Home 3. Identify Priority Wetlands 3c. Assess Wetland Functions (field)

Field Assessments of Wetland Function

The watershed-based preliminary assessment of wetland functions is a useful tool to predict the likely functions of individual wetlands. However, it is not intended to replace field-based assessments, which are necessary to verify actual functions and can also evaluate factors such as wetland condition, boundaries and potential stressors. Communities can conduct field assessments of wetland function and use the results to refine their initial prioritization of wetlands for conservation/restoration in their watersheds. 

Note that in the context of the WARPT, wetland functional assessments are only recommended for mapped wetlands that have been assigned preliminary functions.  Sites designated as ‘potential wetlands’ will require field confirmation of wetland presence (e.g., delineation of boundaries), which must be done prior to conducting functional assessments.  Both wetland confirmation and functional assessments can be conducted during the same field assessment, but it is important to consider when budgeting time and resources.

Determine the Scope of Wetlands to Assess

Detailed and accurate wetland functional assessments are usually expensive and require multi-disciplinary expertise.  Therefore, choices must be made in terms of the geographic range and number of wetlands assessed, types of information gathered, and the scales and degrees of accuracy.  Some potential options for determining the scope of wetlands to assess in the field are listed below:

  • Conduct a brief field visit of all wetlands identified as priority conservation sites and also to confirm the presence of the wetland, if this has not already been done in a previous step.  This “Simple Approach” can be used to conduct a preliminary assessment of wetland functions and help to narrow down the list of wetlands for which to conduct functional assessments in the future.  It can also help to screen out any sites that have recently been developed or otherwise altered.  While this simple approach can glean valuable information if conducted by trained professionals, it is important to understand that it does NOT replace a more formal functional assessment using an accepted methodology (see below).  However, it may be a less time-consuming and valuable exercise for certain mapping efforts (see Table 3c.1).  This step does not include field delineation of wetland boundaries and is primarily a quick check to identify sites where there is obviously no wetland present.
  • Conduct functional assessments for all wetlands identified as priority conservation sites.  This option is most expensive, but may be doable for a community with few remaining wetlands.
  • Conduct functional assessments for a subset of wetlands identified as priority conservation sites.  For example, survey the top 20 to 30 sites of a particular wetland type, or the top sites located in a priority subwatershed.  Set a schedule for continuing the assessment process each year.
  • Coordinate wetland functional assessments with the Section 404 permit program. Functional assessments are encouraged under this program for all proposed impacts to wetlands, and this approach shifts the burden onto the developer. However, identifying wetland functions at this late stage is less likely to result in any significant protection for the wetland in question.

Select a Wetland Functional Assessment Protocol

Field-based wetland functional assessments of individual wetlands are important to verify the preliminary assessment of wetland functions and can also be used to assess condition, establish compensatory mitigation ratios, evaluate restoration potential, or to design appropriate restoration projects. Many (perhaps several hundred) different wetland assessment methodologies exist across the country.  Most protocols are designed to be conducted by trained environmental consultants and/or wetland ecologists due to the complexity of wetland ecosystems. These assessments can be time consuming and are often applicable to specific regions or wetland types.

Table 3c.1 provides some guidance on selecting an appropriate method based on the overall purpose of the wetland mapping or inventory effort.  A “Simple Approach” has also been developed as part of the WARPT. This method is not designed to replace a formal functional assessment, but represents a quick field check for wetland inventories and mapping efforts (non-regulatory) in cases where staff time and budgets are limited.  The “Simple Approach” should still be conducted by trained wetland professionals, as it is simply a structured checklist for professionals to make quick observations in the field.  In some cases, this approach can be used to narrow the list of sites that will require a fuller functional assessment.

Table 3c.1. Guidance for Selecting An Assessment Method Based on Overall Purpose

Purpose of Field Assessment

Guidance on Selecting a Method

General mapping for comprehensive plans, community inventories, or watershed plans.  Purposes that are NOT related to regulatory considerations (e.g., feed into Section 401 or 404 reviews).  Situations where the list of potential wetlands must be narrowed down to limit the number of future functional assessments.

