biogeochemical properties of wetlands - uf/ifas · 2008-06-22 · biogeochemical properties of...

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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

Biogeochemical Biogeochemical Properties of Wetlands Properties of Wetlands

Wetland Biogeochemistry LaboratorySoil and Water Science Department

6/22/2008 16/22/2008 WBL 1

InstructorK. Ramesh Reddy

Soil and Water Science DepartmentUniversity of Florida


Topic OutlineTopic Outline

DefinitionWetland soilsBiogeochemical features of wetlands

Presence of molecular oxygenSequential reduction of inorganic electron

acceptorsOxidized soil-floodwater interface

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Exchange of dissolved substances between soil and water column

Presence of hydrophytic vegetationTypes of wetland soils

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Learning ObjectivesDefine biogeochemical features of wetlands, specifically

Why anaerobic conditions exist in wetlandsHow microbes use alternate inorganic electron acceptors

to support their metabolic activitiesJuxtaposition of aerobic and anaerobic zonesExchange of dissolved substances between soil and

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Exchange of dissolved substances between soil and water column

Adaptation of wetlands to anaerobic soil conditionsUnderstand the differences among different wetland soils

• "HYDRIC SOILS (WETLAND) ARE THOSE

WETLAND DEFINITIONWETLAND DEFINITION

• HYDRIC SOILS (WETLAND) ARE THOSE IN THEIR NATURAL CONDITIONS ARE SATURATED, FLOODED, OR PONDEDLONG ENOUGH DURING THE CROPPING SEASON TO DEVELOP ANAEROBIC CONDITIONS THAT FAVOR THE GROWTH

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AND REGENERATION OF HYDROPHYTIC VEGETATION.”

– Source: USDA. Natural Resource Conservation Service

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• Wetland contains biologically active soil

WETLAND DEFINITIONWETLAND DEFINITION

• Wetland contains biologically active soil or sediment in which the content of water in or the overlying water column is great enough to inhibit oxygen diffusion into the soil/sediment and stimulate

bi h i l d bi l i l

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anaerobic chemical and biological processes, that help biotic communitiesto adapt to anaerobic conditions.

Main Characteristics of Main Characteristics of WetlandsWetlands

• Wetlands typically lie between terrestrialWetlands typically lie between terrestrial (upland) and aquatic (water) systems.

• Wetlands are seasonally and periodically flooded or have saturated soils for significant periods of time.

• Presence of unique soil characteristics

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• Presence of unique soil characteristics.• Presence of special vegetation adapted

to saturated soil conditions.

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DEEPWATER AQUATIC SYSTEMWETLANDTERRESTRIAL SYSTEM

Wetland EcosytemWetland Ecosytem

Import/Export of nutrients and

species

HydrologyDry

Intermittently to permanently

fl d dPermanently

floodedBiogeochemical Role

ProductivityLow to

Medium

flooded

Generally high,

sometimes low

Source, sink, or

transformer

flooded

Generally low

Sink or transformer

Source, sink, or

transformer

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Wetland FunctionsWetland Functions -Biogeochemical Function

Nutrient/contaminant storage (long-term)Nutrient/contaminant sinksNutrient/contaminant sourceTransformers

Adsorption and precipitationMi bi l b kd f OM

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Microbial breakdown of OMDenitrification Methanogenesis

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Wetland Biogeochemistry

Depending on wetland type hydrologicDepending on wetland type, hydrologic regime, and nutrient/contaminant inputs, wetland can serve as:

SINKSOURCE

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TRANSFORMERS

Drained SoilDrained Soil Flooded SoilFlooded Soil

WETLAND SOIL

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Soil aggregatePore spaces PorewaterPorewater

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WETLAND SOIL

Water

Soil [drained]Soil

Soil

Oxygen

Oxygen Oxygen

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[saturated][saturated]Soil

Flooded Drained

[saturated]

Biogeochemical Biogeochemical Characteristics of WetlandsCharacteristics of Wetlands

