The Relationship Between Sediment Geochemistry, Manganese Oxidation, Human Traffic, and Microbial Community Structure Across Three Southern Appalachian Caves
Publication Date: 2026/09/01
Publication Volume: Journal of Cave and Karst Studies 88 #3
DOI Link: https://dx.doi.org/10.4311/2025MB0100
ABSTRACT:
Three southern Appalachian caves were assessed in a multiproxy analysis to determine if human visitation and modification of the cave environment could influence cave mineralogy, inorganic geochemistry, and microbial community assemblages. Cave sediments were collected from Daniel Boone Caverns in Fort Blackmore, VA (gated and locked with few visitors); Worley’s Cave in Bluff City, TN (a wild show cave); and Linville Caverns outside of Marion, NC (a developed show cave). Sediments were all analyzed using Illumina sequencing for microbial community structure, as well as a combination of X-ray diffraction, whole-rock geochemistry, particle size distributions, and transmission electron microscopy (TEM) for mineral characterization. Distinct geochemical and microbial signatures were found both within and between the caves. Biological manganese oxidation was present in all three caves, with significant differences in geochemistry across sites that contained Mn oxides and those that did not. Geochemistry and mineralogy of sediments primarily reflected the local bedrock rather than human-associated trafffic and detritus. PCA plots using whole-rock geochemistry (cross-referenced with X-ray diffraction data) indicate that sediment variability between caves was due to the amount of clay minerals relative to detrital feldspars and quartz, as well as the amount of detrital heavy minerals relative to Mn oxidation and phosphate. Sediment-hosted microbial communities from Linville Caverns (the most highly developed of the three caves) contained more Bacteroidota (a phylum associated both with high-molecular weight carbon and humans) than the other two caves, while Daniel Boone Caverns, a relatively pristine cave, contained more Thermoplasmatota, Chloroflexota, and Nitrospirota (oligotrophic phyla). Overall, our data corroborate studies demonstrating that Bacteroidota are positively correlated and Nitrospirota are negatively correlated with anthropogenic and nutrient input, and that bedrock type exerts a strong influence both on sediment geochemistry and on microbial community structure.
SIMPLE LANGUAGE SUMMARY:
Caves can be changed by the people who visit them. This study looked at three caves in the southern Appalachian Mountains that get very different numbers of visitors: Daniel Boone Caverns in Virginia, which is locked and rarely visited; Worley’s Cave in Tennessee, a “wild” cave visited by tour groups and cavers; and Linville Caverns in North Carolina, a show cave with paths, stairs and lights that gets more than 100,000 visitors a year. The researchers collected cave mud and dirt (sediment) and studied the minerals and chemicals in it, as well as the tiny living things (microbes such as bacteria) that live there. They found that the kind of rock each cave formed in mattered more for the sediment’s chemistry than the number of visitors did. In all three caves, some microbes were turning manganese, a metal dissolved in water, into dark coatings. The busiest cave had more of a group of bacteria linked to people and to food-rich conditions, while the quiet cave had more microbes that survive on very little food. This suggests that some microbes could be used as signs of human impact in caves.
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