Topographic variability and the influence of soil erosion on the carbon cycle

Abstract

Soil erosion, particularly that caused by agriculture, is closely linked to the global carbon (C) cycle. There is a wide range of contrasting global estimates of how erosion alters soil-atmosphere C exchange. This can be partly attributed to limited understanding of how geomorphology, topography, and management practices affect erosion and oxidation of soil organic C (SOC). This work presents a physically based approach that stresses the heterogeneity at fine spatial scales of SOC erosion, SOC burial, and associated soil-atmosphere C fluxes. The Holcombe's Branch watershed, part of the Calhoun Critical Zone Observatory in South Carolina, USA, is the case study used. The site has experienced some of the most serious agricultural soil erosion in North America. We use SOC content measurements from contrasting soil profiles and estimates of SOC oxidation rates at multiple soil depths. The methodology was implemented in the tRIBS-ECO (Triangulated Irregular Network-based Real-time Integrated Basin Simulator-Erosion and Carbon Oxidation), a spatially and depth-explicit model of SOC dynamics built within an existing coupled physically based hydro-geomorphic model. According to observations from multiple soil profiles, about 32% of the original SOC content has been eroded in the study area. The results indicate that C erosion and its replacement exhibit significant topographic variation at relatively small scales (tens of meters). The episodic representation of SOC erosion reproduces the history of SOC erosion better than models that use an assumption of constant erosion in space and time. The net atmospheric C exchange at the study site is estimated to range from a maximum source of 14.5 g m À2 yr À1 to a maximum sink of À18.2 g m À2 yr À1 . The small-scale complexity of C erosion and burial driven by topography exerts a strong control on the landscape's capacity to serve as a C source or a sink.

Soil Organic Carbon and Isotope Composition Response to Topography and Erosion in Iowa

“…Although soil erosion would preferentially remove high SOC fraction and cause depletion of SOC at eroded sites, the depleted SOC pool can be dynamically replaced by newly deposited SOC from above‐ and belowground detritus decomposition (Dialynas et al, ; Harden et al, ; Lal, ). SOC derived from native prairie vegetation has strong C3 vegetation characteristics indicated by the strong correlation between 137 Cs inventory and C3‐derived SOC density ( r 2 = 0.66).…”

Impact of hydrologically driven hillslope erosion and landslide occurrence on soil organic carbon dynamics in tropical watersheds

“…Relatively high values of a k represent a significant effect of land use on altered oxidation, while low values reflect little effect on eroding soil profiles. Similar is the effect of a I to SOC production, respectively [ Dialynas et al ., ]. According to Figure , a net erosion‐induced C sink can result from relatively low values of a k and high values of a I .…”

Soil Erosion and Gaseous Emissions

“…The magnitude of SOC erosion by fluvial processes varies widely (Table 1) depending on a range of factors. Important among these are climate [10,13], soil [15][16][17], terrain [18] and land use [13][14][15][19][20][21][22][23]. On the basis of some empirical data from 240 runoff plots studied over the entire rainy season from diverse global ecoregions, Mueller-Nedebock and Chaplot [18] estimated that the total amount of SOC displaced by sheet erosion from its source would be 1.32 ± 0.20 Pg C, or about 11.4% of the annual anthropogenic emission of 11.5 Pg C in 2019 [21].…”