Hillslope hydrology and soil morphology for a wetland basin in south-central Minnesota

Knowledge of soil and landscape hydrology is essential to evaluating the processes and quality of terrestrial ecosystems. Of particular interest in Southern Minnesota is the extensive Clarion-Nicollet-Webster catena, for which little quantitative work has been done in the region. The objective of this study was to investigate the relationship between soil hydrology and morphology for an undrained catena in south-central Minnesota. Seven points along a 125-m summit-to-wetland transect were instrumented with piezometers (25, 50, 100, and 200 cm), observation wells (300 cm), Pt electrodes (25, 50, 100 cm, footslope only), and thermocouples (10, 25, 50, 100 cm). Mollic epipedons were 77-cm thick at the footslope (Cumulic Endoaquoll), thinning to 39 cm at the summit (Oxyaquic Hapludoll). The lower hillslope positions had low chroma colors below the mollic horizon, indicative of reducing conditions. The water table frequently was located in the mollic horizon for these soils and redox potentials at the footslope were frequently <200 mV. Fe content decreased from summit to footslope, indicating the reduction and removal of Fe in the lower landscape positions. With the exception of the wetland, soils had equal piezometric head with depth, indicating lateral throughflow. The wetland had alternating recharge and discharge hydrology during the study. Profile Darkness Index (PDI) had strong correlation with the duration of saturation (r = 0.88, α = 0.05). Thickness and color of surface horizons in this landscape are strong indicators of landscape hydrology, especially when redoximorphic features associated with normal water table levels are masked by thick mollic epipedons.