US Army Corps of Engineers
New England District

Mitigation Study: Success of Corps-Required Wetland Mitigation in New England

The Corps Regulatory Program has long been concerned with the success and effectiveness of compensatory mitigation, but comprehensive studies of this effectiveness have generally not been conducted. In June 2001, the National Academy of Sciences' National Research Council (NRC) issued a report on the effectiveness of mitigation in the Corps of Engineers Regulatory Program. This report, Compensating for Wetland Losses Under the Clean Water Act, identified a variety of weaknesses in the mitigation aspects of the Corps' program. In response to this report and general needs of the Regulatory Program, HQUSACE issued Regulatory Guidance Letter (RGL) 01-1, dealing with mitigation, on 31 October 2001, and RGL 02-2, dealing with the same subject and rescinding RGL 01-1, on 24 December 2002.

Prior to release of the NRC report, the Environmental Resources Section of the Policy Analysis and Technical Support Branch in the Regulatory Division was tasked with developing a study to analyze the effectiveness of compensatory mitigation projects in New England. One focus of the regulatory program in the New England District is to have staff dedicated to mitigation review and monitoring, which has helped with both collection and consistency of data relating to mitigation. This organization has helped track mitigation and made this type of study possible. This study was designed to determine the effectiveness of compensatory mitigation (creation and restoration) for permitted impacts in New England, and to provide a basis for making programmatic improvements as warranted. There are two principal ways of addressing the issue of mitigation success. The first measures success against the permit requirements: does the mitigation meet the standards stated in the permit? The second has generally proven to be more difficult to assess: does the mitigation compensate for the lost functions from the permitted activities? This study addressed both aspects of success.

The methodology proposed for this study underwent review by members of a New England mitigation technical committee, comprised of wetlands scientists from academia, federal, state, and local governments, and the private sector. Their comments and recommendations were incorporated into the study methods. In addition, there was a final review of this study report by the committee. A stratified random selection of 60 mitigation sites was studied in depth in order to determine if the mitigation was successful in terms of meeting the permit objectives and if the level of function approximated that of a natural wetland of the type proposed for creation (or restoration). Mitigation sites for the study were chosen from each of the six New England states, but more sites were selected in states where there were more permitted wetlands impacts requiring compensatory mitigation. Sites also covered the range of time periods from those just recently constructed to those that were several years old.

Mitigation comprised of preservation or enhancement was not included in this study. Each site was visited and a variety of data collected, including wetland delineations, functions assessments, site photographs, species diversity, and site problems. An early finding of the study was that there were not always adequate records and data management, particularly for older projects, making it difficult, and in some cases impossible, to determine what the initial impacts had been, the types, functions and values of the impacted wetlands, and the proposed compensatory mitigation. Improvements in compensatory mitigation and fully replacing functions lost to authorized impacts are first dependent upon adequate and available information. All mitigation site locations must be properly mapped and identified. Information on quality, type, and functions and values of impacted resources must be thorough. Mitigation plans should be retained and tracking of all mitigation project information complete. Several improvements in data management are underway to address these deficiencies, both in data generated (e.g., latitude and longitude for all new sites) and management of that data.

Forty of the mitigation projects (67%) were determined to meet permit conditions and would be considered successful by that standard. However, only ten (17%) were considered to be adequate functional replacements for the impacted wetlands. Information on permit conditions was missing for seven projects 2 (12%) and information on functions and values or types of impacted wetlands was missing for six projects (10%), making it impossible to determine success for those projects. Even where a specific function may have been replaced, it was often at a different or lower level than had been lost. Some of the reasons for this low functional replacement are clearly evident in this study. While 177.69 acres of forested wetland were impacted by the 60 study projects, only 24.74 acres of mitigation were proposed to be forested. Few forested wetlands were proposed as mitigation for a variety of reasons, including focus on only a few functions, fear of failure, difficulty to establish, and non-specific information on impacted functions to be replaced. Of these 24.74 acres, only approximately 17 acres appear to be reasonable precursors to forested wetland. At the same time, there were impacts to 6.81 acres of palustrine open water systems, but 47.41 acres of proposed open water systems as compensatory mitigation. This study found approximately 56 acres of palustrine open water systems as actual mitigation. Since there was considerable out-of-kind mitigation, there were increased losses in the more complex wetland types. The general replacement of forested wetlands with open water and emergent systems has resulted in considerable loss of function, particularly for wildlife habitat and water quality. It should be noted that non-vegetated open water systems do not constitute wetlands as defined by the Corps using the 1987 Corps of Engineers Wetlands Delineation Manual (Environmental Laboratory, 1987) and therefore, are not "special aquatic sites" under the Clean Water Act. So, while these systems are still jurisdictional as waters, their functions are recognized as different from those of wetlands by the Clean Water Act.

The study results further indicate that insufficient compensatory mitigation has been required to offset project impacts on both an acreage and functional basis. With impacts to 352.31 acres of wetlands and proposed compensatory mitigation of 324.12 acres, of which no more than 317.65 acres are wetland, there is an overall net loss in acreage of wetlands. Enhancement and preservation had been part of the mitigation for some of the projects, however, this was not evaluated in this study as these mitigation methods do not replace lost acreage, and only in the case of enhancement or preservation of degraded uplands (which subsequently "heal" and eliminate degradation of adjacent wetlands) may replace some lost functions (preservation does prevent future losses of function, but that was not evaluated for this study). While there is a net loss in wetland function and acreage, over 300 acres of wetlands and waters have been restored or created as part of these mitigation projects and they do provide a variety of functions. The overall net loss of function is much less than the 352.31 impacted acres and on an individual project basis, there were some cases of net functional gain for the project where the impacts had been to highly degraded systems.

Causes of degradation of mitigation site functions resulted from adjacent land uses, improper hydrology, use of cultivars, inadequate maintenance and protective measures, and invasive plant species. All but eight of the study sites had invasive species, most commonly purple loosestrife (Lythrum salicaria) and common reed (Phragmites australis). Finally, development and approval of compensatory mitigation should concentrate on identifying and replacing the functions proposed to be impacted. In order to truly replace lost functions, increased quality or quantity efforts should be considered, especially for forested habitat replacement. This is especially important for mitigating impacts to systems which entail large temporal losses in function, e.g., forested wetlands. These goals are consistent with current movement on mitigation at the national level, as seen in the National Wetlands Mitigation Action Plan and Regulatory Guidance Letter 02-2, both released on 24 December 2002.