Applying wetland reference data to functional assessment, mitigation, and restoration

This study demonstrates an approach for rapidly collecting quantitative field data on reference wetland sites and using those data to assess functions (ecological processes) in wetlands. We demonstrate the hydrogeomorphic (HGM) assessment procedure by identifying ecological functions performed by mineral soil wet flats, obtaining quantitative field data from 19 wet Bats (reference sites) in southeastern North Carolina, and modeling wetland functions using variables derived from those field data. We chose a subset of the 19 reference sites to demonstrate how HGM assessment can be used to measure ecosystem functions before and after a project site is altered and the degree to which ecosystem restoration can compensate for a reduction in functions caused by a project's impact. We also illustrate how HGM assessment can be used to determine the minimum area over which restoration should be applied to achieve a no-net-loss in function objective. This minimum area can be determined by dividing the degree to which a function is reduced through project alteration by the degree to which a function is increased through restoration. The ratio of wetland area restored to wetland area altered by a project impact (compensatory mitigation ratio) varies among functions and is influenced by (1) the magnitude to which any given function occurs at a project site both before and after the site is altered, (2) the magnitude to which any given function occurs at a compensatory mitigation site both before and after restoration is applied, and (3) the rate at which any given function is restored.