Transcript NO 2

WETLAND BIOGEOCHEMISTRY
BIO GEO CHEMISTRY
• availability of nutrients (i.e.fertility)
• cycling of materials between soil/sediment,
water column, and atmosphere
a) organic
inorganic
b) particulate
dissolved
gas
• mediated by biotic and abiotic factors
= sink
= source
= transformer
exchanges within the ecosystem
exchange between ecosystems
mangrove
seagrass
What might determine a wetland’s ability to be
a source, sink or transformer of materials?
Why is this important for the ecosystem?
Why might exchanges of materials within a
system (i.e. recycling) be more important than
exchanges between systems?
Redox Potential is a measure of the electron pressure
(availability) in a solution: measured in mV.
Oxidation occurs during the uptake of oxygen or when
a chemical gives up an electron.
Reduction takes place when oxygen is released or an
electron is gained.
Mineralization is the process of decomposition and
transformation of organic matter to forms of inorganic matter.
Immobilization or Fixation is the process in which inorganic
matter is converted to organic matter.
Heterotroph an organism that utilizes organic materials as
a source of energy and nutrients (consumers).
Autotroph an organism that assimilates energy from the sun
or inorganic compounds into biomass (producers).
SOIL OXYGEN POOL IN A WETLAND
AIR ENTRY
(WATER TABLE DRAWDOWN)
CHEMICAL
OXIDATION
DIFFUSION
SOIL O2
DECOMPOSITION
ADVECTION
RESPIRATION
BIOLOGICAL
(AUTOTROPHY,
O2 PUMPING
Oxygen is not always totally
depleted in a wetland soil.
There is often a thin, oxic layer
at the surface. The thickness of
this layer is dependent upon:
1. The rate of oxygen transport
across the “air”-”surface water”
boundary.
2. The respiring organisms on the
soil surface.
3. O2 production by benthic algae.
4. Mixing and bioturbation
Plants can also serve
as conduits for gas
exchange between the
soil and atmosphere
and can effectively
oxidize areas of the
soil.
Oxidized rhizosphere
• plaque found along roots
• indicates presence of oxygen
• reddish hue = oxidized iron (Fe3+)
• plant is a conduit for gases
MACROPHYTE EFFECTS ON REDOX POTENTIAL
Wetland Soils
• Hydric Soils: soils that formed under
conditions of saturation, flooding, or
ponding long enough during the
growing season to develop anaerobic
conditions in the upper part (12
inches or about 30 cm).
Redoxymorphic features in a
wetland soil are areas of oxidized
iron (Fe3+) that usually occur along
the length of animal burrows or live
roots.
Soil Color
• Organic soils are dark black to dark brown.
• Mineral soils range from black, gray, to
greenish- or blue-gray in color.
• Gleization: transformation of non-hydric
mineral soil to hydric mineral soil. Results from
reduction of Fe3+, Mn3+, and Mn4+ to Fe2+, Mn2+,
respectively.
• presence of oxidized rhizosphere
Redoximorphic
features
Soil Color
• Used to identify wetland soils
• Identification and delineation
• wetlands have low chroma (≤ 2)
Munsell Soil Color
Munsell Notation
Hue
Value
Soil Color Chart Pages
Chroma
Hue
Value
Chroma
What makes a soil organic?
•
Composed of organic material:
1. herbaceous plant material
2. wood and leaf litter
3. roots
•
Processes that control accumulation
1. Accumulation rates
• litterfall
• belowground production
• aboveground production
2. Decomposition rates (factors affecting)
• Oxygen availability
• pH
• Temperature
• Nutrient availability
Organic vs. Mineral Wetland Soils
% organic carbon ≈ % organic content / 2
RESPIRATION DRIVES REDOX POTENTIAL
REDUCTION HALF REACTIONS
FOR ORGANIC MATTER OXIDATION
RXN
Go Kcal/m
EH (mV)
O2 + 4e- ----> 2H2O
~ 400
-686
2NO3 + 10e- ----> N2
~ 250

Mn4+ + 2e- ----> Mn2+
~ 225
Fe3+ + e- ----> Fe2+
~ 120
SO42- + 8e- ----> HS-
~ -100
CO2 + 8e- ----> CH4
~ - 300


