Transcript Dissolved Organic Matter in Wetland Ecosystems

Institute of Food and Agricultural Sciences (IFAS)
Biogeochemistry of Wetlands
Science and Applications
June 23-26, 2008
Topic: Dissolved Organic Matter
Wetland Biogeochemistry Laboratory
Soil and Water Science Department
University of Florida
Instructor
Todd Z. Osborne
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Biogeochemistry of Wetlands
Science and Applications
Topic: Dissolved Organic Matter
Learning Objectives
Define dissolved organic matter [DOM]/ carbon
 Define terminology / nomenclature
 Explore components and characteristics of DOM
 Explore sources and fate of DOM
 Discuss ecological role of DOM in wetlands
 Case study: DOM in Everglades

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“Transformations of POM/DOM by bacteria and
fungi are fundamental to the structure and
dynamics of energy and nutrient fluxes in aquatic
ecosystems.”
- Robert G.Wetzel
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Organic Matter Fractions
DOM vs. DOC
Coarse Particulate Organic Matter (CPOM)
>1 mm
Fine Particulate Organic Matter (FPOM)
1 mm – 250 um
Ultra Fine Particulate Organic Matter (UPOM)
250 um -0.45 um
Dissolved Organic Matter (DOM)
< 0.45 um
Colloidal Dissolved Organic Matter (CDOM)
0.45 um-0.2 um
Note: historical operational definitions
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Sources of DOM
• Degradation products of primary
production
• Degradation products of Secondary/
tertiary production
• By-products of bacterial / fungal / algal /
plant / animal metabolic activity
• Allochthanous organic matter
• Autochthonous organic matter
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Decay Continuum
Live plant
CO2
CH4
Plant
standing dead
Litter layer
Surface peat
DOM
Buried peat
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“Alphabet Soup”
Proteins and amino acids
Carbohydrates (mono +poly saccharides)
Waxes and lipids
Anthropogenic organics
Humic and fulvic acids
High and low molecular weight
intermediates
And many more………
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Anthropogenic Organics
•
•
•
•
Petroleum products (BTEX, MTBE)
Pesticides (DDT, DDE…..)
Herbicides (2,4D, Atrazine)
Industrial wastes (PCB’s, aromatics)
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Humic and Fulvic Acids
Humic Acids
Fulvic Acids
• Acid insoluble / base
soluble
• High Mol. Weight
• 10k – 150+K Da
• Highly unsaturated /
aromatic
• Imparts color (brown)
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• Acid and base soluble
• Medium to High Mol.
Weights
• 3K-10K Da
• Moderately unsaturated
• Aromatic / aliphatic
• Imparts color (yellow)
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Relative Composition of
Humic and Fulvic Acids
Element
Carbon
Oxygen
Hydrogen
Nitrogen
Sulfur
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Humic Acid
Fulvic Acid
53-59%
32-38%
3-6%
0.8-4%
0.1-1.5%
40-50%
40-50%
4-7%
0.9-3%
0.1-3.6%
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Polyphenol Theory of Humic
Formation
Lignin
Cellulose and other
non-lignin substrates
Phenolic aldehydes and acids
Microbial utilization
and oxidation
Microbial
utilization
Polyphenols
Quinones
Humic Acids
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Fulvic Acids
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Fate of DOM
Biotic vs. Abiotic
Mineralization
Sedimentation
Assimilation
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Photolysis
Export
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Photolysis
• Photo induced oxidation
• Photodegradation,
Photodecomposition, Photolytic
oxidation
• Absorbance of high energy UV light
by chromophores, conjugated
double bonds
• Energy has to go somewhere…….
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Ecological Functions of
DOM
Energy, Energy, Energy
Carbon Storage
Source / sink of essential nutrients N&P
Source / sink of metals and major
cations
Light attenuation
Sorption of xenobiotics
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Energy and the Food Web
• 90-99% DOM consumed by bacteria
and fungi
• Microbial loop
• Heterotrophy, chemo-organotrophy,
photoheterotrophy
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Storage Pools of Carbon
[CO2]
Plant Biomass C
[CH4]
Particulate
Organic C [POC]
Microbial
Biomass C [MBC]
Dissolved
Organic C [DOC]
Up to 95% utilizable carbon in system
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Bacteria and Fungi
• Utilize polymeric substrates by stepwise
enzymatic depolymerization and
hydrolosis
• Utilize photolysis / photodegradation
products of DOM
• 50% growth utilizes DOM of 1K Da size
• Passes energy up trophic levels via
microbial loop
• Very efficient
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Microbial Loop
FISH
DOM
Bacteriavores
Bacteria
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Algae
• Photoheterotrophy aka mixotrophy
• Assimilate DOM during light and dark
conditions (carbon dioxide availability)
• Unlike bacteria, only use small MW
compounds such as acetate, lactate,
ethanol, and pyruvate
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DOM as Source/ Sink for
nutrients and important
cations
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•
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Carbon, nitrogen, phosphorus
Cation exchange
pH buffering
Chelation of trace metals
Sequester toxics (Al & Hg!!)
Bind toxic organics (PAH,PCB)
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DOM and Light Attenuation
• Absorb UV light energy = protection
of sensitive biota
• Attenuate Photosyntheticly Active
Radiation (PAR)
• Decrease benthic or epiphytic algal
primary productivity
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DOM Around the World
Site
DOC mg/l
Everglades, USA
35-40
Hubbard Brook, USA
2-3
Papyrus swamp, Uganda
85-107
Amazon River, Brazil
35-88
Wetland, Nova Scotia
52-68
Billabong, Australia
70-75
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Fate of plant derived DOC
in the Everglades
Species
Potentially
Leachable
Carbon
(A)
Bioavailable
DOC
(C)
Microbial
Biomass
Production
(E)
Microbial
Respiration
(D)
Export
(B)
Eleo
40.2
27.7
5.0
22.7
12.6
Typ
34.3
19.6
8.9
10.7
14.6
Clad
21.5
15.1
5.0
10.1
6.4
Spar
38.4
29.3
3.9
25.5
9.0
Thal
87.4
52.8
19.7
33.1
34.6
Nuph
179
97.9
20.3
77.6
81.6
Nym
220
153
38.3
115
66.3
Pan
48.2
27.2
3.9
23.3
21.0
Tax
105
67.6
8.1
59.6
37.7
Particulate Organic
Matter
1 Kg
Leachable DOC
DOC Pool
Export
B
Bioavailable DOC
C
Respiration
Microbial
Community
Biosynthesis
All units are expressed as g C per kg of source plant biomass
A
D
E
Microbial
Biomass
Osborne et al. unpublished data
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DOM Cycle in Wetlands
UV
CO2
CO2 CH4
Decomposition/leaching
Decomposition/leaching
Litter
Import
Peat
Decomposition
leaching
Microbial
biomass
DOM
HCO3-
Microbial
biomass
DOM
HCO3CH4
Export
Decomposition/leaching
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