INVESTIGATING THE ROLE OF BEDROCK WEATHERING IN THE FORMATION OF ALPINE SOILS, WHITE MOUNTAINS, NEW HAMPSHIRE

This study investigated the role of bedrock weathering in the formation and development of alpine soils on Mount Monroe in the White Mountains of New Hampshire. A recently published bedrock map (Eusden, 2010) identifies multiple formations in an area where other soil forming factors are otherwise constant (climate, biologic activity, relief, and time of deposition). Using this map as a guide, 72 soil samples and 5 rock samples were collected from 25 different locations in Monroe Col and analyzed for a variety of soil, chemical, and mineralogical properties. The soil profiles have distinct Oa, A, B, BC and one E horizon and weathering indices reveal an increase in weathering intensity upward from the bedrock. X-ray diffraction reveals biotite in the rock weathering to hydrobiotite in overlying soils and chlorite in soils above all bedrock formations. The presence of chlorite in soils over rocks that do not contain this mineral could indicate glacial origins from a homogeneous bedrock material deposited in the late Wisconsinan. Trace mineral concentrations are relatively uniform for all soils with no clear bedrock control. Differences in median grain size are significant in soils over different bedrock formations, while ammonium-chloride extractable cations, calculated cation exchange capacity, and exchangeable acidity in the soils show no significant differences. The similarity of soil chemical properties is inconsistent with the theory that Potentilla robbinsiana prefers the chemical properties of soils over calcium silicate bedrock. These preliminary results suggest that the soils in Monroe Col have developed in surficial deposits from the last glaciation with a modest amount of in situ weathering of the underlying bedrock. Soil properties, therefore, reflect a generally uniform parent material with some local variation.