Download Biogeochemistry of Wetlands Cycling of Iron and Manganese

6/22/2008
Institute of Food and Agricultural Sciences (IFAS)
Biogeochemistry of Wetlands
S i
Science
and
dA
Applications
li ti
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
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Cycling of Iron and Manganese
Lecture Outline
™
™
™
™
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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
™
Ferromanganese modules
™
Root plaque formation
Fe (III)
™
Ferrolysis
™
Methane emissions
Summary
Mn (IV)
Mn (II)
Fe (II)
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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
pp
of sulfate reduction and methanogenesis
g
™ Formation of minerals (e.g., siderite, vivianite, pyrite, and
others)
™ Mottling and gleying serve as indicators of hydric soils
™ Oxidation of toxic organic contaminants
™
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Iron (Fe) and Manganese (Mn)
Iron
‰ 4th most abundant element in the Earth’s crust,
(average concentration of 4
4.3
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
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Iron (Fe) and Manganese (Mn)
• Required by organisms as nutrients
– Fe is a major component of cytochromes and other
oxidation reduction proteins
oxidation-reduction
– 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 (oxides
( id have
h
low
l
solubility)
– Plants and microorganisms produce chelating agents
(siderophores) which facilitate solubilization and
uptake of Fe/Mn from insoluble minerals
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Fe-Containing Minerals
Siderite FeCO3
Goethite FeOOH
Siderite FeCO3
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Vivianite
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Hematite Fe2O3
6
3
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Mn-Containing Minerals
Rhodocrosite MnCO3
Rhodonite
(Mn,Fe,Mg,Ca)SiO3
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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)
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Oxidation States of
Iron and Manganese
™ MnO2
™
+4
+2
+3
+3
+3
+2
+2
+2
Mn2+
™ FeOOH
™ Fe(OH)3
™ FePO4
™ FeS2
™ FeCO3
™ Fe2+
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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
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Soil pH effects on Metals (Me)
Near neutral to alkaline
pH
H conditions
di i
Low (acid) pH
conditions
Me2+ Me2+ -
Me2+
Me2+
Me2+
MeCO3
MeOH2
Me2+
MeO
Metals in solution
Precipitation
Increased solubility leads
to more bioavailability
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Clay
Adsorption
Decreased solubility leads
to less bioavailability
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Oxidation-Reduction
Fe2+
Me2+
Fe2+
Me2+
2
Me2+
Fe2+
Fe2+
Fe3+ Me2+
Fe3+
Me2+
Fe3+
Particle
Particle
Me2+
Fe3+ Me2+
Reducing or Acid
Conditions
Me2+
Oxidized Conditions
2Fe2+ + 3H2O
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Fe3+
Fe2O3 + 6H+ + 2e-
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Iron cycle
Water
Aerobic
O2 + Fe2+
O2
Soil
FeOOH
Anaerobic
OM-Fe2+
Fe2+
FeOOH
OM-Fe2+
Fe2+
FeOOH
OM-Fe2+
+S2-
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FeOOH
+S2FeS
FeS2
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Manganese cycle
Water
Aerobic
Soil
Anaerobic
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O2 + Mn2+
O2
MnOOH
MnOOH
OM-Mn2+
Mn2+
MnOOH
OM-Mn2+
Mn2+
MnOOH
OM-Mn2+
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Relattive Concentra
ation
Sequential Reduction of
Electron Acceptors
Organic Substrate
[e- donor]
S2-
Fe2+
SO42NO3-
CH4
Mn2+
O2
Oxygen
Iron
Nitrate
Manganese
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Methanogenesis
Time
Sulfate
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Oxidation-Reduction
Mn4+
CO2
Mn2+
CH4
SO42-
-200
Fe3+
S2-
-100
0
Fe2+
+100
NO3-
+200
N2
O2
H2O
+300 +400
Redox Potential, mV (at pH 7)
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Redox Zones with Depth
WATER
Oxygen Reduction Zone
SOIL
Oxygen Reduction Zone
Aerobic
Eh = > 300 mV
I
Nitrate Reduction Zone
Mn4+ Reduction Zone
II
Facultative
D
Depth
Eh = 100 to 300 mV
III
IV
Fe3+ Reduction Zone
Eh = -100 to 100 mV
Sulfate Reduction Zone
Anaerobic
Eh = -200 to -100 mV
Methanogenesis
V
Eh = < -200 mV
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Redox Potential and pH
1000
Eh,[mv]
800
600
400
200
Mn
Fe
0
-200
-400
-600
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0
2
4
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pH
8 10 12
Baas Becking et al.
