A study of aquic conditions in a microtoposequence of seasonally wet soils on the Texas Coast Prairie

Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to digital@library.tamu.edu, referencing the URI of the item.Includes bibliographical references.The purpose of this study was to investigate the aquic conditions of three soils with different wetness characteristics based on microtopographic landform positions. The landform positions included a closed, seasonally ponded depression, an intermound, and a pimple mound. The proposed criteria for aquic conditions as defined by the International Committee on Aquic Moisture Regimes (ICOMAQ) were to be identified by 1) redoximorphic features and 2) measurement of saturation and reduction to locally verify morphological inferences used to predict these conditions. Interpretations of redoximorphic features are complicated by the presence of relict features in some areas. Morphological properties and laboratory analyses were used to establish a relationship between the redoximorphic features and the frequency and direction of saturation and reduction. The criteria of aquic conditions were evaluated for three pedons and related to morphological properties in order to draw inferences regarding wetness conditions. Taxonomic classification of the three pedons representing the toposequence of mound (Oxyaquic Paleudalf), intermound (Typic Natraqualf), and depression (Typic Endoaqualf), were evaluated in the central Texas Gulf Coast Prairie, northwest of Houston, from the upper to the lower topographic positions. During a 19-month period, each of the different landform positions were seasonally saturated and exhibited different perched and groundwater tables within the upper 2 m. During periods of saturation, low oxidation reduction potentials suggested Fe reduction was occurring in each soil. The mound site exhibited a continuous groundwater table with saturation below 50 cm and reduction below 100 cm. Therefore the Fe-Mn nodules and concretions of the mound site above 50 cm were relict features either transported or formed in place during a previous wetter moisture regime. The presence of a natric horizon and intensive crayfish activity at the intermound site caused the more hydrologically restrictive physical characteristics of the subsoil. Saturation at the intermound occurred at the surface and below 100 cm. This corresponds with decreased water movement within the portion of the profile where a natric horizon occurred between 26 and 136 cm. At the intermound site a confined water table evident from a hydrostatic head was exhibited by the piezometer at 497 cm. The depression site exhibited seasonal saturation and reduction throughout the profile with a confined water table evident from a hydrostatic head occurring in the piezometer at 433 cm. Therefore, redoximorphic features in the depression are associated with current as well as perhaps previous aquic conditions. Redoximorphic features generally supported observed saturation and reduction in the upper soil profiles, but features were observed in portions of the unsaturated profile where neither saturation nor reduction was observed. Positive correlation of redoximorphic features with aquic conditions will require longer periods of monitoring with meteorological data for establishing more definitive relationships