Spatial and temporal relations between soil processes, morphology, and hydrology in Minnesota landscapes

The combination of topography and soil properties, such as hydraulic conductivity and texture, control the movement of water within a landscape. Research in pedology has shown that the movement of water and long-term average location of the water table is recorded in the soil morphology. The objective of this research was to quantify the relationships between hydrology and soil morphology for three landscape types in Minnesota. Three study sites, located in northwest, east-central, and southern Minnesota were instrumented to monitor location of the near-surface aquifer, soil temperature, soil water tension, and redox potential. Soils were described and sampled for morphological properties, including organic matter content, pH, and Fe and Al content. Monitoring data was used to determine the influence of current hydrology and environmental factors on the distribution of soil morphological properties. Terrain attributes were used to model the distribution of hydric soils at the southern site. A Saturation Temperature Index (STI) was developed from the northwest site data as a measure of potential development of hydromorphic soils. The distribution of redoximorphic features along the hillslope at the east-central site was not related to current hydrology. However, the distribution of Fe in soil profiles along the hillslope and locations of Fe-dominated spodic materials suggested that the morphology is reflective of both past and present water levels. The soils and monitoring data at the southern site best support the hypothesis that distribution of morphology is controlled by landscape hydrology. The Profile Darkness Index (PDI), which is correlated with landscape position and organic matter content, was highly correlated with duration of saturation (r2 = 0.77) and STI (r2 = 0.93) at the southern site, indicating a quantifiable relationship between hydrology and morphology. This site is a mix of open and closed drainage watersheds. Distribution of hydric soils had high agreement (74%) with the terrain attribute model in the open-drainage areas but only 52% agreement in areas with closed drainage. Overall, the results of this research indicate that landscape hydrology is in part controlled by the combination of topography and soil properties and results in a characteristic distribution of soil morphology.