Incorporating ecological function into a landscape-scale model to prioritize potentially restorable wetland and riparian mitigation locations

Background/Question/Methods

Equivalency in ecological function between destroyed and restored wetlands or riparian areas is an implicit assumption of compensatory mitigation under Section 404 of the Clean Water Act. In practice, the identification of mitigation banks or restoration sites is often most strongly influenced by the happenstance availability of parcels in the real estate market, and is made absent any framework that considers the potential for restoring ecological function. Yet, the ecological function of wetlands and streams is known to vary by landscape location within the watershed, and with associated hydrologic, physiographic and anthropogenic factors. Current restoration efforts may benefit the immediate area and perhaps satisfy “no-net-loss”, but often do not contribute to restoring function within watersheds where wetlands or streams are destroyed. A GIS-based Potential Wetland/Riparian Restoration Model (PWRM) was developed to provide natural resource managers with a spatial framework and information on the location of restorable wetland or riparian sites and their relative, potential contribution to restore ecological functions of water flow, water quality, fish and wildlife habitat, and biodiversity. The PWRM covers the entire state of Georgia which ranks fourth nationally in wetland acreage and where rapid urbanization continues. The PWRM is composed by nine submodels. Three submodels (land cover; hydric soils; jurisdictional protection) were developed to identify potential, restorable wetland or riparian pixels which were then aggregated into restorable patches. Six submodels were developed to classify restorable patches according to functional attributes selected by Georgia and federal natural resource managers (hydrologic connectivity; water quality and quantity index; connectivity to existing conservation lands; terrestrial dispersal corridors between wetland patches; surrounding natural upland vegetation; proximity to high biodiversity streams). In order to remove the influence of ecoregional variation, the values of each functional submodel were rescored and ranked on a scale of one to nine separately for each Level III Ecoregion.

Results/Conclusions

 PWRM results located 2.6 million hectares that have high composite scores for functional attributes, and therefore have highest priority for inclusion in compensatory mitigation banks or in-lieu restoration projects. Eighty-two percent of these hectares were located in the Georgia Coastal Plain. In North Georgia, where urbanization is taking place, less than 500,000 hectares of potentially high-functioning restorable wetlands or riparian areas were located.  PWRM results help direct where to conduct costly site-specific assessment and in-the-field surveys for mitigation planning, and are currently being tested by the USDA Natural Resource Conservation Service to evaluate applications for restoration grants.