THE ROLE OF REFERENCE WETLANDS IN FUNCTIONAL ASSESSMENT AND MITIGATION

Compensatory mitigation for damages to wetlands in the United States o ccurs largely without explicit analysis and replacement of wetland fun ctions. We offer an approach to standardize such analyses and strength en the connection between ecological principles and policies for wetla nd resources. By establishing standards from reference wetlands chosen for their high level of sustainable functioning, gains and losses of functions can be quantified for wetlands used in compensatory mitigati on. Advantages of a reference wetland approach include (1) making expl icit the goals of compensatory mitigation through identification of re ference standards from data that typify sustainable conditions in a re gion, (2) providing templates to which restored and created wetlands c an be designed, and (3) establishing a framework whereby a decline in functions resulting from adverse impacts or a recovery of functions fo llowing restoration can be estimated both for a single project and ove r a larger area accumulated over time. To establish reference standard s, conditions inherent to highly functioning sites must be identified for classes of wetlands that share similar geomorphic settings. Ecolog ical functions are then identified, and variables used to model the fu nctions are employed in developing reference standards. Variables rang e from the highest levels of sustainable functioning to the complete a bsence of functions when a wetland ecosystem is displaced. An example given for wet pine flats in the North Carolina coastal plain illustrat es how to determine the loss of a given function for an impacted wetla nd, how to calculate recovery (gains) in function through compensatory mitigation, and how to use the relationships between the two (loss vs . gain in function) to set minimum replacement ratios of restored to i mpacted area. In all cases, data from reference wetlands provide the b enchmarks for making these estimates and for directing restoration or creation of wetlands toward the standards established for the wetland class. Programs to implement the use of reference wetlands require reg ional efforts that build upon the knowledge base of existing wetlands and their functioning.