Dead-end membrane probes (DEMP) enable continuous in-situ gas monitoring in stagnant porous media

Gases, including noble gases, are effective tracers in environmental sciences, used to investigate fluid dynamics in environmental and geological systems. Recent advances in autonomous, continuous on-site gas measurement techniques (i.e gas-equilibrium membrane inlet mass spectrometry: GE-MIMS) enable real-time monitoring of complex systems with substantially higher temporal resolution than conventional discrete sampling. However, gas-equilibration in GE-MIMS require active and continuous water circulation with a flow rate ≥ 1L/min through the membrane modules, rendering them unsuitable for low-flow or stagnant water environments such as soils, sediments, or plant-tissues, where water extraction would alter the system’s integrity. The dead-end membrane probe (DEMP) is designed for long-term, in-situ gas measurements in low-permeability or low-flow porous media, without requiring any active fluid circulation. The DEMP combines a gas-tight, 3D-printed body, gas-permeable membranes, and a pressure sensor, enabling diffusive gas equilibration from pore fluids into the probe headspace for subsequent quantification. Originally developed for non-destructive measurements in tree xylem, DEMPs are broadly applicable to soils, sediments, rocks, and biological tissues. • Field-deployable probe for in-situ gas quantification in low-flow porous media. • Successful deployment in a long-term field experiment studying gas exchange within the soil–plant–atmosphere continuum. • Full design and construction protocol openly available.