Effectiveness of compensatory wetland mitigation in Massachusetts, USA

This study describes the results of wetland construction projects designed to offset wetland losses authorized under the wetland regulatory program of the Commonwealth of Massachusetts, including analysis of 391 project files identified in the study period between 1983 and 1994 and 114 field sites. Detailed comparisons of replacement plant communities were made with remnant impacted wetlands when these existed. Most projects in the study were relatively small, impacting less than 46.5 m2 (500 ft2) of wetland. The majority of projects (54.4%) were not in compliance with the Massachusetts wetland regulations for a variety of reasons, including no attempt to build the project (21.9%), insufficient size or hydrology (29.8%), or insufficient cover of wetland plants (2.6%). Many of the projects constructed (64.9%) were smaller than required. The majority of constructed projects involved impacts to forested wetlands (71.1%). Most replication projects were designed to produce scrub/shrub systems (61.4%), but projects actually built produced no wetland (38.6%), wet meadows (36.8%), or some other wetland type (24.5%). The plant communities produced at replication sites differed significantly from the wetlands they were designed to replace in terms of number of species, cover, and species composition. The similarity of the replication site plant communities did not increase between projects that were new and projects up to 12-years old, indicating that impacted plant communities may not be replaced at most sites for many years, if at all. The completeness of the replication plan and the Order of Conditions (permit) affected the likelihood that a project complied with the regulations but not the level of similarity between the replicated and impacted plant communities. Larger projects constructed under variances from the Massachusetts Wetland Protection Act were much more carefully designed and were all in compliance with the regulations. However, their plant communities were not similar to those of the impacted wetlands they replaced. Variance projects generally provided replication of water quality and sediment control functions but not of wildlife habitat. The state’s goal of no net wetland loss cannot be met unless the regulatory program succeeds in compensating for all authorized wetland impacts.