It is widely recognized that wetlands can provide significant environmental benefits, including assimilation of pollutants, flood water storage, groundwater recharge, carbon sequestration, and fish and wildlife habitat, and that they are threatened with degradation and loss by various stressors including conversion to agriculture and silviculture as well as pressures from encroaching urban and suburban development. Geographically isolated wetlands can provide the same benefits as all wetlands in general and are particularly vulnerable to loss and degradation because they are geographically isolated and have varying amounts of regulatory protection. They may be seasonally or permanently ponded, depending on local conditions. Typically there is a shallow groundwater connection to other wetlands and streams and these wetlands can be sinks for nutrients; thus, alterations (e.g., ditching and drainage, silviculture) can have negative effects on downstream water quality (Amatya et al. 1998). Drainage has impacts on ecological systems, including “direct loss of habitat for wetland-dependent species, significant alteration of biogeochemical and hydrologic cycles, loss of flood storage and water quality functions of wetlands, and elimination of nutrient and sediment sinks and other buffering capacities of wetlands in relation to adjacent upland and riparian ecosystems” (Blann et al. 2009).

The need to increase our understanding of isolated wetland occurrence and ecological benefits is particularly urgent in the context of the rapid development and human migration transforming the coastal areas of North and South Carolina. This study was designed and implemented to meet these needs by (1) developing, testing, and documenting methods that can be used to assess isolated wetland occurrence and ecological significance and (2) applying these methods to characterize isolated wetlands along the North and South Carolina coast.

The Southeast Isolated Wetland Assessment (SEIWA) explored the condition and history of geographically isolated wetlands in an 8-county portion of the coastal plain of North and South Carolina. SEIWA employed a phased approach based on three levels of wetland assessment described by EPA (U.S. EPA, 2006): Level 1, which used geographical information systems (GIS) to identify isolated wetlands in the study area; Level 2, which was a rapid on-the-ground assessment of the type and condition of a random sample of Level 1 sites; and Level 3, detailed field assessments to measure the hydrologic conditions, water quality, and biota (amphibians, macroinvertebrates, and plants) of selected isolated wetland sites.

Overall Project Results Summary

Overall, isolated wetlands in our study area are numerous (estimate of 52,000 isolated wetlands in the 8 counties), relatively small (median size of 0.41 acres; mean size of 0.77 acres), and occupy a small percentage of overall wetlands that are on the landscape (about 2% of the total wetland area). The results of this study show that isolated wetlands can store significant amounts of water, show apparent connectivity through groundwater to downslope streams, seem to be acting as sinks for nutrients, metals, and carbon, and generally range in fair to good ecological condition. Isolated wetlands that are in good condition have relatively intact biological communities as compared to other least-disturbed wetlands of similar type. The wetland survey and assessment methods demonstrated in this research project provide some of the technical tools for advancing such further research, as well as for assessing the conditions of isolated wetlands or similar resources in other area. Finally, the maps of candidate isolated wetlands across the study area can serve as a guide to assist wetland regulators and managers in finding isolated wetlands and determining how they may be impacted by surrounding land use.