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9
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Redox Potential (mV)
Stability of Fe - Eh and pH
1200
Fe3+
800
O2
Fe2O3
400
H2O
Fe2+
0
FeCO3
H2O
H2
-400
FeS2
Fe2+
0
2
FeCO3
4
6
8
Fe3O4
10
12
14
pH
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Redox Potential (mV)
Stability of Mn - Eh and pH
1200
800
MnO2
400
Mn2+
0
Mn3O4
MnCO3
-400
0
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Mn2O3
2
4
6
pH
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8
10
12
20
10
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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
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Iron (III) and Manganese (IV)
Reducers
™ Fermentative Fe(III) and Mn(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
™ Organic acid-oxidizing Fe(III) and Mn(IV)
reducers
™ Aromatic compound-oxidizing Fe(III)
reducers - Geobacter spp
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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
™ Transport the substrates directly
into cells as solid
CO2
Fe/Mn oxide
CH2O
Fe2+/Mn2+
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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.
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Iron Respiration
Detrital Matter
Complex Polymers
Enzyme
Hydrolysis
Cellulose, Hemicellulose,
Proteins, Lipids, Waxes, Lignin
Monomers
Sugars, Amino Acids
Fatty Acids
Uptake
Glucose
Glycolysis
Oxidative phosphorylation
Pyruvate
TCA Cycle
CO2
CO2
Mn4+, Fe33+
Substrate level
phosphorylation
Acetate
e-
Organic Acids
Uptake
ATP, Substrate level
phosphorylation
[acetate, propionate, butyrate,
lactate, alcohols, H2, and CO2]
Lactate
Iron Reducing Bacterial Cell
Fermenting Bacterial Cell
Mn2+, Fe2+
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% of Aerobic Energ
gy Yield
120
100
80
60
40
20
0
O2
NO3-
MnO2 Fe(OH)3
SO42-
Electron Acceptors
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13
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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
™NH4 (oxidized to N2 or NO2- with Mn (IV))
™Humic acids (electron shuttles)
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Humic Electron Shuttling
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
substances
b t
iin soils
il and
d
sediments
Fe(OH)3(s)
Abiotic
Humicoxid(aq)
Humicred(aq)
Lovley et al. (1996)
Fe(III)-Reducing Bacteria
(enzymatic activity)
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Fe (III) Reduction
Fe2+ (mg kg-1)
500
400
300
200
100
0
-200
-100
0
100
200
300
400
500
Redox Potential (mv)
Patrick and Henderson, 1981 SSSAJ 45:35-38
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Mn (IV) Reduction
Mn2+ (mg kg-1)
200
160
120
80
40
0
-200
-100
0
100
200
300
400
500
Redox Potential (mV)
Patrick and Henderson, 1981 SSSAJ 45:35-38
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Oxidation of
Iron (II) and Manganese (II)
™ Microbial communities
™ Biotic and abiotic reduction
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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)
•
•
•
Source: Environmental Contaminants; Status and Trends of the Nations Biological Resources
Credit: D. Hardesty, USGS Columbia Environmental Research Center
6/22/2008
Mesophiles (< 40 ºC):
– Thiobacillus,
– Leptospirillum,
Moderate thermophiles (40-60 ºC):
– Sulfobacillus,
– Acidimicrobium,
Acidimicrobium
– Ferroplasma (an extreme
acidophile which grows at pH 0!)
Extreme thermophiles (> 60 ºC)
– Acidianus,
– Sulfurococcus
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16
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Iron
Electron donor
Bacteria
Obligate Lithotrophs
Fe (II)
FeSO4
FeS2
Fe3(PO)4
Thiobacillus
Thi
b ill fferroxidans
id
Ferrobacillus ferroxidans
[pH = 2 to 3.5]
Carbon source = CO2
Facultative Lithotrophs
Leptothrix
Gallionella
FeCO3
FeS2
Organic complexes of Fe
Organic matter
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Heterotrophs
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Eh-pH Iron Stability – Iron Bacteria
Redox
x Potential (mV
V)
800
Fe3+
Thiobacillus
ferrooxidans
Sulfolobus
O2
Metallogenium
Fe2O3
400
Siderocapsa
Leptothrix
gallionella
Fe2+
0
H2O
FeCO3
FeS2
FeCO3
-400
400
Fe3O4
H2
-800
0
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2
4
6
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pH
10
12
14
34
17
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Manganese
Electron donor
Mn(II)
MnCO3
Bacteria
Obligate Lithotrophs
Arthrobacter; Bacillus;
Leptothrix; Metallogenium;
Flavobacterium;
Pseudomonas
Organic complexes of Mn
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Heterotrophs
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Oxidation of Fe and Manganese
• Can occur under aerobic and anaerobic
conditions
– Fe(II) oxidized where sulfate reduction and
methanogenesis occur.
