Primary purpose
To assess wetland functions when addressing a minimal effect or mitigation request under the 1996 Farm Bill (Federal Agriculture Improvement and Reform Act of 1996) (NRCS 1997). When the models are developed into approved HGM Approach models (e.g., calibrated using reference wetlands), then they may also be used in the 404 Regulatory Program.
Expertise needed
Interdisciplinary team of experts required during development phase. Application phase should be done by an individual(s) who has personal knowledge and field experience with the regional wetland subclass under consideration.
Applicable habitat types
All wetland types in the United States; however, not all assessment models are developed.
Categories assessed
Variety of wetland functions, the list of which depends upon the wetland regional subclass. Includes functions related to hydrologic processes, biogeochemical processes, and habitat. A framework for assessing values may also be included in the NRCS functional assessment manuals to satisfy the requirements of the minimal effects/mitigation procedure (NRCS 1997), but the value assessment procedures are not considered part of the Interim HGM models.
Procedure
There are two main phases to wetland functional assessment: development and application. During the development phase an interdisciplinary team of experts (A-team) develops a guidebook with models for assessing functions of wetlands in a regional subclass. The A-team consists of individuals from NRCS, Corps of Engineers, EPA, US Fish and Wildlife Service, and the State. The application phase consists of applying the models to an actual project following three steps: characterization, assessment, and analysis. The user(s) visits a wetland assessment area (or reviews plans for predicted future conditions) and completes data sheets that (a) identify the individual model variables, (b) list direct or indirect measures of model variables, (c) assign a subindex (scale 0-1.0) to conditions for each variable, and (d) include the equation for calculating the functional capacity index (FCI). The functional capacity units (FCUs) are also calculated for each function and all results are analyzed.
Key Terminology
NOTE: Check definitions/usage of terms in each set of models, because terminology in the Interim HGM models is not consistent (e.g., subindex may be called index). The following terms, except those marked *, follow the HGM Approach.
Functional capacity: the rate or magnitude at which a wetland ecosystem performs a function.
Functional capacity is dictated by characteristics of the wetland ecosystem and the surrounding landscape, and interaction between the two.
Functional capacity index (FCI): an index of the capacity of a wetland to perform a function relative to other wetlands within a regional wetland subclass in a reference domain. An index of 1.0 indicates the wetland performs a function at the highest sustainable functional capacity, the level equivalent to a wetland under reference standard conditions in a reference domain. An index of 0.0 indicates the wetland does not perform the function at a measurable level, and will not recover the capacity to perform the function through natural processes. [Note: Interim HGM models may not be calibrated using reference wetlands].
Contact person
Michael Whited, NRCS Wetland Science Institute, USDA - NAC, East Campus - UNL, Lincoln, NE 68583-0822 phone: (402) 437-5178 ext. 37; fax: (402) 437-5712; e-mail: wetsoil@aol.com
Information also available at Web site: http://159.189.24.10/wetsci.htm
Functional capacity units (FCUs): measure of functional capacity incorporating size of the wetland area (FCU = FCI x size of wetland assessment area)
*Red flag features: preemptive conditions that exist that would automatically not quality for a determination of minimal effects or mitigation.
Reference domain: the geographic area from which reference wetlands are selected. A reference domain may or may not include the entire geographic area in which a regional wetland subclass occurs.
Reference standards: conditions exhibited by a group of reference wetlands that correspond to the highest level of functioning (highest, sustainable level of functioning) across the suite of functions performed by the regional subclass. The highest level of functional capacity is assigned an index value of 1.0 by definition.
Reference wetlands: wetland sites that encompass the variability of a regional wetland subclass in a reference domain. Reference wetlands are used to establish the range of conditions for construction and calibration of functional indices and establish reference standards.
Regional guide book: a report summarizing the characteristics of a specific regional subclass and the assessment models prepared during the development phase.
Variable: an attribute or characteristic of a wetland ecosystem or the surrounding landscape that influences the capacity of a wetland to perform a function.
Wetland functions: the normal activities or actions that occur in wetland ecosystems, or simply, the things that wetlands do.
*Yellow flag features: cautionary conditions that exist that would automatically not quality for a determination of minimal effects. Mitigation may be possible.
Output
Measure of functional capacity of a site relative to wetlands from the same regional wetland subclass.
Estimated time to assess 1 acre site
Total 1-2 hours per wetland assessment area (WAA) (if models are available)
1-2 hours: Characterization (step 1), assessment (step 2), and analysis (step 3).
Total 161-162 hours (if models must be developed)
160 hours [Month of work]: Development phase (prior to steps 1-3).
1-2 hours per WAA: Characterization (step 1), assessment (step 2), and analysis (step 3).
