Lake Kivu will not explode anytime soon, says miniRUEDI

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

Deconvolution and compensation of MS interferences

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

Running on Batteries

We frequently get asked how to run the miniRUEDI on batteries for field work at remote locations with no mains power.

Here are the basics to run the miniRUEDI on batteries:

  • The miniRUEDI runs on a voltage of 24 V.
  • The miniRUEDI draws about 2 A current during normal operation, and up to about 5 A or slightly more during startup of the pumps.
  • You need a fuse. Batteries do not like short circuits or similar mishaps. A 10 A rating should be fine.
  • Unplug the 24 V connections of the main power supply unit in the miniRUEDI, and connect the batteries to the miniRUEDI instead.

There are many ways to set up a battery power supply, but here is a simple setup that uses two simple «12 V car batteries»:

The capacity of the batteries determines how long they will be able to supply power to the miniRUEDI. Two of the typical «12 V car batteries» with a capacity rating of 60 Ah may last up to a full day before they need to be recharged.

Video: miniRUEDI at work on Lake Rotsee

Eawag made a video about how a miniRUEDI is used to study the dynamics and the turnover of gases in Rotsee – hear me speak good old Swiss German (with English subtitles). Sorry for the field-work background noise!

In-situ monitoring of noble gases in groundwater during rock fracking

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).

Eawag News article:

miniRUEDI goes sailing

Researchers from the Max Planck Institute for Chemistry (Germany) installed a miniRUEDI on the Eugen Seibold, the world’s greenest research vessel. Since May of 2019, the innovative yacht has been sailing the high seas, and the miniRUEDI is set up to continuously analyse the dissolved gas concnetration in the surface water. By gradually gathering data on the various marine provinces, the climate geochemists at the Max Planck Institute for Chemistry in Mainz will be able to chart a detailed description of the world’s oceans, characterising their current properties and even reconstructing how they change over time.

miniRUEDI goes to college

miniRUEDI used for college teaching: Noble gas lab manager Darren Hillegonds from the University Oxford Earth Scienes visited Brockenhurst College with his miniRUEDI for British Science Week. Great talks with A-Level Chemistry and Geology students!

A New in Situ Method for Tracing Denitrification in Riparian Groundwater

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, 1562-1572, DOI: 10.1021/acs.est.9b05393

Using a miniRUEDI to identify and quantify groundwater mixing

In their recent paper “Integrating Bayesian Groundwater Mixing Modeling With On‐Site Helium Analysis to Identify Unknown Water Sources“, Andrea Popp and her Eawag colleagues studied a groundwater system used for drinking water production. The drinking water field needs to be protected from several potential sources of contamination by artificially controlling the groundwater flow. In view of these problems, the Eawag team identified the origins of the different groundwater components in the drinking water field and quantified their mixing ratios using a miniRUEDI by analysing He and other dissolved gases as natural tracers for the different groundwater components.

Namn Ghum river run for science

Eddie Banks from Flinders University took all his instruments to Laos to study the river/groundwater exchange over hundreds of kilometers along the Namn Ghum river. Take a look at his photos of how the very first miniRUEDI made by Gasometrix sniffs the waters!