Investigating alpine pedogenesis on Mt. Mansfield, Vermont

FARRUGIA, Gianina and MUNROE, Jeffrey

Geology Department, Middlebury College, Bicentennial Hall, Middlebury, VT 05753

Alpine soils were investigated on Mount Mansfield (~1300 m asl) to determine their physical and chemical properties and to elucidate the role of bedrock weathering in their formation. An AMS radiocarbon date of 890 ± 40 BP on needles retrieved from 48 cm below an Abies krummholz indicates stability of the alpine landscape over millennial timescales. Soil thickness was measured by probing at 200 random points, and samples of soil horizons and underlying bedrock were taken at 21 locations. Soil thickness ranges from 0 to 55 cm. The area dominated by Vaccinium uliginosum (39%) is more than twice that covered by Carex bigelowii (16%) and there is no difference in mean soil thickness (17 cm) under these two vegetation types. The thickest soils (mean of 34 cm) are found under Ledum groenlandicum. In October, basal soil temperatures were directly proportional to soil thickness (r2=0.66), ranging from 2.0 to 7.5ºC. Most profiles (12 of 21) consist of A horizons over bedrock, while 9 profiles contained AC or C horizons. pH values range from 3.1 to 4.8 and are generally lowest in surface horizons. Bulk density ranges from 0.06 to 1.04 g cm-3. Percent loss-on-ignition ranges from 1 to 82% with a mean of 47% in A horizons and 23% in deeper layers. Comparison of the bulk mineralogy and chemistry of paired soil and bedrock samples indicates that bedrock weathering is a component of pedogenesis in this environment.