Issues related to wetland delineation of a Texas, USA bottomland hardwood forest

Methods of wetland delineation require presence of three parameters: hydric soils, wetland hydrology, and hydrophytic vegetation. Currently accepted methods to assess these parameters often have inconsistent agreement among the parameters in bottomland hardwood forested wetlands. This study characterized soil morphology, hydrology, and vegetative composition in a bottomland hardwood forest in east Texas, USA. Alternate methods for assessment of the three parameters were examined with the aim of determining if there is an approach that provides better agreement among parameters than methods in current use. We compared four methods for determining dominance ratios and a prevalence index to assess the status of vegetation. The most stringent method of assessment and the method that provided best agreement with soil and hydrology parameters at this site was a prevalence index. We compared three criteria to assess the hydrology parameter: (1) length of growing season as defined by air temperature greater than −2°C (28°F) vs. 0°C (32°F), (2) saturation or inundation for 5% vs. 12.5% of the growing season, and (3) saturation to within 30 cm vs. 15 cm of the soil surface. Length of growing season had little or no effect on the outcome at this site; duration of required hydrology had the greatest influence over agreement with vegetation and soil parameters. We also compared the field method used to determine presence of hydric soil when sampling was conducted in 1995 with currently used field indicators. The combination that, in general, provided better agreement among the three parameters at this site was saturation to within 15 cm of the surface for 12.5% of the growing season, using current field indicators for hydric soil. Despite having been mapped as a wetland by the National Wetlands Inventory, under current federal guidelines, most of this bottomland hardwood forest would not be a jurisdictional wetland as defined by Clean Water Act regulations.