Use “Simple Approach" as part of WARPT OR consult Bartoldus (2000) Step 1b for methods applicable to “inventory or planning”

Purposes that require a more detailed functional assessment, such as for regulatory review, impact analysis, related to possible use as a mitigation site, guide to mitigation or restoration design, prioritizing sites for purchase or protection, or as part of development review.

Review and select an available method from Table 3c.2, select approved method for state or region, OR consult Bartoldus (2000) or other resources listed below to select an appropriate functional assessment method.

Careful consideration should be given to choosing an appropriate method that corresponds to your community's goals. The suitability of the assessment depends on the objectives, geographic area, wetland type, level of detail, availability of applicable models, etc.

No single method for evaluating wetland functions can be widely recommended because no one method is suitable for all assessment situations. Even the USACE does not recognize any one methodology as the best or most acceptable. The suitability of a procedure for a project depends upon the assessment objectives, geographic area, wetland type, desired level of detail, availability of applicable models, and other considerations. Therefore, special consideration should be given to choosing an appropriate method that corresponds to your community’s goals.

Several researchers have compiled and reviewed information on the numerous wetland functional assessment protocols that are available today.  Based on this data and considering the goals of the WARPT, we present a limited number of techniques in Table 3c.2 that appear to be most applicable.  The factors we considered to narrow down the list of protocols included:

  • Considers watershed or landscape-scale functions as opposed to site-specific functions
  • Provides a quantitative scoring system so that wetlands of the same type can be compared to one another
  • Ability to rank each function separately
  • Is ‘rapid’ (this is a relative term), e.g., looks at indicators of function
  • Can be applied to isolated wetlands
  • Also considers condition and/or social values (these can be used in prioritizing sites)
  • Provides good documentation of the protocols to ensure they are applied consistently

 

Table 3c.2. Rapid Field Assessments of Wetland Function (derived from: Bartoldus (2000), Fennessey et al. (2004), and Hatfield et al. (2004)) 

Name

Geographic Applicability and Wetland Types Assessed

Functions Evaluated

Description

Source

Delaware Comprehensive Assessment Procedure

Tidal and non-tidal wetlands in DE

Hydrology, Water Quality, Habitat, Shoreline/Sediment Stabilization

Collects data that can be used to assess the condition of wetlands in relation to minimally disturbed sites. Variables are then combined into functions and an Index of Wetland Condition that provides an overall assessment of the ecological integrity of the site.

Jacobs et. al (2008)

Evaluation for Planned Wetlands

All wetland types nationally

Hydrology, Water Quality, Habitat, Shoreline/Sediment Stabilization

EPW is a simple procedure which documents and highlights differences between wetlands based on their capacity to provide six functions. The differences between wetlands are expressed in terms of individual elements, Functional Capacity Index, and Functional Capacity Units.

Bartoldus et al. (1994)

 

Hollands /

Magee Method

Non-tidal wetlands of the glaciated Northeast and Midwest

Hydrology, Water Quality, Habitat, Shoreline/Sediment Stabilization, Groundwater

Assesses wetland functions in the Section 404 regulatory program as well as other situations. Evaluates 10 wetland functions/values giving each functional indicator a numerical score. Output is a measure of function of a wetland site relative to the functional model mean score and/or scores for other wetlands in a defined area.

Hollands and Magee (1985)

MA Coastal Zone Management Method

Freshwater wetlands and salt marshes in the MA coastal zone

Habitat

Assessment based on 5 landscape indicators and 8 wetland quality indicators (indicators scored 0-6) with separate versions for freshwater wetlands and salt marshes.  Total score calculated from sum of all indicators divided by total points possible. 

