Physical and chemical controls on the abundance and composition of stream microbial mats from the McMurdo Dry Valleys, Antarctica
PhD: University of Colorado Boulder, .
Microbial mats are ancient in origin, diverse taxonomically, and found in extreme habitats such as polar freshwaters. The McMurdo Dry Valleys of Antarctica are a cold, dry desert, yet mats are abundant in the glacial meltwater streams that flow during austral summers. Due to a lack of lateral inflows, allochthonous organic inputs, and negligible grazing, these streams are ideal for controlled ecological study of microbial mats. Here, these natural controls are utilized to investigate how mats respond to physical disturbance, alterations in the hydrologic regime, and nutrient liberation from future permafrost melt. Specifically, I: 1) quantify and characterize the regrowth of mat biomass, community structure, and elemental stoichiometry after a disturbance, 2) investigate how geomorphology and taxonomy have influenced the hydrologic control of mat biomass over the last two decades, and 3) quantify differences in elemental and isotopic composition for different mats types, as well as track trends therein over a geochemical gradient in Taylor Valley.
Mats recovered ~20-50% of their biomass over the course of an austral summer. Algal communities were sensitive to disturbance, though naturally varied in their species and stoichiometry over a flow season. When the long-term record of mat biomass was compared with hydrologic variables, mats living in the stream channel had the greatest correlations, while those at the margins showed weaker relationships with flow regime. Patterns also differed based on stream geomorphology, indicating the importance of substrata stability. Lastly, mat types showed different elemental and isotopic compositions, and exhibited different trends over nutrient concentration gradients based on composition and habitat use. These differences provide insight to how stream microbial mat communities are formed, maintained, and ultimately persist. This research also provides a foundation for subsequent investigators studying mats under a changing climate, an increasing human presence, and as an analogue for the early Earth and Mars.