Poster.-- VIII International Symposium on Marine Science, Las Palmas de Gran Canaria, 6-8 July 2022, Submarine groundwater discharge (SGD) refers to any flux of water originated from the seafloor. This includes the discharge of continental groundwater that often occurs through a subsurface mixing zone called subterranean estuary (STE). Previous research has identified significant volumetric SGD in the Ría de Vigo, a highly productive coastal system in the NW of the Iberian Peninsula. (Ibánhez et al., 2021). Yet, the impact of SGD over the biogeochemistry and microbial ecology of the embayment is still unknown. Thus, this study focuses on evaluating the potential, SGD-driven microbial and biogeochemical connectivity in the embayment in order to assess the ecological impact that SGD can produce in the coastal zone.Samples were taken from different water bodies within the ria and its surrounding basin, including surface and deep pore-water samples from two contrasting STEs, surface seawater, riverine water and groundwater samples.
Samples were used to determine a complete set of microbial and biogeochemical variables, such as taxonomic composition, salinity, temperature, inorganic and organic nutrients, carbonate system, radioisotopes, biogases and dissolver organic matter. We have found very diverse microbial communities, with higher diversity in the STEs compared to land and sea endmembers, likely related to the variety of niches in this transitional ecosystems. Most operational taxonomic units (OTUs) (ca. 87%) were exclusive of a single environment (river, groundwater, seawater or STEs), revealing a poor microbial connection between land and sea. Overall STEs shared a significantly higher proportion of OTUs with seawater than with freshwater endmembers.
Despite that a biogeochemical connectivity can be observed, the contrasting biogeochemical conditions found in the different environments may explain the low level of common microbial species, in contrast to what was expected from 222Rn and salinity-based estimates of water flow between the local groundwaters and the sea, This research was financed by the SUBACID project (SUBmarine groundwater discharge (SGD) impact on coastal ACIDification processes in contrasting Atlantic Shores: towards securing ecosystem services and food production), funded by theIrish Research Council and the European Union’s Horizon 2020 Research and Innovation Program under the Marie Skłodowska-Curie grant agreement No. 713279 through the CAROLINE program (CLNE/2017/210) and the INTERES project, funded by the Spanish Ministry of Economy and Competitiveness (CTM2017-83362-R), No