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.
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:
CASE STUDY - Wetlands of Cape Cod and the Islands, Massachusetts
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)
Resources for Conducting a Desktop Assessment of Wetland Functions