1. Wetland Ecology and Dynamics
Prof. Dr. Paul J. DuBowy
Ecohydrology Associates, LLC
Lovell, Wyoming USA

2. Outline Hydrology Overview Hydrogeomorphic Approach
Wetland Water Budgets
Hydrogeomorphic Approach
Hydrological Consequences to Wetland Ecosystems
Biogeochemistry/Redox Reactions
Hydric Soils
Vegetation/Plant Indicators
Animal Communities

3. What is a Wetland? Defined on the basis of three characteristics:
presence of water at surface or in root zone (hydrology)
unique soil conditions (hydric soils)
vegetation adapted to wet conditions (hydrophytes)

4. Wetland Hydrology Pn ET
dV/dt Si So T Gi Go

5. USGS Water Supply Paper 2425

6. USGS Water Supply Paper 2425

7. Hydrogeomorphic Approach
Hydrogeomorphic (HGM) classification system (Brinson 1993) developed to assess physical, chemical and biological functions of wetlands
HGM links hydrology and geomorphology with wetland functions in order to provide an index of environmental services that wetlands provide

8. Hydrogeomorphic Approach
HGM based on three principal physical factors that differentiate wetlands:
position of wetland in landscape (geomorphic setting)
water source (hydrology)
flow and fluctuation of water once in the wetland (hydrodynamics)
Taken together, these factors separate wetlands into different functional groups
Wetlands within each group share similar characteristics and, by extension, provide similar functions

9. Examples of Subclasses
HGM
Hydrogeomorphic Class
Dominant Water Source
Dominant Hydrodynamics
Examples of Subclasses
Eastern USA
Western USA and Alaska
Riverine
Overbank flow from channel
Unidirectional, horizontal
Bottomland hardwood forests
Riparian forested wetlands
Depressional
Return flow from groundwater and interflow
Vertical
Prairie pothole marshes
California vernal pools
Slope
Return flow from groundwater
Fens
Avalanche chutes
Mineral soil flats
Precipitation
Wet pine flatwoods
Large playas
Organic soil flats
Peat bogs; portions of Everglades
Peat bogs
Estuarine fringe
Overbank flow from estuary
Bidirectional, horizontal
Chesapeake Bay marshes
San Francisco Bay marshes
Lacustrine fringe
Overbank flow from lake
Great Lakes marshes
Flathead Lake marshes
Brinson et al. 1995

10. Depressional WetlandsPn ET
dV/dt Si So T Gi Go

11. Prairie Potholes

12. Recharge Wetlands Pn ET
dV/dt Si So Gi Go

13. Discharge Wetlands Pn ET
dV/dt Si So Gi Go

15. Vernal Pools

18. Organic Flats HydrologyPn ET
dV/dt Si So Gi Go

19. Quaking Bog

20. Everglades

21. Tropical Peatlands

22. Ecosystem Consequences
Soil Texture
coupled with elevation gradients
Biogeochemistry
hydric soils
Vegetation Responses

23. Geomorphic Features
Backwater deposits of fine sediments deposited between natural levees and along valley walls
Terraces are earlier floodplains that may have been formed by river’s alluvial deposits, but are not connected hydrologically with present river (except during high floods)
Low topographic relief deceptive  elevation change of few centimeters may produce quite different hydrologic conditions, soils, and plant communities

24. Saucier 1974

25. 25 km

27. Biogeochemical Elements
“See Hopkin's Cafe? Mighty good!”
for plant nutrients:
C, H, O, P, K, N, S, Ca, Fe, Mg, (plus Mn)

28. Wetland Redox Reactions
Redox rxns different in wetlands than in lakes/ponds
Wetlands are shallow
no thermocline—no dense cold deoxygenated water
some wetlands dry out—aerobic processes
plants (or algae) can grow on bottom across wetland—aerobic root zone
Anaerobic/aerobic wetland soil interface  leads to reductive/oxidative processes

