Compensatory Wetland Mitigation Research Articles

On the road again: A study valuing wildlife crossings for wetland mitigation on State Road 40 in Volusia County, Florida

AbstractOver the past few decades, wildlife crossings have effectively reduced wildlife–vehicle collisions and improved habitat connectivity and genetic exchange for animals. However, wildlife crossings are expensive to construct, and the cost may discourage transportation agencies from implementing new wildlife crossings on public roadways. Additionally, transportation agencies and planners rarely consider the permitting and mitigation costs that wildlife crossings can require. A road profile must be raised to accommodate a wildlife underpass on many Florida roadways, particularly in low‐lying areas. Raising the road can result in new wetland impacts that would not occur but for the wildlife crossing. Consequently, new or more compensatory wetland mitigation may be required to satisfy § 404 of the Clean Water Act—a cost to the transportation agency and taxpayers. We used Florida's Uniform Mitigation Assessment Method (UMAM) to calculate the value of functions in habitats before and after planned wildlife crossings on State Road 40 in Volusia County, Florida. The results of our analysis show that wildlife crossings will enhance the functions in remnant habitats adjacent to the wildlife crossings, generating wetland mitigation credits that reduced the amount of compensatory wetland mitigation required by the U.S. Army Corps of Engineers. Our case study provides a novel application of the UMAM in valuing wildlife crossings. We believe the UMAM can be used in cost–benefit models and transportation planning to determine the functional value of new wildlife crossings, thereby producing a monetary value that can incentivize new wildlife crossing projects.

Wetland compensation and its impacts on β-diversity.

The anthropogenic degradation of natural ecological communities can cause biodiversity loss in the form of biotic homogenization (i.e., reduced β-diversity). Biodiversity offsetting practices, such as compensatory wetland mitigation, may inadvertently cause biotic homogenization if they produce locally homogenous or regionally recurring communities. The fact that compensation wetlands often resemble degraded wetlands suggests that potential impacts to β-diversity are likely. Yet, it is unknown how high-quality, low-quality (degraded), and compensation wetlands compare in terms of β-diversity. We compared the β-diversity of high-quality, low-quality, and compensation wetlands at local and regional scales. β-diversity was quantified as the average distance to group centroids in multivariate space based on pairwise comparisons of community composition. The local spatial structure of β-diversity was assessed using species turnover across plots. Indicator species analysis was used to describe compositional differences potentially contributing to differences in β-diversity. Overall, the β-diversity of compensation sites did not differ from high-quality or low-quality natural wetlands. However, compensation wetlands had a high degree of internal turnover along the hydrological gradient, which culminated in homogenous zones in the wettest areas. Compared to high-quality wetlands, low-quality wetlands had significantly lower β-diversity at local scales, but significantly greater β-diversity at regional scales. Indicator species results showed that compensation wetlands were distinguished by low conservation value species typically found in old fields and waste areas. This analysis also indicated that the invasive grass Phalaris arundinacea was indicative of low-quality and compensation wetlands. This species is likely contributing to differing patterns of β-diversity between high-quality and low-quality wetlands. These results indicate that conclusions regarding β-diversity depend on scale and scope of analysis. Particularly, the unique architecture of compensation wetlands makes conclusions regarding within-site β-diversity dependent on the observer's position along the hydrological gradient. Additionally, while we conclude that compensation wetlands are not contributing to biotic homogenization at the regional scale, these wetlands are distinct from both high-quality and low-quality wetlands in their composition and structure. Therefore, assessments of the overall success of wetland mitigation programs should acknowledge the reality of these differences.

Long-term development of tidal mitigation wetlands in Florida

Monitoring periods for compensatory wetland mitigation projects are relatively short, typically 3 to 5 years. Although forested wetlands may require decades to develop structural characteristics similar to those of natural systems, studies that describe long-term trends in site development are rare. Eighteen mitigation sites in Florida that had originally been sampled in 1988 were re-visited in 2005. Changes in mangrove community composition and stand structure occurring over this timeframe at ten of these sites are described and compared with other mangrove wetlands in Florida. Factors limiting development of the remaining sites are discussed. The continued persistence and development of the majority of these mitigation sites indicates that the mitigation process can be successful, at least in terms of compliance with the typical permit requirements. Basal area and height had increased at most sites, and some were difficult to visually distinguish from adjacent natural stands of mangroves. However, even after 13–25 years, stand structure in mangrove mitigation wetlands in Florida still differed from that of natural sites. Although the number of mangrove species was similar, mitigation sites had lower basal area and height than natural sites, and were more dense and complex than natural sites.

