title: Chemodenitrification in the cryoecosystem of Lake Vida, Victoria Valley, Antarctica.
abstract: Lake Vida, in the Victoria Valley of East Antarctica, is frozen, yet harbors liquid brine (~20% salt, >6 times seawater) intercalated in the ice below 16 m. The brine has been isolated from the surface for several thousand years. The brine conditions (permanently dark, -13.4 °C, lack of O2, and pH of 6.2) and geochemistry are highly unusual. For example, nitrous oxide (N2O) is present at a concentration among the highest reported for an aquatic environment. Only a minor17O anomaly was observed in N2O, indicating that this gas was predominantly formed in the lake. In contrast, the17O anomaly in nitrate (NO3-) in Lake Vida brine indicates that approximately half or more of the NO3- present is derived from atmospheric deposition. Lake Vida brine was incubated in the presence of15N-enriched substrates for 40 days. We did not detect microbial nitrification, dissimilatory reduction of NO3- to ammonium (NH4+), anaerobic ammonium oxidation, or denitrification of N2O under the conditions tested. In the presence of15N-enriched nitrite (NO2-), both N2and N2O exhibited substantial15N enrichments; however, isotopic enrichment declined with time, which is unexpected. Additions of15N-NO2- alone and in the presence of HgCl2and ZnCl2to aged brine at -13 °C resulted in linear increases in the δ15N of N2O with time. As HgCl2and ZnCl2are effective biocides, we interpret N2O production in the aged brine to be the result of chemodenitrification. With this understanding, we interpret our results from the field incubations as the result of chemodenitrification stimulated by the addition of15N-enriched NO2- and ZnCl2and determined rates of N2O and N2production of 4.11-41.18 and 0.55-1.75 nmol L-1day-1, respectively. If these rates are representative of natural production, the current concentration of N2O in Lake Vida could have been reached between 6 and 465 years. Thus, chemodenitrification alone is sufficient to explain the high levels of N2O present in Lake Vida.
authors.affiliation: Department of Integrative Biology, Michigan State University, East Lansing, MI, USA. ostromn@msu.edu.
authors.forename: N E
authors.initials: NE
authors.lastname: Ostrom
authors.affiliation: Department of Integrative Biology, Michigan State University, East Lansing, MI, USA.
authors.forename: H
authors.initials: H
authors.lastname: Gandhi
authors.affiliation: Division of Earth and Ecosystem Sciences, Desert Research Institute, Reno, NV, USA.
authors.forename: G
authors.initials: G
authors.lastname: Trubl
authors.affiliation: Division of Earth and Ecosystem Sciences, Desert Research Institute, Reno, NV, USA.
authors.forename: A E
authors.initials: AE
authors.lastname: Murray
mesh_terms: D000864:Antarctic Regions; D058440:Denitrification; D060106:Lakes / Q000737:chemistry* / Q000382:microbiology*; D009566:Nitrates / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism*; D009587:Nitrogen Isotopes / Q000032:analysis; D009609:Nitrous Oxide / Q000378:metabolism
chemical_list: D009566:Nitrates; D009587:Nitrogen Isotopes; D009609:Nitrous Oxide; D009584:Nitrogen