Detalle de: Nitrogen transformations at the land-sea interface: Digging into the microbial regulation of the biofiltering potential of subterranean estuaries

Coastal aquifers, subterranean water reservoirs located in coastal zones, act as natural biofilters that catalyze chemical transformations in groundwater

before it enters the sea via submarine groundwater discharge (SGD). Nitrogen (N) transformations are particularly critical because coastal groundwater

worldwide is polluted with nitrate from human activities, leading to ecological impacts such as eutrophication, hypoxia, and harmful algal blooms in

marine waters. Understanding the role of coastal aquifers is therefore urgent, as SGD is an invisible yet efficient pathway for terrestrial nitrogen pollution

to reach the ocean. However, our knowledge of how coastal aquifers transform or transfer nitrogen is limited by the poor understanding of the diverse

and complex coastal groundwater microbial communities, which silently regulate SGD chemical fluxes to marine environments. In this context, the

NIGUIRI project aims to unravel the complex microbially driven N transformations occurring in coastal aquifers before discharge, in the so-called

subterranean estuaries (STEs), and to assess their impact on groundwater quality. Specifically, NIGUIRI will investigate the most important microbial

metabolisms driving N cycling at the land-sea interface, identify key microbial taxa, their interactions and their physicochemical drivers, and explore their

variability across Mediterranean coastal aquifers. This will be achieved through a multidisciplinary approach never applied before in STEs, which

combines metagenomics and metatranscriptomics -to characterize microbial functions-, stable isotope incubations to quantify metabolic rates, and

integrates field sampling with experimental assays, complemented by advanced bioinformatics to reconstruct genomes and infer metabolic

interdependencies among taxa. Despite the recognized importance of SGD as a nutrient source to the Mediterranean Sea, no study has yet explored the

extent to which, and how, STE microbiomes modulate groundwater quality. Ultimately, the knowledge generated will improve our ability to estimate SGD-

derived nitrogen fluxes to the ocean and enhance understanding of the role of coastal groundwater in marine ecosystem functioning.