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

Plan paper 1

Authors: Eric Roden; Matt Ginder-Vogel

Affiliations: Department of Geoscience, University of Wisconsin−Madison, United States.

This paper works on the Hanford 300 Area surface sediments where we either amended 300 Area sediments with additional Fe(III) oxide (synthetic high surface area goethite) coatings or stripped away the endogenous Fe(III) oxide pool by CDB extraction, after which we incubated the sediments under either oxic or anoxic conditions, with or without addition of fresh particulate organic matter (algal biomass grown from periphyton obtained from the rocks at the 300 Area). We followed total inorganic carbon production, DOC, sodium pyrophosphate-extractable organic carbon (OC), and nitrate/ammonium generation, as well as nitrate consumption, Fe(III) reduction, sulfate reduction, and CH4 production in the anoxic incubations.

Plan paper 2

Authors: Alisa Aleshina, Maria-Anna Rusakova, Olga Drozdova, Oleg S. Pokrovsky and Sergey Lapitskiy

Affiliations: Geoscience and Environment Toulouse (GET), UMR 5563 CNRS University of Toulouse, France

Abstract: Iron is one of the main biogenic elements, and it exists in dissolved, suspended, and colloidal states in river water. Predicting the composition and size of Fe compounds is crucial for assessing water quality. The studies of Fe speciation in European boreal fluvial waters were carried out using a combination of size fractionation (ultrafiltration), chemical techniques (ion exchange chromatography), and computational methods (Visual Minteq). This approach allowed assessment of the forms of Fe present in the studied rivers. Rivers with a predominance of both allochthonous and autochthonous organic compounds were investigated. It was demonstrated that the dissolved organic matter (DOM) in the studied rivers varies in molecular weights and the degree of humification. It was found that in all studied rivers, the predominant form of Fe during the summer low-water period is colloidal, in the form of anionic complexes of the type [MeL]^n-.

Plan paper 3

Author: Pere Rovira

Affiliation: Forest Sciences Centre of Catalonia (CTFC), Carretera St Llorenç de Morunys, Spain

The paper deals about the relevance of each of the factors that determine SOM stability (taking subalpine grasslands as an example), and focus on what is the precise role of free iron forms, which could be not exactly what is usually assumed.