Total organic carbon concentrations in clastic cave sediments from Butler Cave, Virginia, USA: implications for contaminant fate and transport.

Abstract

Clastic cave deposits are representative of sediments throughout the karst aquifer and thus are an abundant and accessible resource through which to study the chemistry of karst aquifer. Clastic cave sediments are attributed to depositional facies based on cave location, sorting, and particle size. These facies settings may influence different chemical parameters of the sediments, like concentrations of total organic carbon (TOC). The TOC concentrations in clastic cave sediments have not been well constrained nor has the role of clastic sediments in contaminant fate and transport through karst systems been well described. In this study, particle size, TOC, and total nitrogen were measured in sediments representing different facies in Butler Cave, Virginia, USA. TOC concentrations ranged from 0.08 - 0.87 weight percent and C:N molar ratio ranged from 3 - 15, indicating a possible terrestrial source of organic carbon in these sediments. The diamicton facies was sandier and but had similar TOC concentrations compared to the channel facies. TOC concentrations measured in Butler Cave were within the same range as those observed in above water, eogenetic clastic cave sediments from two caves in Puerto Rico. Estimated retardation factors calculated based on the TOC concentrations in the Butler Cave sediments indicate the range of TOC in this cave could be responsible for 39 - 987% increase in retardation of selected contaminants. This study highlights the importance of measuring the ranges of TOC in clastic cave sediments across different facies and their role in contaminant fate and transport.