User:Dmpopson/Lake Bonney (Antarctica)

Lake Ecology
Lake Bonney is located in the McMurdo Dry Valleys, Antarctica. The McMurdo Dry Valley is the largest ice free region in Antarctica and is a polar desert. This relative lack or water in the surrounding area makes Lake Bonney and the other lakes in the region (see the McMurdo Dry Valleys page for a full list) particularly influential to the biota there. It is comprised of the East and West lobes, which are connected by a shallow channel which allows for minimal connectivity between the lobes. The west lobe of the lake receives inputs from the Taylor Glacier and is also the sight of Blood Falls, an inflow area that appears red due to high concentrations of iron oxide deposits. The East lobe of the lake is the larger section spanning 4.8km with a maximum depth of 37m. The West lobe spans 2.6km, and reaches 40m in depth. Year-round ice cover on the lake results in permanent thermal stratification of the water column in both lobes. This stratification results in isolated regions of varying temperature, salinity, and nutrient levels that result in unique communities at varying depths in the lake. While both lobes are stratified, the West lobe has lower average temperatures ranging from approximately -5°C to approximately 3°C depending on depth. Whereas the East lobe ranges from around -2°C to 6°C. In addition to the extreme cold, communities and processes within the lake are heavily influenced by the 4 months of 24 hour darkness experienced in Antarctic winter. Current research there focuses on the effects of extreme conditions on microbial communities, as well as the current and potential impacts of climate change on the lake.

Use as a Research Model
The extreme environment of Lake Bonney makes it an area of interest for various types of research. The ice cover on the lake makes it a potential model for astrobiology research as it can serve as a model for areas like Europa which are thought to have similar ice covered water systems. Additionally, the organisms in the lake are subjected to a number of stresses including low temperature, high salinity, and low light levels, which allows for study of adaptations and interactions that may contribute to survival under these pressures. One particular area of interest has been how photosynthetic organisms in the lake mediate salt and temperature stress. Crop plants are particularly susceptible to salt and temperature stress and thus research into engineering mechanisms for protection is an area of particular interest. Lake Bonney is also unique as an area of study due to it being inhabited solely by microbial organisms. This separation from higher trophic levels as well as any significant anthropogenic influences makes the lake a unique case study on microorganism activities and interactions.

Long-Term Ecological Research Program
The McMurdo Dry Valleys, where Lake Bonney is located, are one of 28 sites part of the National Science Foundation (NSF) Long-Term Ecological Research (LTER) Program. The aims of this project focus on the lakes, soils, and glaciers in the area to gain a more detailed understanding of how extreme environments shape the organisms that live there. Study of this microbial dominated area is useful in studying the influence of human activities and climate change. Lake Bonney and the surrounding environment have been the subject of study as a part of this program since 1992 and field teams have been deployed annually since 1993. Throughout this time the research has focused on a number of areas with the most recent research looking at how climate change may influence connectivity in this generally isolated and unchanging environment. LTER researchers predict that increasing temperature will result in lake level rise and influx of more freshwater into the lake which may disrupt the stratified ecosystems within the lake. This mixing of communities has potential to impact the diversity of the communities and their resistance and resilience to environmental changes.

Primary Production
Lake Bonney is inhabited solely by microbial organisms. Thus, the activity of phytoplankton as primary producers is essential to the biogeochemical cycling in the lake. Previously, little was known about how these communities fluctuate seasonally, as studying the lakes during polar night presents unique challenges. However, using data detected using a fluoroprobe, which measures phytoplankton group abundances, new insights into these communities was established. Seasonal differences were distinct in the West lobe and East lobe of the lake, with both lobes being dominated by Chlorophytes. Additionally, chlorophyll levels remained at a steady level throughout the dark period providing evidence of the importance of mixotrophic organisms in this system. In addition to seasonal light limitations, the ice cover leads to limited light within the lake even during the light season. In addition to limiting the overall productivity of the lake, this light limitation has pushed the photosynthetic organisms located there to adapt to extreme shade conditions resulting in altered photochemistry. Adaptation to the stable conditions within the lake is a driving force into current research on how organisms such as these shade adapted phytoplankton may respond to environmental fluctuations in light of global warming.

Biogeochemical Cycling
The lack of higher organisms in Lake Bonney also makes it an interesting proxy for studying biogeochemical cycling. The permanent ice cover acts as a barrier which limits the input of nutrients from the air, thus much of the influx of nutrients comes from adjacent glaciers. The lake is oligotrophic, so recycling of nutrients is important for maintenance of the communities within the lake. Additionally, Nitrogen to phosphorus ratios within the lake show that the system is extremely phosphorus limited which largely impact the phytoplankton communities and thus the rate of carbon fixation. While gas exchange may be limited, soil aggregate in the ice cover of the lake seem to play a larger role in the nutrient availability within the lake. Soil from the surrounding valley can get stuck in divots in the ice as it gets blown across allowing nutrients to enter the system. These soil aggregates serve as hotspots of microbial activity which further enhances the role these inputs have in nutrient cycling.