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Aquatic Microbial Ecology

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AME 31:33-47 (2003)  -  doi:10.3354/ame031033

What limits bacterial production in the suboxic region of permanently ice-covered Lake Bonney, Antarctica?

B. B. Ward1,*, J. Granger1,3, M. T. Maldonado2,3, M. L. Wells2

1Department of Geosciences, Guyot Hall , Princeton University, Princeton, New Jersey 08544, USA
2School of Marine Sciences, Libby Hall, University of Maine, Orono, Maine 04469, USA
3Present address: Department of Earth and Ocean Sciences, Biological Sciences Bldg, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada

ABSTRACT: Bacterial production assays (thymidine incorporation rates) were used to evaluate the activity of heterotrophic bacteria at the chemocline region in both the East (ELB) and West (WLB) Lobes of permanently ice-covered Lake Bonney, in the Taylor Valley of Antarctica. The magnitude of activity varied dramatically within the depth interval of 1 to 2 m from moderate to very low levels below the chemocline, especially in the East Lobe, where chemical distributions indicate the absence of a normally functioning nitrogen cycle. Several parameters (e.g. addition of nutrients or chelators, dilution) were manipulated in incubation experiments in order to identify factors that would enhance activity in the suboxic deep waters of the East Lobe. Activity, in terms of thymidine incorporation, was consistently detected in the deep-water communities, implying that, although the water may be Œtoxic¹, the cells remain viable. None of the treatments resulted in consistent enhancement of thymidine incorporation rates in samples from below the chemocline. Bacterial populations above the chemocline appear to be phosphorus-limited. The nature of the limitation, toxicity or inhibition that limits bacterial activity in the suboxic waters has not been identified.

KEY WORDS: Antarctica · Metal chelators · Trace metals · Bacteria · Thymidine incorporation · Lake Bonney

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