Section 404 wetland mitigation and permit success criteria in Pennsylvania, USA, 1986-1999.

Twenty-three Section 404 permits in central Pennsylvania (covering a wetland age range of 1-14 years) were examined to determine the type of mitigation wetland permitted, how the sites were built, and what success criteria were used for evaluation. Most permits allowed for mitigation out-of-kind, either vegetatively or through hydrogeomorphic class. The mitigation process has resulted in a shift from impacted wetlands dominated by woody species to less vegetated mitigation wetlands, a trend that appears to be occurring nationwide. An estimate of the percent cover of emergent vegetation was the only success criterion specified in the majority of permits. About 60% of the mitigation wetlands were judged as meeting their originally defined success criteria, some after more than 10 years. The permit process appears to have resulted in a net gain of almost 0.05 ha of wetlands per mitigation project. However, due to the replacement of emergent, scrub-shrub, and forested wetlands with open water ponds or uplands, mitigation practices probably led to a net loss of vegetated wetlands.