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Grad student talk - Physical and chemical controls on the abundance and composition of microbial...

Thursday, October 23, 2014, 4:30PM - 5:30PM


Tyler Kohler


RL-1 room 269

Full title

Physical and chemical controls on the abundance and composition of microbial mats from McMurdo Dry Valley streams, Antarctica


Microbial mats have an ancient history, include a diverse assemblage of taxa, and are generally found in extreme environments such as polar freshwaters. The McMurdo Dry Valleys of Antarctica are among the coldest, driest deserts on Earth, and here perennial microbial communities are abundant in the ephemeral glacial meltwater streams that flow during the austral summer. Due to a lack of lateral inflows, allochthonous organic inputs, and negligible grazing activity, these streams are ideal for studying the ecology of microbial mats. Here, I use these natural controls to investigate how mats respond to physical disturbance, alterations in the hydrologic regime, and nutrient liberation from permafrost melt in the future. Specifically, I

  1. Quantify and characterize the regrowth of mat biomass, community structure, and elemental stoichiometry after a scouring disturbance,
  2. Investigate how geomorphology and taxonomic identity influences hydrologic controls on the biomass of three different mat types in transects monitored over two decades, and
  3. Quantify differences in elemental and isotopic composition for four different microbial mats types, as well as track trends therein over a geochemical gradient in Taylor Valley.

I found that mats recover 30-50% of their biomass over the course of an austral summer. Algal communities were sensitive to disturbance, though naturally varied in their species and elemental composition 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 were less correlated with flow regime. These patterns differed based on stream geomorphology, and indicate the importance of substrata stability. Lastly, mat types showed different elemental and isotopic compositions, and exhibited different trends over nutrient concentration gradients. These differences highlight the importance of life history traits to modeling primary production, and provide valuable insight to how stream microbial mat communities are formed, maintained, and persist. This research provides a foundation for subsequent investigators studying microbial mats here and elsewhere under a changing climate, as well as an analogue for the ecology of ancient stream systems that may have been present on early Earth and Mars.