Coupled Iron–Carbon Biogeochemical Processes

A special issue of Environments (ISSN 2076-3298).

Deadline for manuscript submissions: closed (29 May 2024) | Viewed by 4218

Special Issue Editors


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Guest Editor
Department of Civil and Environmental Engineering, Carnegie Mellon University, Pittsburgh, PA, USA
Interests: iron; natural organic matter; photochemistry; catalysis
Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA, USA
Interests: iron; mineralogy; soil organic matter; biogeochemistry
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Guest Editor
Institute of Environmental and Ecological Engineering, Guangdong University of Technology, Guangzhou 510006, China
Interests: soil remediation; natural organic matter; carbon sequestration; biochar; microplastics
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Iron (Fe) is ubiquitous and ranks 4th in natural abundance in Earth’s crust. Same as iron, carbon (C) is also abundant and the major element for organic and inorganic substances. They are both omnipresent in nature and reactive in chemical reactions. Most importantly, iron and carbon coupling is one of the most important natural processes that influence the cycles of major and minor active elements in the atmosphere, hydrosphere, biosphere, and geosphere. It drives important chemical reactions, such as oxygen delivery, nitrogen fixation, and climate change. Fe minerals have been suggested to play an important role in interacting with and stabilizing C in soils and sediments. C associated with Fe minerals by sorption and co-precipitation showed higher stability, indicated by longer turnover times, than non-Fe-bound C. Thus, it is crucial to understand the biogeochemical reactions of Fe-bound C in soils. This session will utilize interdisciplinary efforts to have an advanced understanding of the mechanisms of the coupled iron-carbon biogeochemical processes as well as their direct and indirect impacts on environmental processes.

Dr. Xiaopeng Huang
Dr. Qian Zhao
Dr. Lanfang Han
Guest Editors

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Keywords

  • iron
  • organic carbon
  • biogeochemistry
  • environment
  • climate change

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Published Papers (3 papers)