Comparison of habitat types
Can directly compare wetlands within the same regional subclass (e.g., riverine wooded wetlands of Kansas). Cannot directly compare wetlands from different subclasses (e.g., closed depression wetland and upper perennial riverine wetland within same region) or different regions. However, results from assessing different regional subclasses can be used to aid in decisions.
Use as guide to design
Some Interim HGM assessment models can be used as a guide to design. Each model needs to be reviewed to determine its suitability. For example, the models may not be suitable if (a) threshold values for a variable are not validated, (b) a variable measures the presence of fauna (e.g., occurrence of an invertebrate species) which cannot be incorporated into the design, or (c) an upper limit is not set on the opportunity variables (e.g., fetch > 1 mile) which may substantially reduce the functional capacity. If the model is suitable, users can refer to the variables to determine which conditions increase or decrease functional capacity. Functional capacity for the "maintains characteristic plant community" function is increased when the wetland is designed to have >75% canopy cover of herbaceous vegetation (variable VCANOPY). This type of information is also useful because it provides design criteria with explicit measurements (e.g., design wetland with >75% canopy cover).
Related procedures
Interim HGM is based on the HGM Approach (Smith et al. 1995), but differs in the following ways:
• To date, the models have not been calibrated to reference wetlands. Models have been developed based on the literature and best professional judgement. These models are being used to meet the immediate needs of NRCS with regard to addressing minimal effects or mitigation requests. NRCS has agreed to collect data for model verification and validation, and to complete development of regional guidebooks.
• Interim HGM only addresses priority wetland functions.
• HGM Approach does not address values. NRCS documents may include both Interim HGM models and a value assessment procedure (e.g., NRCS 1997, 1998d).
Extent of use/field testing
To date, draft Interim HGM models have been completed for Kansas wooded riverine wetlands (LRRTT 1997), Alaska (NRCS 1997), playa wetlands (NRCS 1998a), southeast coastal states (NRCS 1998b), the prairie pothole region in Eastern South Dakota (NRCS 1998c), Hawaii (NRCS 1998d). Models are under development in other states. The Interim HGM models have been used on minimal effect determinations and Farm Bill related mitigation. The extent of use of these models during the last 2 years is unknown.
Proposed future revisions
Models for individual regional wetland subclasses are being prepared and will continue to be prepared as dictated by the needs and funding. The Draft Interim HGM models will be revised into approved HGM Approach models after they are calibrated using data from reference wetlands. The schedule will be decided by the NRCS state offices in conjunction with other federal and state agencies.
Key References
Whited, M. 1997. The NRCS interim hydrogeomorphic approach to functional assessment: what should it entail? Natural Resources Conservation Service. Web site: http://159.189.24.10/wlinews/editin5a.htm
Lawrence Regional Riparian Technical Team. 1997. Draft interim HGM model for Kansas wooded riverine wetlands. Web site: http://159.189.24.10/wlistates/kansas.htm
Natural Resources Conservation Service (NRCS). 1997. Interim guidance for making wetland minimal effect/mitigation decisions for USDA programs in Alaska (Aug. 1997). Web site: http://159.189.24.10/wlistates/alaska.htm
NRCS. 1998a. Interim functional assessment model for playa wetlands (revised draft 1/22/98). Web site: http://159.189.24.10/wlistates/playas.htm
NRCS. 1998b. Interim functional assessment model for Southeast coastal states. Initial model format by R. Rheinhardt and M. Brinson. Modified and compiled by N.E. Fleming and J.G. Sandifer, Jr. Web site: http://159.189.24.10/wlistates/secoast.htm
NRCS. 1998c. Interim functional assessment model for slope (linear) wetlands of the prairie pothole region in eastern South Dakota (Initial review draft). Web site: http://159.189.24.10/wlistates/sdakota.htm
NRCS. 1998d. Interim Hawaii procedure for determinations of wetland minimal effect (MW). Web site: http://159.189.24.10/wlistates/hawaii.htm
[NOTE: Not all of the Interim HGM models are available through web sites. Please contact the NRCS state offices to check status in individual states.]
Additional references
Smith, R.D., A. Ammann, C. Bartoldus, and M.M. Brinson. 1995. An Approach for Assessing Wetland Functions Using Hydrogeomorphic Classification, Reference Wetlands, and Functional Indices. Wetlands Research Program Technical Report WRP-DE-9. US Army Corps of Engineers, Waterways Experiment Station, Vicksburg, MS. 88 pp.
Brinson, M.M. 1993. A Hydrogeomorphic Classification for Wetlands. Wetlands Research Program Technical Report WRP-DE-4. US Army Corps of Engineers, Waterways Experiment Station, Vicksburg, MS. 79 pp. + Appen.