Keynote

Microbial Community Structuring and Nitrogen Transformations along a Mediterranean Subterranean Estuary

  • Romano-Gude, Daniel (Institut de Ciències del Mar (ICM-CSIC))
  • Mena, Catalina (Instituto Español de Oceanografía (IEO-CSIC))
  • Diego-Feliu, Marc (Universitat Politècnica de Catalunya (UPC))
  • Almillategui, Bella (Universitat Politècnica de Catalunya (UPC))
  • G. Bravo, Andrea (Institut de Ciències del Mar (ICM-CSIC))
  • Montero-Curiel, María (Institut de Ciències del Mar (ICM-CSIC))
  • Carrera, Jesús (Universitat Politècnica de Catalunya (UPC))
  • Folch, Albert (Universitat Politècnica de Catalunya (UPC))
  • Garcia-Orellana, Jordi (Universitat Autònoma de Barcelona (UAB))
  • J. Székely, Anna (Swedish University of Agricultural Sciences)
  • Bertilsson, Stefan (Swedish University of Agricultural Sciences)
  • Rodellas, Valentí (Universitat Autònoma de Barcelona (UAB))
  • Ruiz-González, Clara (Institut de Ciències del Mar (ICM-CSIC))

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Submarine Groundwater Discharge (SGD) supplies large amounts of solutes to the ocean. In coastal areas, the confluence of fresh and saline groundwater results in subterranean estuaries (STEs), biogeochemically active sites in which biogeochemical transformations mediated by microbes can control SGD-driven nutrient fluxes to the ocean. However, the understanding of microbial communities inhabiting these areas and of their functional capabilities remains very limited. Our aim was to explore the spatio-temporal variations in abundance, heterotrophic activity, taxonomical composition and functional capabilities of prokaryotic communities within a Mediterranean STE characterized by pronounced physicochemical gradients. For this purpose, we collected groundwater samples from several piezometers (depths 6 – 22m) covering the entire salinity gradient along a transect perpendicular to the shoreline in two hydrological seasons. Our results show large spatial variations in prokaryote abundance and activity, as well as in microbial composition following gradients in salinity, nutrient availability and dissolved organic carbon concentration. qPCR analysis of functional genes involved in nitrification (amoA) and denitrification (nirK and nirS) unveiled significant spatial variability, indicating different microbial niches influencing nitrogen transformations through the STE. Conversely, communities were less variable between both seasons, suggesting temporal stability. Our findings highlight the high spatial heterogeneity in the microbial communities, in terms of biomass, activity, taxonomical composition and their role in nitrogen transformations throughout the coastal aquifer. This variability highlights the importance of conducting detailed spatial analyses for a more comprehensive understanding of the microbial contribution to SGD-driven biogeochemical processes in these key ecosystems.