Soil morphology and moisture regimes along a hillslope in the Texas coastal plain

Abstract

Some soils of the Texas coastal plain are saturated for several months of each year, but do not exhibit the low chroma colors normally associated with poor drainage. Without direct measurement of the water table levels in these soils, their saturated nature could not be predicted simply on the basis of the low chroma color criterion currently used in the soil classification system, Soil Taxonomy. The objective of this study was to identify soil morphological features which could be used to assess seasonal saturation in solid exhibiting few low chroma colors. Relations between selected morphological features and moisture regimes were examined in four Alfisols along a toposequence in south-eastern Texas, 35 miles north of Houston. Soils ranged from Paleudalfs to Ochraqualfs from upper to lower topographic position. In upland soils exhibiting few low chroma colors, Fe nodules and cutanic eluvial zones were conspicuous morphological features. These two features were characterized with regard to abundance, particle size distribution, total Fe content, and relation to structural voids in selected horizons of two upland soils. Moisture regimes were characterized by monitoring water table fluctuation during 1978 and 1979 with tensionmeters placed at depths of approximately 60 cm, 127 cm, and 178 cm in each soil. Redox potentials were monitored during 1979 at 76 cm and 152 cm in each soil, with total dissolved Fe contents in the ground water determined concurrently. Each soil of the toposequence was found to be seasonally saturated. In the upland soils, water tables rose to the surface in January and fell below a depth of 2 m in May of June for both 1978 and 1979. Unlike a typical toposequence, the duration of saturation within 1 m of the soil surface did not increase in the downslope direction. For the soil in the lowest topographic position, the water table rose three months after that in the upland, and also remained below a depth of 1 m in both 1978 and 1979. This delayed water table rise results from a combination of two factors. A slowly permeable A2 horizon in the lowland soils ponds water and restricts infiltration, thus limiting moisture inputs from precipitation and runoff...