Carbon dynamics in a large ultra-oligotrophic epishelf lake (Beaver Lake, Antarctica) during summer

• Published in: Freshwater Biology
• Main Authors: Laybourn-Parry, J, Madan, NJ, Marshall, WA, Marchant, HJ, Wright, SW
• Format: Article in Journal/Newspaper
• Language: English
• Published: Blackwell Publishing Ltd 2006
• Subjects: Biological Sciences; Microbiology; Microbial ecology; Austral; Beaver Lake; Antarc*; Antarctica
• Online Access: http://interscience.wiley.com; https://doi.org/10.1111/j.1365-2427.2006.01560.x; http://ecite.utas.edu.au/49046

1. Microbial plankton dynamics in an ultra-oligotrophic epishelf lake (Beaver Lake,Antarctica) were investigated over an austral summer (December 2002 to January 2003).The aim was to characterise carbon cycling in an environmentally extreme lake.2. The lake had an unusual temperature profile with peak temperatures of 1.3-1.9 Cbetween 20 and 25 m. Photosynthetically active radiation penetrated to the lake bottom(110 m) on occasions. The ice cover underwent marked thinning and melting during thestudy period.3. Chlorophyll a concentrations were consistently low, usually below 1 lg L)1, withhighest concentrations close to the lake bottom, where the photosynthetic elementsshowed strong autofluorescence. Mean photosynthetic nanoflagellates ranged between34.9 104 L)1 +/- 33.5 (23rd December) and 130.9 104 L)1 +/- 112.3 (4th December). Highestphotosynthetic activity was usually recorded below 25 m. Rates of carbon fixationvaried between 0.089 lg C L)1 h)1 +/- 0.002 and 0.579 lg C L)1 h)1 +/- 0.156. Primary productionwas limited by low temperature and orthophosphate availability.4. Mean bacterial concentration throughout the water column ranged between9.3 107 L)1 +/- 1.2 (23rd December) and 14.0 107 L)1 +/- 1.8 (28th January). Bacterialproduction was low, less than 10% of primary production and ranged between2.1 ng C L)1 h)1 +/- 0.8 and 12 ng C L)1 h)1 +/- 0.9. Highest rates coincided with times ofhighest primary production. On occasion dissolved organic carbon (DOC) concentrationsdropped to 20 lg L)1, probably below accurate limits of detection, suggesting that carbonsubstratum and phosphorus may have limited bacterial growth.5. Heterotrophic nanoflagellates varied significantly over the summer from a mean of26.6 104 L)1 +/- 14.2 (23rd December) to 133.8 104 L)1 +/- 33.5 (14th December). Theyimposed a significant grazing impact on the bacterioplankton, removing in excess of 100%of bacterial production in December.6. The total organic carbon pool [DOC and particulate organic carbon (POC)] was below600 lg L)1. The ratio ...