The climate changes in recent years in the southern Baltic have been resulting in an increased frequency of natural extreme phenomena (i.e. storms, floods) and intensification of abrasion processes, which leads to introduction of large amounts of sedimentary deposits into the marine environment. The aim of this study was to determine the mercury load introduced to the Baltic Sea with deposits crumbling off the cliffs—parts of the coast that are the most exposed to abrasion. The studies were carried out close to five cliffs located on the Polish coast in the years 2011–2014. The results show that coastal erosion could be an important Hg source into the marine environment. This process is the third most important route, after riverine and precipitation input, by which Hg may enter the Gulf of Gdańsk. In the Hg budget in the gulf, the load caused by erosion (14.3 kg a−1) accounted for 80 % of the wet deposition and was 50 % higher than the amount of mercury introduced with dry deposition. Although the Hg concentration in the cliff deposits was similar to the natural background, due to their large mass, this problem could be significant. In addition, the preliminary studies on the impact of coastal erosion on the Hg level in the marine ecosystem have shown that this process may be one of the Hg sources into the trophic chain.Electronic supplementary materialThe online version of this article (doi:10.1007/s11356-016-6753-7) contains supplementary material, which is available to authorized users.

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Mercury (Hg) can be introduced into the marine environment in many different ways. In the case of the Baltic Sea, rivers and atmospheric deposition are the predominant ones. However, in the face of ongoing climate change, a new potential source, coastal erosion, is starting to become more important and is currently considered to be the third largest source of Hg in the Gdansk Basin region. It is especially significant along sections of coastline where, due to the higher frequency of extreme natural phenomena such as storms, heavy rains, and floods, increased erosion processes have already been noted. Cliffs, which account for about 20% of the Polish coastline, are particularly vulnerable. The aim of the study was to estimate the annual load of labile Hg entering the Gdansk Basin as a result of coastal erosion. Samples of down-core sediments (0–65 cm) were collected in the years 2016–2017 from selected cliffs situated in the Gulf of Gdansk area. The thermodesorption method was used to distinguish between labile and stable fractions of Hg. Considering the mean total Hg concentrations in the collected sediments (9.7 ng g−1) and the mean share of labile (64%), bioavailable mercury, it was estimated that the load of labile Hg originating from coastal erosion entering the Gdansk Basin is 10.0 kg per year. The load can increase by up to 50% in the case of episodic abrasion events during heavy storms and rains.Electronic supplementary materialThe online version of this article (10.1007/s11356-018-2856-7) contains supplementary material, which is available to authorized users.

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The study aimed to determine the level of mercury (Hg) and its labile and stable forms in the surface sediments of the Baltic Sea. The work considers the impact of current and historical sources of Hg on sediment pollution, together with the influence of different environmental parameters, including water inflows from the North Sea. Surface sediments (top 5 cm) were collected in 2016–2017 at 91 stations located in different areas of the Baltic Sea, including Belt Sea, Arkona Basin, Bornholm Basin, Gdańsk Basin, West Gotland Basin, East Gotland Basin, and the Bothnian Sea. Besides, the particulate matter suspended in the surface and near-bottom water was also collected. The analysis of total Hg concentration and individual Hg forms in collected samples was carried out using a 5-step thermodesorption method. This method allows for the identification of three labile and thus biologically available, fractions of Hg, which are mercury halides, organic Hg, mercury oxide and sulphate. Two stable fractions, mercury sulphide and residual Hg, were also determined. The highest Hg concentrations, reaching 341 ng g−1, were measured in the highly industrialised Kiel Bay, which was additionally a munition dumping site during and after World War II. High Hg level, ranging from 228 to 255 ng g−1, was also recorded in the surface sediments of the Arkona Basin, which was a result of the cumulative effect of several factors, such as deposition of Hg-rich riverine matter, favourable hydrodynamic conditions and military activities in the past. The relatively elevated Hg concentrations, varying from 60 to 264 ng g−1, were found in the Gdańsk Basin, a region under strong anthropopressure and dominated by soft sediments. The sum of labile Hg in sediments was high and averaged 67% (with the domination of organic Hg compounds), which means that a large part of Hg can be released to the water column. It was found that the water inflows from the North Sea intensify the remobilisation of Hg and its transformation into bioavailable labile forms. As a consequence, the load of Hg introduced into the trophic chain can increase. Despite the significant reduction of Hg emission into the Baltic in the last decades, surface sediments can be an important secondary Hg source in the marine ecosystem. This is especially dangerous in the case of the western Baltic Sea.