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A condition-based approach to assessing functional replacement for wetland mitigation has been developed using a reference wetland data set of natural wetlands that includes data from the major wetland types that span a gradient of human disturbance. From this data set wetland program tools were developed 1) multimetric biological indices (IBIs) and hydrological and biogeochemical indicators; 2) a rapid (conditionbased) wetland assessment tool (Ohio Rapid Assessment Method for Wetlands); and 3) a wetland classification scheme based on landscape position and dominant vegetation that accounts for variability in ecosystem processes (functions) and ecological services (values) of different types of natural wetlands. Ensuring functional replacement occurs in a several step process. First, as part of permit application, the HGM class and dominant plant community of the impacted wetland(s) are determined. This determination accounts for the ecosystem processes (functions) and ecological services (values) of different wetland types without the necessity of developing a comprehensive list of those functions and values. Second, the condition of the impacted wetland is assessed with the rapid condition tool (ORAM v. 5.0) or a wetland IBI providing a measure of "functional capacity." Third, the size of the wetland to be impacted is determined and appropriate mitigation ratios are applied. Fourth, any residual moderate to high functions or values the impacted wetland(s) may still be providing, despite moderate to severe degradation, are evaluated using checklist with a narrative discussion. Finally, requirements for mitigation are specified in the permit. If there is 1) replacement by size of the impacted wetland, 2) replacement of the type of wetland impacted, 3) and replacement of the quality of the impacted wetland as measured by quantitative, condition-based ecological performance targets, then there is very strong assurance that functional replacement is occurring since there was “no net loss” of wetland acreage, a mitigation wetland of same HGM class and dominant plant community was created with functions and ecological services equivalent to the impacted wetland, and a mitigation wetland was created of equivalent “quality” as measured by biological (e.g. IBIs), hydrological, and biogeochemical indicators (and therefore of equivalent functional performance). Fundamentally, the above approach is strongly data-driven and it follows then that meaningful and adequate mitigation monitoring is absolutely necessary to determine whether the mitigation wetland has "succeeded" or "failed." Performance standards, quantitative monitoring, and data analysis techniques were developed for wetland size, basin morphometry, perimeter:area ratio, hydrologic regime, basic vegetation establishment, woody species establishment (successional trends), soil chemistry, and wetland IBIs.


Ohio EPA Technical Report



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