User:Fernandesi/Lake Fryxell

Introduction Paragraph of Article
Lake Fryxell is a permanently ice-covered lake 4.5 km long and 20 m deep. It is located between Canada Glacier and Commonwealth Glaciers at the lower end of Taylor Valley within the McMurdo Dry Valleys in Victoria Land, Antarctica. It was mapped in the early 1900s and named during Operation Deep Freeze in the 1950s. There is an established campsite there for scientific studies of the several forms of microorganisms living in the waters as well as a weather station located at the lake.

Lake Ecology
There is a lack of oxygen within Lake Fryxell, which is unique when compared to other lakes in the region because the anoxic region extends up to 9 metres (30 ft) below the lake surface. This creates an environment similar to the planet about 2.4 billion years ago. The border between the anoxic and oxic zone, the chemocline, is around 9 to 11 m. Above the chemocline, sulfate increases with depth, maximum concentration at 11 m; below the chemocline, sulfate decreases to zero at the bottom and bisulfide increases with depth, maximum concentration at sediment boundary.

Within anoxic areas, scientists have found microbial mats that create small pockets saturated with oxygen. There are multiple forms of these mats within the lake, holding a sizable population of sulfate-reducing bacteria. Some samples of these bacteria live in very specific areas, such as specific water depths or locations causing them to experience differing physiochemical conditions. There are also a few archaea living in the anoxic zone, that contribute to the methane pockets under 11 m below the surface. Besides bacteria and archaea, there are many other organisms living with Lake Fryxell including algae, phytoplankton, fungi, as well as some microfauna.

Bacteria and Archaea
Microbial mats, including sulfate-reducing bacteria and archaea, are creating oxygen and methane pockets below the chemocline. In 2001 and 2003, Karr and others researched the archaea living in Lake Fryxell. Water samples were collected in depths between 9 and 17 metres, and used PCR analysis to determine the organisms. They discovered three clusters of Euryarchaeota and one cluster of Crenarchaeota. Two of the Euryarchaeota clusters were found to be methanogenic and all three catalyzed neighboring sulfate-reducing bacteria. In another study, Karr and others took water samples between 8 and 17 m as well as sediment samples in the same years. They discovered three genera of sulfate-reducing bacteria in Lake Fryxell: Desulfobulbus, Desulfobacter, and Desulfovibro. Desulfobulbus occurred in the sediment as well as at 9 metres. Desulfobacter was only found within the chemocline (9 - 11 metres). Desulfovibro was found throughout the anoxic region below the chemocline. The dominant bacterium and phototroph throughout Antarctica are the diverse Cyanobacteria. In Lake Fryxell alone, 8 different morphotypes were found in the field and 3 in a microbial mat sample taken from the benthic zone.

Algae and Phytoplankton
There are blue-green algae and green algae that occur in the euphotic zone just above the chemocline. McKnight and others wondered how photosynthetic algae maintained growth throughout the dark winters of Antarctica. Their study reported that there were phytoplankton present year-round, and how during the austral winter some taxa survived. They found 23 taxa occurring during summer and only 15 during winter. Of the taxa, most consisted of genera Chlorophyta, Cyanophyaea, and Cryptophyta. Two cryptophytes were found to live year round just about the chemocline. It was also reported that green algae survived the winter months by grazing on cyanobacteria. Another study investigated how phytoplankton above the chemocline responded to nutrient enrichment during the summer. They collected samples from 4.5 m to 9 metres, as the lake is covered by about 4 metres of ice. It found that nitrogen and phosphorous increased as depth did, and that 'surface' level algae were most nutrient deficient. Only samples at 4.5 m had a increased photosynthetic capacities with increased nitrogen. The other samples had no significant response to increased nitrogen or increased nitrogen and phosphorous.

Fungi
Research into the fungal species of Antarctica is still in the early stages and not widely researched. Connell and others drilled holes in the ice in 2003, 2008 and 2010, to investigate fungal biodiversity. Water samples were collected at various depths between 7 and 14 m. Fungal growth was monitored weekly up to 18 months after the sample was collected. They found 30 different species in Lake Fryxell over all the different depths. All of the fungi came from the genera Ascomycota and Basidiomycota. Most species lived above and below the chemocline or throughout the water no matter the depth. There are two species - Glaciozyma and Penicillium - that did not occur below the chemocline. There were three species as well that were only found below 11 m, the chemocline. The Glaciozyma species appeared to make up 69% of the total fungi.

Microfauna
The first study of microfauna throughout the lakes of Southern Victoria Land by Cathey and others found multiple genera of protozoa, rotifers, tardigrades, and nematodes. They collected algal mat samples at all depths in 1977 and 1978, that were analyzed within a couple days at the nearby lab McMurdo Station. In Lake Fryxell specifically, 75 different microfauna taxa were discovered, including 5 different orders of protozoa as well as 2 genera of rotifers, and one genus of tardigrades.