29. Wetland Redox Reactions 2
Anaerobic environment (saturated soil): reduction processes
e- are donated
O atoms stripped off
H atoms added
Aerobic environment (root zone): oxidative processes

30. Wetland Redox Reactions 3
Oxidation  Reduction
Fe+3  Fe+2
Mn+4  Mn+2
(Fe and Mn important for hydric soil determination)
Organic N  NH3  NH (ammonification; N mineralization)
NO3-  NO2-  NH (nitrification)
NO3-  N2O  N2 (denitrification)

31. Wetland Redox Reactions 4
Oxidation  Reduction
Organic P  SOP  PO4-3  HPO4-2  H2PO4-  insoluble inorganic P (complexes with Ca, Fe, Al; adsorption on clay/organic particles)
CO3-2  HCO3-  CO2 C(H2O) (carbonate system)
(methanogenesis) C(H2O)  CH4
SO4-2  S-2 ( H2S)

32. Wetland Soils
In order to understand wetland soils, we need to know something about:
sediment type/origin
organic material
hydrology/inundation
soil drainage/water flux
biogeochemical redox reactions
soil color

33. Hydric Soils
Defined (USDA-NRCS) as soils that formed under conditions of saturation, flooding, or ponding long enough during growing season to develop anaerobic conditions in upper part of soil (Federal Register, 13 July 1994)

34. Hydric Soil Identification
Soil Color
indirect measure of other soil characteristics
Fe+3  Fe+2; Mn+4  Mn+2
red – unhydrated iron oxide
yellow – iron oxides
brown – iron oxides and organic matter
grey – permanently saturated; reduced iron
easy to measure
Munsell color chart
in temperate climates, dark soils are relatively higher in organic content

37. Hydric Soil Identification 2
Mottling
refers to repetitive color changes that cannot be associated with compositional properties of the soil
mottles are described by quantity, size, contrast, color, and other attributes in that order
redoximorphic features are a type of mottling that is associated with wetness (alternating aerated and saturated conditions)
these gray/brown/red spots are caused principally by migration, depletion or concentration of Fe and Mn within the soil

40. Hydric Soil Identification 3
Gleying
condition that develops when soil is wet for most of the year
soil matrix color is gray or bluish gray due to transformation of iron caused by prolonged reducing conditions
characteristic of very poorly drained soils
Specific soil ID often difficult
palustrine wetlands may be young with flooding/deposition/erosion
floodplain soils can have poorly developed characteristics

42. Vegetation Dynamics
Floodwaters and subsequent groundwater levels determine type and productivity of vegetation in floodplain
Hydroperiod (flooding duration, intensity, timing) limits species composition and influences ecosystem structure and function
import nutrient-rich sediments to floodplain
export organic and inorganic material
timing important  flooding in growing season has greater effect on species survival and ecosystem productivity

43. Vegetation Gradients

44. Riparian Vegetation Zonation
Zone I (open water river corridor)
present day river channel; continuous flooding
Zone II (river swamp forest; deep water alluvial swamps)
have surface water throughout all or most of growing season, but water levels vary seasonally and annually
Zone III (lower hardwood swamp forest; first bottom)
do not stay wet during the entire growing season, nor do they flood every year

45. Vegetation Zonation 2 Zone IV (backwaters or flats; second bottom)
typically has standing water during less than 25% of growing season; many spp. as in zone III, but more diverse
Zone V (upper hardwood swamp)
highest elevations of floodplain; encompass natural levees and terraces as well as very old ridges and dunes
only covered with water for very brief periods during growing season, flood no more than 50% of years within a 100-year cycle, and have a water table which is below soil’s surface

47. Vegetation Dynamics Prairie potholes: fluctuating hydrologic regime
dry marsh  regenerating marsh  degenerating marsh  open water  dry marsh
vegetation composed of pronounced concentric rings
length of time wetland holds water  complexity of zonation (number of zones)
water permanence  species richness
Estuaries: salinity gradients: fresh  salt water
corresponding vegetation gradients

48. Prairie Potholes

49. Connecticut River

50. Salt Marsh Vegetation