Restricted oxygen supplyRestricted oxygen supplyPresence of aerobic soil-floodwater interfaceReduction of alternate electron acceptorsExchange of dissolved species between soil

d t l

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and water columnAccumulation of organic matterPresence of hydrophytic vegetation

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PHOSPHORUS

OXYGEN

Oxygen

Anaerobic-Aerobic Interface

CarbonCarbon

NITROGEN PHOSPHORUS

Water

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SULFUR METALSXENOBIOTICS

Soil

0 2 4 6

Dissolved oxygen (mg L-1)

Anaerobic-Aerobic Interface

0 2 4 6

Water

Soil

0

10

20

th (m

m)

Air

AerobicSoil

-20

-10Dep

t

Anaerobic

Aerobic

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Anaerobic-Aerobic Interface[Flooded Paddy Soil]

High SOM Low SOM

Aerobic Zone

FloodwaterFloodwater

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Anaerobic Zone

Oxidized Soil Profile Reduced Soil Profile

Aerobic and Anaerobic Soils

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Drained SoilDrained Soil Flooded SoilFlooded Soil

Gas Exchange in Soil-Water-Plant System

OO22

OO22

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COCO22CO2, CH4, andother gasesDissloved metals

sulfides, and organic acids


Restricted oxygen supplyRestricted oxygen supplyPresence of aerobic soil-floodwater interfaceReduction of alternate electron acceptorsExchange of dissolved species between soil and water column

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Accumulation of organic matterPresence of hydrophytic vegetation

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OxidationOxidation--ReductionReductionReductant Oxidant + e-

Reductant = Electron donor

Oxidant + e- Reductant

Oxidant = Electron acceptor

[Organic matter, NH4+, Fe2+, Mn2+, S2-, CH4, H2, H2O]

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Oxidant = Electron acceptor

[O2, NO3-, MnO2, Fe(OH)3, SO4

2-, CO2, and some organic compounds]

UPLAND SOILSUPLAND SOILS FLOODED SOILSFLOODED SOILS

OxidationOxidation--ReductionReduction

Reduction

N2 NH4+

Mn2+

Fe2+

S2-

CH

H2O

NO3-

Mn4+

Fe3+

SO42-

CO

O2

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OxidationOxidation CH4

PH3

H2

CO2

PO43-

H2O

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Sequential Reduction of Sequential Reduction of Electron Acceptors Electron Acceptors

Organic Substrate[e- donor]

ratio

n

O2

NO3-

SO42-

Mn2+

Fe2+ S2-

CH4

elat

ive

Con

cent

r

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O2

Oxygen Nitrate Iron Methanogenesis

Sulfate Manganese

Time

Re



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Exchange of Dissolved Solutes

NH3 NO3- SO4

2- Water column

Aerobic

Fe2+NH4+ Mn2+

CH4

NO3-

AnaerobicDRP

Soil column

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10ENR WCA-1

Dep

th (c

m)

(20)

(10)

0October 1990

April 1991

October 1990

April 1991

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Ammonium N (mg/L)(30)

October 1990

0 2 4 6 8 10 1 2 3 4

13

10

Wetland receiving Secondarily Treated Sewage Effluent

(20)

(10)

0

Dep

th (c

m)

Water

Soil

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0 1 2(40)

(30)D

0 1 2 0 1 2 1 20

Nitrate N (mg/L)

Station 1 Station 2 Station 4 Station 6

Sulfate-reducing and Methanogenic Zones in Lake Apopka Marsh Profile

20 W

Dep

th, c

m

-20

0

20

CH4-C

Water

Floc sediment

Peat soil

6/22/2008 WBL 26Porewater concentration, mg/L

D

-400 3 6 9 1

2

4

SO4-S

14



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Detrital Plant Biomass

Organic Matter Accumulation

Detritus

Peat

Decomposition

Burial

Compaction

Aerobic

Anaerobic

Wat

er ta

ble

Dep

thW

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Carbon Accumulation in Wetlands[g C/m2 year][g y ]

Alaska - Sphagnum 11-61Finland - Sphagnum – Carex 20-28Ontario - Sphagnum bog 30-32Georgia - Taxodium 22.5Georgia Taxodium 22.5Florida - Cladium 70-105Florida – Typha 300-400

