IMPACT OF EXOGENOUS NUTRIENTS ON MN-OXIDIZING MICROBIAL CONSORTIA AMONG CAVES OF THE SOUTHERN APPALACHIAN MOUNTAINS

Eutrophication events in cave systems in the southern Appalachians can be visually observed as dark brown to black Mn oxide biofilms. Cave and karst systems are ideal natural laboratories for controlled field studies of Mn oxidation because they are nutrient-limited and therefore sensitive to exogenous nutrient sources. To test the response of microbial communities within Mn oxide deposits to nutrient input, biotic Mn oxidation was stimulated in situ via a variety of carbon sources. Changes to bacterial and fungal communities in response to stimulation were determined using Illumina amplicon sequencing.

Preliminary results suggest that bacterial Mn oxidation was stimulated with organic acids, while fungal Mn oxidation was stimulated with simple sugars and complex carbohydrates. β-diversity analyses using PERMANOVA suggests that bacterial communities prior to carbon addition were significantly different (P-value= 0.044) when compared to bacterial communities after Mn oxidation was stimulated, at least at the Watermark test site in Carter Salt Peter Cave (CSPC). α-diversity analyses based on Shannon’s Diversity Index suggest that bacterial communities at Watermark after carbon addition were more evenly distributed (0.75) when compared to the communities before carbon addition (0.68). Additional factors observed to enhance or inhibit biotic Mn oxidation were total organic carbon (TOC) and quality of carbon (i.e. labile vs. recalcitrant carbon sources) infiltrating cave ecosystems through water infiltration, as well as metal concentrations in the surrounding bedrock. Preliminary tests suggest that higher concentrations of TOC were correlated with visible Mn oxide deposition at sites Unweathered Closet in CSPC, Milton’s Sandwich in Daniel Boone Caverns (DBC) and Bacon Cove in DBC, while sites with lower TOC concentrations lacked visible Mn oxide deposits. Overall, these data demonstrate that exogenous carbon impacts metal cycling and microbial community assemblages and further suggests that anthropogenic impacts like cave litter and sewage dumping may alter microbial ecology and biogeochemical cycling within cave and karst systems. This work has far reaching implications for water quality within karst aquifers that house a significant portion of the drinking water for the eastern United States.