The discharge of groundwater from coastal aquifers to the coastal ocean (i.e., the so-called submarine groundwater discharge, SGD) represents a relevant hydrologic pathway, delivering large amounts of nutrients, pollutants and other terrestrial elements to the sea with large effects on coastal ecosystems. However, SGD-driven processes have been poorly studied from a microbiological point of view: On the one hand, the below-ground mixing of seawater and groundwater results in areas of active microbial activity and diverse communities that can modify the chemistry of the groundwater reaching the ocean, but almost nothing is known about the microorganisms inhabiting the coastal aquifers, much less studied than inland groundwaters. On the other hand, SGD can largely influence marine microbial communities through the delivery of chemical compounds but also microorganisms, yet the potential consequences of these groundwater inputs on marine microbial communities, specially on planktonic microorganisms and the biogeochemical cycles they control, remain unknown.
Since September 2019, I am leading the GRAMMI project, whose main objective is to study the microbial dimension of SGD in coastal areas of the Mediterranean Sea, considering the diversity, functional potential and connectivity of microbial communities at this terrestrial-marine interface. Working in close collaboration with experts in SGD processes (Jordi Garcia-Orellana and Valentí Rodellas from the Universitat Autònoma de Barcelona), and with microbiologists and biogeochemists from ICM-CSIC (Josep M. Gasol, Andrea G. Bravo), we will characterize the taxonomic and functional diversity of the microbial communities along the whole hydrologic continuum, from the coastal groundwater to the open coastal sea. Spatio-temporal samplings will be performed across different coastal aquifer sites in order to elucidate the microbial diversity hidden in these systems, its environmental drivers and its role in biogeochemical cycling at the land-sea interface. Finally, the potential consequences of these groundwater inputs for the structure and functioning of marine microbial communities will be investigated.
This project integrates different disciplines (chiefly microbiology, hydrogeology and oceanography) and will combine field samplings, experimental manipulations and modern molecular techniques such as sequencing methods, microscopic visualization, and techniques that allow linking taxonomy to activity to gain insight into the microbial dimension of SGD processes.