Published in Environmental Microbiology, this research explores how microbial communities regulate nitrogen cycling within a Mediterranean subterranean estuary.

These hidden transition zones, where fresh groundwater mixes with seawater, act as bioreactors that transform groundwater-derived nitrogen before it reaches coastal ecosystems.

The study analysed groundwater samples collected at different depths and distances from the shoreline during winter and summer. The researchers examined microbial abundance, activity, composition and nitrogen-cycling genes.

📈 Key insights from the paper:

🔹 Microbial abundance, activity and diversity varied strongly across hydrochemical zones and aquifer depths.
🔹 Despite these spatial differences, microbial communities showed limited seasonal variation.
🔹 Different microbial taxa encoded distinct nitrogen-cycling pathways across the subterranean estuary.
🔹 Ammonia-oxidising archaea were more prevalent in fresh groundwater, while bacterial denitrifiers were enriched in deep saline layers.
🔹 Microbial properties predicted nitrite and ammonium concentrations more accurately than environmental variables alone.
🔹 The results reveal a complex and spatially organised microbiome that helps explain nitrogen transformations within coastal aquifers.

This work advances our understanding of microbial ecology, groundwater–seawater interactions and the biogeochemical processes regulating nitrogen inputs to coastal ecosystems.