Spodosol Development as Affected by Geomorphic Aspect,

Baraga County, Michigan

Robert V. Hunckler and Randall J. Schaetzl

In midlatitude locations with steep slopes, geomorphic aspect can be an important factor in determining spatial variations in soil development. This study examines the influence of aspect on soil development in Baraga County, Michigan, as a means of explaining within-landform variability. The soils are sandy and have spodic morphologies. All are located on steep slopes (45-73%) of contrasting aspect. Ten pedons each from backslopes on north-to-northeast-(N-NE) and south-to-southwest-(S-SW) facing slopes were described, sampled, and compared using standard techniques.

Variation in slope gradient was not, statistically, a determining factor in the differential soil development found here. Aspect has strongly influenced soil development, however, with soils more strongly developed (i.e., more podzolized) on N-NE slopes than on S-SW slopes. Several soil characteristics indicative of strong podzolization were found on N-NE slopes, including higher values of solum thickness and POD index, greater losses of extractable Fe and Al from E horizons and concomitant gains in B horizons, and darker and redder B horizon colors. Soils were generally cooler on N-NE slopes in summer, with essentially similar temperatures under snowpacks in winter. Cooler temperatures and greater amounts of infiltrating water in soils with N-NE aspects may have accelerated podzolization by allowing more organo-metallic complexes to be formed and translocated. Podzolization driven by translocation of amorphous, inorganic compounds appears, however, to be nearly equivalent on sites of differing aspect.

Of the ten pedons on N-NE slopes, nine classified as Spodosols (Entic or Typic Haplorthods) and the other was an Entisol. Seven of the 10 pedons on S-SW slopes classified as Entisols (Udipsamments or Udorthents), and the remaining three were Spodosols.