Cavity Ring Down Spectrometer (CRDS)

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The relatively new technology Cavity Ring Down Spectroscopy (CRDS) enables fast and reliable measurement of absolute concentrations of isotopic 13C- and 12C-CO2, and 13C-C and 12C-CH4, in gas samples. CRDS is superior to conventional methods such as GC isotope-ratio mass spectrometry (GC-IRMS): the instrument is comparatively small, robust and easy to maintain, and it can be deployed also to in situ measurement campaigns in the field. CRDS to detect these gases not only by their isotopic ratio but in their absolute quantities, is essential for two main research applications proposed here: (i) improving the biodegradability of novel polyethylene-like polymers, and (ii) assessing the processes responsible for the distribution and the fluxes of methane in freshwater lakes.In a collaborative project, we are optimizing the microbial degradation of novel, fully recyable, long-chain polyester materials synthesised from renewable resources (plant oil). Complete degradation of plastic by environmental microbial communities is typically monitored via the evolution of CO2. However, to differentiate the CO2 evolved from background activity in complex environmental matrices (e.g. soil, compost), labelling of the polymers with 13C-carbon isotope is the method of choice. At University of Konstanz exists an unprecedented opportunity in that sufficient amounts of 13C labelled long-chain polyesters can be made accessible for biodegradation experiments. CRDS enables us to selectively and very precisely follow the plastic-carbon through the cascade of transformation processes towards the end product 13C CO2 in complex natural matrices. Thereby, we can fine-tune in iterative cycles the frequency of ester-links and side groups breaking up the crystallinity of the polymers, towards a development of novel polymers that combine sufficient material properties and complete biodegradability within few years instead of decades or centuries.Additionally, CRDS enables us to evaluate spatial and temporal distributions and release of the greenhouse gases CO2 and CH4 from freshwater ecosystems such as Lake Constance and other lakes and reservoirs, in unprecedented in-situ studies, e.g., field campaigns on a research ship and when sampling along the water column. This will acquire 13C/12C-CH4 ratios and parent concentrations and thus, allow for distinguishing of CH4 production (anaerobic and aerobic methanogenesis), transport (e.g., diffusive emission) and transformation (e.g., aerobic and anaerobic CH4 oxidation) processes. We thereby will disentangle the origin of the dissolved CH4 in the stratified water column and the oversaturation of CH4 in the oxic water layers of lakes (‘methane paradox’). Overall, CRDS may enable us to resolve several long-standing questions on the CH4 production, transformation, transport and emission phenomena for freshwater lakes to, ultimately, improve climate models.H4