Home 3. Identify Priority Wetlands 3a. Assess Wetland Functions (desktop)

Desktop Assessment of Wetland Function

This step of the WARPT is designed to make a preliminary estimate of wetland functions remotely through a desktop GIS analysis. While field assessments of individual wetlands are necessary to more accurately evaluate wetland functions, a remote sensing approach to estimate wetland function provides a cost-effective way to rapidly identify priority sites for conservation and/or restoration. This screening process can also reduce a large number of wetland sites to a manageable level that can then be assessed in the field.  In this step, hydrogeomorphic descriptors interpreted using GIS are added to wetland inventory data and are then correlated to wetland functions based on best professional judgment of various specialists. For a technical review of wetland functions, see Mitsch and Gosselink (2000).

Assigning functions to wetlands provides some basis for determining which ones have the most value, in terms of the wetland functions and services (Table 3a.1) that are of most importance to the community, or by assigning economic value to wetland functions.  Tiner (2003b) has identified ten major functions provided by wetlands.  Not all wetlands perform all functions nor do they perform all functions equally well. Factors that may affect wetland functions include geographic location, location within a watershed, climatic conditions, quantity and quality of water entering the wetlands, and disturbances or alteration within the wetland or surrounding ecosystem. This information can be useful to guide conservation efforts towards those wetlands providing the functions of interest.  Communities can go one step further and evaluate vulnerability of wetlands to future land use changes and quantify the associated loss of function to help make the case for protecting wetlands through conservation, changes to development codes or comprehensive plans, or adoption of more stringent wetland protection measures.

Table 3a.1.  Wetland Services and Functions

Wetland Services

Wetland Functions Associated with Services

Flood protection

  • Surface water detention
  • Coastal storm surge detention

Recreation

  • Provision of habitat for fish and other aquatic animals
  • Provision of waterfowl and waterbird habitat
  • Provision of other wildlife habitat

Maintain drinking water quality

  • Nutrient transformation
  • Retention of sediments and other particulates

Shoreline property protection

  • Shoreline stabilization
  • Coastal storm surge detention

Maintain baseflow in streams

  • Streamflow maintenance

Wildlife habitat and biodiversity

  • Provision of habitat for fish and other aquatic animals
  • Provision of waterfowl and waterbird habitat
  • Provision of other wildlife habitat
  • Provision of habitat for unique, uncommon, or highly diverse wetland plant communities

Commercial products from wetlands (e.g., peat, timber, cranberries, rice, fish, shellfish)

  • Provision of habitat for fish and other aquatic animals
  • Provision of waterfowl and waterbird habitat
  • Provision of other wildlife habitat
  • Provision of habitat for unique, uncommon, or highly diverse wetland plant communities

Reduce pollutants in streams and stormwater

  • Nutrient transformation
  • Retention of sediments and other particulates

Identifying the specific functions that individual wetlands are providing can offer more regulatory ‘teeth’ to protect wetlands from direct impacts. For example, if certain wetlands are designated as being critical to water quality, then states can use this information to support conditioning or denying permits that would impact these wetlands under CWA Section 401 water quality certification.  Communities can also provide their results to the local Army Corps district office to aid in making CWA Section 404 permitting decisions that require information on wetland functions. This information can be particularly useful in watersheds with very high wetland density where most development approvals require making decisions about which wetland impacts will be allowed. 

The process of estimating wetland functions in a watershed can also be applied to historic wetland data to determine what functions have been lost over time and identify candidate wetland restoration sites based on potential to provide certain functions.

There are two potential options for assigning preliminary functions to wetlands in your community:

  1. Hire the U.S. Fish and Wildlife Service (FWS) or its primary cooperator, Virginia Tech’s Conservation Management Institute, to do it for you. This service generates an historical assessment of pre-settlement wetland types, acreage, functions and general trends; a watershed characterization of current wetland status and functions; and an identification of potential wetland restoration sites.  Costs for these services vary with the type and density of wetlands in a geographic area, the amount of historic loss, the recency of the NWI data, and the availability of digital data sources (e.g., land use/cover and soils). 
  2. Follow the "Watershed-based Preliminary Assessment of Wetland Functions" approach developed by the U.S. FWS.
 

CASE STUDY - Wetlands of Cape Cod and the Islands, Massachusetts

Wetlands in Massachusetts were among the first to be inventoried as part of the National Wetland Inventory (NWI) program based on data from the mid-1970s. However, this original mapping is no longer relevant for most areas due to development and changes within the region. Tiner (2010b) describes the process for updating the NWI for the Cape Cod region as well as the addition of descriptors for landscape position, landform, water flow path, and waterbody type (LLWW).  

Read more...

 

CASE STUDY - Frederick County, Maryland

Frederick County is located in western Maryland and is the largest county in the state (Figure 3a.3). The land use and landscape is quite varied and includes agriculture, large forest tracks, mountains and rolling hills, and urban/suburban development. In recent decades, development has increased significantly as development pressure from the Washington DC and Baltimore, MD metropolitan areas has increased.  Because of this development pressure, it is important for the County to identify wetlands and their functions that are most vulnerable to development.

Two components of the WARPT process were tested in Frederick County, MD.

Step 1. Update Wetland Maps

Step 3a. Assess Wetland Functions (desktop)

Read more...

 

Resources for Conducting a Desktop Assessment of Wetland Functions

Read more...

 
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.