Biogeochemistry of Sulfur in Small Forested Catchments of the Great Smoky Mountains National Park

This dissertation presents three studies designed to investigate sources and biogeochemical processing of sulfur in the Great Smoky Mountains National Park (GRSM). First, a geochemical study of first- and second-order streams throughout the GRSM was conducted to determine variability in water quality and the influence of natural land disturbances on the water quality. The study identified three categories of sites, each with distinct water chemistry: lower elevation sites, high-elevation sites, and sites influence by sulfidic bedrock. Stream water chemistry was statistically significantly different in catchments with and without known areas of land disturbances that exposed sulfidic bedrock to the atmosphere. A second study focused on soil/stream water geochemistry and the influence of bedrock composition on it. Three sites overlying sulfidic bedrock were statistically compared to two overlying sandstone and two overlying a bedrock transition zone. Stream water from the two sites adjacent to exposed sulfidic bedrock had the lowest pH and acid-neutralizing capacity, the highest sulfate concentrations, as well as the highest metals and cations concentrations. Results also showed that the soil organic phase was the primary locus of sulfur retention in high-elevation forest catchments. The third study focused on stable isotope geochemistry in the same seven catchments. It showed that stream water chemistry, and the sulfur (δ34S) and oxygen (δ18O) isotope composition of stream water sulfate and soil sulfur, reflects atmospheric sulfate in the absence of significant sulfur/sulfate inputs from sulfidic bedrock. All three studies were consistent in providing evidence that influence of sulfidic bedrock on stream water geochemistry in high-elevation catchments is dependent on the bedrock’s exposure to the atmosphere. The soil mantel has a stronger direct influence on GRSM stream water chemistry than bedrock composition, as indicated by the sulfur and oxygen isotope composition of soil sulfur and soil organic sulfur and by the similarity in sulfur isotope composition of sulfate in stream water and subsurface soil. Geochemical indicators of acidification of GRSM stream water and soil at the selected study sites appear to be caused by the characteristically low-neutralizing potential of high-elevation soil than to the composition of underlying bedrock