Success of Wetland Mitigation Projects in California

Much of the wetland restoration conducted in the United States is required as compensatory mitigation for impacts to natural wetlands, but questions have been raised about the success of these mitigation projects.  We evaluated permit compliance and wetland condition at 129 mitigation projects permitted between 1992 and 2002 throughout California.  Mitigation sites were largely represented by low gradient riverine (46%) and depressional (36%) wetland classes.  On average, projects complied with 73% of the conditions associated with their permits under Section 401 of the Clean Water Act, with 46% of the projects complying fully with all conditions.  Wetland condition was assessed using the California Rapid Assessment Method (CRAM), which consists of 15 different metrics under the general attributes of landscape context, hydrology, physical structure and biotic structure.  Most mitigation sites were not optimally functioning wetlands.  In comparison to 47 reference sites, only 19% of the mitigation files were classified as optimal, with just over half sub-optimal and approximately one-quarter marginal to poor.  Project age was not related to wetland condition except for the very youngest sites.  There was only a weak relationship between permit compliance and wetland condition.  The findings of this study indicate that permittees were, for the most part, complying with their permit conditions, but the ecological condition of the resulting mitigation projects were not optimal.  To improve the success of wetland mitigation, regulatory agencies must improve mitigation performance standards, in particular to encompass the full range of wetland functions and services being impacted in natural wetlands.