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Aquatic Microbial Ecology

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AME 38:295-307 (2005)  -  doi:10.3354/ame038295

Denitrification in the hypolimnion of permanently ice-covered Lake Bonney, Antarctica

B. B. Ward1,*, J. Granger1,4, M. T. Maldonado2,4, K. L. Casciotti1,5, S. Harris3, M. L. Wells2

1Geosciences Department, Princeton University, Princeton, New Jersey 08544, USA
2School of Marine Sciences, University of Maine, Orono, Maine 04469, USA
3Mother of Mercy High School, Cincinnati, Ohio, USA
4Present address: Department of Earth and Ocean Sciences, University of British Columbia, 6270 University Blvd., Vancouver, British Columbia V6T 1Z4, Canada
5Present address: Woods Hole Oceanographic Institution, 360 Woods Hole Road, Woods Hole, Massachusetts 02543, USA

ABSTRACT: The distribution of denitrification was investigated in the hypolimnion of the east and west lobes of permanently ice-covered Lake Bonney, Taylor Valley, Antarctica. Anomalously high concentrations of dissolved inorganic nitrogen (DIN; nitrate, nitrite, ammonium and nitrous oxide) in the oxygen-depleted hypolimnion of the east lobe of the Lake implied that denitrification is or was active in the west, but not in the east lobe. While previous investigations reported no detectable denitrification in the east lobe, we measured active denitrification in samples from both the east and west lobes. In the west lobe, measured denitrification rates exhibited a maximum at the depth of the chemocline and denitrification was not detectable in either the oxic surface waters or in the deep water where nitrate was absent. In the east lobe, denitrification was detected below the chemocline, at the depths where ammonium, nitrate, nitrite and nitrous oxide are all present at anomalously high levels. Trace metal availability was manipulated in incubation experiments in order to determine whether trace metal toxicity in the east lobe could explain the difference in nitrogen cycling between the 2 lobes. There were no consistent stimulatory effects of metal chelators or nutrient addition on the rate of denitrification in either lobe, so that the mechanisms underlying the unusual N cycle of the east lobe remain unknown. We conclude that all the ingredients necessary to allow denitrification to occur are present in the east lobe. However, even though denitrification could be detected under certain conditions in incubations, denitrification is inhibited under the in situ conditions of the lake.

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

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