![]() ![]() Acme Meat Co Bristol foods, Inc, d/b/a Gold Pak Meat Co Delta Meat Packing Co Federal Meat Co Gem Packing Co Globe Packing Co Great Western Packing Co Meat Packers, Inc O.K. Danny Abrishamian, a/k/a "Kamran Abrishamian" ABB Middle East & Africa Participations AG The AAV Companies ARA Services Inc., and Western Vending Machine Company (ORNL), Oak Ridge, TN (United States) Sponsoring Org.U.S. Publication Date: Sat Mar 25 00:00: Research Org.: Oak Ridge National Lab. Kent State Univ., Kent, OH (United States).Future predictions of carbon storage and respiration in the arctic tundra should consider such influences of mineral stabilization under changing redox conditions. The distribution of iron in organic complexes and inorganic phases throughout the soil column constrains Fe(III) availability to anaerobic iron-reducing microorganisms that oxidize organic matter to produce CO 2 and CH 4 in these anoxic environments. Organic matter released through acid-dissolution of iron oxides could represent a small pool of readily-degradable organic molecules temporarily stabilized by sorption to iron oxyhydroxide surfaces. Our results suggest that iron oxides may inhibit organic carbon degradation by binding low-molecular-weight organic compounds, stabilizing soil aggregates, and forming thick coatings around particulate organic matter. Precipitation of iron oxides at the redox interface has the potential to contribute to mineral protection of organic matter and increase the residence time of organic carbon in arctic soils. We conclude that organic horizons were enriched in poorly crystalline and crystalline iron oxide phases derived from upward translocation of dissolved Fe(II) and Fe(III) from mineral horizons. Integrated over the entire depth of the active layer, soils contained 11± 4 kg m -2 low- density, particulate organic C and 19 ± 6 kg m -2 high-density, mineral-associated organic C, indicating that 63 ☑9% of organic C in the active layer was associated with the mineral fraction. Conversely, water-soluble organic molecules and organics solubilized through acid-dissolution of iron oxides comprised < 2% of soil organic C and were consistent with a mixture of alcohols, sugars, and small molecular weight organic acids and aromatics released through decomposition of larger molecules. C), and organic matter was dominated by base-extractable and insoluble organics enriched in aromatic and aliphatic moieties. % C) were approximately twice the concentrations in the mineral horizons (14 ± 2 % wt. Concentrations of organic carbon in the organic horizons (28 ± 5% wt. Minor amounts of ferrous iron were present in iron sulfides (i.e., pyrite and greigite) in mineral horizon soils and iron phosphates (vivianite) in organic horizons. Ferrihydrite and goethite were present as coatings on mineral grains and plant debris, and in aggregates with clays and particulate organic matter. Organic horizons were more » enriched in poorly crystalline and crystalline iron oxides, and approximately 60% of total Fe stored in organic horizons was calculated to derive from upward translocation from anoxic mineral horizons. ![]() Spectroscopic techniques, including micro-X-ray fluorescence ( XRF) mapping, micro-X-ray absorption near-edge structure ( XANES) spectroscopy, and Fourier transform infrared spectroscopy (FTIR), were coupled with chemical sequential extractions and physical density fractionations to evaluate the spatial distribution and speciation of Fe-bearing phases and associated organic matter in soils. Here in this paper, we examine chemical properties of solid-phase Fe and organic matter in organic and mineral horizons within the seasonally thawed active layer of Arctic tundra on the North Slope of Alaska. The accumulation of iron (Fe) oxyhydroxides and organo- iron precipitates at redox interfaces may be particularly important for carbon cycling given that ferric iron species can enhance decomposition by serving as terminal electron acceptors in anoxic soils or inhibit microbial decomposition by binding organic molecules. Geochemical interactions between soil organic matter and minerals influence decomposition in many environments but remain poorly understood in Arctic tundra systems and are not considered in decomposition models. As the climate warms, these carbon reservoirs are susceptible to increased rates of decomposition and release to the atmosphere as the greenhouse gases carbon dioxide (CO 2) and methane (CH 4). Arctic tundra stores large quantities of soil organic matter under varying redox conditions. ![]()
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