PEDOGENIC DEVELOPMENT ACROSS A WISCONSIN DRIFTLESS AREA LANDSCAPE

A toposequence of 12 upland soil profiles within a prairie watershed in the southern Driftless Area (sDA) was studied to determine the influence that aspect, landscape position, and slope gradient have on the pedogenic development of soils. The profiles represented contrasting north and south aspects, a slope range from 1-20%, and summit, shoulder, backslope, and footslope positions. Physical, chemical, and mineralogical analyses of each profile were conducted to give complete characterizations of each profile. The sDA landscape and soils have been exposed to both periglacial conditions during the Pleistocene and temperate climates during the Holocence. The soils in the study area are derived from late Pleistocene loess and dolomite residuum. The clay mineralogy at these sites reflects the contributions to these soils from late Pleistocene loess. The typical upland soil profile consists of silty Ap and Bt horizons overlying a clay-rich 2Bt horizon. The 2Bt overlies a fine sandy loam saprolite developed from the underlying dolostone bedrock. Mean depth of solum on south slopes is significantly greater (110cm) than on north slopes (63cm). Clay content in the 2Bt horizons of the south profiles (mean 62%, range 50-83%) is higher than in the north profiles (mean 53%, range 41-65%). Relative redistribution of total P, extractable Al, and total Fe content are greater in south profiles than in north profiles. These characteristics indicate an increased degree of pedogenic development on the south slopes, which is related to the greater solar radiation that those slopes receive. Solar radiation controls the microclimate on a slope, including soil temperature and moisture, which influence weathering and illuviation. Extractable Fe, Mn, Mg, and Al, and percent clay in the Ap horizon increased with increasing slope. These results indicate that there is a significant amount of redistribution occurring downslope by surface flow. Soils in the backslope position had the lowest values of base saturation and exchangeable Ca and Mg. Loss of these leachable cations illustrates the hydrologic pattern across the landscape. Topography influences the microclimate of a slope and the water flow and distribution; which play a major role in the development and distribution of soil characteristics over a landscape.