Hicks and Carlisle, (1998)

MT Wetland Assessment Method

All wetlands in MT

Hydrology, Water Quality, Habitat, Shoreline/Sediment Stabilization, Groundwater

Regulatory method to evaluate sites where proposed impacts may occur, especially from highway projects.  Evaluates 12 functions and assigns wetlands overall ratings to facilitate avoidance priorities (e.g., based on uniqueness or high value, disturbance and replacement potential)

Berglund (1999)

Guidance for Rating the Values of Wetlands in NC

Non-tidal freshwater wetlands in NC and SC

Hydrology, Water Quality, Habitat, Shoreline/Sediment Stabilization

Designed to rate freshwater wetlands when making decisions regarding 401 Water Quality Certifications. Also provides a tool for evaluating wetland acquisition, restoration, and mitigation banks. Six wetland values are addressed.

NCDENR (1995)

OH Rapid Assessment Method

Freshwater wetlands in OH, may be applicable to throughout the Midwest

Habitat, Hydrology

Used for regulatory and condition assessment purposes. Easy to use and provides overall quality rating based on 6 metrics (presence or absence of disturbance indicators and ecological condition). Used to place wetlands into three management categories.  Method includes some value added measurements. With regard to reference, the user is directed to score the assessment wetland in comparison to wetlands of the same type. While the definition of reference wetlands is simple and not explicit, the method scoring is supported by the IBI data.

Mack (2001)

Penn State Stressor Checklist

Freshwater wetlands in PA

 

Tabulates number of stressors present and accounts for ameliorating effects of buffer.  Weights all stressors the same, but overall score lowered if buffer is impaired (outfalls or encroachment). Requires landscape analysis prior to fieldwork.

Brooks et al. (2002) 

WA State Wetland Rating System (Western)

Freshwater wetlands in western WA

Hydrology, Water Quality, Habitat

Categorizes wetlands into four categories based on their sensitivity to disturbance, their rarity, our ability to replace them, and the functions they provide. The “rating” categories are intended to be used as the basis for developing standards for protecting and managing the wetlands to reduce further loss of their value as a resource.

WA Dept of Ecology, (1993)  

WA State Wetland Rating System (Eastern)

Freshwater wetlands in eastern WA

Hydrology, Water Quality, Habitat

Categorizes wetlands into four categories based on their sensitivity to disturbance, their rarity, our ability to replace them, and the functions they provide. The “rating” categories are intended to be used as the basis for developing standards for protecting and managing the wetlands to reduce further loss of their value as a resource.

WA Dept of Ecology, (1993)  

Wetland Rapid Assessment Procedure

Freshwater wetlands in FL

Hydrology, Water Quality, Habitat

Provides a consistent, timely regulatory tool for evaluating freshwater wetlands that have been created, enhanced, preserved, or restored through FL’s regulatory programs and permit process. Cannot use to compare different wetland types. 

Miller and Gunsalus (1997)

All methods are rapid (1 day or less per site).  All require field visits.  Methods that require development of regional models are not included. Most can evaluate isolated wetlands based on the description of wetland types assessed, but this should be confirmed with the protocol documentation.  Methods with poor documentation were eliminated. All methods result in quantitative scores and, if they evaluate multiple functions, have the ability to generate separate scores for each function.  Methods evaluating social values or biological condition only (e.g., site-specific values) were eliminated. Methods designed solely for mitigation sites were not included.  It is unclear from a cursory review of the literature on these methods, whether use of a reference site is required. This should be verified before deciding on a method. Some methods may also have the ability to evaluate condition, restoration potential or social factors but this information was not considered in selection of the methods presented here.  Most assessments require wetland delineation and many of these methods use HGM as the wetland classification system.

Note that just because a method is not included in Table 3c.2 does not mean it should not be used to conduct wetland functional assessments.  Communities conducting this step of the WARPT should carefully consider their specific objectives related to field assessments of wetlands and use the additional following tools to select an appropriate procedure.

