EFFECTS OF FRESHWATER FREEZING ON MICROBIAL HABITABILITY

Bacteria play a crucial role in the transformation of organic carbon in freshwater lakes. Despite their fundamental involvement in organic matter biogeochemistry, most analyses have been conducted during warm periods dominated by open water. During winter nearly half of all freshwater lakes globally are subject to seasonal freezing, which directly influences the distribution of bacteria across snow-ice-water transects. Ice accretion for example has been shown to alter both the chemistry and distribution of organic matter in the water column, via the exclusion of aromatic components of dissolved organic carbon (DOC) from ice. On the other hand, evidence also shows that some bacteria are preferentially incorporated into the ice. The cross-season effects on habitability resulting from these processes remain unknown. To explore the consequences of seasonal freezing for microbial habitability within and beneath ice, we conducted a series of controlled freezing experiments on water collected from a North temperate freshwater lake. Samples were taken before and after freezing, then analyzed for changes in organic matter fluorescence, dissolved organic carbon (DOC) concentration, and cellular abundance. Results showed changes in the composition of dissolved organic material between time points, as indicated by excitation emission matrix spectroscopy. Significant differences in the concentrations of DOC between pre- and post freeze samples were also observed. Plans for future experiments include determination of the favorability of ice-DOC as a substrate for microbial growth.

Primary Presenter: Garrett Lukosavich, Michigan Technological University (gnlukosa@mtu.edu)

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