Fabian Bärenbold and his coworkers studied the gases in Lake Kivu in East Africa, which is well known for its huge reservoir of CH4 and CO2 dissolved in the deep waters. In view of the ongoing and planned extraction of CH4 for energy production, Fabian Bärenbold and his colleagues used a miniRUEDI and other gas analysis techniques (gas chromatography, laser spectrometery, and a total dissolved gas pressure). The measurement results show good agreement within 5–10%. The CH4 and CO2 dioxide concentrations in Lake Kivu are very similar to earlier results observed during the past few decades, which indicates that the risk for a limnic gas erruption of Lake Kivu has not increased.
Full paper: Fabian Bärenbold, Bertram Boehrer, Roberto Grilli, Ange Mugisha, Wolf von Tümpling, Augusta Umutoni, Martin Schmid. No increasing risk of a limnic eruption at Lake Kivu: Intercomparison study reveals gas concentrations close to steady state. PLOS, doi: 10.1371/journal.pone.0237836
For many gas species (e.g., He, Ar, Kr, N2, O2, CO2) the partial pressures measured with the miniRUEDI can usually be calibrated by simple peak-height comparison relative to ambient air or gas standard with well known partial pressures. However, depending on the composition of the analysed gases, the ion currents measured at certain m/z ratios may result from overlapping ion currents of multiple species (for example CH4, O2 and N2 at m/z=15 and 16; or Ne, Ar and H2O at m/z=20).
We developed a method that extends the miniRUEDI peak-height comparison in order to resolve such overlap interferences. The method uses spectral deconvolution and was incorporated in the ruediPy software toolbox. The deconvolution method substantially improves the analytical accuracy in situations where mass-spectrometric interferences cannot be avoided.
Full details are availalble in the original publication: M.S. Brennwald, Y. Tomonaga, R. Kipfer: Deconvolution and compensation of mass spectrometric overlap interferences with the miniRUEDI portable mass spectrometer, MethodsX, 2020, doi: 10.1016/j.mex.2020.101038
Clement Roques and his colleagues published a paper in Nature Scientific Reports, where they used a miniRUEDI to study changes of dissolved-gas concentrations in groundwater in response to hydraulic stimulation and fracturing of the reservoir rocks (Nature Scientific Reports, 10, 6949, 2020). The miniRUEDI was installed on-site to continuously analyse the dissolved-gas concentrations of the groundwater. The high-frequency He and Ar measurements indicate that trapped fluids were mobilized from the rocks in response to the fracking. The miniRUEDI revealed the nature and evolution of the fracture network and flow paths, and showed the effect of the fracking procedures on groundwater quality.
Full paper: “In situ observation of helium and argon release during fluid-pressure-triggered rock deformation.” Sci Rep 10, 6949 (2020). https://doi.org/10.1038/s41598-020-63458-x
Eawag News article: https://www.eawag.ch/en/news-agenda/news-portal/news-detail/observing-how-fissure-systems-are-formed-thanks-to-the-gas-sniffer/
Andrea Popp and her colleagues used a miniRUEDI to study the dynamics of the biogeochemical N2 turnover in a river/groundwater system over a six-month period (Environ. Sci. Technol. 2020, 54). In addition to N2, they analysed He, Ar and Kr concentrations in the water in order to quantify the air-derived N2 component in the groundwater. These miniRUEDI data allowed them to rigorously quantify the N2 excess produced by denitrification, and to unravel the spatio-temporal dynamics of N2 denitrification in the riparian groundwater system. The results show that denitrification is highly variable in space and time, emphasizing the need for spatially and temporally resolved data to accurately account for denitrification dynamics in groundwater.
Full paper: “A New in Situ Method for Tracing Denitrification in Riparian Groundwater”, Environ. Sci. Technol. 2020, 54, 3, DOI: 10.1021/acs.est.9b05393
In their recent paper “A Novel Approach To Quantify Air–Water Gas Exchange in Shallow Surface Waters Using High-Resolution Time Series of Dissolved Atmospheric Gases“, Uli Weber and his colleagues developed a new method to study and quantify the air-water gas exchange in a shallow surface waters. The method uses a miniRUEDI to quantify the natural variations of dissolved atmospheric gases in the water. The resulting high-resolution time series of dissolved gas concentrations in the water yield accurate gas exchange rates without adding artificial tracers.
In their recent paper “On-line monitoring of the gas composition in the full-scale emplacement experiment at Mont Terri (Switzerland)“, Yama Tomonaga and his colleagues at Nagra, Eawag and ETH Zurich used a miniRUEDI to study the dynamics and the fate of the gas species in a tunnel of a full-scale experiment targeted at radioactive waste disposal in Switzerland.
- An on-line gas monitoring has been implemented for the FE experiment at Mont Terri underground rock laboratory.
- The monitoring of gas species was performed successfully over several months.
- Rapid gas exchange occurs between drift backfilling and FE niche/host rock.
- Terrigenic gases (e.g., 4He, 40Ar, CH4, CO2) accumulated in the backfill pore space.
- Fast gas exchange partly explains the O2 removal from the backfill pore space.