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1
Biogeochemistry of WetlandsS i d A li tiS i d A li ti
Institute of Food and Agricultural Sciences (IFAS)
Science and ApplicationsScience and Applications
Wetland Biogeochemistry LaboratorySoil and Water Science Department
Cycling of Iron and ManganeseCycling of Iron and Manganese
6/22/2008 WBL 16/22/2008 WBL 1
InstructorK. Ramesh Reddy
University of Florida
Lecture Outline
Cycling of Iron and ManganeseCycling of Iron and Manganese
IntroductionMajor components of metal cycle Reduction of Iron and ManganeseOxidation of Iron and ManganeseMobility of Iron and ManganeseEcological significance
Nutrient regeneration/immobilizationFerromanganese modules
Mn (IV)Mn (IV)
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Ferromanganese modulesRoot plaque formationFerrolysisMethane emissions
Summary
Fe (III)Fe (III)
Fe (II)Fe (II)Mn (II)Mn (II)
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Learning Objectives
Cycling of Iron and ManganeseCycling of Iron and Manganese
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 alkalinitySuppresion of sulfate reduction and methanogenesis
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pp gFormation of minerals (e.g., siderite, vivianite, pyrite, and
others)Mottling and gleying serve as indicators of hydric soils Oxidation of toxic organic contaminants
Iron (Fe) and Manganese (Mn)Iron
4th most abundant element in the Earth’s crust, (average concentration of 4 3 % in soils and(average concentration of 4.3 %, in soils and sediments 0.1-10%)
ManganeseOn average 60 time less abundant than Fe (In soils and sediments 0.002-0.6%)
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Fe & Mn are generally considered to be trace elements in open-water aquatic systems, but major elements in soils and sedimentary environments
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• Required by organisms as nutrients – Fe is a major component of cytochromes and other
oxidation reduction proteins
Iron (Fe) and Manganese (Mn)
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 ( id h l
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readily available for organisms (oxides have low solubility)– Plants and microorganisms produce chelating agents
(siderophores) which facilitate solubilization and uptake of Fe/Mn from insoluble minerals
Fe-Containing Minerals
Siderite FeCO3
Goethite FeOOHSiderite FeCO3
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Mn-Containing Minerals
Rhodocrosite MnCO3
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Rhodonite (Mn,Fe,Mg,Ca)SiO3
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
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• Alteration of pH/alkalinity conditions• Mobilization/immobilization of trace metals• Formation minerals (siderite, vivianite, magnetite)
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Oxidation States of Iron and Manganese
MnO2 +42
Mn2+ +2FeOOH +3Fe(OH)3 +3FePO4 +3FeS2 +2
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FeCO3 +2Fe2+ +2
Forms of Iron and Manganese
Water soluble (dissolved, pore water)
Exchangeable (sorbed on cationExchangeable (sorbed on cationexchange complex)
Reducible (insoluble ferric compounds)
Residual (crystalline stable pool)
Forms of Fe and Mn compounds
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Amorphous
Crystalline
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Low (acid) pH Near neutral to alkalineH di i
Soil pH effects on Metals (Me)
Me2+
Me2+
Low (acid) pHconditions pH conditions
Me2+
Me2+ -
-
--
-MeCO3
MeOH2
MeO
Me2+
Me2+
Clay
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Increased solubility leads to more bioavailability
Decreased solubility leads to less bioavailability
Metals in solution Precipitation Adsorption
Oxidation-ReductionMe2+
Me2+2
Fe2+Fe2+
Me2+Me2+
