This project aimed at updating the scientific background for the assessment of different strategies for methane extraction from Lake Kivu.
As part of the project, we adapted the portable field mass-spectrometer recently developed by the Environmental Isotopes research group at Eawag for vertical profiling of gas concentrations in deep lakes. With this instrument, we contributed to an international intercalibration campaign with the aim of updating the concentrations of dissolved methane and carbon dioxide in Lake Kivu. The results showed that there was no significant increase of gas concentrations since the measurements that were performed in the 1970s.
The same instrument was also used to measure a vertical profile of the concentrations of dissolved noble gases and their isotopic composition in the lake. The results showed a a striking lack of atmospheric noble gases as well as a distinct non-atmospheric isotopic signal in the deep waters. The most likely explanation for these observations is that concentrations of atmospheric noble gases are depleted in the groundwater sources feeding the lake.
Finally, we developed a new transient model for Lake Kivu that considers the dynamic properties of the lake and can account for densitiy-driven stratification of the groundwater inflows. For this purpose, we coupled our successful one-dimensional physical lake model Simstrat to the Aquatic EcoDynamics Modelling Library AED2 of the University of Western Australia. The long-term simulations performed with this model showed that the previously postulated and subsequently partially detected groundwater inflows are fully sufficent to allow the emergence of the current density structure of the lake within a time frame of about 2000 years even from a completely mixed lake.