THE HYDROGEOMORPHIC APPROACH TO FUNCTIONAL ASSESSMENT FOR PIEDMONT SLOPE WETLANDS

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

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