Microbial competition for electron acceptors
Chemical comparison of rivers and the oceans
Influenced by:
1.
2.
3.
4.
5.
6.
Groundwater
Climate
Geomorphology
Stream flow
Ecosystem
Humans
SEASONAL VARIABILITY
WINTER
SUMMER
GENERALIZED CARBON CYCLE
What happens now?
Primer on decomposition
•
•
Represents a major flux of fixed C and nutrients
Controlled by:
1. litter quality or nutritional value (nutrient
content, lignin content, etc.)
2. abiotic conditions (temp., pH, moisture)
3. microbial and faunal communities
•
Characterized by 3 phases:
fastest in wetlands
1. leaching
2. fragmentation
depends on fauna
3. mineralization
slowest in wetlands
DECOMPOSITION
exchanges within the ecosystem
exchange between ecosystems
mangrove
seagrass
Simplified Estuarine Food Web
GENERALIZED CARBON CYCLE
QUIZ #7
1. Describe a process that contributes to the accumulation of organic matter (i.e.,
peat) in wetland soils?
2. Why are oxidized areas of a wetland soil generally reddish in color?
3. In which wetland type are internal recycling processes most important in
controlling the availability of nutrients?
4. In a newly inundated wetland, what is the first terminal electron acceptor
used in organic matter oxidation?
5. a) List 2 factors/processes that lead to an increase in soil oxygen pools in
wetlands
b) List 2 factors/processes that lead to a decrease in soil [O2].
6. TRUE/FALSE The net flow of O2 into a wetland is greater than the net flow
out of wetland soils.
RESPIRATION DRIVES REDOX POTENTIAL
REDUCTION HALF REACTIONS
FOR ORGANIC MATTER OXIDATION
RXN
Go Kcal/m
EH (mV)
O2 + 4e- ----> 2H2O
~ 400
-686
2NO3 + 10e- ----> N2
~ 250

Mn4+ + 2e- ----> Mn2+
~ 225
Fe3+ + e- ----> Fe2+
~ 120
SO42- + 8e- ----> HS-
~ -100
CO2 + 8e- ----> CH4
~ - 300


Microbial competition for electron acceptors
GENERALIZED CARBON CYCLE
NITROGEN CYCLE…IMPORTANCE OF REDOX BOUNDARY
Organic
• amino acids
• proteins
• nucleic acids
Inorganic
• di-nitrogen (N2; gas)
• ammonia (NH3; volatile)
• ammonium (NH4+)
• nitrite (NO2-)
• nitrate (NO3-)
• nitrous oxide (N2O)
N2
THE NITROGEN
CYCLE
N2O
NH4+
NO2-
NO2-
NO3-
NO
RXNs OF THE N CYCLE
Fate of Oxidised Nitrogen
Origin of Reduced Nitrogen
Assimilatory nitrate reduction
Nitrogen Fixation:
N2 + 3H2of---->
2NH
Kcal
consumption)
3 (160
Reduction
nitrate
after
uptake
by energy
plants, algae,
or bacteria.
Nitrate is reduced to C-NH2 by nitrate reductase enzyme.
This reaction requires a lot of energy expenditure and is only conducted by a
Fate of Reduced Nitrogen
certain
group
of microorganisms. The process is inhibited by oxygen and high
Dissimilatory
nitrate
reduction
ammonium. It is the only pathway for molecular nitrogen from the atmosphere to
Denitrification:
Nitrification:
the biota.
C6H12O
yield)
+ 6 + 4NO3 ----> 6CO2 -+ 6H20 + 2N2 (545
+ Kcal energy
-
NH4 + 3O2 ----> 2NO2 + 2H2O + 4H , NO2 +O2 ----> 2NO3 (66 Kcal energy yield)
Ammonification:
This
a microbially-mediated reaction where the microbes (such as Pseudomonas
+
NH
2NH3as+ the
CO2terminal
; microbes
NH3 + Helectron
NH
(176
Kcal
energy
yield) will use it as an
2 +H
20 ---->
20 ---->
4 + OH
denitrificans)
are
using
nitrate
acceptor
to breakdown
organic
This2-CO-NH
reaction
yields
energy
and
(Nitrosomonas
and
Nitrobacter)
matter.
occurs
when the
productaerobic
is a gas, nitrous
oxide or
energyDenitrification
source with specifically
which to fix
carbon.
It end
requires
conditions
and an
This
is
the
process
by
which
organically-bound
nitrogen
is
released
back
to the
molecular nitrogen. It requires anaerobic conditions and an adequate nitrate source.
adequate
supply
of inorganic
ammonium.
environment
form. using oxygen (686 Kcal energy yield)
Compare nitrogen
energyinyield
to respiration
exchanges within the ecosystem
exchange between ecosystems
mangrove
seagrass
THE NITROGEN CYCLE IN DIFFERENT WETLANDS
THE SULFUR CYCLE
Organic
- amino acids
1. cysteine
2. methionine
- enzymes and coenzymes
Inorganic
sulfate (SO42-)
sulfide (H2S)
sulfur (S)
sulfur dioxide
(SO2)
pyrite (FeS2)
SULFUR CYCLE simplified
SO4-2
H2S
deposition
emission
sulfide oxidation
Surface water
input
diffusion
uptake
diffusion
sulfate reduction
H2S
FeS, FeS2
PHOSPHORUS
Biogeochemical control on
Phosphorus availability
redox-driven example:





In iron-containing soils
Eh > 120 mV = Fe3+
Eh < 120 mV = Fe2+
reddish hue = oxidized iron (Fe3+)
Fe3+ is solid and binds readily
with P (PO43-)
 Fe2+ is soluble no rxn w/ P
PHOSPHORUS…INDIRECTLY INFLUENCED BY REDOX
Biogeochemical control on P-availability
pH-driven example:
 Calcium carbonate soils
 Diurnal DO fluctuations in water column
 In high pH = precipitated Ca-carbonate
 Under low pH = dissolved Ca-carbonate
 Precipitated Ca-carbonate/Aragonite scavenges P
SMALL SCALE
Root enclosures:
exchanges with water column
influence of epibionts
effects of water source/salinity
more
SMALL SCALE
Examples
LARGE
SCALE
Quiz 5
1. What is the renewal rate of a wetland that has a maximum volume
of 25,000 m3 and an inflow rate of 750 m3 day-1?
2. A constructed wetland has an average depth of 20 cm and a
surface area of 15000 m2. What is the volume of water in the
wetland?
3. There is a single channel feeding this wetland and its average
depth is 20 cm, channel width is 15 m, and mean current velocity is
0.10 m second-1. Calculate the discharge of water into the wetland.
4. What is the wetland’s residence time (in days)?
5. T/F Darcy’s Law states that groundwater flow is proportional to
the slope of the piezometric surface (hydraulic gradient) and the
water velocity (m sec-1).
QUIZ #7
1. Describe a process that contributes to the accumulation of organic matter (i.e.,
peat) in wetland soils?
2. Why are oxidized areas of a wetland soil generally reddish in color?
3. In which wetland type are internal recycling processes most important in
controlling the availability of nutrients?
4. In a newly inundated wetland, what is the first terminal electron acceptor
used in organic matter oxidation?
5. a) List 2 factors/processes that lead to an increase in soil oxygen pools in
wetlands
b) List 2 factors/processes that lead to a decrease in soil [O2].
6. TRUE/FALSE The net flow of O2 into a wetland is greater than the net flow
out of wetland soils.
QUIZ #6
• Why do wetland soils go anaerobic when flooded or saturated
for extended periods?
•
What is the regulatory term used for wetland soil?
•
Why are oxidized areas of a wetland soil generally reddish in
color?
•
In which wetland type are internal recycling processes most
important in controlling the availability of nutrients?
•
TRUE/FALSE Mineralization is a process that results in the
transformation from inorganic to organic matter.
QUIZ #6
•
Why is the rate of oxygen depletion accelerated in the warmer
months of the year?
•
After oxygen has been depleted from a wetland soil, what is
the next terminal electron acceptor used for respiration? Why?
•
Why is sulfate reduction more predominant in coastal wetland
soils than in FW wetlands?
•
Why is nitrogen fixation limited by high ammonium
concentrations?
QUIZ #7
•
Describe a process that contributes to the accumulation of
organic matter (i.e., peat) in wetland soils?
•
Describe a process that contributes to the loss of organic matter
in wetland soils?
•
List two abiotic factors that govern the net accumulation
(balance between accumulation and consumption) of organic
matter in wetland soils?
•
Generally, what color are organic soils?
QUIZ #8
•
Besides abiotic factors (e.g., temperature, oxygen availability,
and pH), what factors determine the rate at which a dead plant
will decompose?
•
Which terminal electron acceptor is used by soil microbial
communities after oxygen has been depleted? Why?
•
Why is sulfate reduction more prevalent in coastal wetland
soils than in freshwater wetland soils?
•
TRUE/FALSE: Technically, a mineral soil with high iron can
be entirely reddish in color (indicating presence of Fe3+) and
still be considered a wetland (i.e., hydric) soil?