Determinants of Spatial and Temporal Patterns in Compensatory Wetland Mitigation

Development projects that impact wetlands commonly require compensatory mitigation, usually through creation or restoration of wetlands on or off the project site. Over the last decade, federal support has increased for third-party off-site mitigation methods. At the same time, regulators have lowered the minimum impact size that triggers the requirement for compensatory mitigation. Few studies have examined the aggregate impact of individual wetland mitigation projects. No previous study has compared the choice of mitigation method by regulatory agency or development size. We analyze 1058 locally and federally permitted wetland mitigation transactions in the Chicago region between 1993 and 2004. We show that decreasing mitigation thresholds have had striking effects on the methods and spatial distribution of wetland mitigation. In particular, the observed increase in mitigation bank use is driven largely by the needs of the smallest impacts. Conversely, throughout the time period studied, large developments have rarely used mitigation banking, and have been relatively unaffected by changing regulatory focus and banking industry growth. We surmise that small developments lack the scale economies necessary for feasible permittee responsible mitigation. Finally, we compare the rates at which compensation required by both county and federal regulators is performed across major watershed boundaries. We show that local regulations prohibiting cross-county mitigation lead to higher levels of cross- watershed mitigation than federal regulations without cross-county prohibitions. Our data suggest that local control over wetland mitigation may prioritize administrative boundaries over hydrologic function in the matter of selecting compensation sites.

Two Birds With One Stone – The Fairview Church Wetland Mitigation Case Study

Stormwater treatment basins, properly designed, control runoff and reduce sedimentation. Whether they can also be used as wetland mitigation sites has been a topic for debate among natural resource agents, academics, and consultants. Natural resource agencies, when reviewing wetland mitigation plans, often reject designs that include dual use stormwater treatment facilities/wetland mitigation sites for several reasons. First, routine maintenance at stormwater treatment basins usually includes vegetation removal (mowing) and dredging of accumulated sediment, both serious impediments to wetland viability. Second, the basins are meant to capture stormwater runoff, which translates to unpredictable flows and duration of water, and a high potential for capturing nutrients, heavy metals, hydrocarbons, and other pollutants found in runoff. Pollution and an uncertain water table can prevent the establishment of quality habitat. Finally, stormwater treatment basins and wetland mitigation sites are each subject to regulations regarding water quality and quantity, and one set of regulations may conflict with the other. In spite of these obstacles, a dual use stormwater/wetland mitigation site may be the best option available for on-site, in-kind remediation in certain situations. This article presents a situation in which a compensatory wetland mitigation design was successfully incorporated into an active stormwater management facility in York, Pennsylvania. The following includes a discussion of the rationale for selecting the wetland creation site, the significant design constraints, construction issues, and the results of the fi rst post-construction monitoring visit. Wetland mitigation project design, construction, and post-construction monitoring efforts are primarily overseen by two regulatory agencies in Pennsylvania: the U.S. Army Corps of Engineers (USACE) and the Pennsylvania Department of Environmental Protection (PADEP). USACE and PADEP guidelines for mitigation design stipulate that wetland mitigation projects should incorporate function for function replacement in their design. In other words, if a project impacts a mature silver maple forested wetland, a cattail marsh would not be an appropriate replacement, because it would not provide the same ecological functions and values. In this project, the original wetland site was a palustrine emergent marsh associated with an unnamed perennial tributary to Tyler Run. The original wetland was dominated by an herbaceous community of redtop (Agrostis alba L.), soft rush (Juncus effusus L.), and New York Ironweed (Vernonia noveboracensis (L.) Michx). The wetland site offered minimal riparian stabilization, terrestrial/semi-aquatic habitat, and floodflow attenuation functions as it was subjected to periodic mowing by local township personnel to remove the “weeds” along the stream banks. Water was supplied to the wetland from shallow groundwater sources, flood flows from the unnamed tributary flowing through the center of the site, direct precipitation, and overland flows from the surrounding agricultural, commercial, and residential areas. The upper seventeen inches of the soil profile were characterized by distinct silty clay A and B soil horizons, with B horizon soils showing clear hydric soil coloration (10YR 4/1).

