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Iron and Manganese 6/22/2008 Institute of Food and Agricultural Sciences (IFAS) Biogeochemistry of Wetlands SiScience an dAd App litilications Cycling of Iron and Manganese Wetland Biogeochemistry Laboratory Soil and Water Science Department University of Florida Instructor K. Ramesh Reddy [email protected] 6/22/2008 WBL 1 Cycling of Iron and Manganese Lecture Outline Introduction Major components of metal cycle Reduction of Iron and Manganese Oxidation of Iron and Manganese Mobility of Iron and Manganese Ecological significance Nutrient regeneration/immobilization Mn (IV) Ferromanganese modules Root plaque formation Fe (III) Ferrolysis Methane emissions Mn (II) Summary Fe (II) 6/22/2008 WBL 2 1 6/22/2008 Cycling of Iron and Manganese Learning Objectives Understand the stability of iron and manganese solid phases as function of Eh and pH Role of Fe (III) and Mn(IV) reduction in organic matter decomposition and nutrient regeneration Adverse effects of reduced Fe (II) and Mn (II) Alteration soil pH and alkalinity Suppresion of sulfate reduction and methanog enesis Formation of minerals (e.g., siderite, vivianite, pyrite, and others) Mottling and gleying serve as indicators of hydric soils Oxidation of toxic organic contaminants 6/22/2008 WBL 3 Iron (Fe) and Manganese (Mn) Iron 4th most abundant element in the Earth’s crust, (average concentration of 4. 3 %, in soils and sediments 0.1-10%) Manganese On average 60 time less abundant than Fe (In soils and sediments 0.002-0.6%) Fe & Mn are generally considered to be trace elements in open-water aquatic systems, but major elements in soils and sedimentary environments 6/22/2008 WBL 4 2 6/22/2008 Iron (Fe) and Manganese (Mn) • Required by organisms as nutrients – Fe is a major component of cytochromes and other oxidation-reduction proteins – Mn is a cofactor for various enzyme systems. Plants assimilate 20-500 mg/kg in dry matter • Although abundant in the Earth’s crust, unlike other elements (e.g. C, N, S), they are often not readily available for organisms (idh(oxides have l ow solubility) – Plants and microorganisms produce chelating agents (siderophores) which facilitate solubilization and uptake of Fe/Mn from insoluble minerals 6/22/2008 WBL 5 Fe-Containing Minerals Siderite FeCO 3 Goethite FeOOH Siderite FeCO3 Vivianite6/22/2008 Fe3(PO4)2 WBLHematite Fe2O3 6 3 6/22/2008 Mn-Containing Minerals Rhodocrosite MnCO3 Rhodonite (Mn,Fe,Mg,Ca)SiO3 6/22/2008 WBL 7 Importance of Fe and Mn in wetlands • Role in decomposition of organic matter • Precipitation of sulfides – Adverse effects of sulfide on plant growth – Reduces available phosphorus – Toxic to plants at high levels • Suppression of sulfate reduction and, methanogenesis • Alteration of pH/alkalinity conditions • Mobilization/immobilization of trace metals • Formation minerals (siderite, vivianite, magnetite) 6/22/2008 WBL 8 4 6/22/2008 Oxidation States of Iron and Manganese MnO2 +4 Mn2+ +2 FeOOH +3 Fe(OH)3 +3 FePO4 +3 FeS2 +2 FeCO3 +2 Fe2+ +2 6/22/2008 WBL 9 Forms of Iron and Manganese Water soluble (dissolved, pore water) Exchangeable (sorbed on cation exchange complex) Reducible (insoluble ferric compounds) Residual (crystalline stable pool) Forms of Fe and Mn compounds Amorphous Crystalline 6/22/2008 WBL 10 5 6/22/2008 Soil pH effects on Metals (Me) Near neutral to alkaline Low (acid) pH pHdiiH conditions conditions Me2+ Me2+ - 2+ - Me MeCO3 Clay Me2+ - Me2+ Me2+ MeOH2 - - MeO Metals in solution Precipitation Adsorption Increased solubility leads Decreased solubility leads to more bioavailability to less bioavailability 6/22/2008 WBL 11 Oxidation-Reduction Fe2+ 2+ Me2+ Fe 2+ Me2+ Me 2+ Fe Fe2+ 2+ Fe3+ Me2+ Fe3+ Me Fe3+ Particle Particle Me2+ Fe3+ Me2+ Fe3+ Me2+ Reducing or Acid Conditions Oxidized Conditions 2+ + - 2Fe + 3H2O Fe2O3 + 6H + 2e 6/22/2008 WBL 12 6 6/22/2008 Iron cycle Water 2+ FeOOH OM-Fe2+ O2 + Fe Aerobic O 2+ 2 Fe2+ FeOOH OM-Fe Soil FeOOH 2+ Fe2+ FeOOH OM-Fe Anaerobic 2- +S2- +S FeS FeS2 6/22/2008 WBL 13 Manganese cycle Water 2+ MnOOH OM-Mn2+ O2 + Mn Aerobic O 2+ 2 Mn2+ MnOOH OM-Mn Soil MnOOH 2+ Mn2+ MnOOH OM-Mn Anaerobic 6/22/2008 WBL 14 7 6/22/2008 Sequential Reduction of Electron Acceptors Organic Substrate - tion [e donor] a 2+ S2- 2- Fe SO4 NO - CH4 3 Mn2+ ive Concentr t O2 Rela Oxygen Nitrate Iron Methanogenesis Manganese Time Sulfate 6/22/2008 WBL 15 Oxidation-Reduction Mn4+ Mn2+ CO2 CH4 2- 2- 3+ 2+ - SO4 S Fe Fe NO3 N2 O2 H2O -200 -100 0 +100 +200 +300 +400 Redox Potential, mV (at pH 7) 6/22/2008 WBL 16 8 6/22/2008 Redox Zones with Depth WATER Oxygen Reduction Zone SOIL Oxygen Reduction Zone Aerobic I Eh = > 300 mV Nitrate Reduction Zone Facultative II Mn4+ Reduction Zone Eh = 100 to 300 mV Fe3+ Reduction Zone III Eh = --100100 to 100 mV epth D Sulfate Reduction Zone Anaerobic IV Eh = -200 to -100 mV V Methanogenesis Eh = < -200 mV 6/22/2008 WBL 17 Redox Potential and pH 1000 800 600 400 Mn 200 Fe 0 Eh,[mv] -200 -400 -600 0 2 4 6 8 10 12 pH 6/22/2008 WBLBaas Becking et al. 18 9 6/22/2008 Stability of Fe - Eh and pH 1200 Fe3+ (mV) 800 O2 Fe2O3 400 H O Fe2+ 2 FeCO 0 H2O 3 dox Potential H2 FeS2 Re -400 Fe2+ FeCO3 Fe3O4 0 2 4 6 8 10 12 14 pH 6/22/2008 WBL 19 Stability of Mn - Eh and pH 1200 (mV) 800 MnO2 400 Mn2+ Mn2O3 0 Mn O dox Potential 3 4 MnCO3 Re -400 0 2 4 6 8 10 12 pH 6/22/2008 WBL 20 10 6/22/2008 Reduction of Iron (III) and Manganese (IV) Microbial communities Biotic and abiotic reduction Forms of iron and manganese Shewanella oneidensis Growing on the surface of hematite Courtesy Pacific Northwest National Laboratory Geobacter metallireducens 6/22/2008 WBL 21 Iron (III) and Manganese (IV) Reducers Fermentative Fe(III) and Mn(IV) reducers Bacillus;; Ferribacterium; CloClostridium;stridium; Desulfovibrio; Escherichia Geobacter; . Sulfur-oxidizing Fe(III) and Mn(IV) reducers Thiobacillus spp., Sulfolobus spp Hydrogen-oxidizing Fe(III) and Mn(IV) reducers - Pseudomonas spp., Shewanella spp Organic acid-oxidizing Fe(III) and Mn(IV) reducers Aromatic compound-oxidizing Fe(III) reducers - Geobacter spp 6/22/2008 WBL 22 11 6/22/2008 Reduction of Iron (III) and Manganese (IV) Oxidized forms are solid phases under most conditions Bacterial reduction depends on the ability of bacteria to: Solubilize solid phases Attach directly to substrate and directly transfer electrons CO Transport the substrates directly 2 into cells as solid Fe/Mn oxide CH2O Fe2+/Mn2+ 6/22/2008 WBL 23 Reduction of Iron (III) and Manganese (IV) Bacterial reduction of Fe(III) and Mn(IV) depends on: The amount of bioavailable reductant (organic and inorganic substances) for microbial utilization The amount of bioavailable oxidant (manganese or iron) for microbial utilization. 