Effects of interrill erosion, soil crusting and soil aggregate breakdown on in situ CO2 effluxes

Abstract

Soil and carbon redistribution on arable land and the associated impacts on carbon sequestration and mineralisation may play an important role in the global carbon cycle. While our insight in the process-chain of erosion, transport and deposition has significantly grown over recent years, there are still major gaps in understanding making it difficult to make an overall assessment of erosion processes on carbon exchange between the soil and the atmosphere. One issue is the potential effect soil degradation and erosion processes may have on CO2 effluxes at eroding sites. The major goal of this study was therefore to analyse and understand the effects of interrill erosion, soil crusting and soil aggregate breakdown on in situ CO2 effluxes. Therefore a set of rainfall simulations were carried out on bare loess-burden soil with different antecedent soil moisture content. All treatments were compared with controls protected from rain drop impact using a fine-meshed geotextile. As expected, runoff and sediment delivery was significantly larger on bare compared to covered soils, while surface runoff and sediment delivery increased (in most cases) with rising antecedent soil moisture as well as rainfall duration. Crust thickness increased with antecedent soil moisture and rainfall intensity and was in general smaller for the controls. However, variations in crust thickness did not result in significant differences in in situ measured CO2 effluxes. Also the destruction of the soil crust after six to seven days of measurements did not have a significant effect. This leads to the conclusion that crusting and interrill erosion has no or only a minor effect on in situ CO2 effluxes. Nevertheless, it should be recognised that topsoil carbon is preferentially removed due to interrill erosion which may result in additional CO2 release at depositional sites or in stream and/or standing water bodies.