Category Archives: Papers

How gases travel in lakes

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An international team of researchers used several miniRUEDIs to study the 3D transport of dissolved gases in a eutrophic lake. The water in the littoral zone cools faster during the night and therefore causes a lateral «syphon stream» that transports water along the sediment, and which is balanced by corresponding water flow at the surface. Krypton was injected into the littoral water to track the syphon stream, and to quantify the transport of other, naturally abundant gases in the lake. High-frequency miniRUEDI measurements demonstrate that daily convective horizontal circulation generates littoral-pelagic transport one order of magnitude larger than typical horizontal fluxes assumed in previous gas budgets. These lateral fluxes are sufficient to redistribute gases at the basin-scale and generate concentration anomalies reported in other lakes.

Tomy Doda, et al., “Lake surface cooling drives littoral-pelagic exchange of dissolved gases”, Science Advances, 2024. DOI: 10.1126/sciadv.adi0617

An unusual marriage of miniRUEDI data, environmental DNA and vanadium tracers shows that Mt. Fuji isn’t as easy as previously thought

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Mount Fuji’s freshwater springs are not only fed by water recharged at high altitude, but also by the upwelling of deep groundwater. This was observed by Oliver Schilling and his team, who used miniRUEDI data combined with environmental DNA and vanadium tracers. Read the full story in Nature Water.

miniRUEDI shows how gases control the accumulation of arsenic in drinking water resources

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Alex Lightfoot and her colleagues at Eawag, CSIRO, RIBES, and KIT used a miniRUEDI to study the interaction of groundwater with gases trapped in an aquifer in the Red River delta (Vietnam). They demonstrated how the gas controls the mobilisation and accumulation of arsenic in the groundwater, which is an important drinking water source.

Full paper: Alexandra K. Lightfoot, Matthias S. Brennwald, Henning Prommer, Emiliano Stopelli, Michael Berg, Martyna Glodowska, Magnus Schneider, Rolf Kipfer. Noble gas constraints on the fate of arsenic in groundwater. Water Research, doi: 10.1016/j.watres.2022.118199

Understanding PCE contamination of groundwaters

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In their recent recent paper, Chrisitan Moeck and his Eawag colleagues used a miniRUEDI to study the groundwater flow and perchloroethylene (PCE) transport in an urban aquifer system. They used dissolved He concentrations measured with a miniRUEDI to establish a relationship with 3H/3He groundwater ages, which allowed them to characterize the water flow and provided conceptual understanding of the groundwater system. The combination of the groundwater age data (miniRUEDI He, 3H/3He) with hydrochemical data, water isotopes (18O and 2H), and PCE concentrations showed the spatial inter-aquifer mixing between artificially infiltrated groundwater and water originating from regional flow paths. Furthermore, the correlation of groundwater age with PCE concentration explained the spatial distribution of PCE contaminations within groundwater system. In addition, faults were observed to provide preferential flow paths that lead to elevated PCE concentrations.

Full paper: C. Moeck, A.L. Popp, M.S. Brennwald, R. Kipfer, M. Schirmer: Combined method of 3H/3He apparent age and on-site helium analysis to identify groundwater flow processes and transport of perchloroethylene (PCE) in an urban area. J. Contaminant Hydrology, doi: 10.1016/j.jconhyd.2021.103773

From Snow to Groundwater

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Oliver Schilling (Université Laval and Centre for Hydrogeology and Geothermics) and his colleagues used a miniRUEDI for on-site quantification of dissolved He, Ar, Kr, N2, O2 and CO2 in groundwaters of a boreal catchment in Canada. The gas data allowed them to quantify the contribution of snowmelt to groundwater recharge, to analyze the temporal recharge dynamics, and to identify the primary recharge pathways. Furthermore, they observed a systematic depletion of N2 in groundwater, which provides insights into the biological N‐fixation in boreal forest soils.

Full paper: O. S. Schilling, A. Parajuli, C. Tremblay Otis, T. U. Müller, W. Antolinez Quijano, Y. Tremblay, M. S. Brennwald, D. F. Nadeau, S. Jutras, R. Kipfer, R. Therrien. Quantifying groundwater recharge dynamics and unsaturated zone processes in snow‐dominated catchments via on‐site dissolved gas analysis. Water Research, doi: 10.1029/2020WR028479

Lake Kivu will not explode anytime soon, says miniRUEDI

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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

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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.

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

Some typical examples for such overlap interferences:

  • Methane (CH4): The main CH4 peaks occur at m/z = 15 and 16, which are affected by interference signals from 15N, 16O, and doubly ionised O2 molecules.
  • Neon (Ne): The peaks of the main Ne isotopes (at m/z = 20 and 22) overlap with those of isotopically heavy H2O and the peaks of doubly ionised Ar and CO2.
  • Propane (C3H8), ethane(C2H6), or similar hydrocarbons in air-like samples: some peaks of the hydrocarbon mass spectra tend to overlap those of N2 and CO2.
  • Hydrogen (H2): the the mass-spectrometric peak of the H2 in the sample gas may be masked by H2 produced in the ion source of the mass spectrometer. Ionisation of molecules containing hydrogen may “knock off” one or multiple H atoms, which then interfere with the analysis of the H2 in the sample gas. H2 analysis therefore works best if the concentration in the sample gas is high (about 1‰ vol/vol or higher), and the concentrations of H-containing gas species is low.

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

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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/

A New in Situ Method for Tracing Denitrification in Riparian Groundwater

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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

miniRUEDI used to quantify air-water gas exchange in surface waters – without adding tracer gases!

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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.