USING PUBLIC DOMAIN DATA TO AID IN FIELD IDENTIFICATION OF HYDRIC SOILS

Hydric soil field identification is a common activity for natural resource professionals and planners, but it can be time consuming and labor intensive. This study used Soil Survey Geographic Database (SSURGO), National Wetlands Inventory (NWI), National Land Cover Data (NLCD), and other public domain data to make digital hydric soil predictive maps of two study areas in western Virginia. Soil scientists used the predictive maps as guides to conduct hydric soil field surveys and compared the results to delineations of SSURGO map units dominated by hydric soils and NWI and NLCD wetlands. At Stuarts Draft, 15% of the 1296-ha study area was composed of hydric soils compared with 14% estimated by SSURGO. At Blacksburg, 3% of the 828-ha study area was composed of hydric soils compared with 1% estimated by SSURGO. Both NWI and NLCD estimated 1% wetlands at each area. Locational correspondence was higher between the field survey and SSURGO than between the field survey and the NWI and NLCD wetlands at both study areas. The predictive maps were useful because the SSURGO delineations were closely aligned with field survey delineations, had <2% false negative identifications compared with >13% for NWI and NLCD at Stuarts Draft, and had ≤ 2% false positive identifications. Overlaying NWI and NLCD onto SSURGO polygons resulted in ≤ 1% improvement of predictive map utility, but all indicators of hydric soils were useful in narrowing the specific location of hydric soils within large SSURGO delineations.