Differential N2O dynamics in two oxygen‐deficient lake basins revealed by stable isotope and isotopomer distributions. (24th June 2016)

• Record Type: Journal Article
• Authors: Wenk, Christine B.; Frame, Caitlin H.; Koba, Keisuke; Casciotti, Karen L.; Veronesi, Mauro; Niemann, Helge; Schubert, Carsten J.; Yoshida, Naohiro; Toyoda, Sakae; Makabe, Akiko; Zopfi, Jakob; Lehmann, Moritz F.
• Is Part Of: Limnology and oceanography. Volume 61:Number 5(2016)
• Page Start: 1735
• Page End: 1749
• Publication Date: 2016-06-24
• Subjects: Limnology -- Periodicals; Oceanography -- Periodicals; Océanographie; Limnologie; Limnology; Oceanography; Computer network resources; Périodique électronique (Descripteur de forme); Ressource Internet (Descripteur de forme); Periodicals; 551.4805
• DOI: 10.1002/lno.10329
• Languages: English
• ISSNs: 0024-3590

Abstract

Abstract: Lakes are a nitrous oxide (N2 O) source to the atmosphere, but the biogeochemical controls and microbial pathways of N2 O production are not well understood. To trace microbial N2 O production (denitrification, nitrifier denitrification, and nitrification) and consumption (denitrification) in two basins of Lake Lugano, we measured the concentrations and N and O isotope compositions of N2 O, as well as the intramolecular 15 N distribution, i.e., site preference (SP). Our results revealed differential N2 O dynamics in the two lake basins, with N2 O concentrations between 12 nmol L −1 and > 900 nmol L −1 in the holomictic South Basin, and significantly lower concentrations in the meromictic North Basin (<13 nmol L −1 ). In the South Basin, the isotope signatures reflected a complex combination of N2 O production by nitrifying bacteria through hydroxylamine (NH2 OH) oxidation, N2 O production through incomplete denitrification, and N2 O reduction to N2, all occurring in close vicinity within the redox transition zone (RTZ). In the North Basin, in contrast, the N2 O isotopomer signatures suggested that nitrifier denitrification was the main N2 O source. The pronounced decrease in N2 O concentrations to undetectable levels within the RTZ, in tandem with an increase in δ 15 N‐N2 O, δ 18 O‐N2 O, and SP indicated quantitative N2 O consumption by microbial denitrification. In the northern basin this was primarily sulfide‐dependent. The apparent N and O isotope enrichment factors associated with net N2 O consumption were 15 ε ≈ 3.2‰ and 18 ε ≈ 8.6‰, respectively. The according 18 O to 15 N enrichment ratio ( 18 ε : 15 ε ≈ 2.5) is consistent with previous reports for microbial N2 O reduction, underscoring its robust nature across environments.