Developing and Testing a Robust and Reliable Field Method for In-Situ Analysis of Dissolved Gases in Streams

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Reliably measuring dissolved concentrations of major and trace gases enables assessing the dynamics of water fluxes and biochemical turnover in aquatic systems. We want to establish a robust and reliable method for on-site gas-tracer measurements and continuous gas monitoring in rivers using a gas-equilibrium membrane inlet mass spectrometer capable of measuring concentrations of dissolved gases in a quasi-continuous manner. We further want to develop a consistent method for the determination of reaeration rate coefficients in streams using the mentioned field gas analyzer to determine the loss of dissolved gas tracers and the concentration of dissolved oxygen in streams and the hyporheic zone. Towards this ends we will adapt the instrument for gas-tracer tests in streams and test the applicability of different gas tracer compounds (namely noble gases and propane), conduct and evaluate gas-tracer tests in streams close to Tübingen, and adapt the method for small water volumes to make the application together with mini piezometers in the streambed feasible. The reliable measurements of injected gas tracers and dissolved oxygen will help to disentangle the interacting processes of gas-exchange, photosynthesis, and aerobic metabolism of dissolved oxygen in streams.