soils reach a new equilibrium following conversion. Overall, it was estimated that after 1000 years of arable land use SOC redistribution by tillage and water erosion results in a landscape scale C sink of up to 0.66 ‰ per year.