Research (Lehmann Group)
One of the foci of recent research activities is to understand the isotope effects of individual biological N transformations (and associated microbiological controls). Specifically, we are interested in linking the N and O isotope distributions in dissolved inorganic nitrogen species (i.e., NOx and N2O) and N2O dynamics in aquatic environments to the rates of key microbial nitrogen transformations such as ammonia oxidation, nitrite oxidation, denitrification, and anammox.
A second important research theme within our group is the Biogeochemistry of CH4. We study aerobic and anaerobic methane oxidation in various lacustrine and marine environments, investigating environmental controls on CH4 turnover and on the microbial community structure, and developing methane budgets on different spatial scales. Integrating Biomarker geochemistry with isotope analyses, the identification and isotopic characterization of specific lipids in environmental samples provides information on the community structure and thus biogeochemical processes, both in modern and paleo environments.
Another important research theme is the Cycling and bacterial degradation of organic matter in aquatic environments, its role in the generation of permanently or temporarily anoxic conditions, as well as its impact on solute exchange and Redox reactions within sediment pore waters of marine and lacustrine environments. We study the fate of sedimentary organic matter not only in the context of compositional changes during microbial remineralization and their relevance for elemental budgets, but also with regards to the susceptibility of different organic compounds, their biomarker signatures, as well as their isotopic composition to post-burial alteration.
Our work in modern ecosystems, and our experimental work validating the preservation potential of primary organic-geochemical and isotopic signatures, provides the basis for using isotope and biomarker proxies in Paleoenvironmental studies, for example the reconstruction of paleo-temperature or paleo-productivity in Swiss lakes through the analysis of specific bacterial membrane biomarkers and the isotopic composition of lacustrine organic material in sediment cores.