Constraining a coupled erosion and soil organic carbon model using hillslope‐scale patterns of carbon stocks and pool composition

Abstract

A large amount of soil organic carbon (SOC) is laterally redistributed by agricultural erosion.Recent studies have shown that this leads to strong horizontal (i.e., spatial) and vertical (i.e., with soil depth) gradients in SOC stock and C pool distribution in eroding landscapes. However, the mechanisms leading to these gradients in relation to erosion and deposition are still poorly documented. In particular, the effect of the inherent properties of SOC (as controlled by the SOC pool composition) versus the effect of depth-related soil environmental condition (i.e., differences in soil humidity, temperature, aeration, etc.) on the persistence of SOC in eroding landscapes is uncertain. Nonetheless, a detailed understanding of these factors is important to correctly assess landscape-scale soil C turnover and vulnerability to disturbance from human activities. This study utilizes observational data on long-term erosion/deposition rates and C pool composition derived from soil C fractionation experiments along an eroding agricultural hillslope to constrain a coupled erosion-SOC dynamics model. The simulation results show that the data set used can result in a robust parameter estimation of a multipool C model for an eroding landscape with parameter values that are consistent with incubation experiments. A scenario analysis, where we evaluate the contribution of different processes, demonstrates that soil redistribution is essential to explain the observation that depositional locations contain more SOC in subsoils, while the SOC content of the surface layer is similar to those observed along an eroding hillslope. The spatial variability of plant production could explain some of the observed variability in SOC content, but our results suggest that the spatial variability of SOC pool composition is mainly related to soil redistribution. Finally, we suggest that environmental factors may play a more important role than the inherent properties of SOC in determining the vertical variation of SOC mineralization. This implies that depositional C stocks might be highly vulnerable to disturbance from human activities that may reconnect the buried SOC with the atmosphere.

From soilscapes to landscapes: A landscape‐oriented approach to simulate soil organic carbon dynamics in intensively managed landscapes

“…SOC within the downslope net depositional CV (red colored line) for all periods was found to be much higher than the upslope net erosional CV, which has been reported in the literature [e.g., Stavi and Lal , ; Du and Walling , ; Navas et al ., ; Wang et al ., ]. Throughout the CCOMM period, the gradient of SOC stocks increased as the frequency of deposition events (Figure c) and production rates also increased starting in the late 1950s (see Figure ).…”

“…The degree that these changes influence SOC redistribution and storage may vary depending on the hillslope location and the magnitude of the hydrologic event. In fact, SOC changes may be significantly different in erosion‐dominated (i.e., upslope) areas of a hillslope versus deposition‐dominated (i.e., downslope) areas, with significant effects on net gains or losses in the SOC stored in these zones [ Van Oost et al ., ; Wang et al ., ]. It is, therefore, not surprising that most of the available biogeochemical models, being soil profile models or “point models in space,” tend to overestimate or underestimate SOC storage predictions in IMLs as they do not account for outputs or inputs of mobilized SOC [e.g., Parton et al ., ; Paustian et al ., ; Harden et al ., ; Manies et al ., ; Mangan et al ., ; Jarecki et al ., ; Tornquist et al ., ; Wilson et al ., ; Van Oost et al ., ; Bortolon et al ., ; van Groenigen et al ., ; Vaccari et al ., ].…”

Global soil organic carbon removal by water erosion under climate change and land use change during AD 1850–2005

“…1a). The SOC pools are not vertically discretized in the version of the ORCHIDEE LSM used to build the emulator, so we implemented a simple vertical discretization scheme for the SOC pools in the emulator based on the concept of Wang et al (2015a, b). In this scheme the carbon dynamics of each soil layer are calculated separately, based on layerdependent litter input and respiration rates (Fig.…”

“…Some studies coupled process-oriented soil erosion models with carbon turnover models calibrated for specific micro-catchments on timescales of a few decades to a millennium, (Billings et al, 2010;Van Oost et al, 2012;Nadeu et al, 2015;Wang et al, 2015a;Zhao et al, 2016;Bouchoms et al, 2017). Other studies focused on the application of parsimonious erosion-SOC-dynamics models using the Revised Universal Soil Loss Equation (RUSLE) approach together with sediment transport methods at regional or continental spatial scales (Chappell et al, 2015;Lugato et al, 2016;Yue et al, 2016;Zhang et al, 2014).…”

Global soil organic carbon removal by water erosion under climate change and land use change during 1850–2005 AD

“…Some studies coupled process-oriented soil erosion models with C turnover models calibrated for specific micro-catchments on timescales of a few decades to a millennium, (Billings et al, 2010;Van Oost et al, 2012;Nadeu et al, 2015;Wang et al, 2015a;Zhao et al, 2015;Bouchoms et al, 2017). While other studies focused on the application of parsimonious erosion-SOC dynamics models using the RUSLE approach together with sediment transport methods at regional or continental spatial scales 80 (Chappell et al, 2015;Lugato et al, 2016;Yue et al, 2016;Zhang et al, 2014).…”