An Application of the Runge “Energy Model” of Soil Development in Michigan’s Upper Peninsula

 

Randall Schaetzl and Charles Schwenner

 

           This paper is examines some soils in Michigan’s upper peninsula that are seemingly “out of place” and do not “fit” with the typical zonal soils of the region. The typical upland soils in this part of the Pictured Rocks National Lakeshore, when not constrained by bedrock or high water tables, are strongly-developed Spodosols (Haplorthods). We used the Energy Model (Runge 1973) to explain the genesis of nearby soils, whose chemistry and morphology are quite different. The Energy Model presupposes that soils are affected mainly by water available for leaching and organic matter production, as conditioned by parent material. In our study area, where water available for leaching is limited (or even negative), as on steep slopes shallow to bedrock with multiple springs and seeps, horizonation in the classical sense does not form. Instead, shallow Histosols (Saprists) form above bedrock, even on 45% slopes. Oxyaquic Haplorthods developed on gentle slopes, on the same bedrock, are strongly horizonated, as most of the water that impacts them is available for leaching, percolation and pedogenesis. In another example, soils that have formed above calcareous bedrock maintain such high pH values that their faunal assemblages are rich and diverse, and base cycling is strong, leading to thick O-plus-A horizon sequences. These soils (Lithic Udipsamments) resemble Mollisols and exhibit few marks of podzolization. Conversely, nearby Oxyaquic Haplorthods above acid sandstone bedrock have limited faunal assemblages, slow organic matter decomposition, and horizonation indicative of strong podzolization. These examples highlight the importance of using conceptual models to understand and explain soil genesis and distribution.