Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
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Volume 13, issue 16
Biogeosciences, 13, 4777–4788, 2016
https://doi.org/10.5194/bg-13-4777-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Biogeosciences, 13, 4777–4788, 2016
https://doi.org/10.5194/bg-13-4777-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 24 Aug 2016

Research article | 24 Aug 2016

Iron-bound organic carbon in forest soils: quantification and characterization

Qian Zhao1, Simon R. Poulson2, Daniel Obrist3, Samira Sumaila4,5, James J. Dynes4, Joyce M. McBeth4,5, and Yu Yang1 Qian Zhao et al.
  • 1Department of Civil and Environmental Engineering, University of Nevada, Reno, Nevada, 89557, USA
  • 2Department of Geological Sciences and Engineering, University of Nevada, Reno, Nevada, 89557, USA
  • 3Division of Atmospheric Sciences, Desert Research Institute, Reno, Nevada, 89512, USA
  • 4Canadian Light Source, 44 Innovation Blvd, Saskatoon, SK, S7N 2V3, Canada
  • 5Department of Geological Sciences, University of Saskatchewan, Saskatoon, SK, S7N 5E2, Canada

Abstract. Iron oxide minerals play an important role in stabilizing organic carbon (OC) and regulating the biogeochemical cycles of OC on the earth surface. To predict the fate of OC, it is essential to understand the amount, spatial variability, and characteristics of Fe-bound OC in natural soils. In this study, we investigated the concentrations and characteristics of Fe-bound OC in soils collected from 14 forests in the United States and determined the impact of ecogeographical variables and soil physicochemical properties on the association of OC and Fe minerals. On average, Fe-bound OC contributed 37.8 % of total OC (TOC) in forest soils. Atomic ratios of OC : Fe ranged from 0.56 to 17.7, with values of 1–10 for most samples, and the ratios indicate the importance of both sorptive and incorporative interactions. The fraction of Fe-bound OC in TOC (fFe-OC) was not related to the concentration of reactive Fe, which suggests that the importance of association with Fe in OC accumulation was not governed by the concentration of reactive Fe. Concentrations of Fe-bound OC and fFe-OC increased with latitude and reached peak values at a site with a mean annual temperature of 6.6 °C. Attenuated total reflectance–Fourier transform infrared spectroscopy (ATR-FTIR) and near-edge X-ray absorption fine structure (NEXAFS) analyses revealed that Fe-bound OC was less aliphatic than non-Fe-bound OC. Fe-bound OC also was more enriched in 13C compared to the non-Fe-bound OC, but C ∕ N ratios did not differ substantially. In summary, 13C-enriched OC with less aliphatic carbon and more carboxylic carbon was associated with Fe minerals in the soils, with values of fFe-OC being controlled by both sorptive and incorporative associations between Fe and OC. Overall, this study demonstrates that Fe oxides play an important role in regulating the biogeochemical cycles of C in forest soils and uncovers the governing factors for the spatial variability and characteristics of Fe-bound OC.

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To mitigate the harmful effects of global climate change, it is essential to completely understand the cycles of carbon. In this study, we found the iron oxides play an important role in regulating the accumulation of carbon in forest soil, and uncovered the governing factors for the spatial variability and characteristics of iron-bound organic carbon. Such information is important for predicting the turnover of carbon in global soils.
To mitigate the harmful effects of global climate change, it is essential to completely...
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