Distribution,production and consumption of nitrous oxide in the Baltic Sea |
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| Authors: | Ulf Rönner |
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| Institution: | Department of Marine Microbiology, University of Göteborg, Carl Skottsbergs Gata 22, S-413 19 Göteborg, Sweden |
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| Abstract: | Nitrous oxide supersaturation was measured in the Bothnian Bay, Bothnian Sea and four depth zones of the Baltic proper along with O2, NO?3, NO?2 and other parameters useful in interpreting the sources of the N2O. In the Baltic Sea supersaturation of N2O (123%) was found in the surface water of 0 to 0.5 m. The supersaturation resulted in a flux of N2O to the atmosphere of 2.8 × 10?2Tg N · yr?1 which was 5% of the estimated total nitrogen loss for the Baltic. For the entire photic zone (0 to 20 m) the N2O saturation was 135%. The source of the N2O is not clear, as the nitrification and denitrification were ruled out as sources. The N2O saturation was the lowest (118%) in the intermediate zone. Nitrification appears to be the likely N2O sorce in this region. At the halocline zone, an increasing oversaturation of N2O (200 to 300%) correlated with decreasing O2 concentrations and increasing NO?3 concentrations, indications of nitrification. Of the NH+4 that was oxidized to NO?3, 0.56% was produced as N2O. In the deep water zone, the supersaturation of N2O remained very high (150 to 200%). Sufficient O2, high NO?3 and the presence of nitrifying activity suggested nitrification as most likely source, however in deeper waters of this zone where oxygen was less than 2% saturation the N2O production could be due to denitrification. In anoxic waters the N2O concentrations rapidly decreased to zero suggesting N2O consumption by denitrification, further evidenced by a developing nitrate anomaly. |
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