Assessing the substitutability of mitigation wetlands for natural sites: estimating restoration lag costs of wetland mitigation

Abstract The extent and rate to which mitigation wetlands can replace the functions of natural ones remains uncertain. Further, the economic time lag costs of wetland function restoration and therefore cost-effective and efficient means of wetland mitigation have yet to be adequately addressed. In this study, 16 mitigation wetlands were assessed, comprised of eight low elevation inland freshwater emergent marshes in Ohio and eight high elevation (>2285 m) freshwater emergent marshes in a wetland complex in Colorado, USA. This research identified the ecological substitutability of mitigation inland freshwater marshes for natural ones, estimated economic restoration lag costs to society and addressed least-cost approaches to successful mitigation. Years required to achieve full functional equivalency for both floristics and soils for the Ohio sites under logarithmic growth ranged from 8 to 50 years with a median of 33 years. Years required to achieve floristic functional equivalency for the Colorado sites ranged from 10 to 16 years with a median of 13 years. Restoration lag costs per acre (0.4 ha) in Ohio ranged from $3460 to $49,811 per acre with an average of $16,640 per acre (2000 US$). Lag costs as a percentage of total restoration costs ranged from 5.6% to 52.8% with an average of 25%. Restoration lag costs per acre to achieve full floristic equivalency in Colorado ranged from $22,368 to $31,511 per acre with an average $27,392 per acre. Time lag costs as a percentage of total restoration costs ranged from 44% to 53% with an average of 49%. Findings of this research suggest that society is currently incurring significant wetland restoration costs due to time lags of mitigation sites. Requiring the posting of an interest accruing performance bond can serve to internalize the time lag costs to the permittee and provide an incentive for more cost-effective wetland restoration efforts.