Microbial mats are the principal autotrophic communities of terrestrial ecosystems in the McMurdo Dry Valleys (MDV), Antarctica. Dominated by cyanobacteria (e.g., Nostoc spp.), these microbial mats are the main source of productivity in the region. While there are long-term observations of aquatic productivity, there are no systematic estimates of terrestrial productivity. Recent work has demonstrated that microbial mats can be identified along stream margins in the MDV using multispectral satellite imagery. We’re examining the relationship between multispectral data and microbial mat density, AFDM, and chlorophyll a content in multiple wetland systems adjacent to ephemeral melt-water streams in Taylor Valley, Antarctica. In January 2018, the WorldView-2 satellite collected images of Taylor Valley while we surveyed plots in areas with abundant mats. We used a random stratified sampling design and point-intercept surveys with three 100 m2 plots and one 400 m2 plot for hydrologic status and groundcover type, and we collected samples of mats to measure standing biomass and chlorophyll. Plots were surveyed using a Trimble Kinetic GPS System with centimeter-level accuracy. Photos were taken at each survey point to estimate percent groundcover. The satellite imagery was atmospherically corrected and analyzed using vegetation indices in ENVI.
Results/Conclusions
Microbial mat communities were overwhelmingly dominated by Nostoc spp., which ranged from approximately 30 to 70% cover across the four plots. Average Nostoc cover was 68, 67, 67, and 33% for the plots at Canada Stream, Green Creek, and McKnight Creek, respectively. Chlorophyll a content ranged from 0.074 to 18.71 μg/g dry material across sites, with high concentrations of accessory pigments (phaeophytin). Average chlorophyll a content for the plots at Canada Stream, Green Creek, and McKnight Creek were 3.86, 3.64, 4.02, and 3.88 μg/g dry material, respectively. Initial analysis of multispectral data indicate strong reflectance in red and near-infrared wavelengths in the plots, indicative of active photosynthesis. In ongoing analysis we are evaluating the relationships between ground cover, AFDM, chlorophyll a content, and satellite derived vegetation indices (e.g., NDVI). Once validated, this method will be scaled up to systematically estimate the terrestrial productivity of Taylor Valley. With recently acquired and archived imagery this approach will allow us to examine spatial and temporal variability in microbial mat dynamics.