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Wetland Symposium

A Comparison of Methods for Evaluating Wetland Functions and Values


U.S. Fish and Wildlife Service, Office of Information Transfer, Fort Collins, CO 80525

A major responsibility of many federal and state natural resource, construction, and regulatory agencies is to conduct environmental assessments and determine the impacts of Section 10/404 permits on fish and wildlife resources. Reports are then prepared documenting their findings and recommendations. These reports provide information regarding the nature and magnitude of project-related impacts and recommendations on project alternatives or mitigation measures to minimize adverse effects on fish and wildlife.

Existing methods for evaluating wetland functions and values have been relatively ineffective, primarily because they have proven to be (or are believed to be) difficult to use, are impractical at the field level, or are ineffective from a regulatory perspective. Consequently, they have not been employed by Federal or state biologists to any extent. The objectives of this study are to review the more important techniques for evaluating wetlands and compare and contrast the variables used to measure wetland functions. By examining the similarities between the methods, a conceptual framework for a practical procedure to measure and quantify wetland functions may be developed.

From an impact assessment perspective, an evaluation method should: (1) allow the user to quantify existing or baseline wetland functions, (2) compare between and among wetlands for determining site acquisition or development priorities, (3) predict project-related impacts, (4) develop a mitigation plan to offset unavoidable project impacts, and (5) develop design criteria for wetland creation or restoration.

Many of the current methods are based on generalized techniques developed in the late 1970's and early 1980's that were designed to examine only one major function such as hydrology, wildlife, or recreation. Based on current thinking and agency guidelines, a more holistic or systems approach is needed, as wetland functions are now seen as interrelated and interdependent.

It is generally agreed that wetland functions can be classified into four broad categories: hydrology/water quality, landscape, wildlife/habitat, and recreation/aesthetic. Seventeen methods were reviewed to determine if they addressed each of these major functional categories, the types of variables used to measure the functions, and the similarities between methods, relative to the variables measured.

Fifteen methods included variables related to hydrology/water quality. All methods contained variables related to landscape functions. Twelve methods included variables related to wildlife/habitat and recreation/aesthetic functions. However, several of the methods contained fewer than four variables to measure many of the functions.

More than 300 variables were used within the 17 methods reviewed; however, the number of variables used in common by three or more methods was 69: hydrology/water quality (15), landscape (30), wildlife/habitat (8), and recreation (16). This smaller list, with refinements, may form the basis for a modified method.

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