Abstract

The Calhoun, South Carolina Critical Zone (CCZO) research site provides valuable insight into the interactions between all biotic and abiotic components of an area. The critical zone encompasses everything that spans from the top of impermeable bedrock to the top of the trees, where geology meets biology. Biotites (K(Mg,Fe)3AlSi3O10(OH)2) collected from a deep core in this research site are able to reflect the cycling of potassium, a factor of plant nutrition, at various depths. As biotite weathers and its compositional iron oxidizes, potassium is released from the mineral in order to satisfy a charge balance. More intensely weathered biotite is hypothesized to contain lower relative abundance of potassium due to higher levels of oxidation. In connection, potassium content of biotite near the surface will be less abundant, as these layers are more heavily weathered. Using the TENEO® Scanning electron microscope, oriented, sand-sized biotite grains were analyzed for chemical composition using energy dispersive spectroscopy (EDS) and imaged at a magnification of 5000x. Notably, weathered biotite grains displayed “frayed” ends when viewed perpendicular to the principle c-axis. Analysis of these weathered ends in comparison to less weathered grains yielded less relative percentage of potassium in the chemical composition. Resultant persistence of unfixed potassium in the near surface suggests that the degraded biotite can still serve as a stock for nutrient cycling. This leads to a new idea, whereby in the oscillating, reducing, and oxidizing cycle there is the potential for these degraded biotites to act as refugia for potassium in the near surface.

Citation

Sanders, Sophia Chason (2018): The fate of degraded biotites in the deep critical zone: Implications for the K-uplift hypothesis. Center for Undergraduate Research Opportunities (CURO) Symposium, University of Georgia, Athens, 9 April 2018.

This Paper/Book acknowledges NSF CZO grant support.