6/22/2008 WBL 24 12 6/22/2008 Iron Respiration Detrital Matter Enzyme Complex Polymers Hydrolysis Monomers Cellulose, Hemicellulose, Sugars, Amino Acids Proteins, Lipids, Waxes, Lignin Fatty Acids Uptake Glucose Glycolysis Oxidative phosphorylation TCA Cycle Pyruvate CO Substrate level 2 CO 2 Acetate phosphorylation Mn4+, Fe3+ e- Uptake Organic Acids Lactate [acetate, propionate, butyrate, ATP, Substrate level lactate, alcohols, H2, and CO2] phosphorylation Iron Reducing Bacterial Cell Fermenting Bacterial Cell Mn2+, Fe2+ 6/22/2008 WBL 25 120 100 y Yield g 80 60 40 of Aerobic Ener 20 % 0 - 2- O2 NO3 MnO2 Fe(OH)3 SO4 Electron Acceptors 6/22/2008 WBL 26 13 6/22/2008 Abiotic reduction of Fe (III) and Mn (IV) Microbial end products Citrate Malate Oxalate Pyruvate (oxidized to acetate with non enzymatic Mn(IV) reduction) Sulfides Nitrite - NH4 (oxidized to N2 or NO2 with Mn (IV)) Humic acids (electron shuttles) 6/22/2008 WBL 27 Humic Electron Shuttling Fe(II) Fe(OH)3(s) • Process may have important Abiotic implications for controls on rate and extent of Fe(III) oxide reduction - depending on concentration and reactivity of humic Humicoxid(aq) Humicred(aq) subtbstances in so ils an d sediments Lovley et al. (1996) Fe(III)-Reducing Bacteria (enzymatic activity) 6/22/2008 WBL 28 14 Patrick and Henderson, 1981 SSSAJ 45:35-38 Patrick and Henderson, 1981 SSSAJ 45:35-38 6/22/2008 WBL 29 6/22/2008 WBL 30 2+ -1 Mn2+ (mg kg-1) Fe (mg kg ) 100 200 300 400 500 120 160 200 40 80 0 0 Mn (IV)Reduction Fe (III)Reduction -200 -100 100 -200 -100 100 Redox Potential(mv) Redox Potential(mV) 0 200 300 400 500 0 200 300 400 500 6/22/2008 15 6/22/2008 Oxidation of Iron (II) and Manganese (II) Microbial communities Biotic and abiotic reduction 6/22/2008 WBL 31 Oxidation of Iron (II) and Manganese (II) Iron hydroxide precipitate in a Missouri stream receiving acid drainage from surface coal mining. Fe(II) oxidizing bacteria) • Mesophiles (< 40 ºC): – Thiobacillus, – Leptospirillum, • Moderate thermophiles (40-60 ºC): – Sulfobacillus, – Acidimicrobium, – Ferroplasma (an extreme acidophile which grows at pH 0!) • Extreme thermophiles (> 60 ºC) – Acidianus, Source: Environmental Contaminants; Status and Trends of the Nations Biological Resources Credit: D. Hardesty, USGS Columbia Environmental Research Center – Sulfurococcus 6/22/2008 WBL 32 16 6/22/2008 Iron Electron donor Bacteria Obligate Lithotrophs Fe (II) Thio bac illus ferrox idans FeSO4 Ferrobacillus ferroxidans FeS 2 [pH = 2 to 3.5] Fe3(PO)4 Carbon source = CO2 Facultative Lithotrophs FeCO 3 Leptothrix FeS 2 Gallionella Organic complexes of Fe Heterotrophs Organic matter 6/22/2008 WBL 33 Eh-pH Iron Stability – Iron Bacteria Fe3+ 800 Thiobacillus O ferrooxidans 2 Sulfolobus ) Metallogenium V 400 Fe2O3 Siderocapsa Leptothrix Fe2+ gallionella 0 H2O FeCO3 FeS2 Potential (m FeCO x -400 3 Fe3O4 H2 Redo -800 0 2 4 6 8 10 12 14 6/22/2008 WBLpH 34 17 6/22/2008 Manganese Electron donor Bacteria Mn(II) Obligate Lithotrophs MnCO3 Arthrobacter; Bacillus; Leptothrix; Metallogenium; Flavobacterium; Pseudomonas Organic complexes of Mn Heterotrophs 6/22/2008 WBL 35 Oxidation of Fe and Manganese • Can occur under aerobic and anaerobic conditions – Fe(II) oxidized where sulfate reduction and methanogenesis occur.
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