Me2+ Me2+Me2+
Fe3+ Fe3+Fe3+
Fe3+Fe3+
Oxidized Conditions
Particle
Me2+Me2+Fe2+ Fe2+
Reducing or Acid Conditions
Particle
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Oxidized Conditions
Fe2O3 + 6H+ + 2e-
Conditions
2Fe2+ + 3H2O
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Iron cycle
AerobicFe2+
FeOOHFeOOH
O2
Water
Soil
O2 + Fe2+ FeOOH
FeOOH
Fe2+
OM-Fe2+
OM-Fe2+
OM-Fe2+
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Anaerobic+S2-
FeSFeS2
+S2-
Manganese cycle
AerobicMn2+O2
Water O2 + Mn2+ MnOOH
MnOOH OM-Mn2+
OM-Mn2+
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Anaerobic
MnOOHMnOOH
SoilMn2+ OM-Mn2+
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Sequential Reduction of Electron Acceptors
Organic Substrate[e- donor]
atio
n
O2
NO3-
SO42-
Mn2+
Fe2+ S2-
CH4
tive
Con
cent
ra
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O2
Oxygen Nitrate Iron Methanogenesis
Sulfate Manganese Time
Rel
at
Oxidation-Reduction
CO2 CH4
Mn4+ Mn2+
2 4
SO42- S2- Fe3+ Fe2+ NO3
- N2 O2 H2O
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-200 -100 0 +100 +200 +300 +400Redox Potential, mV (at pH 7)
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Redox Zones with DepthOxygen Reduction ZoneOxygen Reduction Zone
WATER
SOIL AerobicOxygen Reduction ZoneEh = > 300 mV
Nitrate Reduction ZoneMnMn4+4+ Reduction ZoneReduction ZoneEh = 100 to 300 mVEh = 100 to 300 mV
FeFe3+3+ Reduction ZoneReduction ZoneEh = Eh = --100 to 100 mV100 to 100 mV
SOILI
II
III
Aerobic
Facultative
Dep
th
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Sulfate Reduction ZoneEh = -200 to -100 mV
MethanogenesisEh = < -200 mV
IV
V
Anaerobic
D
Redox Potential and pH1000
800600
400200
0
-200
Eh,
[mv]
Fe
Mn
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Baas Becking et al.
0 2 4 6 8 10 12
-400
-600
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10
1200
(mV)
Fe3+
Stability of Fe - Eh and pH
800
400
0
dox
Pote
ntia
l
Fe2+
Fe2O3
FeCO3
O2
H2O
H2OH2
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0 2 4 6 8 10 12 14
-400
pH
Re
Fe2+
Fe3O4
FeS2
H2
FeCO3
1200
(mV)
Stability of Mn - Eh and pH
800
400
0
dox
Pote
ntia
l
Mn2+
MnO2
Mn2O3
Mn3O4
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0 2 4 6 8 10 12
-400
pH
Re MnCO3
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Reduction of Iron (III) and Manganese (IV)
Microbial communitiesBiotic and abiotic reductionForms of iron and manganese
Growing on the surface of hematite
Shewanella oneidensis
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Geobacter metallireducens
Courtesy Pacific Northwest National Laboratory
Fermentative Fe(III) and Mn(IV) reducersBacillus;; Ferribacterium; Clostridium; Desulfovibrio;
Iron (III) and Manganese (IV)Reducers
Bacillus;; Ferribacterium; Clostridium; 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
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Organic acid-oxidizing Fe(III) and Mn(IV) reducers
Aromatic compound-oxidizing Fe(III) reducers - Geobacter spp
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Oxidized forms are solid phases under most conditions
Reduction of Iron (III) and Manganese (IV)
under most conditionsBacterial reduction depends on the ability of bacteria to:
Solubilize solid phasesAttach directly to substrate and directly transfer electronsTransport the substrates directly into cells as solid Fe/Mn oxideFe/Mn oxide
COCO22
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into cells as solidCHCH22OO
FeFe2+2+/Mn/Mn2+2+
Reduction of Iron (III) and Manganese (IV)Bacterial reduction of Fe(III) and Mn(IV)Bacterial reduction of Fe(III) and Mn(IV) depends on:
The amount of bioavailable reductant (organic and inorganic substances) for microbial utilization
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The amount of bioavailable oxidant (manganese or iron) for microbial utilization.
