6/22/2008

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

krr@ufl.edu

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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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