Monday, December 06, 2010, 12:00PM - 1:00PM
Full title: "The McMurdo Dry Valleys, Antarctica: Climate change reconnects terrestrial and aquatic ecosystems."
The McMurdo Dry Valleys of Antarctica are comprised of alpine and terminal glaciers, 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 cyanobacterial mats that are freeze-dried through the winter and begin photosynthesis with the onset of flow.
As part of the McMurdo Dry Valleys Long-Term Ecological research project, we have studied the responses of soil, lake and stream ecosystems through a sustained 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. We studied the stream ecosystem response in a formerly abandoned channel, which was experimentally reactivated by a flow diversion in 1994 and in a stream that only flows during the rare flood events. We found that the mats where flow is typically low with episodic periods of high flows typically have diatom communities that are dominated by species of two aerophilic genera, many of which are endemic. Further, by comparing the abundance of invertebrates and diatoms in the cyanobacterial mats and sediments during cold (low flow) and warm (high flow) summers, we found that during the cold summer invertebrates were less abundant in the mats than in the underlying sediments, while during the warm summer this pattern was reversed.
These findings suggest that the optimal habitat for invertebrates in mats and sediments is partially driven by stream hydrology. This limitation on potential grazers (which are important nutrient transformers) during low flow may account for the accumulation of algal biomass and subsequent nutrient immobilization in the mats over many summers.