Wetland ecological and compliance assessments in the San Francisco Bay Region, California, USA

The San Francisco Bay Region of the California Regional Water Quality Control Board (SFB CRWQCB) and the San Francisco District of the US Army Corps of Engineers (US ACOE) are looking for an expeditious means to determine whether regulated wetland projects produce ecologically valuable systems and remain in compliance with their permits (i.e. fulfill their legal requirements) until project completion. A study was therefore undertaken in which 20 compensatory wetland mitigation projects in the San Francisco Bay Region were reviewed and assessed for both permit compliance and habitat function, and this was done using a rapid assessment method adapted for this purpose. Thus, in addition to determining compliance and function, a further goal of this study was to test the efficacy of the assessment method, which, if useful, could be applied not only to mitigation projects, but also to restoration projects and natural wetland systems. Survey results suggest that most projects permitted 5 or more years ago are in compliance with their permit conditions and are realizing their intended habitat functions. The larger restoration sites or those situated between existing wetland sites tend to be more successful and offer more benefits to wildlife than the smaller isolated ones. These results are consistent with regulatory experience suggesting that economies of scale could be realized both with (1) large scale regional wetland restoration sites, through which efforts are combined to control invasive species and share costs, and (2) coordinated efforts by regulatory agencies to track project information and to monitor the increasing number and size of mitigation and restoration sites. In regard to the assessment methods, we find that their value lies in providing a consistent protocol for evaluations, but that the ultimate assessment will rely heavily on professional judgment, regulatory experience, and the garnering of pre-assessment information.

Public Preferences for Compensatory Mitigation of Salt Marsh Losses: a Contingent Choice of Alternatives

Abstract: Human activities continue to eliminate or degrade wetlands that provide rich habitat for many species. Compensatory mitigation, including creation of new wetlands, restoration of previously degraded wetlands, or preservation of existing wetlands, is one policy option that seeks to maintain no net loss of wetland habitat. Public support of wetland mitigation is essential because the public incurs the cost for many mitigation projects in the form of higher taxes. Therefore, public preferences should be considered when decisions are made about wetland mitigation options. We used a contingent‐choice survey in Rhode Island to identify factors affecting public support for different types of compensatory wetland mitigation. Results were based on 640 survey responses. The amount of wetland lost during the original development project had no significant effect on the preferred mitigation alternative. Preferences for preservation, restoration, and no‐action alternatives varied according to respondents' gender, education, and income. Certain general considerations applied, however, regardless of mitigation type. Respondents were willing to incur increases in taxes and fees for most mitigation projects. The larger the mitigation project and the lower the cost, the more likely it was to gain public support. The presence of endangered species contributed to public support, but less significantly than public access. Public access can be critical to public support, particularly if the size of the wetland is small or the cost is high. If the cost of providing public access, such as a boardwalk or viewing tower, is relatively small, the gain in public support for mitigation expenditures may well allow a substantial expansion of the area involved in mitigation projects and thus a greater increase in the amount of habitat conservation.

Characterization of wetland mitigation projects in Tennessee, USA

We characterized wetland mitigation projects at 50 randomly selected sites across Tennessee, USA. Mitigation in the form of creation, restoration, enhancement, and preservation was used to replace the 38 ha of jurisdictional wetlands destroyed. Over 104 ha of compensatory wetland mitigation were proposed for this loss; however, only 77.7 ha were present when each of the sites was delineated. A large percentage of the mitigation area (61%) was in the form of preservation and enhancement of existing wetlands. The majority of sites (72%) contained less area than was stipulated in the permit. Poor design resulting in improper hydrology and poor survival of planted stock was likely the primary cause of this reduced area. Wetland mitigation efforts in Tennessee likely could be improved if greater emphasis was placed on design of the project, especially with regard to the hydrology of the site.

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.

Validity of Performance Criteria and a Tentative Model for Regulatory Use in Compensatory Wetland Mitigation Permitting.

/ Wetland policy in the United States is guided by the goal of no net loss of wetland habitat and is enforced primarily through the permitting requirements instituted under the Clean Water Act, which regulates the waters of the United States. Under these regulations, a permit applicant may be required to provide compensatory mitigation or restoration when wetland loss cannot be avoided or minimized. The practice has been to measure gains and losses primarily in terms of functions and values, the assessment of whichhas been rendered difficult because the agencies operate under limitations of time and experience, and because there are large areas of uncertainty in wetland science itself.The purpose of this paper is to develop the principles for a manageable and practical set of performance criteria that will reasonably assure no net loss in a situation in which it cannot be absolutely assured. To this end, the performance criteria proposed for 116 compensatory wetland projects on file with the Army Corps of Engineers in San Francisco, between 1988 and 1995, were examined. The trends discerned in the project proposals were analyzed and evaluated in light of the current state of wetland science. Specific suggestions for the development of uniform criteria in each of four major wetland types-riparian, perennial tidal, perennial nontidal, and seasonal-are discussed, and a system of regulation tying qualitative assessment with quantitative requirements is outlined as a reasonable solution to the enforcement of the no-net-loss policy.KEY WORDS: Wetlands; Compensatory mitigation projects; 404 permits; Clean Water Act; Performance criteria, San Francisco, Californiahttp://link.springer-ny.com/link/service/journals/00267/bibs/24n3p327.html

