The McMurdo Dry Valleys are the largest ice-free region in Antarctica and have been a focus of polar ecosystem research for more than 30 years. Wright Valley in particular has been noted for a series of small (< 1.0 ha) ponds scattered across a maze-like landscape of small canyons known as the Labyrinth. Mean annual temperatures range from -16°C to -21°C, with only a 3-month summer that permits melt-water generation and allows production of localized cyanobacterial mats and a few species of invertebrate consumers (e.g., tardigrades, rotifers, and nematodes). While some ponds may be connected via subsurface flow, many are hydrologically closed systems with only snowmelt contributions and evaporative losses. This heterogeneity has resulted in geochemically unique ponds, potentially supporting equally distinctive resident biotic communities. The objective of this study is to examine the influence of geochemical variability in these relatively productive (and potentially isolated) ponds upon the diversity of resident biota.
Results/Conclusions
We sampled five ponds in the Labyrinth of Wright Valley in January 2010, and characterized the geochemistry of surface water and sediments in conjunction with identification and enumeration of biota to provide an assessment of how abiotic factors drive community composition. Preliminary data illustrate a broad range in geochemistry among the sampled ponds. Major ion concentrations of surface waters span more than two orders of magnitude, e.g., chloride concentrations range from 20ppm to 5000ppm. Additionally, sediment chemistry (major ions, TN/TOC), microbial biomass and invertebrate abundances varied significantly among ponds. A strong negative correlation between chloride concentrations and invertebrate abundance and microbial biomass was evident among the pond sediments examined. Despite such variability among ponds, the C:N ratio of benthic sediments is very consistent, averaging 5.5, typical of cyanobacterial biomass. In ongoing analyses we will continue to examine the unique geochemistry of these ponds and related patterns of biodiversity through additional analytical testing (e.g. chlorophyll concentrations, 15N and 13C signatures of organic matter and 18O/16O; D/H ratios in surface water) and field collections.