Iron oxidizing bacteria
Neutrophilic: (Leptothrix spp.; Gallionella spp.; Ferroglobus spp.)
e-D: FeCO3; FeS2
e-A: Oxygen
Manganese oxidizing bacteria
Arthrobacter spp.; Bacillus spp.; Leptothrix spp.; Flavobacterium spp.; Pseudomonas spp.;
e-D: Mn(II); MnCO3
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e-A: Oxygen
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Pyrite Oxidation
FeS2 + 3.5 O2 + H2O = Fe2+ + 2 SO42- + 2 H+
Fe2+ + 0.25 O2 + H+ = Fe3+ + 0.5 H2O
Fe3+ + 3 H2O = Fe(OH)3 (S) + 3 H+
FeS2 + 14 Fe3+ + 8 H2O = 15 Fe2+ + 2SO42- + 16 H+
O2
FeS2 + 15 O2 + 2 H2O = 2 Fe2 (SO4)3 + 2 H2SO4
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Oxidation of
Iron (II) and Manganese (II)
Oxidation of Fe(II) and Mn(II) is
regulated by:
™ Soil or sediment pH and redox potential
™ Oxygen flux and thickness of aerobic layer
™ Presence of oxidants with higher reduction
potentials
™ Flux of soluble Fe(II) and Mn(II)
™ Soil cation exchange capacity
™ Metal-dissolved organic matter complexation
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Iron and Manganese FluxesSoil and Water Column
MnOOH [s]
MnO2 [s]
FeOOH [s]
Fe(OH)3 [s]
Fe2O3 [s]
Mn(II)
Fe(II)
Aerobic/Oxic
MnOOH [s]
MnO2 [s]
(CH2O)n
Mn(II)
CO2
FeOOH [s]
Fe(OH)3 [s]
Fe(II)
Fe2O3 [s]
Anaerobic/Anoxic
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Mobile and Immobile Iron
Depth below soil surfa
ace
0
Fe2+
Aerobic
2
Insoluble Fe
4
6
Anaerobic
8
0
1
2
3
% Fe
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40
20
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Talladega Wetland, North Central AL
Amorphous
p
Fe(OH)
(
)3
Solid-Phase Fe(II)
( )
(0.5M HCl Extraction)
(0.5M HCl Extraction)
Fe(III) (μ mol cm-3)
0
50
100
Fe(II) (μ mol cm-3)
0
100
200
0
2
4
6
8
10
Depth
h (cm)
Depth (cm)
[E. Roden, 2002]
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0
2
4
6
8
10
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Lake Apopka Marsh
Soluble P, mg L-1
0
Deepth, cm
30
2
4
6
8
Phosphorus
Dissolved Fe, mg L-1
1
0
2
3
Iron
20
Water
10
0
-10
Soil
-20
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21
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Stratification of Electron Acceptors –Black Sea
0
1
0
20
0.1
0
100
0
0
2
Mn (μM)
2
3
S (μM)
40
60
Fe (μM)
0.2
O (μM)
200
NO3- (μM)
4
6
4
5
80
100
0.3
300
8
10
0
Dep
pth (m)
O2
NO3-
50
Mn2+
100
Fe2+
150
H 2S
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Ecological and Environmental
Significance of OxidationReduction of Iron and Manganese
™
™
™
™
™
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Nutrient regeneration/immobilization
Ferromanganese modules
Root plaque formation
Ferrolysis
M th
Methane
emissions
i i
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Nutrient
regeneration/immobilization
Organic Matter decomposition
™ 35-65% CO2 by Fe (III) reduction (Lovley, 1987)
™ Positive relationship between iron oxide
reduction and organic nitrogen mineralization in
tropical wetland soils (Sahrawat,
(Sahrawat 2004)
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Extractable Iron
Ferro
ous Iron (mg kg
g-1)
(Mississippi River Floodplain Soils)
4
3
2
1
0
0
5
10
15
20
25
Total Organic Carbon (mg g-1)
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23
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Organic Matter and Fe and Mn
Reduction
Organic Matter = H+ + e- + CO2 + H2O
F (OH)3 + 3 H+ + e- = Fe
Fe(OH)
F 2+ + H2O
Eh = 1.06 – 0.059 log Fe2+ + 0.177 pH
Fe2+
M 2+
Mn
Organic Matter
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Organic matter decomposition
and nutrient release
Electron Donor: (CH2O)106 (NH3)16 (H3PO4)1
Electron Acceptor or Oxidant
[EA]
Molar Ratio
EA /NH3
Molar Ratio
EA /H3PO4
O2
6.6
106
NO3-
5.3
85
MnO2
13.3
202
Fe(OH)3
26.5
424
SO42-
3.3
53
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24
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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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25
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Iron
™Reduction capacity Fe minerals decreases
