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 methano genesis 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. 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 – 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

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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 Mn2+ +2 FeOOH +3

Fe(OH)3 +3

FePO4 +3

FeS2 +2

FeCO3 +2 Fe2+ +2

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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 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

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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

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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

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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

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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)

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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

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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

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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

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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 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

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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 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.

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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+

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120

100 y Yield g 80

of Aerobic Ener 20

% 0 - 2- O2 NO3 MnO2 Fe(OH)3 SO4 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

- NH4 (oxidized to N2 or NO2 with Mn (IV))

Humic acids (electron shuttles)

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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 i n so ils an d sediments Lovley et al. (1996) Fe(III)-Reducing Bacteria (enzymatic activity)

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Fe (III) Reduction

500 )

1 400 -

300 (mg kg

2+ 200 Fe

100

0 -200 -1000 100 200 300 400 500 Redox Potential (mv) Patrick and Henderson, 1981 SSSAJ 45:35-38

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Mn (IV) Reduction

200

) 160 1 -

120 (mg kg 2+ 80 Mn

0 -200 -1000 100 200 300 400 500 Redox Potential (mV) Patrick and Henderson, 1981 SSSAJ 45:35-38 6/22/2008 WBL 30

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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)

• 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

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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

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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

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Manganese

Electron donor Bacteria

Mn(II) Obligate Lithotrophs

MnCO3 Arthrobacter; Bacillus; Leptothrix; Metallogenium; Flavobacterium; Pseudomonas

Organic complexes of Mn 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 e A: Oxygen 6/22/2008 WBL 36

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Pyrite Oxidation

2+ 2- + FeS2 + 3.5 O2 + H2O = Fe + 2 SO4 + 2 H 2+ + 3+ Fe + 0.25 O2 + H = Fe + 0.5 H2O 3+ + Fe + 3 H2O = Fe(OH)3 (S) + 3 H

3+ 2+ 2- + FeS2 + 14 Fe + 8 H2O = 15 Fe + 2SO4 + 16 H

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 Fluxes- Soil and Water Column

MnOOH [s] Mn(II) MnO2 [s] FeOOH [s] Fe(OH) [s] 3 Fe(II) Fe2O3 [s] Aerobic/Oxic

MnOOH [s] Mn(II) MnO2 [s] (CH2O)n CO2 FeOOH [s] Fe(OH)3 [s] Fe(II) Fe2O3 [s] Anaerobic/Anoxic

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Mobile and Immobile Iron

ce Fe2+ a Aerobic 2 Insoluble Fe 4

6 th below soil surf Anaerobic Dep 8 0 123 % Fe

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Talladega Wetland, North Central AL [E. Roden, 2002]

Amorpp()hous Fe(OH)3 Solid-Phase Fe(()II) (0.5M HCl Extraction) (0.5M HCl Extraction)

-3 -3 Fe(III) (μmol cm ) Fe(II) (μmol cm ) 0 50 100 0 100 200 0 0 2 2

(cm) 4 (cm) 4 6 h 6 Dept

Depth 8 8 10 10

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Lake Apopka Marsh

Soluble P, mg L-1 Dissolved Fe, mg L-1 0 2 4 6 8 0 1 2 3

30 Phosphorus Iron 20 10 Water

pth, cm 0 e Soil D -10 -20

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Stratification of Electron Acceptors –Black Sea Mn (μM) 0 1 23 4 5 S (μM) 0 20 40 60 80 100 Fe (μM) 0 0.1 0.2 0.3 O (μM) 0 100 200 300 - NO3 (μM) 0 2 46810 0 O2

50 - NO3

th (m) Mn

p 100 De Fe2+

150 H2S

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Ecological and Environmental Significance of Oxidation- Reduction of Iron and Manganese

Nutrient regeneration/immobilization Ferromanganese modules Root plaque formation Ferrolysis MthMethane em iss ions

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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, 2004)

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Extractable Iron (Mississippi River Floodplain Soils) 4 ) -1 g 3

us Iron (mg k 1 o

Ferr 0 0152025510 Total Organic Carbon (mg g-1) 6/22/2008 WBL 46

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Organic Matter and Fe and Mn Reduction + - Organic Matter = H + e + CO2 + H2O + - 2+ Fe (OH)3 + 3H3 H + e = Fe + H2O Eh = 1.06 – 0.059 log Fe2+ + 0.177 pH

Fe2+ Mn2+

Organic Matter

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Organic matter decomposition and nutrient release

Electron Donor: (CH2O)106 (NH3)16 (H3PO4)1

Electron Acceptor or Oxidant Molar Ratio Molar Ratio [EA] EA /NH3 EA /H3PO4

O2 6.6 106

- NO3 5.3 85

MnO2 13.3 202

Fe(OH)3 26.5 424

2- SO4 3.3 53

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Phosphorus Release and Retention

+ - FePO4 . 2H2 H2O+2HO + 2 H +e+ e = 2+ - Fe + 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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Iron Reduction capacity Fe minerals decreases with increasing crystalinity

FePO4 >Fe(OH)> Fe (OH)3 >FeOOH>Fe> FeOOH > Fe2O3

Slow Rapid reduction oxidation 3+ 2+ 3+ Fe Fe Fe [FeOH3] Rapid Amorphous [FeOOH] reduction Geothite oxides

Slow Crystallization

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Iron -Phosphorus-Phosphorus Interactions under Anaerobic Soil Conditions

2+ 3- Fe + PO4 FePO4 FeS [Strengite]

fast forming Fe(OH)2-PO4 2- SO4 H2S + FePO4 [Strengite] Fe3(PO4)2 Stable, Slow [Vivianite] forming

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Oxidation –Reduction of IronIron-- Phosphate Minerals

Anaerobic Aerobic

Vivianite [Fast] Kertschemite 2+ 3+ 3- Fe3(PO4)2 8 H2O (hydrated Fe , Fe , PO4 )

Crystallization [Slow] [Fast] [Fast] Am Ferric Phosphate Am Ferric Phosphate Fe (PO ) n H O 3 4 2 2 Fe(PO4) 4 H2O

[Slow] Crystallization

[Slow] Strengite Fe(PO ) 4 H O 6/22/2008 WBL4 2 53

Ferromanganese nodules

Concretions, nodules, or mottles rich in iron and manganese

pelagite of 3 cm

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Root plaque formation

Protection from reduced phytotoxins ItInterf erence with nut tirient upt tkake

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Methane emissions

80 15 ) )

-3 Inhibition of methanogenesis CO 2 -3 60 10 Fe(II) mol cm mol cm μ μ

40 ( 4 5 e(III) ( CH ,

20 2 CH Fe(III) 4 CO Fe(II),F 0 0 0 5 10 15 20 25 Time (d) 6/22/2008 WBL 56

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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.

3+ Fe FeS + H2O Fe (OH)3 + H2SO4 Flooded Drained

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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.. 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 Oxid ati on of F e (II) and Mn (II) resu lts i n: Bioavailability of metals decreases Co-Precipitation of other metals pH of soil decreases to acidic conditions Solubilityyp of phos phorus dereases Oxidized Fe and Mn serves as electron acceptor upon flooding

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General Chemical Transformations of Metals Water soluble metals Soluble free ions, e. 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

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