engleski

Speciation of mercury and microbial biomass in the coastal and open middle Adriatic Sea

Chemical and biological processes can transform mercury species which facilitate its entrance into the marine food webs. Biologically mediated reactions are of great importance for the production and/or decomposition of various mercury species in the upper layer of the water column. Being a part of the marine food web, mercury bioaccumulates and biomagnifies through trophic levels, especially in organometallic form of methylmercury (MeHg). Small singled-celled organisms like heterotrophic bacteria, photosynthetic picoplankton (Prochlorococcus, Synechococcus and picoeukaryotes), autotrophic and heterotrophic nanoplankton and ciliates represent the major components of marine community, especially in oligotrophic areas such as the Adriatic Sea. In oligotrophic conditions, these small organisms are better competitors for inorganic and organic nutrients because of lower energetic costs (simple biomass composition), rapid metabolism and small size, and they form characteristic food web (microbial loop and microbial food web) which dominate over classical (herbivorous) food web in this conditions. One of the hypotheses of our research was that the same factors that enable scavenging nutrients at low concentration also facilitate contaminant accumulation in the biomass of microorganisms for subsequent transfer to other components in the food web. Therefore, due to their great potential for bioconcentration of methylmercury, we hypothesize that prokaryotic microorganisms may be a critical component of the food web that can promote our understanding of the behaviour of mercury in the marine ecosystems. The sampling of microbial biomass and mercury species/fractions in seawater were performed from February to December 2014 in the Middle Adriatic Sea. Mercury speciation and its distribution in the Adriatic Sea were studied during seven oceanographic cruises aboard the Croatian research vessel Bios Dva. Deep water profiles of total mercury (THg), dissolved gaseous mercury (DGM) and methylmercury in non-filtered seawater samples were created for coastal and open Adriatic waters. Sampling routes followed mercury contamination gradient – from the pristine marine environment of island of Vis to the Kaštela Bay that had been affected by previous contamination from chlor-alkali industrial waste 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 (0.02-0.07 pM and 0.02-0.10 pM near island of Vis and in the Kaštela Bay, respectively). Our results of microbial and mercury measurements will be presented herein.

Mercury speciation; microbial biomass; Adriatic Sea

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