with increasing crystalinity
™FePO4 > Fe (OH)3 > FeOOH > Fe2O3
Rapid
oxidation
Slow
reduction
Fe3+
Fe2+
[FeOOH]
Geothite
Fe3+
Rapid
reduction
[FeOH3]
Amorphous
oxides
Slow Crystallization
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Iron -Phosphorus Interactions under
Anaerobic Soil Conditions
FeS
SO4
2-
Fe2+ + PO43-
H2S + FePO4
[Strengite]
FePO4
[Strengite]
Fe(OH)2-PO4
Fe3(PO4)2
[Vivianite]
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fast forming
Stable, Slow
forming
52
26
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Oxidation – Reduction of Iron
Iron-- Phosphate Minerals
Anaerobic
Aerobic
[Fast]
Vivianite
Fe3(PO4)2 8 H2O
Kertschemite
(hydrated Fe2+, Fe3+, PO43-)
Crystallization
[Fast]
[Slow]
[Fast]
Am Ferric Phosphate
Am Ferric Phosphate
Fe3(PO4)2 n H2O
Fe(PO4) 4 H2O
[Slow]
Strengite
[Slow]
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Crystallization
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Fe(PO4) 4 H2O
53
Ferromanganese nodules
Concretions, nodules, or mottles rich in iron and manganese
pelagite of 3 cm
mage credit: Roger Suthren. Upper Devonian, Cabrières, Hérault, S France
6/22/2008
Photo © Antonio Borrelli
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Root plaque formation
™ Protection from reduced phytotoxins
™ Interference
I t f
with
ith nutrient
t i t uptake
t k
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55
Methane emissions
Fe(II),Fe(III) (μmol cm-3)
Inhibition of methanogenesis
60
10
Fe(II)
40
5
20
Fe(III)
CH4
0
0
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CO2
5
10
15
Time
(d)
WBL
20
25
CO2,CH4 (μmol cm-3)
15
80
0
56
28
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Ferrolysis
™
™
™
™
™
During flooding..reduction of Fe3+ to Fe2+
Accumulation of Fe2+ displaces base cations from CEC
Drainage of these soils removes base cations during leaching
Oxidation of Fe2+ to Fe3+ releases H+ (acid conditions)
H+ saturated clay is unstable..results in high aluminum
concentration
™ Repeated cycles of flooding and draining decreases base
saturation
™ Ferrolysis occurs in surface soil horizons with abundant supply
of bioavailable organic matter to support microbial reduction of
Fe(III) oxides.
Fe3+
FeS + H2O
Flooded
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Drained
Fe (OH)3 + H2SO4
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57
Iron and Manganese
™ Fe forms more stable organic-metal bonds than Mn
™ Stable organic-metal complexes will protect Fe from
precipitation
™ Extent of complexation is greater under anaerobic
conditions
™ Significant amounts of Fe2+ can be present under
aerobic conditions for several days..
y Due to
complexation with organics
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Iron and Manganese
Summary
Reduction of Fe ((III)) and Mn ((IV)) results in:
™ Concentration of water soluble Fe and Mn
increases
™ pH of acid soil increases
™ Cation exchange capacity of soil is occupied by
Fe and Mn
™ Solubility of phosphorus increases
™ Breakdown of OM and nutrient release
™ New minerals are formed
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Iron and Manganese
Summary
O id ti
Oxidation
off Fe
F (II) and
d Mn
M (II) results
lt in:
i
™ Bioavailability of metals decreases
™ Co-Precipitation of other metals
™ pH of soil decreases to acidic conditions
y of p
phosphorus
p
dereases
™ Solubility
™ Oxidized Fe and Mn serves as electron
acceptor upon flooding
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30
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General Chemical
Transformations of Metals
™ Water soluble metals
™ Soluble free ions
ions, e
e.g.,
g Fe2+
™ Soluble as inorganic complexes
™ Soluble as organic complexes
™ Exchangeable metals
™ Metals precipitated as inorganic compounds
™ Metals complexed with large molecular weight humic
materials
™ Metals adsorbed or occluded to precipitated hydrous
oxides
™ Metals precipitated as insoluble sulfides
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http://wetlands.ifas.ufl.edu
http://soils.ifas.ufl.edu
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