Wednesday, November 15, 2006 - 9:30 AM

Environmental and Digital Data Analysis of the National Wetlands Inventory (NWI) Landscape Position Classification System.

Alexis Sandy, John Galbraith, Stephen Prisley, Jim Campbell, and W. Lee Daniels. Virginia Polytechnic Institute and State Univ, Dept of Crop and Soil Environmental Science, 417 Smyth Hall (0404), Blacksburg, VA 24061

National Wetland Inventory (NWI) is the definitive source for wetland resources in the United States.  The NWI production unit in Hadley, MA has begun to upgrade their digital map database, integrating descriptors for assessment of wetland functions.  Updating is conducted manually and some automation is needed. This study was conducted to assign landscape position descriptor codes to NWI wetland polygons and correlate polygon environmental properties with public domain terrain, soils, hydrology, and vegetation data within the Coastal Plain of Virginia. Environmental properties were applied to a non-metric multidimensional scaling technique to identify similarities within individual landscape positions based on wetland plant indicators, primary and secondary hydrology indicators, and field indicators of hydric soils.  Individual NWI landscape position classes were linked to field-validated environmental properties.  Mean pixel attribute values extracted from the 180 field-validated wetlands were analyzed using cluster analysis technique. The SSURGO hydric soil component percent had the greatest variance when compared to VBMP elevation and slope curvature, NHD streamflow and waterbody, NWI Cowardin classification, and NLCD wetland vegetation type.  Soil survey data had limitations including variable date of acquisition, scale, and quality.  Streamflow had limitations related to its linear attributes, therefore is often found insignificant when evaluating mean pixel values of wetland landscape position classes.  There are two essential sources of information for wetland mapping: current high resolution aerial photography captured in leaf off condition and high-quality soil survey data. High resolution elevation data source are imperative to modeling the changes in elevation and slope curvature that characterize wetland landscapes.