THE INFLUENCE OF ORGANIC LOAD ON SUBTERRANEAN GEOMICROBIAL ACTIVITY AND SECONDARY SPELEOGENESIS

Due to the oligotrophic nature of cave environments, microorganisms have adapted to this starved environment by utilizing a number of different methods to fix carbon, generate energy and obtain nutrients. One such mechanism of energy produced is through oxidation and reduction of elements found within the bedrock matrix of the cave. Carlsbad cavern is a hypogenic cave system found in New Mexico that formed through sulfuric acid speleogenesis. The host rock comprises of the dolomitic Yates formation and the Capitan reef massif, which often had a calcitic speleogenic surface. Within this bedrock are numerous secondary elements, including iron, manganese, titanium, silica and other constituents of sedimentary minerals. Samples were taken from three locations within Carlsbad Cavern in relation to the local geology. These samples were subsequently broken down into three horizons (outer, middle and inner) corresponding to the relative position of the rock to the cave surface. The samples were subsequently analyzed for total organic content by liquid chromatography and mineralogical changes with the use of X-ray diffraction, scanning electron microscope with energy dispersive spectroscopy and Mossbauer Spectroscopy.

Our results suggest that higher levels of organic input into the cave system limits the amount of microbial mineral transformation, presumably due to the higher efficency of obtaining carbon and energy from organic versus inorganic processes. Subsequently, we have demonstrated higher microbial mineral transformations in a nutrient deprived environment, such as the oxidation of dolomite (MgCa(CO3)2) to release usable carbon dioxide (CO2), followed by subsequent formation of clays, and the oxidation of Fe(II) to Fe(III) or subsequent reduction to Fe(0) (elemental iron). Our results suggest that the relative levels of organic input into subterranean environments may have a profound impact on the ensuing geomicrobial processes taking place.