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COMPENSATING FOR WETLAND LOSSES UNDER THE CLEAN WATER ACT
and, if possible, quantified, as should the functions of the proposed compensatory mitigation project. Even if the mitigation goal does not seek in-kind replacement of functions, functional assessment provides a foundation for considering the watershed consequences of out-of-kind mitigation. Functional assessment helps determine whether the location and design of a compensation wetland will secure the functions that are emphasized for the watershed.
In practice, mitigation attention often is focused on relatively few of the numerous functions that wetlands can provide—for example, habitat, water-quality improvement, and various hydrological functions (groundwater recharge and floodwater desynchronization). The committee does not believe that a science-based functional assessment should be used to assess or rank all the societal values of a wetland. In some cases, technical assessment and the social values of each function have been merged into one assessment procedure. It is recognized that these functions have human value by the societal, economic, and other services they provide and that the values emphasized should be reflected in the location and design of the compensatory wetland. However, the committee believes there are other points in the process of mitigation planning to consider tradeoff among functions where, based on a systematic functional assessment that evaluates all functions objectively, weighting factors can be introduced into the mitigation planning process to consider the broader perspectives about their relative importance (see Chapter 8 for a discussion of this point).
Complete characterization of a compensatory mitigation site requires an assessment of the level of performance attainable for each wetland function under different site designs. This would include consideration of various natural hydrological, geochemical, and ecological attributes and processes. In addition, functional assessment of prospective compensation sites will help establish the design and the monitoring and assessment procedures for the wetland to be created or restored.
Most wetland scientists argue that science-based, regionally standardized procedures are preferable to best professional judgment in comprehensively evaluating wetland function for both impacted and mitigation sites. As a result, the general absence of a uniform approach to assessing wetlands as multifunctional ecosystems have likely encouraged less complex wetland mitigation designs and rudimentary measures of achieving mitigation goals.
THE FLORISTIC APPROACH
In early wetland mitigation efforts, functional assessment was usually confined to lists or qualitative descriptions. Furthermore, although