Stability of organic matter in soils of the Belgian Loess Belt upon erosion and deposition

Abstract

Summary Soil erosion has significant impacts on terrestrial carbon (C) dynamics. It removes C‐rich topsoil and deposits it in lower areas, which might result in its stabilization against microbial decay. Subsequently, C‐poor deeper horizons will be exposed, which also affects C stabilization. We analysed factors governing soil organic C (SOC) mineralization in topsoil (5–10 cm) and subsoil (75–100 and 160–200 cm) horizons from two contrasting sites (up‐slope compared with down‐slope) in the Belgian Loess Belt; we refer to these as eroding and depositional sites, respectively. Deposition of eroded soil material resulted in significantly increased SOC contents throughout the entire soil profile (2 m) and microbial biomass C in the topsoil. In a 28‐day incubation experiment we studied effects of O2 concentrations (0, 5 and 20%) and substrate (glucose) availability on C mineralization, soil microbial biomass and CaCl2‐extractable C. Carbon enrichment at the depositional site was accompanied by weak mineralization rates and small contents of water‐extractable organic C. Addition of glucose stimulated microbial growth and enhanced respiration, particularly in the subsoil of the depositional site. Availability of O2 showed the expected positive relationship with C mineralization in topsoils only. However, small O2 concentrations did not decrease C mineralization in subsoils, indicating that controls on C dynamics were different in top‐ and subsoils. We conclude that reduced C mineralization contributed to C accumulation as observed at depositional sites, probably because of poor availability of C in subsoil horizons. Limited availability of O2 in subsoils can be excluded as an important control of soil C accumulation. We hypothesize that the composition of the microbial community after burial of the organic‐rich material might play a decisive role.

Soil Organic Carbon Redistribution by Water Erosion – The Role of CO2 Emissions for the Carbon Budget

“…Although we did not scale up our results to the landscape level, it is important to know whether the fluxes measured do compare with observed field measurements and make any sense, also in comparison with previous indirect measurements on eroded sediments and soil profile investigations [5], [12]. In the present study, CO 2 efflux rates measured (0.12 to 4.34 g C m −2 day −1 ) were in the range of soil respiration rates from agricultural loess soils [5], [19].…”

Assessment of changes in different fractions of the organic carbon in a soil amended by nanozeolite and some plant residues: incubation study

“…Although it has been assumed that dissolved organic matter (DOM) represents a labile part of SOM and that total DOC concentration and especially its easily degradable part resembles soil microbial activity, it has been suggested that a great part of DOM in soil represents a relatively stable by-product of microbial activity (Zhao et al 2008;Wang et al 2013). The movement of DOM is significant to the cycling and distribution of nutrients and carbon within and between ecosystems and contributes to soil forming processes .…”

“…Therefore, humus is probably the main source of DOC because of the relatively large amount of humus present in soil relative to that contributed by the microbial biomass or recently deposited plant residues. DOC inputs to soil solution originate from biological decomposition, throughfall or litter leaching, root exudates and from deposition of soot and dust (Wang et al 2013).…”

Soil redistribution and weathering controlling the fate of geochemical and physical carbon stabilization mechanisms in soils of an eroding landscape

“…The removal of weathered topsoil material from eroding positions, the replacement of eroded SOC, and its burial at depositional sites can potentially lead to a net sink for atmospheric C depending on the fate of the eroded SOC (Harden et al, 1999;Doetterl et al, 2012;Wiaux et al, 2014a). SOC at the depositional site is often regarded as more stable with longer turnover times, depending on microbial activity, environmental conditions (Wang et al, 2013), and biogeochemical characteristics of the transported C fractions. However, areas (or landscapes) with a fast burial can lead to the accumulation (storage) of labile SOC, which is still vulnerable to decomposition if the conditions at the site of burial change (Wiaux et al, 2014b).…”