Hydromorphic Soil Development in the Coastal Temperate Rainforest of Alaska

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Predictive relationships between soil drainage and soil morphological features are essential for understanding hydromorphic processes in soils. The linkage between patterns of soil saturation, reduction, and reductimorphic soil properties has not been extensively studied in mountainous forested terrain. We measured soil saturation and reduction during a 4-yr period in three catenas of the perhumid coastal temperate rainforest of Alaska and compared these measurements to soil morphological features of Spodosols and Histosols. Soil saturation and anaerobic conditions indicated by redox potential corresponded to low-chroma colors, Fe concentrations, and accumulation of organic matter. Hue changes from 7.5YR to 10YR, 2.5Y, and 5GY were observed, at depths corresponding to water table position and Fe depletion, in Spodosol B horizons of backslope landscape positions. The depth to the features was dependent on the distance from the top of the catena, with a consistent pattern of near-surface soil saturation evident below the topographic break of 10% slope. The mean annual water table position was 34 cm below the surface in upper slope positions and 14 cm below the surface in lower slope positions. The association of color changes confirms the influence of saturation and reduction on the soil morphology of Spodosols. The consistent patterns in soil saturation, reduction, and soil morphological features offers guidance for hydric soil identification, wetland delineation, and ecological processes related to near-surface soil saturation.