OOS 42-10 - Hydrologic controls on diatom community composition in microbial mats in dry valley streams: responses to extreme flows and sustained dessication

Thursday, August 11, 2011: 4:40 PM
12A, Austin Convention Center
Lee F. Stanish, Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, CO and Diane McKnight, Institute of Arctic and Alpine Research, Univerisity of Colorado, Boulder, CO

The McMurdo Dry Valleys of Antarctica is comprised of alpine and terminal glaceirs, large expanses of patterned ground, and permanently ice-covered lakes in the valley floors, which are linked by glacial meltwater streams that flow during the austral summer.  Many streams have thriving microbial mats composed chiefly of cyanobacteria and diatoms. These mats represent hotspots of primary productivity on the landscape, existing in a freeze-dried state through the winter and beginning to photosynthesize within an hour of the onset of flow.  As part of the McMurdo Dry Valleys Long-Term Ecological research project, we studied stream ecosystem response and changes in diatom community composition through a sustained 18 year cooling period that has been driven by atmospheric changes associated with the ozone hole. This cooling period has been interrupted by two warm summers that created "flood events" in the valleys. 


Flood events act to scour microbial mats, reducing biomass and transporting particulate organic materials to the littoral zone of the lakes.  The recovery of mat biomass occurred over several years. By comparing diatom communities in streams which flow every summer with those in an abandoned channel which was experimentally reactivated and in a stream that only flows during the rare flood events, we found that hydrologic flow regime acts as a strong environmental filter on diatom community composition.  In microbial mats where flow is typically low and periods of desiccation are common during the summer, diatom communities are dominated by species of two aerophilic genera, many of which are endemic. The diatom community composition was resilient to change through the flood events for all but one of the streams studied. These results can be used to interpret the changes diatom communities recorded in lake sediments in terms of the flow regimes that have occurred in the past millennia and to project how diatom communities will change under future warming in this region of Antarctica.

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