Using Stable Isotopes of Water and Strontium to Investigate the Hydrology of a Natural and a Constructed Wetland

AbstractWetlands cannot exist without water, but wetland hydrology is difficult to characterize. As a result, compensatory wetland mitigation often only assumes the proper hydrology has been created. In this study, water sources and mass transfer processes in a natural and constructed wetland complex were investigated using isotopes of water and strontium. Water isotope profiles in the saturated zone revealed that the natural wetland and one site in the constructed wetland were primarily fed by ground water; profiles in another constructed wetland site showed recent rain was the predominant source of water in the root zone. Water isotopes in the capillary fringe indicated that the residence time for rain is less in the natural wetland than in the constructed wetland, thus transpiration (an important water sink) was greater in the natural wetland. Strontium isotopes showed a systematic difference between the natural and constructed wetlands that we attribute to the presence or absence of peat. In the peat‐rich natural wetland, δ87Sr in the pore water increased along the flowline due to preferential weathering of minerals containing radiogenic Sr in response to elevated Fe concentrations in the water. In the constructed wetland, where peat thickness was thin and Fe concentrations in water were negligible, δ87Sr did not increase along the flowline. The source of the peat (on‐site or off‐site derived) applied in the constructed wetland controlled the δ87Sr at the top of the profile, but the effects were restricted by strong cation exchange in the underlying fluvial sediments. Based on the results of this study, neither constructed wetland site duplicated the water source and weathering environment of the adjoining natural wetland. Moreover, stable isotopes were shown to be effective tools for investigating wetlands and gaining insight not easily obtained using non‐isotopic techniques. These tools have potential widespread application to wetlands that have distinct isotopic endmember sources.

A method to investigate wetland mitigation banking for Saipan, Commonwealth of the Northern Mariana Islands

The Commonwealth of the Northern Mariana Islands (CNMI) government is considering developing a wetlands mitigation bank on the island of Saipan. The goals of developing the bank are to maximize cost effectiveness of compensatory wetland mitigation, streamline the wetland regulatory framework, and minimize environmental impacts from compensatory wetland mitigation. This article describes the method being employed by the Joint Federal/CNMI Environmental Working Group (Group) to make a recommendation to Governor Froilan C. Tenorio concerning whether the CNMI should establish a Saipan wetland mitigation bank. The Group's method has three components: (1) considering alternative methods to streamline the wetland regulatory framework and enhance the protection of wetlands that may be more suitable to the Saipan context than a wetland mitigation bank; (2) conducting a cost-benefit analysis of potential environmental, economic, and regulatory outcomes of using a mitigation bank; and, (3) analysing regulatory, economic, and ecological risks associated with establishing and using a Saipan bank. A description of the CNMI's wetland resources and the wetland regulatory framework justifies the method being employed by the Group. Federal and CNMI regulators of Saipan's wetlands currently do not possess the technical ability to ensure that there is no net loss of all wetland functions, but are managing Saipan's wetlands solely based on concerns with impacts to bird habitat. Thus, the siting and design of a Saipan bank would currently only be based on managing wetlands according to habitat concerns, and use of the bank would not necessarily prevent a net loss of wetland quality. The Group recognizes the need for a wetland assessment method that can account for the full suite of CNMI wetland functions in order for a Saipan bank to fulfill the Federal mandate for no net loss of wetland quality or quantity. The CNMI's tropical freshwater wetland ecology and level of technical expertise in wetland science require a specific bank design, monitoring and maintenance activities, and enabling instrument in order to be successful in the CNMI context. Fortunately, Federal guidance on the establishment, use, and administration of wetland mitigation banks is flexible enough to enable the CNMI to establish a Saipan bank that fits their unique environmental and social context. Federal guidance appears to unconditionally encourage the establishment and use of banks. However, a wetland mitigation bank may not be appropriate for the local environmental, regulatory, and economic context of a specific city or island. Banking is not a definite panacea to streamline the wetland regulatory framework and enhance wetland protection, and can just as likely worsen problems as remedy them depending on the local context. It is therefore important to investigate economic, regulatory, and environmental risks, costs, and benefits, and to consider all available methods to improve wetlands management as described in this article. This article is a working paper of the Joint Federal/CNMI Environmental Working Group.