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MonomersSugars, Amino Acids
Fatty Acids
Detrital MatterEnzymeHydrolysisComplex Polymers
Cellulose, Hemicellulose,Proteins, Lipids, Waxes, Lignin
Iron RespirationIron Respiration
Glucose
PyruvateGlycolysis
Substrate level phosphorylation Acetate
TCA CycleOxidative phosphorylation
Mn4+ Fe3+
Uptake
Organic AcidsUptake
CO2
e-
CO2
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Mn , Fe3 Organic Acids[acetate, propionate, butyrate, lactate, alcohols, H2, and CO2]
LactateUptake
Iron Reducing Bacterial Cell Fermenting Bacterial Cell
ATP, Substrate level phosphorylation
e
Mn2+, Fe2+
100
120
gy Y
ield
20
40
60
80
of A
erob
ic E
nerg
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0O2 NO3
- MnO2 Fe(OH)3 SO42-
%
Electron Acceptors
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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
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Nitrite
NH4 (oxidized to N2 or NO2- with Mn (IV))
Humic acids (electron shuttles)
Humic Electron ShuttlingFe(OH)3(s)Fe(II)
• Process may have important implications for controls on rate and extent of Fe(III) oxide reduction - depending on concentration and reactivity of humic
b t i il dHumicoxid(aq) Humicred(aq)
Abiotic
substances in soils and sediments
Fe(III)-Reducing Bacteria(enzymatic activity)
Lovley et al. (1996)
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--11))
500
400
Fe (III) ReductionFeFe
2+2+(m
g kg
(mg
kg--
300
200
100
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Redox Potential (mv)
0-200 -100 1000 200 300 400 500
Patrick and Henderson, 1981 SSSAJ 45:35-38
--11))
200
160
Mn (IV) Reduction
Mn
Mn2
+2+(m
g kg
(mg
kg--
120
80
40
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Patrick and Henderson, 1981 SSSAJ 45:35-38Redox Potential (mV)
0-200 -100 1000 200 300 400 500
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Oxidation of Iron (II) and Manganese (II)
Microbial communitiesBiotic and abiotic reduction
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Iron hydroxide precipitate in a Missouri stream receiving acid drainage from surface coal mining. Fe(II) oxidizing bacteria)
Oxidation of Iron (II) and Manganese (II)
• Mesophiles (< 40 ºC):– Thiobacillus, – Leptospirillum,
• Moderate thermophiles (40-60 ºC):– Sulfobacillus,
Acidimicrobium
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Source: Environmental Contaminants; Status and Trends of the Nations Biological ResourcesCredit: D. Hardesty, USGS Columbia Environmental Research Center
– Acidimicrobium, – Ferroplasma (an extreme
acidophile which grows at pH 0!)• Extreme thermophiles (> 60 ºC)
– Acidianus, – Sulfurococcus
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Electron donor Bacteria
Fe (II)Obligate LithotrophsThi b ill f id
Iron Iron
Fe (II)FeSO4FeS2Fe3(PO)4
Thiobacillus ferroxidansFerrobacillus ferroxidans
[pH = 2 to 3.5]Carbon source = CO2
Facultative LithotrophsFeCO3FeS
Leptothrix
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FeS2 Gallionella
Organic complexes of FeOrganic matter
Heterotrophs
800
V)
O2
Sulfolobus
Thiobacillus ferrooxidans
Fe3+
Eh-pH Iron Stability – Iron Bacteria
400
0
400x Po
tent
ial (
mV
Fe2+
Fe2O3
FeS2
FeCO
H2OFeCO3
Metallogenium
Siderocapsa
Leptothrix gallionella
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-800
-400
pH
Red
ox Fe3O4
FeCO3
H2
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Electron donor Bacteria
ManganeseManganese
Mn(II)MnCO3
Obligate LithotrophsArthrobacter; Bacillus; Leptothrix; Metallogenium; Flavobacterium; Pseudomonas
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Organic complexes of Mn Heterotrophs
Oxidation of Fe and Manganese• Can occur under aerobic and anaerobic
conditions– Fe(II) oxidized where sulfate reduction and
methanogenesis occur.Iron oxidizing bacteriaNeutrophilic: (Leptothrix spp.; Gallionella spp.; Ferroglobus spp.)
