Iron traps terrestrially derived dissolved organic matter at redox interfaces

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 110; no. 25; pp. 10101 - 10105
• Main Authors: Riedel, Thomas, Zak, Dominik, Biester, Harald, Dittmar, Thorsten
• Format: Journal Article
• Language: English
• Published: Washington, DC National Academy of Sciences 18-06-2013; National Acad Sciences
• Subjects: Acid soils; Aromatic compounds; Bacteria - metabolism; Biogeochemistry; Carbon Cycle - physiology; Carbon Sequestration - physiology; Chemical compounds; Chemical precipitation; Coagulation; Dissolved organic matter; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; Fatty Acids - chemistry; Fens; Hydrocarbons, Aromatic - chemistry; Hydroxybenzoates - chemistry; Iron - chemistry; Iron - metabolism; Marine geology; Mass spectrometry; Oceans and Seas; Organic soils; Oxidation-Reduction; Oxygen - chemistry; Peat; Peatlands; Physical Sciences; Pollution, environment geology; Seawater - chemistry; Soil - chemistry; Soil organic matter; Soils; Surface water; Surficial geology; Water samples; Wetlands; interfaces; oxides; biogeochemical cycle; oxidation-reduction conditions; dissolution; carbon sequestration; carbon cycle; hydroxides; precipitation; wetlands; ocean; wetland restoration; iron; flux; organic compounds; soils; organic carbon; sediments; phenolics
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1221487110

Reactive iron and organic carbon are intimately associated in soils and sediments. However, to date, the organic compounds involved are uncharacterized on the molecular level. At redox interfaces in peatlands, where the biogeochemical cycles of iron and dissolved organic matter (DOM) are coupled, this issue can readily be studied. We found that precipitation of iron hydroxides at the oxic surface layer of two rewetted fens removed a large fraction of DOM via coagulation. On aeration of anoxic fen pore waters, >90% of dissolved iron and 27 ± 7% (mean ± SD) of dissolved organic carbon were rapidly (within 24 h) removed. Using ultra-high-resolution MS, we show that vascular plant-derived aromatic and pyrogenic compounds were preferentially retained, whereas the majority of carboxyl-rich aliphatic acids remained in solution. We propose that redox interfaces, which are ubiquitous in marine and terrestrial settings, are selective yet intermediate barriers that limit the flux of land-derived DOM to oceanic waters.