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Research

13 pages, 8668 KiB  
Article
The Formation and Stability of HA–Fe/Mn Colloids in Saturated Porous Media
by Junhao Zheng, Mei Jiang, Qingzhu Li and Weichun Yang
Environments 2024, 11(7), 136; https://doi.org/10.3390/environments11070136 - 27 Jun 2024
Cited by 1 | Viewed by 955
Abstract
Fe/Mn (hydr)oxides are metallic compounds that exhibit significant redox activity in environmental media and play a pivotal role in geochemical processes, thereby influencing the fate of metals in porous media. The morphology of Fe/Mn (hydr)oxides in natural environments and their interactions with trace [...] Read more.
Fe/Mn (hydr)oxides are metallic compounds that exhibit significant redox activity in environmental media and play a pivotal role in geochemical processes, thereby influencing the fate of metals in porous media. The morphology of Fe/Mn (hydr)oxides in natural environments and their interactions with trace metals are significantly influenced by the presence of natural organic matter (NOM). However, there is limited understanding regarding the formation, transport, and stability of Fe/Mn (hydr)oxides in the environment. The present study employed humic acid (HA) as a representative NOM material to investigate the positive influence of HA on the formation of Fe/Mn colloids. However, there remains limited comprehension regarding the formation, transport, and stability of Fe/Mn (hydr)oxides in the natural environment. In this study, we investigated the positive effect of natural organic matter (NOM) on the formation of Fe/Mn colloids using humic acid (HA) as a representative NOM material. We comprehensively characterized the chemical and physical properties of HA–Fe/Mn colloids formed under various environmentally relevant conditions and quantitatively analyzed their subsequent aggregation and stability behaviors. The findings suggest that the molar ratios of C to Fe/Mn (hydr)oxide play a pivotal role in influencing the properties of HA–Fe/Mn colloids. The formation and stability of HA–Fe/Mn colloids exhibit an upward trend with increasing initial molar ratios of C to Fe/Mn. Redox and metal–carboxylic acid complexation reactions between HA and hydrated iron/manganese oxides play a pivotal role in forming colloidal HA–Fe/Mn complexes. Subsequent investigations simulating porous media environments have demonstrated that the colloidal structure resulting from the interaction between HA and Fe/Mn facilitates their migration within surrounding porous media while also enhancing their retention in the surface layers of these media. This study offers novel insights into the formation and stabilization mechanisms of HA–Fe/Mn colloids, which are pivotal for comprehending the behavior of Fe/Mn colloids and the involvement of Fe/Mn (hydr)oxides in geochemical cycling processes within porous media. Full article
(This article belongs to the Special Issue Coupled Iron–Carbon Biogeochemical Processes)
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24 pages, 12143 KiB  
Article
Constraints on Organic Matter Stability in Pyrenean Subalpine Grassland Soils: Physical Protection, Biochemical Quality, and the Role of Free Iron Forms
by Pere Rovira, Teresa Sauras-Yera and Rosa Maria Poch
Environments 2024, 11(6), 126; https://doi.org/10.3390/environments11060126 - 14 Jun 2024
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Abstract
The stability of soil organic matter (SOM) depends on its degree of physical protection, biochemical quality (q), and mineralogical features such as the abundance of iron or aluminum oxyhydroxides: All constraints stabilize SOM, but the relevance of each is herein discussed. [...] Read more.
The stability of soil organic matter (SOM) depends on its degree of physical protection, biochemical quality (q), and mineralogical features such as the abundance of iron or aluminum oxyhydroxides: All constraints stabilize SOM, but the relevance of each is herein discussed. We studied from this point of view the stability of SOM in four grassland soils. The SOM in these profiles was characterized for its physical protection (ultrasonic dispersion + size fractionation) and its q (acid hydrolysis, carbohydrates, phenolics, and unhydrolyzable carbon). The profiles were also analyzed for free iron forms extracted with several chemicals: dithionite-citrate-bicarbonate, citric acid, oxalic-oxalate (Tamm’s solution), and DTPA. Soil horizons were incubated under optimal conditions to obtain the C lost after 33 days (Cresp33) and basal respiration rate (BRR). The microbial C was obtained at the end of the incubation. The microbial activity rate (MAR: mg C respired per g microbial C per day) was obtained from these measures. The sum soluble + microbial C was taken as the active C pool. As expected, the stability of SOM depends on its distribution between the size fractions: The higher the proportion of particulate organic matter (POM: >20 µm size), the higher the soil respiration rate. In contrast, q barely affects SOM decomposition. Both physical availability (size fractionation) and q (acid hydrolysis) affect the size of the microbial C pool, but they barely affect MAR. The effects of free iron on SOM stability are complex: While dithionite-extracted Fe negatively affected Cresp33, BRR, and MAR, the Fe extracted by smoother methods (Tamm’s reagent and DTPA) positively relates to Cresp33, BRR, and MAR. Free iron apparently modulates soil microbial metabolism because it is the only studied parameter that significantly affected MAR; however, the precise effect depends on the precise free Fe fraction. From our data, SOM stability relies on a net of constraints, including physical availability and free Fe forms, with q being of minor relevance. Our dataset suggests a role for free iron as a modulator of microbial activity, deserving future research. Full article
(This article belongs to the Special Issue Coupled Iron–Carbon Biogeochemical Processes)
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13 pages, 3137 KiB  
Article
Dissolved Iron and Organic Matter in Boreal Rivers across a South–North Transect
by Alisa Aleshina, Maria-Anna Rusakova, Olga Y. Drozdova, Oleg S. Pokrovsky and Sergey A. Lapitskiy
Environments 2024, 11(4), 65; https://doi.org/10.3390/environments11040065 - 26 Mar 2024
Viewed by 1529
Abstract
Iron (Fe) is one of the main nutrients present in dissolved, suspended, and colloidal states in river water. Predicting the composition and size of dissolved Fe compounds is crucial for assessing water quality. In this stud, we used a combination of physical methods [...] Read more.
Iron (Fe) is one of the main nutrients present in dissolved, suspended, and colloidal states in river water. Predicting the composition and size of dissolved Fe compounds is crucial for assessing water quality. In this stud, we used a combination of physical methods (filtration), chemical techniques (ion exchange chromatography), and thermodynamic modeling (Visual MINTEQ) to characterize dissolved Fe speciation in boreal organic-rich rivers across a sizable south–north transect. We chose contrasting rivers with a predominance of either allochthonous or autochthonous organic compounds. We found that the dissolved organic matter (DOM) in the studied rivers varies in molecular weights and the degree of humification. Regardless of the climate parameters of the river watershed, the dominant status of dissolved Fe during the summer low-water period was essentially colloidal and dominated by anionic complexes of the type [MeL]n−. Full article
(This article belongs to the Special Issue Coupled Iron–Carbon Biogeochemical Processes)
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