Quantitative soil-landscape modeling for estimating the areal extent of hydromorphic soils

The spatial distribution of hydromorphic soils across the landscape affects soil survey, broad-scale wetland identification, and ecological studies. The change from upland to wetland is frequently difficult to delineate because it often occurs along a gradual continuum. We have developed a color index, the Profile Darkness Index (PDI). In assist in making these delineations. The PDI is well correlated with the duration of saturated and reducing conditions in specific Mollisol catenas in humid regions of the north-central USA. The objective of this research was to use soil-landscape modeling techniques to relate the variation of PDI to terrain attributes that describe the flow and accumulation of water on hillslopes. Regression models that quantify the relationships between terrain attributes and PDI on a hillslope in west-central Minnesota indicate that variability in slope gradient, profile curvature, and elevation above local depression explained up to 65% of the variability in PDI. These models may be used to estimate the areal extent of hydromorphic soils using terrain attributes derived from a high-resolution (10-m resolution) digital elevation model and to quantify relationships between spatial variability of terrain attributes and of PDI. Knowledge of the terrain attributes that are statistically important according to these models, and their relative effects on PDI (e.g., as slope gradient decreases, PDI increases) may be applied to field-scale delineations of hydric soils.