Hydromorphology of some Alabama Coastal Plain Soils

R.C. Smith, J.N. Shaw, P.G. Martin, J. H. Dane, J. W. Odom, and J. Owen

Abstract

Estimating the seasonal high water table (SHWT) within soils by the interpretation of redoximorphic features is critical for assessing sites for waste disposal, urban development, crop production and wetland status. Certain redoximorphic features indicate contemporary moisture regimes, while others indicate past moisture regimes and are termed relict. Sandy Coastal Plain (CP) soils present challenges in assessing SHWT's due to low Fe concentrations, perched water tables containing dissolved oxygen, low concentrations of organic matter, and presence of plinthite that can slow vertical water movement and/or be a false indicator of a contemporary SHWT. This study, conducted jointly with the USDA-NRCS, is monitoring the depth and duration of SHWTs of some Alabama CP soils to develop relationships between SHWT periodicity, duration and hydromorphic features. Twenty two piezometers were installed within thirteen CP pedons (Paleudults, Kandiudults and Hapludults, most with plinthite and varying thickness of sandy epipedons) at varying depths to monitor SHWTs (December 2003 to present). Pressure transducers installed within each piezometer record data every six hours, and daily rainfall was obtained from weather stations.  Soils were described, sampled, characterized and classified according to standard techniques, and plinthite was quantified by slaking the sample in water for one hour and performing a rupture test. Horizons containing plinthite and horizons containing soft Fe accumulations were saturated 29 % of the monitoring period. Horizons containing chroma 3 Fe depletions were saturated 21% of the monitoring period, while horizons containing chroma 2 Fe depletions were saturated 42% of the monitoring period. Depleted matrices were saturated 85 % of the monitoring period. Our data to date suggest horizons containing Chroma 2 Fe depletions reflect contemporary hydrology.