Mercury transformations in marine coastal sediments as derived from mercury concentration and speciation changes along source/sink transport pathway (Southern Baltic)

In this study the distribution of mercury in coastal marine sediments was investigated. Samples of surface sediments were collected from three areas in the southern Baltic. The Gdansk Basin was selected due to proximity to point sources, while the Arkona and the Bornholm Deeps – because they are distant from point sources. Both total concentration and solid speciation of mercury were measured. Sources, transport routes, and transformation of mercury in bottom sediments were assessed.Total concentrations varied in the range from 20 to 430 ng/g sediment d.w. The dominant forms of mercury were mercury sulphide (50% ± 10%), and mercury bound to both humins and mineral matrix (30% ± 20%). The Odra River seems to be the main source of mercury in the Arkona Deep, whereas diffuse sources contribute to the mercury in the sediments of the Bornholm Deep. In the Gdansk Basin, diversified sources seem to control the distribution of mercury. They include point pollution sources in the western part of the bay; the Vistula River – the main source of mercury in the central Gdansk Bay, its influence extending to the Gdansk Deep area. Sediments of the Gdansk Deep western slope receive mercury from the suspended matter of both the Vistula River and the currents from other coastal regions as well as aerial long-range transport.Mercury species undergo transformation in the course of transport to depositional basins – which leads to partial remobilization of mercury from the sediments.