1. WETLAND BIOGEOCHEMISTRY

2. BIO GEO CHEMISTRY availability of nutrients (i.e.fertility)
cycling of materials between soil/sediment, water column, and atmosphere
organic inorganic
particulate dissolved gas
mediated by biotic and abiotic factors

3. = sink
= source
= transformer

4. exchanges within the ecosystem
mangrove seagrass
exchange between ecosystems

5. Why is this important for the ecosystem?
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?

6. 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.

7. 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).

8. (WATER TABLE DRAWDOWN)
SOIL OXYGEN POOL IN A WETLAND
AIR ENTRY
(WATER TABLE DRAWDOWN)
CHEMICAL
OXIDATION
DIFFUSION
SOIL O2
DECOMPOSITION
ADVECTION
RESPIRATION
BIOLOGICAL
(AUTOTROPHY,
O2 PUMPING

9. Oxygen is not always totally depleted in a wetland soil
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:
The rate of oxygen transport across the “air”-”surface water” boundary.
The respiring organisms on the soil surface.
O2 production by benthic algae.
Mixing and bioturbation

10. Plants can also serve as conduits for gas exchange between the soil and atmosphere and can effectively oxidize areas of the soil.

11. Oxidized rhizosphere plaque found along roots
indicates presence of oxygen
reddish hue = oxidized iron (Fe3+)
plant is a conduit for gases

12. MACROPHYTE EFFECTS ON REDOX POTENTIAL

13. 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).

14. Redoxymorphic features in a wetland soil are areas of oxidized iron (Fe3+) that usually occur along the length of animal burrows or live roots.

15. Redoximorphic features
Soil Color
Redoximorphic features
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

16. Soil Color Used to identify wetland soils
Identification and delineation
wetlands have low chroma (≤ 2)

17. Munsell Soil Color Hue Value Chroma Munsell Notation Hue Value
Soil Color Chart Pages
Chroma
Hue
Value
Chroma

18. What makes a soil organic?
Composed of organic material:
herbaceous plant material
wood and leaf litter
roots
Processes that control accumulation
Accumulation rates
litterfall
belowground production
aboveground production
Decomposition rates (factors affecting)
Oxygen availability pH
Temperature
Nutrient availability

19. Organic vs. Mineral Wetland Soils
% organic carbon ≈ % organic content / 2

21. RESPIRATION DRIVES REDOX POTENTIAL
Go Kcal/m
-686




22. Microbial competition for electron acceptors

23. Chemical comparison of rivers and the oceans
Influenced by:
Groundwater
Climate
Geomorphology
Stream flow
Ecosystem
Humans

24. SEASONAL VARIABILITY
WINTER
SUMMER

25. GENERALIZED CARBON CYCLE

26. What happens now?

27. Primer on decomposition
Represents a major flux of fixed C and nutrients
Controlled by:
litter quality or nutritional value (nutrient content, lignin content, etc.)
abiotic conditions (temp., pH, moisture)
microbial and faunal communities
Characterized by 3 phases:
leaching
fragmentation
mineralization
fastest in wetlands
depends on fauna
slowest in wetlands

28. DECOMPOSITION

29. exchanges within the ecosystem
mangrove seagrass
exchange between ecosystems

30. Simplified Estuarine Food Web

31. GENERALIZED CARBON CYCLE

32. 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.

33. RESPIRATION DRIVES REDOX POTENTIAL
Go Kcal/m
-686




34. Microbial competition for electron acceptors

35. GENERALIZED CARBON CYCLE

36. 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)

37. THE NITROGEN CYCLE N2 NH4+ NO2- N2O R-NH2 NO RXNs OF THE N CYCLE NO2-
N fixation
nitrification
THE NITROGEN
CYCLE
NH4+
NO2-
N2O
ammonification
assimilation
R-NH2 NO
assimilation
denitrification
RXNs OF THE N CYCLE
NO2-
NO3-

38. exchanges within the ecosystem
mangrove seagrass
exchange between ecosystems

39. THE NITROGEN CYCLE IN DIFFERENT WETLANDS

40. THE SULFUR CYCLE Organic - amino acids 1. cysteine 2. methionine
- enzymes and co-enzymes
Inorganic
sulfate (SO42-)
sulfide (H2S)
sulfur (S)
sulfur dioxide (SO2)
pyrite (FeS2)

41. SULFUR CYCLE simplified
SO4-2
H2S
FeS, FeS2
sulfide oxidation
sulfate reduction
uptake
diffusion
emission
deposition
Surface water input

42. PHOSPHORUS

43. 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

44. PHOSPHORUS…INDIRECTLY INFLUENCED BY REDOX

45. 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

46. SMALL SCALE Root enclosures: exchanges with water column
influence of epibionts
effects of water source/salinity

47. more
SMALL SCALE
Examples

48. LARGE
SCALE

49. Quiz 5
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?
A constructed wetland has an average depth of 20 cm and a surface area of m2. What is the volume of water in the wetland?
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.
What is the wetland’s residence time (in days)?
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).

50. 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.

51. 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.

52. 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?

53. 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?

54. 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?