Recent advances in biogeochemistry (biomarker analyses, compound-specific carbon isotope analyses of lipids) and microbiological techniques (FISH, DNA sequencing) have been very successfully employed in deciphering formation and/or transformation processes of organic material in the ocean. In contrast to the marine environment, the contribution of terrestrial ecosystems to the global carbon budget and the concentration of greenhouse gases (carbon dioxide, methane) in the atmosphere are only scarcely known. Terrestrial aquatic ecosystems participate in biogeochemical cycling of carbon species and act as carbon sinks or sources in response to environmental parameters. In this study, we will analyse particulate organic matter from different levels of the water column and on the underlying sediments from a eutrophic (Lake Lugano) and from an oligotrophic lake (Lake Thun, Switzerland). Lipids as markers specific for phytoplankton groups, land plants, bacteria, and archae will be quantified in the extractable organic matter and analysed for their carbon isotopic composition.
The project will also include analyses of water chemistry, isotopic composition of dissolved inorganic carbon species, total organic carbon and sedimentary carbonates. The differences in the net carbon fluxes and isotopic fractionation processes within an oligotrophic lake and a eutrophic limnic environment will be outlined. Information about the environmental parameters affecting the carbon cycles within the water column and their influence o n the net carbon fluxes of the lakes are expected from the proposed research.
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