Long-term changes and distribution of mercury concentrations in surface sediments of the Gdansk Basin (Southern Baltic Sea)

Abstract

Purpose In the Baltic Sea, the reduction of mercury load is estimated to be 44 % compared to the end of the previous century. Confirmation of mercury load decrease is frequently based on sedimentary mercury profiles. This study aims to assess the inter-annual changes of mercury concentration and the net input in surface sediments, in order to assess the effect of decreased emissions and other processes. Materials and methods Surface sediments were collected in 2011-2013 from areas where existing data series were available. Sediments were freeze dried, and total mercury concentrations, loss on ignition and fine fraction content were analysed. We compared recent concentrations of mercury in the coastal zone of the Baltic Sea to values previously reported in the same area since 1993. Net mercury deposition in the analysed sediments and previously reported data were calculated. The observed variability was correlated to climaterelated processes and input changes. Results and discussion Three studied areas-major river mouth, shallow bay and offshore area-were significantly different in terms of sediment type and mercury concentration. Total mercury concentrations in the study area in 2011-2013 ranged between 2 and 260 ng g −1 dry weight (dw) (mean 61 ng g −1 dw; median 36 ng g −1 dw). Nearly 75 % of the obtained results did not exceed 50 ng g −1 dw, while concentrations >200 ng g −1 dw accounted for a little over 5 % of all the obtained results. Mercury input calculated for the area was much smaller than that recorded for the 1990s, but was characterised with large inter-annual variability, attributed to climate-related processes.Conclusions Although a decreasing trend could be observed, it is modified by inter-annual variability. It follows from observations that in the present situation, where mercury emission has been successfully inhibited, that concentrations of this metal in sediments reflect natural metal migration processes rather than the direct influence of anthropogenic sources.

Mercury Cycling in the Gulf of Gdańsk (Southern Baltic Sea)

“…The Hg concentration in sediments from several areas of the southern Baltic Sea was described by Bełdowski et al [23], Jędruch et al [24], and Kwasigroch et al [19]. Samples were collected in the periods 1999-2002 [23], 2011-2013 [24], and 2016-2017 [19]. Detailed information about sampling and storage methods can be found in the publications [19,23,24].…”

“…Samples were collected in the periods 1999-2002 [23], 2011-2013 [24], and 2016-2017 [19]. Detailed information about sampling and storage methods can be found in the publications [19,23,24].…”

“…Based on the mean Hg concentration in the two types of sediment (sandy and silty), their wetness [24], density [44], and surface of the bottom of each type, the load of Hg deposited in the upper layer of the sediments (0-5 cm) in the Gulf of Gdańsk was estimated.…”

The variability of Hg concentration and composition of marine phytoplankton

“…The reduction in Hg emission contributed to a decrease in its inflow into the Baltic (HELCOM 2010), and has led to increased significance of point sources and the remobilisation of mercury from bottom sediments (Jędruch et al 2015) and from land (Saniewska et al 2014b). The latter processes are stimulated by intensive rains which lead to surges, and even floods.…”

Preface: proceedings of the 13th IASWS international conference

“…Kamau et al (2015a, b) present two papers on the impact of sewage on mangroves on the Kenyan coast; mangrove ecosystems are also examined by Kumar and Ramanathan (2015) who examine the distribution of trace metals in the world's largest mangrove ecosystem at Sundarban (India and Bangladesh). Jędruch et al (2015) discuss mercury-sediment relationships in the Baltic Sea.…”