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Cattail RootsCattail Roots[Typha latifolia]

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Aerenchyma (intercellular air space)

H. Brix [Denmark]6/22/2008 31WBL

Oxidized Root ZoneOxidized Root Zone[Oryza sativa]

Reddish brown color on root surface is due tooxidation of ferrous iron to ferric iron

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Oxidized Root ZoneOxidized Root Zone[Oryza sativa]

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Reddish brown color on root surface is due tooxidation of ferrous iron to ferric iron

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WETLAND SOILS

6/22/2008 WBL 34Wade Hurt6/22/2008 34WBL

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Waterlogged Mineral Soils• Increase in organic matter accumulation in

surface horizonsurface horizon• Mottled zone (gley horizon) with Fe and Mn

accumulation• Permanently reduced zone (Bg or Cg)• Formation of secondary minerals

– Pyrite (Fe S2)

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Pyrite (Fe S2)– Siderite (Fe CO3)– Vivianite (Fe3 (PO4)2 . 8H2O)– Jarosite (K Fe3 (SO4)2 (OH)6)

WELL DRAINED SOIL

Aerobic

Fe3+ Mn4+

Oxidation-Reduction

FLOODED FOR LONG PERIOD

RECENTLY FLOODED

Aerobic

Anaerobic

Mn4+Fe3+Mn2+

Fe2+

Fe3+Mn4+

Anaerobic

Mn2+Fe2+

Fe Mn

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RECENTLY DRAINED

Aerobic

Anaerobic

Mn2+Fe2+Mn2+

Fe2+

Fe3+Mn4+

Wade Hurt

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Organic Soils• Organic matter content (> 12% ofOrganic matter content ( 12% of

total C) in the upper soil profile• Soils formed due to plant litter

accumulation• Soils typically have low bulk

density• Soils have high water holding

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Soils have high water holding capacity

• Cation exchange capacity is saturated with H+ ions

Wade Hurt

Everglades Agricultural Area Soil SubsidenceSoil Subsidence

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Paddy Soils• Mineral and organic soils managed for rice

cultivationcultivation• Plowing and land leveling• Flooded with 5 - 15 cm water• Alternate flooding and draining during

growing season• Soils drained after rice harvest and kept

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• Soils drained after rice harvest and kept fallow for 4-6 months

• Development of hard plow pan

Paddy Field Paddy Field -- IndiaIndia

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Marsh Soils

• Accumulation of plant residues• Accumulation of plant residues• Permanently reduced Bg or Cg horizon• Freshwater marsh• Saltwater marsh

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Wade Hurt

Freshwater Marsh

• Upland marshes (ombrotrophic)• Upland marshes (ombrotrophic)– rainfed, hydrodynamically isolated, some

ground water exchange– pH 3 to 4.5

• Lowland marshes (rheotrophic)

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– receive water and nutrient inputs from adjacent areas

– pH 5 to 6

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Saltwater Marsh

• Neutral pHNeutral pH• Presence of Fe S2• Drained soils have pH < 3.5

– Fe (OH)2 + H2S = FeS + 2H2O (Mackinawite)F S + S2 F S (P it )

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– FeS + S2- = Fe S2 (Pyrite)– Fe S2 + O2 = Fe (OH)3 + H2 SO4– Thiobacillus ferroxidans– Thiobacillus thioxidans


SWetland soils exhibit unique features with aerobic and

anaerobic zonesWetland soils are long-term integrators of elemental storage

and ecosystem processesWetland soils support a range of microbial communities and

associated metabolic pathways

Summary

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Wetland accumulate organic matterWetlands accumulate reduced chemical substances Wetlands are source green house gases including methane

and nitrous oxide

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http://wetlands.ifas.ufl.eduhttp://wetlands.ifas.ufl.eduhttp://soils.ifas.ufl.eduhttp://soils.ifas.ufl.edu

biogeochemical properties of wetlands - uf/ifas · 2008-06-22 · biogeochemical properties of...

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