Date of Award
Master of Science
C. Lee Burras
Soils are a product of parent material, organisms, relief, climate, and time. If all factors except climate could be held relatively constant, the effect that climate plays in the formation of soils could be examined. Following that approach, this study collected and analyzed outwash derived soils from three locations on terraces of the Des Moines River. To provide a climosequence, the three selected locations were spaced out along the length of the river from the NW to SE coinciding with mean annual precipitation (MAP) and mean annual temperature (MAT) both increasing from NW to SE. The soils compared all formed on the same landscape (high river terrace), in the same parent material (outwash), with the same organisms (trees followed by prairie) over the same amount of time (about 11,000 years). Soil profiles were described and soil horizons were analyzed for bulk density, soil texture, pH, soil organic carbon (SOC), inorganic carbon, and mineralogy. The sola sampled are typically loams or clay loams in the upper part of the profiles and gravelly sandy loams in the lower part.
Several trends in the soil properties and morphologies were observed that co-vary with the MAP and MAT climate gradients. The SOC in the upper solum decreases from NW to SE while SOC in lower solum increases from NW to SE. The clay amount and mean particle size of the fine earth fraction are correlated. The southernmost location’s sola had fewer coarse fragments, but about 5% more clay in the B horizons. Bulk density increases with depth, but no trend across the three locations was observed. No trend in pH could be determined due to the legacy of land management. Soil survey map accuracy was found to be poor with only seven sola from the 25 sites matching the dominant soil series in their respective consociations. Depth to carbonate minerals increases approximately 10 cm every 50 km from NNW to SSE. The mass per area of carbonates leached to the depth of effervescence ranges from approximately 1600 Mg/ha in the NW to 5100 Mg/ha in the SE. Data collected and analyzed in this project support the hypothesis that the loamy soil textures observed in the upper solum are primarily due to geological processes such as a waning flow event following a high flow event during the Late Wisconsinan. However, with primary carbonate minerals comprising around 25% of the outwash’s mass, leaching of carbonates from the upper solum could also be a significant pedological process that helped alter texture.
Ethan Matthew Dahlhauser
Dahlhauser, Ethan Matthew, "Pedogenesis of outwash derived soils on terraces of the Des Moines River" (2016). Graduate Theses and Dissertations. 15688.