Human Impact on Extracellular Enzyme Activity within Carlsbad Cavern and Lechuguilla and Spider Caves in Carlsbad Caverns National Park, New Mexico

The biotic component of cave ecosystems contains substantial microbial biodiversity, but the extent to which human visitation impacts cave microbial communities is unknown. Nutrients are sparse within some caves or areas of caves, which selects for microorganisms able to acquire nutrients at low concentrations. Human visitation may increase nutrient availability, which may alter microbial community composition and function. One way to measure microbial responses to nutrient availability is to measure extracellular enzyme activity (EEA). EEA measures can determine whether microorganisms are nitrogen, carbon or phosphate limited. We collected samples of cave soils and ferromanganese deposits (FMD) from three limestone caves in New Mexico (Carlsbad Cavern, Lechuguilla Cave, and Spider Cave). Samples were collected in high impact (trails) and low impact areas (off-trails). Samples were assayed for alanine aminopeptidase, phosphatase, and beta-glucosidase activities using L-Alanine-7-amido-4methylcoumarin, 4-methlylumbelliferone (MUB)-phosphate, and 4-MUB-β-d-glusoside as substrates, respectively, following published microplate protocols. We hypothesized that high impact areas would have greater N and P availability, which would lead to lower N (aminopeptidase) and P (phosphatase) acquisition activity in relation to C (glucosidase) acquisition. In areas of low human impact, average alanine aminopeptidase and phosphatase activity was the highest, at 2.2 nmol/h/g and 226.4 nmol/h/g respectively. In areas of medium impact, average ß-glucosidase activity was the highest of all areas, at 376.6 nmol/h/g. Our results suggest that EEA measurements can be used to assess the impact of human activity on cave ecology, which can contribute to our understanding of how to protect rare and unusual cave microbial communities.