  • Some states have developed their own wetland assessment protocols and/or have adopted them as part of their regulatory programs.  The Environmental Law Institute’s 50-state study of wetland programs can be used to determine if your state has officially adopted a specific wetland assessment method, keeping in mind that this data may be as old as 2003, so you should double-check it with your state wetlands program.  If your state has a required methodology, you might simply decide to use it for the WARPT, particularly if you intend to coordinate your wetland functional assessments with the state wetland regulatory program.
  • Bartoldus (2000) has developed a selection matrix to assist wetland managers in distinguishing between approximately 40 existing wetland assessments and for choosing an appropriate protocol for use. These protocol descriptions and selection guidance are available on the USACE Ecosystem Management and Restoration Information System website.
  • The Natural Resources Monitoring Partnership provides a searchable database of monitoring protocols
  • The New Jersey Department of Environmental Protection compiled a database of assessment tools for evaluating wetland quality and functions as part of a study to evaluate the utility of these rapid assessment tools.

Once you determine the scope of wetlands to field-assess and select an assessment method, you will need to either train staff in using the method or hire a qualified wetland consultant to evaluate each site using the established protocols. While each protocol is different, some general guidelines should be considered for wetland field assessments:

  • While in the field, take representative photographs of wetland types or land use and use GPS to provide accurate locations for each of the photos. This will allow you to look back at the wetland to help resolve any questions that arise after fieldwork has been conducted.
  • Training among team members conducting the assessment is important to ensure everyone is conducting the assessment in the same manner. This will help to calibrate the results.
  • Send letters out to local residents and businesses to notify them about the assessment and when it will be taking place. Before conducting the assessment, have a list of back-up sites selected in case some landowners refuse permission, or sites are not accessible.

It is also important to keep in mind the difficulties of wetland assessment when determining the method your community will be conducting. These difficulties include:

  • Season – it is difficult to use a single observation of wetland hydrology, plants, and animals to describe or characterize a wetland because vegetation and water regime change throughout the season. Different water conditions and plant species may predominate on the same site, depending on season.
  • Wetland Alteration - most wetlands are altered to some degree and water regimes are changing due to land use and watershed development.

Next Steps

These field assessments should result in a score for each wetland (and possibly an individual score for each function of interest) that represents that wetland’s potential to provide or actual provision of certain functions (the output will vary depending on the method selected). These quantitative scores can be used to update and refine your preliminary assessment of wetland functions and re-rank sites as needed to identify priorities for conservation and restoration.

 

CASE STUDY - Assessment of Wetland Condition: An Example from the Upper Juniata Watershed in Pennsylvania

Wetland condition was evaluated by Wardrop et al. (2007) in the Upper Juniata Watershed in central Pennsylvania using a multi-level approach.  The Upper Juniata watershed is one of the three subwatersheds of the Juniata River, which is the largest tributary to the Susquehanna River.  The watershed is almost 1,000 mi2 in size and contains 1,770 miles of streams, 76% of which are first and second order. Land cover in the watershed is 70% forested, 27% agriculture, and 3% urban. 

Read more...

 

Resources for Conducting a Field Assessment of Wetland Function

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Digitize
The process of converting features on a paper map into digital format using a trace methodology, which results in the creation of a spatial dataset.
Ecotone

A transition area between two adjacent, but different plant communities.

Indirect Wetland Impacts
Impact to wetlands caused by inputs of stormwater and pollutants generated by land development or other activities within the wetland CDA.
Direct Wetland Impacts
Wetland loss or degradation resulting from activities that occur within wetlands, such as dredging, filling and draining.  Activities that cause direct impacts are largely regulated through the federal and state wetland permitting process.
Stormwater Treatment Practices

A structural or non-structural practice designed to temporarily store or treat stormwater runoff in order to mitigate flooding, reduce pollution, and provide other amenities (also called a Best Management Practice – BMP).

