1. B. Vasilas, UD; L. Vasilas, NRCS; M. Wilson, NRCS
THE HYDROGEOMORPHIC APPROACH TO FUNCTIONAL ASSESSMENT FOR PIEDMONT SLOPE WETLANDS
B. Vasilas, UD; L. Vasilas, NRCS; M. Wilson, NRCS

2. Acknowledgements
Funding provided by EPA, MDE, NRCS, ACOE, and FHA.

3. Outline Introduction to HGM Hydrology of slope wetlands
Model variables

4. HGM Approach
Procedure designed to assess the capacity of a wetland to perform functions.
Functions: biological, chemical, and physical processes (e.g. water storage)

5. HGM Approach Wetland classification Site selection Model development
Identification/selection of functions
Data collection
Generate variables
Calibrate

6. Basic Assumption to HGM
“…the highest, sustainable functional capacity is achieved in wetland ecosystems and landscapes that have not been subject to long-term anthropogenic disturbance.”

7. Reference Wetlands Data collection sites for model development
Represent a range in anthropogenic disturbance

8. Reference Standard Wetlands
Subset of reference wetlands
Exhibit the least anthropogenic disturbance
Represent the highest functional capacity

9. Model Development Variables
Simple variables-presence of a surface flow outlet
Complex variables-water chemistry
Temporal variables-soil Eh

10. “User Friendly” Variables
Visual or easily measured
No temporal restrictions
Correlated to a quantitative measure of an
attribute

11. HGM Approach Function Process Attribute Variable Nutrient cycling
Denitrification
Organic carbon
Leaf litter

12. Hydrologic Characteristics
Hydrologic Source: Groundwater discharge
Toeslope seeps
Sideslope seeps
Hydrodynamics
One directional (downslope)
Low-medium energy

13. Groundwater Driven
High water quality
Uniform inputs
Buffered

14. Hydroperiod Classification
Seasonally saturated
Permanently saturated
Permanently inundated

16. Retention Time
Slope
Surface roughness
Connectivity

17. Piedmont Slope Functions
Provide characteristic wildlife habitat
Carbon export
Temporary water storage
Particulate retention
Removal of pollutants
Nutrient cycling

18. Hydrologic Source Variable
Condition of catchment area
Size
Land use
Disturbance

19. Function: Nutrient Cycling
Process: Microbial transformation
Wetland attributes:
Hydrologic source condition
Organic carbon (energy)
Aerobic/anaerobic fluctuations

20. Function: Nutrient Cycling
Variables:
Carbon (available vs. unavailable)
Soil organic matter
Woody debris
Leaf litter
Herbaceous groundcover (roots)
Aerobic/Anaerobic fluctuations
Hydroperiod (temporal)
Microtopography (spatial)

21. Hydroperiod Variables
Soil
Presence/thickness of O horizons
Color/thickness of A horizons
Depth to redox features
Plants
Species
Strata

22. Summary Piedmont slope wetlands show sig. variability in hydroperiods.
Variability due to position of groundwater discharge sites; as opposed to disturbance.
Variability sig. impacts functional capacity
(esp. nutrient cycling).

24. Function: Temporary Water Storage
Processes: Hydrologic inputs/outputs
Attributes:
Hydrologic source condition
Slope
Surface area
Microtopography
Connectivity

25. Function: Removal of Pollutants
Process: Sequestration
Attributes:
SOM accretion
Plant biomass

26. Function: Removal of Pollutants
Process: Sorption to soil particles
Attributes:
Hydrologic source condition
Retention time
Infiltration
High cation exchange capacity

27. Funtion: Removal of Pollutants
Variable:
Infiltration
Slope
Microtopography
Herbaceous cover
Soil porosity (texture)
CEC
Organic matter content
Clay content (texture)

28. HGM Model Development
Reference domain:
Reference standard sites

29. Functional Assessment
Quantify the functional capacity of individual wetlands.
Functional capacity: the degree to which a function is performed.
Functional capacity is judged relative to a reference standard.

30. Functional Assessment-Why?
Evaluation of wetland quality for Federal mandates
Evaluation of anthropogenic impacts
Evaluation for mitigation purposes (compensation “in kind”)
Site selection for wetland enhancement
Identification of environmentally-sensitive areas

31. Wetland Functions
Definition: biological, chemical, and physical processes that occur in wetlands
Examples
N removal through denitrification
Surface water storage
Soil organic matter accretion

32. Limitations Model development is labor intensive.
Maximum index value limited by “pristine sites”.

33. Strengths Regionalized Specific to a subclass
Attributes easily and quickly measured
Surrounding land use considered

34. Surrounding Land Use Connectivity to other wetlands-wildlife
Agricultural-sediment and nutrient loading
Development-hydrologic inputs

36. HGM Functional Categories
Hydrology
Biogeochemical cycling
Plant community
Wildlife habitat

37. Water Variables
Quantity
Quality
Residence time

38. Function: Carbon Export
Processes:
Organic carbon production
Carbon transport (surface flow)
Attributes:
Carbon production
Carbon transport

39. Function: Carbon Export
Variables:
Carbon production
Woody debris
Leaf litter
Herbaceous cover
Soil organic matter
Carbon transport
Slope
Channelization
Connectivity

40. Function: Particulate Retention
Process: Sedimentation
Physical Attributes:
 water
Retention time = ↓ water velocity
Variables:
Slope
Surface roughness
Microtopography
Herbaceous cover