biostudies-literatureAcciardo ASSwiss National Science Foundation1522714https://www.ebi.ac.uk/biostudies/studies/S-EPMC11897985biostudies-literatureUnknown16Accessing the deep terrestrial subsurface (greater than 1 km below the surface) presents significant practical challenges, leaving these ecosystems largely uncharacterized despite their extensive presence beneath Earth's landmasses. In this study, we introduce the BedrettoLab Deep Life Observatory (DELOS), a new underground laboratory to study the biogeochemical diversity of groundwater in a high-altitude Alpine catchment tens of meters to 1.6 km underground. Biogeochemical monitoring of DELOS over spatial and temporal scales highlight three dominant ecotypes throughout DELOS: (1) Shallow groundwater with low electrical conductivity enriched in <i>Leptospirillia</i>; (2) High-inflow fault zones enriched in ultra-small bacteria and archaea; (3) Bicarbonate-enriched waters that are enriched Frontiers in microbiologySpatial and temporal groundwater biogeochemical variability help inform subsurface connectivity within a high-altitude Alpine catchment (Riale di Ronco, Switzerland).PMC11897985215626Tran HNHArnet MGholizadeh Doonechaly NWenning QBrixel BMagnabosco CZimmerman EHertrich MAcciardo ASRodriguez PCeccato AfalseSpatial and temporal groundwater biogeochemical variability help inform subsurface connectivity within a high-altitude Alpine catchment (Riale di Ronco, Switzerland).Accessing the deep terrestrial subsurface (greater than 1 km below the surface) presents significant practical challenges, leaving these ecosystems largely uncharacterized despite their extensive presence beneath Earth's landmasses. In this study, we introduce the BedrettoLab Deep Life Observatory (DELOS), a new underground laboratory to study the biogeochemical diversity of groundwater in a high-altitude Alpine catchment tens of meters to 1.6 km underground. Biogeochemical monitoring of DELOS over spatial and temporal scales highlight three dominant ecotypes throughout DELOS: (1) Shallow groundwater with low electrical conductivity enriched in <i>Leptospirillia</i>; (2) High-inflow fault zones enriched in ultra-small bacteria and archaea; (3) Bicarbonate-enriched waters that are enriched 2025-01-01T00:00:00Z20252025-04-04T01:29:12.745Z2025-04-04T01:29:12.745ZS-EPMC118979854007854410.3389/fmicb.2025.1522714