A crucial element in better understanding climate change and its impact on hydrological, biogeochemical and ecosystem dynamics lies in the accurate monitoring of hydrological and biogeochemical processes. However, most available analytical techniques for the measurement of (greenhouse) gases in the environment are either laboratory based or based on instrumentation built for in-field applications in warm and temperate climates. In (sub)polar and high-altitude regions, existing analytical techniques face significant challenges due to the very cold and typically harsh environment.
The initial idea to develop a robust tool emerged during a particularly cold and snowy winter in Québec, Canada. Tackling the challenge of understanding groundwater recharge processes by obtaining continuous measurements of noble gases, greenhouse gases, O2 and N2 dissolved in groundwater, it rapidly became clear that the recently developed gas equilibrium-membrane inlet mass spectrometer (GE-MIMS), aka the “miniRUEDI”, [1] was not yet suited for continuous measurement in temperatures regularly dropping below -30°C. While the relative proximity of the field site to Québec City allowed for bi-weekly field campaigns for discrete sampling, continuous monitoring was out of the question. And even the bi-weekly campaigns relied heavily on a custom-built heated snowmobile trailer.
© 2018 O. S. Schilling, all rights reserved
Although the bi-weekly sampling of gases in groundwater over the course of a full year enabled many new insights into snowmelt recharge processes and gas dynamics (including the first direct observation of N2-fixation directly from groundwater in boreal systems [2]), it was impossible to continuously measure gas concentrations and fluxes all the way from the subsurface – through soils, surface water bodies and snowpacks – to the atmosphere in such cold environments. The most important issue was the fact that the existing technology relied on actively and continuously pumping water through a membrane module, which upon even just short power outages would result in nearly instantaneously frozen tubing bringing the continuous measurement to a halt.
With this SPI Technogrant, we therefore aimed at extending the versatile miniRUEDI technology for the continuous and parallel measurement of interstitial air and gases dissolved in water in very cold environments. To avoid the problem of freezing water lines, the new technology builds on direct gas sensing instead of pumping water. It uses extremely robust, passive membrane modules custom built by Solexperts AG (Switzerland). In 2022 and 2023, the new system was developed and systematically tested by us in the laboratory of the Hydrogeology Research Group at the Department of Environmental Sciences of the University of Basel. In the winter of 2023-2024 and with the help of Dr. Stéphanie Musy, Friederike Currle and Michel Walde, the extended cold-regions miniRUEDI system, aka the “snowRUEDI“, was deployed for a pilot measurement phase in the long-term hydrological observatory Alptal, run by Dr. Manfred Stähli of WSL.
© 2023 F. Currle, all rights reserved
The successful pilot deployment in the Erlenbach catchment allowed us to learn how to avoid important pitfalls related to the installation and operation of the snowRUEDI passive membranes and very finicky 10-m-long stainless-steel capillaries in seasonally frozen soils. We were finally ready to implement the new technology at the Pallas atmosphere-ecosystem super site in Northern Finland (67°59’50.2″N 24°12’33.8″E) [3]. Together with our colleagues Prof. Dr. Pertti Ala-Aho, Dr. Anna Autio and Prof. Dr. Hannu Marttila from Oulu University, and with the support of the Finnish Meteorological Institute who operate the atmosphere watch site at the Pallas, we installed our extended snowRUEDI passive membrane system. It was set for continuous monitoring of gases in the groundwater, in the variably saturated, shallow peat layers, in the snow and in the air.
The monitoring has so far been extremely successful. Not a single problem occurred, which is to a large part owed to the generous field support by the team at Pallas. The system indeed allowed tracking gas fluxes from the groundwater and soils through the snow and to the atmosphere, and highly interesting methane and carbon dioxide buildups during winter and releases during the spring melting period could be observed. Owing to the success, after a full year of running smoothly we decided to continue monitoring for another full year in order to see inter-annual changes in greenhouse gas dynamics.
© 2024 O. S. Schilling, all rights reserved
Technological developments and results were presented at several conferences [4-5]. Stay tuned for the upcoming publications on the technological development and the greenhouse gas dynamics in the sub-polar groundwater-peatland ecosystems of Northern Finland!
Dr. Yama Tomonaga is a Laboratory Head and Senior Scientist in the Hydrogeology Research Group at the University of Basel. Prof. Dr. Oliver S. Schilling is group leader of the Hydrogeology Research Group at the University of Basel as well as group leader of the Tracer Hydrogeology Group at Eawag in Switzerland. Their fieldtrips took place in the winters 2023-2024 and 2024-2025 with financial support from an SPI Technogrant.
- Read more about their project here
- References:
- [1] Brennwald, M.B., et al. (2016). A portable and autonomous mass spectrometric system for on-site environmental gas analysis. Environ. Sci. Technol., 50, 13455-12463. https://doi.org/10.1021/acs.est.6b03669
- [2] Schilling, O. S., et al. (2021). Quantifying groundwater recharge dynamics and unsaturated zone processes in snow-dominated catchments via on-site dissolved gas analysis. Water Resour. Res., 57(2), e2020WR028479. https://doi.org/10.1029/2020WR028479
- [3] Marttila, H., et al. (2021). Subarctic catchment water storage and carbon cycling – Leading the way for future studies using integrated datasets at Pallas, Finland. Hydrol. Process., 35, e14350. https://doi.org/10.1002/hyp.14350 Coordinates of the implementation location: Pallas atmosphere-ecosystem super site
- [4] Schilling, O.S. et al., (2023): Quantifying Groundwater Recharge Dynamics and Unsaturated Zone Processes in Snow-Dominated Catchments via On-Site Dissolved (Noble) Gas Analysis. miniRUEDI Symposium 2023, 21.-23.11.2023, Dübendorf, Switzerland.
- [5] Schilling, O.S. et al., (2024): Dissolved (Noble) Gas Analyses as a Complement to Stable Water Isotopes for Snow and Ice Melt Identification in Groundwater. IAH World Groundwater Congress 2024, 8.-13.9.2024, Davos, Switzerland.