engleski

Microbial biomass and mercury speciation in the coastal and open Middle Adriatic Sea

Biologically mediated reactions are of great importance for the transformation of various mercury species in the upper layer of the water column. As a part of the marine food web, mercury bioaccumulates and biomagnifies through trophic levels, especially its organometallic form – methylmercury (MeHg). Our hypothesis was that the same factors that enable scavenging nutrients at low concentration also facilitate MeHg accumulation in the biomass of microorganisms. Prokaryotic microorganisms may be a critical component of the food web that can promote our understanding of the behavior of mercury in the marine ecosystems. Small singled-celled organisms like heterotrophic bacteria, photosynthetic picoplankton, autotrophic and heterotrophic nanoplankton and ciliates represent the major components of marine community, especially in oligotrophic areas such is the Adriatic Sea. In oligotrophic conditions, these small organisms are better competitors for inorganic and organic nutrients because of lower energetic costs, rapid metabolism and small size. The sampling of microbial biomass and mercury species/fractions in seawater were performed from March to December 2014 in the Middle Adriatic Sea. Our research was restricted to transect from the pristine marine environment of island of Vis to the Kaštela Bay, an enclosed bay that had been affected by previous contamination from chlor-alkali industrial waste waters. Mercury speciation and its distribution in the Adriatic Sea were studied during seven oceanographic cruises aboard the Croatian research vessel Bios Dva. Water profiles of total mercury (THg), dissolved gaseous mercury (DGM) and methylmercury in acidified, non- filtered seawater samples were created for coastal and open Adriatic waters. THg concentrations range from 0.71-5.49 pM near island of Vis to 4.60-27.8 pM in the Kaštela Bay. DGM shows higher values in the contaminated area (0.20-1.75 pM) than in the pristine environment (0.11-0.43 pM). MeHg has similar concentrations at both stations (0.02-0.10 pM).

Mercury speciation; microbial biomass; Adriatic Sea

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