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
Biogeochemical Biogeochemical Properties of Wetlands Properties of Wetlands
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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Biogeochemical Biogeochemical Properties of Wetlands Properties of Wetlands
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
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 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
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 and water column
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Accumulation of organic matterPresence of hydrophytic vegetation
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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
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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
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D
-400 3 6 9 1
2
4
SO4-S
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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 and water column
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Accumulation of organic matterPresence of hydrophytic vegetation
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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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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 and water column
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Accumulation of organic matterPresence of hydrophytic vegetation
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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
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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
Biogeochemical Biogeochemical Properties of Wetlands Properties of Wetlands
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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