Evaluation of national wetland inventory maps to inventory wetlands in the southern Blue Ridge of Virginia

Abstract

The area of wetlands in the U.S. is being estimated as part of the National Wetlands Inventory (NWI). Minimal information is available to verify the effectiveness of NWI maps to inventory wetlands or delineate jurisdictional wetlands. We evaluated the use of NWI maps (1∶24,000 scale) to inventory and delineate jurisdictional wetlands in the Virginia Blue Ridge. Each wetland identified in the Woolwine and Meadows of Dan NWI maps was field-checked to determine if the areas met the criteria as a jurisdictional wetland. Of the 171 palustrine wetlands identified, 91% met the criteria. Jurisdictional wetlands were delineated in four 2.5-minute study areas. Two study areas, located in the Blue Ridge Highlands region, contain 91.8 and 109.3 hectares of jurisdictional wetlands. The NWI maps indicated 2.5 and 17.4 hectares of wetlands in these two study areas. A similar but smaller discrepancy occurred in the areas mapped in the Blue Ridge Escarpment region. We concluded, because of the small scale that photo interpreters must work with and the number of wetlands located in dense woodlands, that NWI maps may not adequately inventory wetlands in the Blue Ridge. This conclusion was based on a detailed study of 22% (6888 ha) of the area covered on the NWI maps. Predominant plant species in the forested, scrub-shrub, and emergent wetlands were red maple (Acer rubrum), speckled alder (Alnus rugosa), and yellow nutsedge (Cyperus esculentus), respectively, Wetland soils were classified as Typic Humaquents and Humaqueptic Fluvaquents.