Soil redistribution on arable land significantly affects lateral and vertical soil carbon (C) fluxes (caused by C formation and mineralization) and soil organic carbon (SOC) stocks. Whether this serves as a (C) sink or source to the atmosphere is a controversial issue. In this study, the SPEROS-C model was modified to analyse erosion induced lateral and vertical soil C fluxes and their effects upon SOC stocks in a small agricultural catchment (4Á2 ha). The model was applied for the period between 1950 and 2007 covering 30 years of conventional tillage followed by 28 years of conservation tillage . In general, modelled and measured SOC stocks are in good agreement for three observed soil layers. The overall balance of erosion induced lateral and vertical C fluxes results in a C loss of À4Á4 g C m -2 a -1 at our test site. Land management has a significant impact on the erosion induced C fluxes, leading to a predominance of lateral C export under conventional and of vertical C exchange between soil and atmosphere under conservation agriculture. Overall, the application of the soil conservation practices, with enhanced C inputs by cover crops and decreased erosion, significantly reduced the modelled erosion induced C loss of the test site. Increasing C inputs alone, without a reduction of erosion rates, did not result in a reduction of erosion induced C losses. Moreover, our results show that the potential erosion induced C loss is very sensitive to the representation of erosion rates (long-term steady state versus event driven). A first estimate suggests that C losses are very sensitive to magnitude and frequency of erosion events. If long-term averages are dominated by large magnitude events modelled erosion induced C losses in the catchment were significantly reduced.

High‐resolution soil organic C (SOC) maps are a major prerequisite for many environmental studies dealing with C stocks and fluxes. Especially in hilly terrain, where SOC variability is most pronounced, high‐quality data are rare and costly to obtain. In this study, factors and processes influencing the spatial distribution of SOC in three soil layers (<0.25, 0.25–0.50, and 0.5–0.90 m) in a sloped agricultural catchment (4.2 ha) were statistically analyzed, utilizing terrain parameters and results from water and tillage erosion modeling (with WaTEM/SEDEM). Significantly correlated parameters were used as covariables in regression kriging (RK) to improve SOC mapping for different input data densities (6–38 soil cores ha−1) and compared with ordinary kriging (OK). In general, patterns of more complex parameters representing soil moisture and soil redistribution correlated highest with measured SOC patterns, and correlation coefficients increased with soil depth. Analogously, the relative improvement of SOC maps produced by RK increased with soil depth. Moreover, an increasing relative improvement of RK was achieved with decreasing input data density. Hence, the expected decline of interpolation quality with decreasing data density could be reduced, especially for the subsoil layers, by incorporating soil redistribution and wetness index patterns in RK. The optimal covariable differed among the soil layers. This indicates that bulk SOC patterns derived from topsoil SOC measurements might not be appropriate in sloped agricultural landscapes; however, generally more complex covariables, especially patterns of soil redistribution, exhibit a great potential to improve subsoil SOC mapping.

a b s t r a c tThere is still an ongoing scientific discussion regarding the importance of erosion-induced lateral soil organic carbon (SOC) redistribution for the burial and/or mineralisation of carbon and the resulting long-term C balance at the catchment scale. Especially the effects of the event driven nature of water erosion and the potentially associated enrichment of SOC in sediment delivery are still unclear. In general, two processes lead to enrichment of SOC: (i) enrichment due to selective interrill erosion at erosion sites, and (ii) enrichment due to selective depletion at deposition sites. In this study, the conceptual soil erosion and SOC turnover model SPEROS-C was adapted to integrate these processes and applied in a small arable catchment (4.2 ha) in Germany for a 57-year period. A total number of 901 model runs were performed with different realisations of frequency and magnitude of water erosion as well as realisations of enrichment and depletion ratios taken from literature and compared to a reference model run representing mean annual erosion without enrichment processes. In general, our modelling study indicates that ignoring temporal variability and enrichment processes may lead to a substantial misinterpretation of erosion-induced C fluxes. Especially the vertical C flux (difference between C inputs from plant assimilates and organic fertilizer and SOC mineralisation) at deposition sites strongly depends on the model parameterisation ranging from a maximum C source of −336 g C m −2 to a maximum C sink of 44 g C m −2 . In combination with a substantially higher C export due to enrichment processes, the overall C balance of the catchment potentially turns into a maximum C source of −44 g C m −2 at the end of the simulation period compared to a C source of −1 g C m −2 for the reference run.

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