Hydrogeomorphic
Factors that influence how wetlands function, including geomorphic setting, water source, and hydrodynamics.
Hydrogeomorphic
Factors that influence how wetlands function, including geomorphic setting, water source, and hydrodynamics.
Sinks
A cell or set of spatially connected cells that cannot be assigned flow direction in a raster elevation dataset. This can occur when all neighboring cells are higher than the processing cell or when two cells flow into one another. Sinks can indicate areas where water is likely to pond, but can also be an error in the dataset.
Facultative Wetland Plants
Species that usually occur in wetlands (approximately 67% - 99% probability), but also occur in non-wetland areas (approximately 1% - 33% probability).
Obligate Wetland Plants
Species that occur almost always in wetlands under natural conditions (greater than 99% probability), but which may also occur rarely in non-wetlands (less than 1% probability).
Interferometric Synthetic Aperture Radar (IFSAR)
A radar technique that uses two or more synthetic aperture radar (SAR) images to generate surface elevation using differences in the phase of waves returning to the satellite or aircraft.
Interferometric Synthetic Aperture Radar (IFSAR)
A radar technique that uses two or more synthetic aperture radar (SAR) images to generate surface elevation using differences in the phase of waves returning to the satellite or aircraft.
Light Detection and Ranging (LiDAR)

A remote sensing technique that measures properties of pulsed laser light reflected from objects to determine their position, velocity, and other information.

Light Detection and Ranging (LiDAR)

A remote sensing technique that measures properties of pulsed laser light reflected from objects to determine their position, velocity, and other information.

Light Detection and Ranging (LiDAR)

A remote sensing technique that measures properties of pulsed laser light reflected from objects to determine their position, velocity, and other information.

Digital Elevation Model (DEM)
A digital file consisting of terrain elevations for ground positions at regularly spaced horizontal intervals.
Digital Elevation Model (DEM)
A digital file consisting of terrain elevations for ground positions at regularly spaced horizontal intervals.
Hyperspectral Data

Information collected and processed from across the electromagnetic spectrum. Spectral signatures (unique “fingerprint” left by specific objects) enable identification of materials that make up a scanned object.

Remote Sensing
Gathering and recording information about objects without actual contact through the use of such techniques as photography, infra-red imagery, and radar.
Hydrophytes
A plant that grows wholly or partially submerged in water.
Blackspots
Areas on aerial photos that show up as dark blue, dark grey, or black and are indicative of saturated soil conditions.
Stereoscopic
The ability to see three dimensionally by using two views of a single object from slightly different positions typically through the use of an optical aid known as a stereoscope.
Hydric Soils
Soils that are saturated, flooded, or ponded for a long enough period during the growing season to develop anaerobic conditions in the upper soil horizons.
Hydric Soils
Soils that are saturated, flooded, or ponded for a long enough period during the growing season to develop anaerobic conditions in the upper soil horizons.
Hydric Soils
Soils that are saturated, flooded, or ponded for a long enough period during the growing season to develop anaerobic conditions in the upper soil horizons.
Hydric Soils
Soils that are saturated, flooded, or ponded for a long enough period during the growing season to develop anaerobic conditions in the upper soil horizons.
Hydric Soils
Soils that are saturated, flooded, or ponded for a long enough period during the growing season to develop anaerobic conditions in the upper soil horizons.
Hydric Soils
Soils that are saturated, flooded, or ponded for a long enough period during the growing season to develop anaerobic conditions in the upper soil horizons.
Hydric Soils
Soils that are saturated, flooded, or ponded for a long enough period during the growing season to develop anaerobic conditions in the upper soil horizons.
Hydric Soils
Soils that are saturated, flooded, or ponded for a long enough period during the growing season to develop anaerobic conditions in the upper soil horizons.
Geographic Information Systems (GIS)

A system that integrates hardware, software, and data for capturing, managing, analyzing, and displaying all forms of geographically referenced information.

Geographic Information Systems (GIS)

A system that integrates hardware, software, and data for capturing, managing, analyzing, and displaying all forms of geographically referenced information.

Digitize
The process of converting features on a paper map into digital format using a trace methodology, which results in the creation of a spatial dataset.
Minimum Mapping Unit

The minimum size or dimensions for features to be mapped as lines or areas for a given map scale.