A proposed methodology to determine accuracy of location and extent of geographically isolated wetlands
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Wetlands can provide significant environmental benefits such as assimilation of pollutants, flood water storage, groundwater recharge, and fish and wildlife habitat. Geographically isolated wetlands (IWs) can provide the same benefits as other wetlands, but are particularly vulnerable to losses from urbanization and agriculture since they are isolated, often smaller, and not equal to other wetlands in regulatory protection. There is a need for a reliable assessment of the total number and area of IWs. Access to this information can provide the foundation to monitor IW loss, and can assist in understanding the ecological effects of such loss as well as help to address regulatory shortcomings. A probability sampling survey methodology that balances statistical considerations, expert opinion, and operational considerations is discussed for assessing the accuracy of IW maps. A simulation exercise was used to illustrate how the proposed sampling methodology will produce reliable results in map accuracy assessment. A wetland map for the Lockwood Folly River watershed, in Brunswick County, NC, was created using historical and recent data and used as the sampling frame in the simulation exercise. An updated wetland map for the same watershed, showing exact locations of wetlands, was used to provide “ground-truth” observations based on wetland delineations approved by the U.S. Army Corps of Engineers. Survey-based accuracy estimates were calculated by comparing site classification differences obtained by using both the original and updated wetland maps.
KeywordsDesign-based estimates Geodatabases Isolated wetlands Map accuracy Probability sampling design
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