@article{vepraskas_he_lindbo_skaggs_2004, title={Calibrating hydric soil field indicators to long-term wetland hydrology}, volume={68}, ISSN={["0361-5995"]}, DOI={10.2136/sssaj2004.1461}, abstractNote={Jurisdictional wetlands are required to be saturated to the surface for 5% or more of the growing season in 5 out of 10 yr, but practical field methods for confirming this are lacking. This study determined whether hydric soil field indicators were related to wetland hydrology requirements. Water table levels were monitored daily for 2.5 yr in a toposequence of nine soil plots that included well to poorly drained members (Oxyaquic Paleudults and Typic Albaqualfs). Monitoring data were used to calibrate a hydrologic model that simulated water table levels from inputs of hourly rainfall data. Forty years of rainfall data were then used with the model to compute long‐term daily water‐table levels in each plot. These data were summarized as “saturation events”, which are the frequency that water tables were at or above preselected depths for at least 21 d. Twenty‐one days was the average period needed for Fe reduction to begin in these saturated soils. This condition must occur for hydric soil field indicators to form. Regression equations were developed to relate saturation events to percentages of redoximorphic features. The r2 values for relationships between percentages of redoximorphic features and saturation events were >0.80 for depths of 15 cm, and >0.90 for depths between 30 and 90 cm. Results showed that the depleted matrix field indicator, in which redox depletions occupy >60% of the horizon, occurred in soils that were saturated for 21 d or longer at least 9 yr out of 10. This indicated the depleted matrix indicator occurred in soils that were saturated nearly twice as long, and more frequently, than the minimum requirements needed to meet wetland hydrology requirements.}, number={4}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Vepraskas, MJ and He, X and Lindbo, DL and Skaggs, RW}, year={2004}, pages={1461–1469} }
 @article{he_vepraskas_lindbo_skaggs_2003, title={A method to predict soil saturation frequency and duration from soil color}, volume={67}, ISSN={["0361-5995"]}, DOI={10.2136/sssaj2003.0961}, abstractNote={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 r2 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 ≥21 d by simply estimating the percentage of redoximorphic features at a given depth.}, number={3}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={He, X and Vepraskas, MJ and Lindbo, DL and Skaggs, RW}, year={2003}, pages={961–969} }
 @article{he_vepraskas_skaggs_lindbo_2002, title={Adapting a drainage model to simulate water table levels in coastal plain soils}, volume={66}, ISSN={["1435-0661"]}, DOI={10.2136/sssaj2002.1722}, abstractNote={Seasonal saturation in soils is expensive and time consuming to document, but the information is needed for land use assessments. Hydrologic models can be used to assess saturation occurrence quickly if the models are calibrated for individual sites. This study determined whether a drainage model (DRAINMOD) could predict water table levels in soils with and without a perimeter ditch. Water table levels were monitored for up to 3 yr at two toposequences that contained a total of 21 soil plots (3 m by 3 m). Soils included Typic Paleudults, Aquic Paleudults, and Umbric Paleaquults. Each plot was instrumented with a recording well to monitor daily water table levels. DRAINMOD was calibrated for each soil plot using measurements of in situ saturated hydraulic conductivity, soil water characteristic, depth to impermeable layer, depth of rooting, and rainfall. A plot's water table fluctuation was simulated by a system of virtual drains whose distance and depth were adjusted to produce simulated water table fluctuations in line with those actually measured. Further calibration adjusted drainable porosity in the upper 20 cm of the soil, depressional storage, evapotranspiration rate, and depth to impermeable layer. Adjustments were made by iteration to minimize the absolute average deviation between simulated and measured water table levels. Calibration had to be done by plot. Average absolute deviations were generally <20 cm for periods ranging from 1 to 3 yr. The results showed that DRAINMOD could be adapted to simulate water table levels in landscapes that do not contain a network of parallel drains.}, number={5}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={He, X and Vepraskas, MJ and Skaggs, RW and Lindbo, DL}, year={2002}, pages={1722–1731} }