Interpreting morphological features in wetland soils with a hydrologic model M.J. Vepraskas a, ⁎ , P.V. Caldwell b a North Carolina State University, Dep. of Soil Science, Box 7619, Raleigh, NC 27695-7619, United States b North Carolina Division of Water Quality, Modeling and TMDL Unit, 1617 Mail Service Center, Raleigh, NC 27699-1617, United States Received 28 February 2007; received in revised form 21 June 2007; accepted 18 July 2007 Abstract Wetlands in the United States are protected by law and are identified by their hydric soils, wetland hydrology, and vegetation. Hydric soils are easily identified by color characteristics termed hydric soil field indicators, that form under saturated and anaerobic conditions, but wetland hydrology is difficult to assess. This study determines how often seven hydric soil field indicators met wetland hydrology requirements which require a water table be within 30 cm of the surface for 14 days or more during the growing season in over half the years. Studies were conducted at five sites in North Carolina in both wetland and upland plots. Soils ranged from Aquic Paleudults to Typic Haplosaprists across all sites. The water-table simulation model DRAINMOD was calibrated to soil conditions in individual plots. Long-term rainfall data were used with the calibrated models to compute 40 years of daily water table data to represent both wet and dry years. It was found that the hydric soils with field indicators composed of organic materials in layers over 20 cm thick (Histosol and Histic epipedon field indicators) met wetland hydrology requirements each year, and in addition were ponded with water for periods between 67 to 139 days on average each year during the growing season. Plots in mineral soils having the Dark Surface (S7) indicator as well as the Sandy Mucky Mineral (S1) indicator also met the saturation requirements for wetland hydrology every year, and were ponded for only 3 days per year on average. Other mineral soils with an Umbric Surface (F13) or a Depleted Matrix (F3) field indicator met wetland hydrology requirements in approximately 95% of the years, and had water tables within 30 cm of the surface for 40 days per year on average. The Redox Depressions (F8) field indicator occurred in a small depression that was saturated for 87% of the year for periods averaging approximately 30 days. These results showed that hydric soil field indicators can be calibrated to long-term water table data that will allow precise assessments of wetland hydrology on-site. © 2007 Elsevier B.V. All rights reserved. Keywords: Wetlands; Hydric soils; Wetland hydrology; Modeling 1. Introduction 1.1. Kinds of data needed In the United States the real estate industry is quickly becoming the dominant employer of soil scientists in private practice. These consultants work on multimillion-dollar land development projects that build new single-family homes in subdivisions that are beyond the reach of municipal sewer systems. Soil scientists contribute by evaluating soils for septic systems and also by identifying areas that need to be protected from development such as wetlands. In doing this work, they are required to supply detailed information to real estate developers that includes how often and how long a soil saturates at a given depth. Frequency and duration of soil saturation determine a soil's suitability for a variety of uses such as on-site waste-water disposal, and also determine whether the site is in a jurisdictional wetland (Mitsch and Gosselink, 1993). Saturation data are difficult to obtain directly, and so soil scientists usually predict the shallowest soil depth that is seasonally saturated by looking for the depth to low chroma or gray colors in a soil profile (Schoeneberger et al., 1998; Vepraskas, 1999). Using Available online at www.sciencedirect.com Catena 73 (2008) 153 – 165 www.elsevier.com/locate/catena ⁎ Corresponding author. E-mail address: Michael_Vepraskas@NCSU.edu (M.J. Vepraskas). 0341-8162/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.catena.2007.07.005