A method to predict soil saturation frequency and duration from soil color

Saturation frequency and duration must be estimated to determine if a site is a jurisdictional wetland, and such data also aid in assessing sites for on-site waste disposal. This study developed a method to estimate saturation frequency and duration by calibrating redoximorphic features to a 40-yr record of water table simulations in a catena of Atlantic Coastal Plain soils in North Carolina. Thirteen plots were established along a toposequence with moderately well-drained (Aquic Paleudults) and very poorly drained soils (Umbric Paleaquults) as end members. A hydrologic model (DRAINMOD) was calibrated for each plot. Redox potential measurements showed that an average of 21 consecutive days of continuous saturation was sufficient for Fe reduction to occur in the soils. Historic rainfall data were used in the DRAINMOD model to estimate the number of times each plot was saturated for 21 consecutive days or longer in each year of a 40-yr period. Redoximorphic features were significantly correlated with average number of saturation events computed to have occurred at depths of 45, 60, 75, and 90 cm across all soils. Relationships were linear and varied by depth when all soils were analyzed as a single population. The r(2) values for relationships between redox depletions and saturation events were >0.85 for saturation occurring during the growing season, and were >0.75 for saturation events occurring at any time during the year. These relationships allow prediction of the likelihood that a soil will saturate for greater than or equal to21 d by simply estimating the percentage of redoximorphic features at a given depth.