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

Abstract

Abstract. Erosion is an Earth system process that transports carbon laterally across the land surface and is currently accelerated by anthropogenic activities. Anthropogenic land cover change has accelerated soil erosion rates by rainfall and runoff substantially, mobilizing vast quantities of soil organic carbon (SOC) globally. At timescales of decennia to millennia this mobilized SOC can significantly alter previously estimated carbon emissions from land use change (LUC). However, a full understanding of the impact of erosion on land-atmosphere carbon exchange is still missing. The aim of this study is to better constrain the terrestrial carbon fluxes by developing methods compatible with land surface models (LSMs) in order to explicitly represent the links between soil erosion by rainfall and runoff and carbon dynamics. For this we use an emulator that represents the carbon cycle of a LSM, in combination with the Revised Universal Soil Loss Equation (RUSLE) model. We applied this modeling framework at the global scale to evaluate the effects of potential soil erosion (soil removal only) in the presence of other perturbations of the carbon cycle: elevated atmospheric CO 2 , climate variability, and LUC. We find that over the period AD 1850-2005 acceleration of soil erosion leads to a total potential SOC removal flux of 74 ± 18 Pg C, of which 79 %-85 % occurs on agricultural land and grassland. Using our best estimates for soil erosion we find that including soil erosion in the SOC-dynamics scheme results in an increase of 62 % of the cumulative loss of SOC over 1850-2005 due to the combined effects of climate variability, increasing atmospheric CO 2 and LUC. This additional erosional loss decreases the cumulative global carbon sink on land by 2 Pg of carbon for this specific period, with the largest effects found for the tropics, where deforestation and agricultural expansion increased soil erosion rates significantly. We conclude that the potential effect of soil erosion on the global SOC stock is comparable to the effects of climate or LUC. It is thus necessary to include soil erosion in assessments of LUC and evaluations of the terrestrial carbon cycle.

A substantial role of soil erosion in the land carbon sink and its future changes

“…Another uncertainty in ELM‐Erosion is that it does not account for the spatial heterogeneity of land C inventory and vertical and lateral C fluxes introduced by soil erosion within a land unit. Previous studies argued that these processes would change the land C sequestration in both eroding and depositing areas (Lugato et al, ; Naipal et al, ; Van Oost et al, ; Wang et al, ; Yue et al, ). It is possibly the cause that our estimated SOC loss, which only accounts for the SOC export to inland waters, is not enough to compensate for all of the underestimated R h (Figure ).…”

“…More than amplifying the export of soil organic carbon (SOC) to rivers, human‐induced intensification in soil erosion has stimulated much larger SOC displacement from eroding positions (e.g., steep upslopes) to deposition positions (e.g., gentle downslopes) on land (Berhe, Barnes, Six, & Marín‐Spiotta, ). Conceptually, ignoring the erosion‐driven C cycling may introduce significant uncertainties to the climate–carbon feedback estimates by ESMs, especially for the prediction of the land sequestration of atmospheric C in a changing world (Lugato et al, ; Naipal et al, ; Wang et al, ; Yue et al, ).…”

“…Both studies concluded that at decadal‐to‐millennial scale anthropogenic soil erosion induced a net land sink of atmospheric CO 2 . However, by coupling process‐based land surface models and the Revised Universal Soil Loss Equation based soil erosion models, two studies explicitly evaluated the effect of climate on soil erosion and argued that soil erosion is unlikely to either drive a significant carbon sink in Europe (Lugato et al, ) or even be possible to drive an increase of SOC loss globally (Naipal et al, ). Noticeably, all of the above studies applied either observation‐based soil erosion methods or soil erosion models that are mainly capable of estimating the long‐term soil erosion and lateral SOC flux of erosion.…”

“…Noticeably, all of the above studies applied either observation‐based soil erosion methods or soil erosion models that are mainly capable of estimating the long‐term soil erosion and lateral SOC flux of erosion. In addition, for methods relying on the land–atmosphere C fluxes estimated by land surface models (Lugato et al, ; Naipal et al, ; Yue et al, ), uncertainty in their estimates has largely not been examined. Particularly, such uncertainty may be directly caused by ignoring soil erosion and deposition processes (Regnier et al, ).…”

Soil Organic Carbon Across Mexico and the Conterminous United States (1991–2010)

“…, Food and Agriculture Organization [FAO] ). For global modeling and validating the SOC stored in terrestrial ecosystems, high‐resolution gridded datasets such as the SoilGrids250m system (Hengl et al, ) are increasingly being used to describe spatial SOC patterns (Harden et al, ; Jackson et al, ) and trends (Naipal et al, ; Hengl & MacMillan ). Such datasets are also required to facilitate the formulation of reliable climate change adaptation guidelines and the establishment of regional to global carbon monitoring and information systems (Ciais et al, ; Stockmann et al, ; Vargas et al, ; Villarreal et al, ).…”