e-D: FeCO3; FeS2 e-A: Oxygen
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Manganese oxidizing bacteriaArthrobacter spp.; Bacillus spp.; Leptothrix spp.; Flavobacterium spp.; Pseudomonas spp.;
e-D: Mn(II); MnCO3 e-A: Oxygen
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FeS2 + 3.5 O2 + H2O = Fe2+ + 2 SO42- + 2 H+
Pyrite OxidationPyrite Oxidation
2 2 2 4Fe2+ + 0.25 O2 + H+ = Fe3+ + 0.5 H2OFe3+ + 3 H2O = Fe(OH)3 (S) + 3 H+
FeS2 + 14 Fe3+ + 8 H2O = 15 Fe2+ + 2SO42- + 16 H+
O2
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FeS2 + 15 O2 + 2 H2O = 2 Fe2 (SO4)3 + 2 H2SO4
Oxidation of Fe(II) and Mn(II) is
Oxidation of Iron (II) and Manganese (II)
regulated by:
Soil or sediment pH and redox potentialOxygen flux and thickness of aerobic layerPresence of oxidants with higher reduction
potentialsFlux of soluble Fe(II) and Mn(II)
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Soil cation exchange capacityMetal-dissolved organic matter complexation
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MnOOH [s]MnO2 [s] Mn(II)
Iron and Manganese Fluxes-Soil and Water Column
MnOOH [s]MnO2 [s]
Mn(II)
(CH O) CO
FeOOH [s]Fe(OH)3 [s]Fe2O3 [s] Fe(II)
Aerobic/Oxic
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FeOOH [s]Fe(OH)3 [s]Fe2O3 [s]
Fe(II)
(CH2O)n CO2
Anaerobic/Anoxic
0Fe2+ac
e
Aerobic
Mobile and Immobile Iron
2
4
6
Insoluble Fe
th b
elow
soi
l sur
fa Aerobic
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80 1 2 3
% Fe
Dep Anaerobic
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Solid-Phase Fe(II)Amorphous Fe(OH)3
[E. Roden, 2002]
Talladega Wetland, North Central AL
024
0 100 200Fe(II) (μmol cm-3)
h (c
m)
( )(0.5M HCl Extraction)
024
0 50 100Fe(III) (μmol cm-3)
(cm
)
p ( )3(0.5M HCl Extraction)
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68
10D
epth6
810
Dep
th
Lake Apopka Marsh
Soluble P, mg L-1
2 4 6 8 1 2Dissolved Fe, mg L-1
0 3
Water
epth
, cm
0102030
2 4 6 8 1 20 0 3
Phosphorus Iron
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De 0
-20-10 Soil
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Mn (μM)1 2 3 4 50
S (μM)20 40 60 80 1000
Fe (μM)0.1 0.2 0.30
O (μM)100 200 3000
Stratification of Electron Acceptors –Black Sea
NO3- (μM)
2 4 6 8 100
Mn2+
0
50
pth
(m)
O2
NO3-
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Fe2+
100
150
Dep
H2S
Ecological and Environmental Significance of Oxidation-
Reduction of Iron and ManganeseReduction of Iron and Manganese
Nutrient regeneration/immobilizationFerromanganese modulesRoot plaque formationFerrolysisM th i i
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Methane emissions
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Nutrient regeneration/immobilization
Organic Matter decomposition35-65% CO2 by Fe (III) reduction (Lovley, 1987)
Positive relationship between iron oxide reduction and organic nitrogen mineralization in tropical wetland soils (Sahrawat 2004)
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tropical wetland soils (Sahrawat, 2004)
g-1 )
4
Extractable IronExtractable Iron(Mississippi River Floodplain Soils)(Mississippi River Floodplain Soils)
ous
Iron
(mg
kg 3
2
1
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Ferr
o
05 100 15 20 25
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Organic Matter = H+ + e- + CO2 + H2OF (OH) 3 H+ F 2+ H O
Organic Matter and Fe and MnReduction
Fe(OH)3 + 3 H+ + e- = Fe2+ + H2OEh = 1.06 – 0.059 log Fe2+ + 0.177 pH
Fe2+
M 2+
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Organic Matter
Mn2+
Electron Acceptor or Oxidant Molar Ratio Molar Ratio
Organic matter decomposition and nutrient release
Electron Donor: (CH2O)106 (NH3)16 (H3PO4)1
Electron Acceptor or Oxidant [EA]
Molar RatioEA /NH3
Molar RatioEA /H3PO4
O2 6.6 106
NO3- 5.3 85
MnO2 13.3 202
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2
Fe(OH)3 26.5 424
SO42- 3.3 53
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25
FePO 2 H O + 2 H+ + e- =
Phosphorus Release and Retention
FePO4 . 2 H2O + 2 H+ + e- = Fe2+ + H2PO4
- + 2 H2O
Eh = Eo – 0.059 log [Fe2+] – 0.059 log [H2PO4
-] – 0.118 pH
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Iron solubility - pH and Eh
