Reply on RC1

Abstract

Soil erosion rates on arable land frequently exceed the pace at which new soil is formed. This imbalance leads to soil thinning (i.e., truncation), whereby subsoil horizons and their underlying parent material become progressively closer to the land surface. As subsurface horizons often have contrasting properties to the original topsoil, truncation-induced changes to soil properties might affect erosion rates and runoff formation through a soil erosion feedback system. However, the potential interactions between soil erosion and soil truncation are poorly understood due to a lack of empirical data and the neglection of long-term erodibility dynamics in erosion simulation models. Here we present a novel model-based exploration of the soil erosion feedback system over a 500-year period, using measured soil properties from a diversified database of 265 soil profiles in the United Kingdom. We found that modelled erosion rates in 39 % of the soil profiles were sensitive to truncation-induced changes in soil properties and that most of these truncation-sensitive profiles (75 %) displayed a deaccelerating erosion trend over the simulation period. This was largely explained by decreasing silt contents in the soil surface due to selective removal of this more erodible particle size fraction and the presence of clayey or sandy substrata. Moreover, the profiles with deaccelerating erosion trends had an increased residual stone cover, which armoured the land surface and reduced soil detachment. Contrastingly, the soils with siltier subsurface horizons continuously replenished the plough layer with readily erodible material, which accelerated the soil losses over time. Ultimately, our results demonstrate how soil losses can be sensitive to erosion-induced changes in soil properties, which in turn may accelerate or slow down soil thinning. These findings are likely to affect how we calculate soil lifespans and make long-term projections of land degradation.