EVALUATION OF MANGANESE OXIDE DEPOSITION IN CAVE STREAM PASSAGES, SOUTHERN WEST VIRGINIA

It has been observed that black manganese oxide coatings are found more commonly in cave streams than in surface streams. In order to understand the occurrence of, and processes leading to, this phenomena, a geochemical, morphological, and microbiological investigation of several caves in West Virginia was carried out. Two substantial underground stream reaches were characterized, both within dendritic epigene cave systems formed in the Greenbrier Group limestones (Mississippian) of the Appalachian Plateaus physiographic province, West Virginia. In Scott Hollow Cave (Monroe County), 0.6 km (13 locations) of Mystic River was examined. In Greenbrier County 0.7 km (12 locations) of Cove Creek were studied in Maxwelton Sinks Cave. Both streams are swallet and sinkhole fed from the Big Levels karst upland surface. In each case sampling stations were established over the length of the stream reach and multiple rounds of geochemical sampling were conducted. Additionally, biological cultures were obtained. PHREEQC analysis confirms the cave waters are supersaturated in respect to birnessite. Manganese oxide precipitation occurs everywhere throughout the cave stream passages. Coating occurs on bedrock walls as well as alluvium adjacent to the active stream. This may be due to splashing/misting, or submergence. The mineral form of manganese oxide was confirmed to be birnessite through x-ray diffraction analysis of multiple samples. Active microbial mediation was proved to be ongoing by plating samples using a manganese enhanced k-medium. The reason for preferential accumulation of Mn-oxide in cave streams may be related to the absence of light, which provides advantages to bacteria that facilitate such metal deposition.