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Reduction capacity Fe minerals decreases with increasing crystalinityFePO > Fe (OH) > FeOOH > Fe O
Iron Iron
FePO4 > Fe (OH)3 > FeOOH > Fe2O3
[FeOOH]Geothite
Fe3+ Fe2+ Fe3+
Slowreduction
Rapidoxidation
Rapidreduction
Amorphousoxides
[FeOH3]
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Slow Crystallization
Iron Iron --Phosphorus Interactions under Phosphorus Interactions under Anaerobic Soil ConditionsAnaerobic Soil Conditions
SO42- H2S + FePO4
Fe2+ + PO43- FePO4FeS
Fe(OH)2-PO4
[Strengite]
fast formingfast forming
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Fe3(PO4)2[Vivianite]
[Strengite]Stable, Slow Stable, Slow formingforming
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Anaerobic Aerobic
Oxidation Oxidation –– Reduction of IronReduction of Iron-- Phosphate Minerals Phosphate Minerals
VivianiteFe3(PO4)2 8 H2O
Kertschemite(hydrated Fe2+, Fe3+, PO4
3-)
Am Ferric Phosphate Am Ferric Phosphate
Crystallization[Slow]
[Fast]
[Fast]
[Fast]
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Am Ferric PhosphateFe3(PO4)2 n H2O
Am Ferric PhosphateFe(PO4) 4 H2O
StrengiteFe(PO4) 4 H2O
Crystallization
[Slow]
[Slow]
Concretions, nodules, or mottles rich in iron and manganese
Ferromanganese nodules
pelagite of 3 cm
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mage credit: Roger Suthren. Upper Devonian, Cabrières, Hérault, S FrancePhoto © Antonio Borrelli
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Protection from reduced phytotoxinsI t f ith t i t t k
Root plaque formation
Interference with nutrient uptake
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80 15
)
Methane emissions
40
60
Fe(II)
Inhibition of methanogenesis CO2
5
10
e(III
) (μm
ol c
m-3
)
CH
4(μ
mol
cm
-3)
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0
20
Time (d)
Fe(III)
0 5 10 15 20 25
CH4
0
Fe(II
),F
CO
2,
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FerrolysisDuring flooding..reduction of Fe3+ to Fe2+
Accumulation of Fe2+ displaces base cations from CECDrainage of these soils removes base cations during leachingOxidation of Fe2+ to Fe3+ releases H+ (acid conditions)H+ saturated clay is unstable..results in high aluminum concentrationRepeated cycles of flooding and draining decreases base saturationFerrolysis occurs in surface soil horizons with abundant supply of bioavailable organic matter to support microbial reduction of Fe(III) oxides.
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Fe3+ FeS + H2O Fe (OH)3 + H2SO4Flooded Drained
Fe forms more stable organic-metal bonds than Mn
Iron and Manganese
Stable organic-metal complexes will protect Fe from precipitationExtent of complexation is greater under anaerobic conditionsSignificant amounts of Fe2+ can be present under aerobic conditions for several days.. Due to
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ycomplexation with organics
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SummaryReduction of Fe (III) and Mn (IV) results in:
Iron and Manganese
( ) ( )Concentration of water soluble Fe and Mn
increasespH of acid soil increasesCation exchange capacity of soil is occupied by Fe and MnSolubility of phosphorus increasesBreakdown of OM and nutrient releaseNew minerals are formed
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SummaryO id ti f F (II) d M (II) lt i
Iron and Manganese
Oxidation of Fe (II) and Mn (II) results in:Bioavailability of metals decreases Co-Precipitation of other metalspH of soil decreases to acidic conditionsSolubility of phosphorus dereasesy p pOxidized Fe and Mn serves as electron
acceptor upon flooding
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General Chemical Transformations of Metals
Water soluble metalsSoluble free ions e g Fe2+Soluble free ions, e.g., FeSoluble as inorganic complexesSoluble as organic complexes
Exchangeable metalsMetals precipitated as inorganic compoundsMetals complexed with large molecular weight humic materials
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Metals adsorbed or occluded to precipitated hydrous oxidesMetals precipitated as insoluble sulfides
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http://wetlands.ifas.ufl.eduhttp://wetlands.ifas.ufl.eduhttp://soils.ifas.ufl.eduhttp://soils.ifas.ufl.edu