Quantifying the Energetics of Pedogenesis Using Thermal Analysis.

Thermodynamic concepts and techniques have been broadly applied to understanding the energy and mass flows associated with pedogenesis. Previous applications range from the conceptual treatment of soils as open thermodynamic systems to explicitly quantifying the energy and mass flows associated with water and carbon cycling and mineral weathering.  Here we couple a conceptual model of open soil thermodynamic systems with empirical measures of pedogenic development across a range of environmental gradients.  Specifically, the objective of this work was to couple thermal and geochemical techniques to quantify energy consumption and storage resulting from pedogenenic processes. The work focused on well characterized field sites that encompass three environmental gradients on the western slope of the Sierra Nevada Mountains, California, that range from thermic, xeric systems on low elevation to frigid, udic systems at high elevation, and span basaltic, andesitic and granitic parent materials.  Thermal analyses were used to quantify the net energy change of the soil system associated with storage of organic carbon and mineral weathering.  Profile integrated thermal data indicate a strong relationship of net soil energy change to empirical measures of the rate of effective energy and mass transfer associated with net primary production and effective precipitation.  The data suggest thermal analyses provide a means to quantify the energy storage and consumption associated with pedogenesis and provide a quantitative link to conceptual models of soil as an open thermodynamic system.