The influence of cold season warming on the mercury pool in coastal benthic organisms

One of the tendencies for climate changes in the southern Baltic region is towards the warming of the cold season (late autumn, winter, early spring), which leads to the disappearance of icing even in the coastal zone and affects the fluxes of chemicals in the surface sediments of the coastal zone. This will lengthen the period in which the deposited chemicals may become remobilized from the sediments into pore and near-bottom water. Studies into the mercury concentration in macrophyto- and macrozoobenthos were conducted at two stations in the coastal zone of the southern Baltic, in the Puck Lagoon, from January 2012 to May 2013. It was estimated that the mean annual Hg pool (mass of Hg in flora or fauna per m−2 of sediments) in macrophytobenthos in a year without icing was higher by 30%, and in macrozoobenthos by 25%, compared to an estimated previous year in which the icing period lasted approximately 90 days (as was usual in the period between 1946 and 1991). Taking into account the combined total mass of flora and fauna, it was estimated that lack of icing on the lagoon increases the mean Hg pool in benthic organisms (macrophyto- and macrozoobenthos) by 30%, which in turn considerably increases the Hg load on the first levels of the trophic chain despite a decrease in Hg emissions. The warming of the cold season has a particular influence in areas where macroalgae species are predominant in the biomass over angiosperms. Of the zoobenthic taxa, Corophiumspp. exhibited a tendency for intense growth and Hg accumulation in late autumn.

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