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EU13 - Biodiversity of offset habitats compared to the biodiversity of the affected areas.

If forested, freshwater or wetland ecosystem areas must be disturbed during the construction of new facilities, efforts are made to minimize the amount of habitat that is impacted.  Once construction starts, disturbed areas that are of ecological value are replaced through compensatory mitigation.

AEP is required by the Clean Water Act to restore and maintain wetlands or habitat near lakes and rivers that is lost or destroyed due to the construction of new facilities.  In the past, no data were available on the biodiversity of replacement forested or landscape areas, however, the Ohio Environmental Protection Agency (OEPA) conducted a comparison of mitigation and natural wetlands during 1995 (Fennessy and Roehrs 1997).  In this assessment, the mitigation wetlands at the Gavin Plant in Gallia County, OH, were assessed.

The Gavin mitigation wetlands were created in 1993 to replace those that were lost due to the construction of an FGD landfill.  The mitigation area includes 20 acres of constructed wetlands and buffer areas, a nature trail, and wildlife enhancements.  The wetlands were assessed by Ohio EPA during 1995.  Plant community composition, wetland size, basin shape, and soil characteristics were assessed.  Identical measurements were taken at reference wetlands for comparison.

According to the report, “there was not a single case where a wetland impact had occurred and a corresponding mitigation project had not been done” (Fennessy and Roehrs 1997). This is consistent with how AEP mitigates disturbed habitats.  It was also noted in the report that there has been a surplus acreage for every acre of wetland impact.  In other words, there is a net gain of wetland acreage, however, the minimum required mitigation acres are not always achieved.  AEP was required to create 15 acres of wetlands at the Gavin site, while only 7.6 acres were achieved.  It is believed that excess open-water areas have decreased the amount of available wetlands.  At other AEP sites, such as the Conesville site in Coshocton, OH, the required acreages have been successfully created. 

While no significant differences were found in the diversity of wetland plants, there was a decrease in the diversity of native plants associated with the mitigation projects (Fennessy and Roehrs 1997).  The Gavin site had 76% native plant species, while the average percent native species at the natural wetlands was 88%.  In addition, the Gavin site is 50% open water, as compared to an average of 25% open water for the natural sites. 

The mitigation projects are also not yet measuring up to natural sites with respect to flood-water retention, water quality improvement and habitat provision (Fennessy and Roehrs 1997).  For example, at the Gavin site, 60% of soil samples were indicative of hydric soils, while an average of 80% of natural wetland samples indicated hydric or wetland-type soils.  This could be due to the young age of the mitigation wetlands (only 2 to 5 years old) at the time of the study and it was believed that this condition would improve as the wetlands age.

Current stream and wetland mitigation projects will be assessed using recently developed biological indices that will provide better information regarding biodiversity lost versus biodiversity replaced.

Source Information - Fennessy, S. and J. Roehrs.  1997.  A functional assessment of mitigation wetlands in Ohio:  Comparisons with natural systems.  State of Ohio Environmental Protection Agency, Division of Surface Water.  Columbus, OH.

2012