nitrogen cycle; denitrification; anammox; DNA analyses; stable isotopes; microbial community structures; biomarker; Lake Lugano; nitrogen; isotope effects; core incubations; sediment fluxes; nitrate; N2O; 15-N tracer; microbial ecology
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. (2016), Differential N 2 O dynamics in two oxygen-deficient lake basins revealed by stable isotope and isotopomer distributions Differential N 2 O Dynamics in Two Lake Basins, in Limnology and Oceanography
, 61(5), 1735-1749.
Wenk Christine, Zopfi Jakob, Blees Jan, Veronesi Mauro, Niemann Helge, Lehmann Moritz F. (2014), Community N and O isotope fractionation by sulfide-dependent denitrification and anammox in a stratified lacustrine water column, in Geochimica et Cosmochimica Acta
, 125, 551-563.
Wenk Christine B., Zopfi Jakob, Gardner Wayne S., McCarthy Mark J., Niemann Helge, Veronesi Mauro, Lehmann Moritz F. (2014), Partitioning between benthic and pelagic nitrate reduction in the Lake Lugano south basin, in Limnology and Oceanography
, 59(4), 1421-1433.
Wenk Christine B., Blees Jan, Zopfi Jakob, Veronesi Mauro, Bourbonnais Annie, Schubert Carsten J., Niemann Helge, Lehmann Moritz F. (2013), Anaerobic ammonium oxidation (anammox) bacteria and sulfide-dependent denitrifiers coexist in the water column of a meromictic south-alpine lake, in LIMNOLOGY AND OCEANOGRAPHY
, 58(1), 1-12.
Brunner B., Contreras S., Lehmann M. F., Matantseva O., Rollog M., Kalvelage T., Klockgether G., Lavik G., Jetten M. S. M., Kartal B., Kuypers M. M. M. (2013), Nitrogen isotope effects induced by anammox bacteria, in Proceedings of the National Academy of Sciences
, 110(47), 18994-18999.
Freymond Chantal V. (2013), NOx reduction is the main pathway for benthic N2O production in a eutrophic, monomictic south-alpine lake, in Biogeosciences Discussions
, 10, 4969-4993.
Bioavailable nitrogen (N) from anthropogenic sources is an important driver of lacustrine eutrophication. However, N loading in lakes is partially mitigated by microbially mediated processes that take place in redox transition zones (RTZ) within the water column and in sediments. Modes of bacterial N2 production other than canonical denitrification (e.g., the anaerobic oxidation of ammonium, or anammox) have barely been investigated in lakes, and the microbial communities involved in N transformations in lacustrine RTZ are mostly unknown.Nitrogen isotope ratios can provide important constraints on natural N cycles. In order to use natural abundance stable isotope ratios of dissolved inorganic N (DIN) species as a means to trace fluxes and transformations of N in aquatic systems, it is imperative to understand the isotope effects associated with these specific N transformations. This will also provide information on the transformations themselves. Yet, the possible impact of N2 production processes other than denitrification on global and regional N-isotope budgets has been ignored thus far.Lake Lugano is an excellent model biosystem for an anthropogenically impacted lake. Previous studies have revealed that this lake represents an important sink for fixed N. In addition, they indicate the presence of suboxic consumption of ammonium and, thus, suggest that "non-traditional" N2 production processes are active in anaerobic portions of the lake. We propose to address the following main research questions:1.)What are the different metabolic pathways of suboxic N2 production in the Lake Lugano water column and in sediments? What are the associated N-isotope effects?2.)Which microorganisms are responsible for observed N transformations and what are their interactions?3.)What are the respective transformation rates and fluxes and how are they regulated? We propose one interdisciplinary PhD project that will combine microbiological (phylogenetic/molecular genetic analysis) with organic-geochemical (anammox lipid analysis) and isotopic techniques (natural abundance and 15N tracer experiments), to gain complementary information on specific N transformations and mechanisms of N2 loss in Lake Lugano sediments and in the water column, on the microorganisms involved in these transformations, their relevance for the Lake Lugano nitrogen budget, and their effects on the N isotope balances, both at the enzyme and ecosystem levels. The project will culminate in a mathematical model that will simulate microbial N-transformations within the lake sediments, allowing the assessment of the response of elemental and isotope budgets to changes in environmental conditions at various spatial and temporal scales. The project will provide extensive multidisciplinary training for one student at the graduate level in a field of high environmental relevance. The research proposed here will result in the first microbiological assessment of N transformations in Lake Lugano, and may help gaining insights into novel modes of autotrophic life in lakes. Quantitative estimates of N elimination in both the water column and sedimentary RTZ of Lake Lugano will be a prerequisite for ecosystem-scale N budgets and will be integrated in box-model simulations. Moreover, estimates of isotope effects of specific N transformations in the modern lake will provide the basis for paleolimnological extrapolation. Thus, the proposed research will help us address biogeochemical processes that are important for the general understanding of a complex ecosystem, both today and in the past. It will also provide useful information that is directly pertinent to the health of an important Swiss water body.