Submarine Groundwater Discharge a Source of Total Mercury at Cabrera Archipelago National Park and Ría de Vigo

  • G.BRAVO, ANDREA (Institut de Ciències del Mar (ICM-CSIC))
  • CASAS, GEMMA (Institut de Ciències del Mar (ICM-CSIC))
  • MONTERO CURIEL, MARÍA (Institut de Ciències del Mar (ICM-CSIC))
  • ROMANO-GUDE, DANIEL (Institut de Ciències del Mar (ICM-CSIC))
  • RODRÍGUEZ PUIG, JÚLIA (Universitat Autònoma de Barcelona (UAB))
  • RODELLAS-VILA, VALENTÍ (Universitat Autònoma de Barcelona (UAB))
  • RUIZ-GONZÁLEZ, CLARA (Institut de Ciències del Mar (ICM-CSIC))
  • M. GASOL, JOSEP (Institut de Ciències del Mar (ICM-CSIC))
  • ÁLVAREZ-SALGADO, XOSÉ ANTÓN (Instituto de Investigacións Mariñas(IIM-CSIC))
  • PINO IBÁNHEZ, JUAN SEVERINO (Instituto de Investigacións Mariñas(IIM-CSIC))

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Submarine groundwater discharge (SGD) is an important yet understudied pathway for mercury (Hg) transport to coastal waters. This study examines SGD as a source of total mercury (THg) and methylmercury (MeHg) in two distinct Spanish coastal systems: the Cabrera Archipelago National Park (Balearic Islands, Spain) and the Vigo Ría (Galicia, Spain). Seasonal variations in Hg concentrations were analyzed in different water compartments, including wells, seawater, porewater, and river water, to assess the influence of SGD on Hg cycling. THg concentrations ranged from 2.5 to 213.2 pM, with significantly higher levels in wells (median: 95.4 pM in summer, 78.9 pM in winter) compared to porewater (6.5 pM in summer, 5.5 pM in winter) and seawater (1.5 pM in summer, 1.0 pM in winter). Similarly, in Vigo, THg was highest in wells (4.5 pM in summer and 6.6 in winter) and porewater (6.8 pM in summer, 2.7 in summer) and, with lower levels in seawater (1.9 pM in summer, 1.2 pM in winter). A negative correlation between THg and salinity, along with a positive correlation with radium isotopes, suggests that SGD significantly contributes to Hg inputs in both coastal regions. MeHg concentrations in Cabrera ranged from 0.04 to 1.8 pM, with the highest values in wells (0.56 pM in summer), followed by porewater (0.11 pM) and seawater (0.13 pM). While SGD was a major source of THg, no significant correlation was found between MeHg and SGD indicators, suggesting additional biogeochemical controls on Hg methylation. This study highlights submarine groundwater discharge (SGD) as a significant source of total mercury (THg) in coastal waters. THg and MeHg levels are influenced by hydrological and biogeochemical processes. Understanding Hg transport and transformation is crucial due to its ecological and health risks. Future research should quantify SGD contributions and microbial methylation processes.