Improving the understanding of the biogeochemical functioning of aquatic ecosystems aims to accurately quantify the spatial and temporal dynamics of ecosystem metabolism. This metabolism is closely linked to water flows and mixing from various sources, gas exchange with the atmosphere, and biological responses. In particular, dissolved gas tracers are used to identify where, when, and how different stages of water movement occur within hydrosystems. These dissolved gases originate from diverse sources : the atmosphere (N₂, O₂, Ar, etc.), the lithosphere (⁴He, ²²²Rn, etc.), the biosphere (N₂, O₂, CO₂, CH₄, N₂O, H₂, H₂S, etc.), and anthropogenic activities (CFCs, SF₆, etc.). They also possess a wide range of properties : some are stable (He, Ne, Ar, Kr, Xe), others radioactive (³⁷Ar, ³⁹Ar, ⁸¹Kr, ⁸⁵Kr, ²²²Rn, etc.) or reactive (N₂, O₂, CO₂, CH₄, N₂O, H₂, H₂S, etc.). This diversity in origin and behavior makes these tracers highly versatile and particularly relevant for studying water pathways and associated physical and biogeochemical processes.

The Membrane Inlet Mass Spectrometer (MIMS) developed as part of the TERRA FORMA project is a continuation of the instrumentation research conducted by GR (Equipex+ CRITEX), which led to the design of a first prototype for high-frequency in situ measurements (every 30 minutes or better) of dissolved gases directly involved in metabolism (O₂, N₂, CO₂, CH₄, N₂O), as well as inert gases used as flow tracers (notably He, Ar, Rn). The MIMS technology has gained increasing interest in environmental sciences for its ability to perform high-frequency dissolved gas measurements in laboratory settings. Recently, MIMS has advanced in portability, miniaturization, sensitivity, and the range of measurable dissolved volatile compounds, enabling on-site high-frequency measurements. Measurement intervals of just a few seconds are now possible for all dissolved gases, allowing its deployment in controlled experiments such as tracer tests, as well as for long-term monitoring to characterize the physical and biogeochemical dynamics of studied environments.

The objective of the current development is to make the measurement device communication-enabled, optimize its energy consumption, and define a deployment methodology (sample filtration and calibration to ensure measurement stability) for use in hyporheic zones and rivers. Its measurement capabilities will be tested across different contexts and over long time periods (several months).

This portable, connected, and easy-to-deploy device opens new opportunities for field data acquisition at high frequency (<30 minutes), sustained over long durations (months). The collected data will support the development and validation of coupled models of water flows and the biogeochemical functioning of hydrosystems, capturing daily to seasonal dynamics.

Themes : Water Resources, Pollution

Updated on 23 juin 2025