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Submarine groundwater discharge into a semi-enclosed coastal bay of the southern Baltic Sea: A multi-method approach

Von Ahn Cátia Milene Ehlert, Dellwig Olaf, Szymczycha Beata, Kotwicki Lech, Rooze Jurjen, Endler Rudolf, Escher Peter, Schmiedinger Iris, Sültenfuß Jürgen, Diak Magdalena, Gehre Matthias, Struck Ulrich, Vogler Susan, Böttcher Michael Ernst

Oceanologia

2024

No. 66 (1)

111-138

The present study aims to understand the impact of submarine groundwater discharge (SGD) on a coastal area with different lithology and degrees of SGD. Sampling campaigns took place in Puck Bay and the Gulf of Gdańsk, southern Baltic Sea encompassing years between 2009 and 2021. The methodological approach combined geophysical characterization of the surface sediments with detailed spatial and temporal (isotope) biogeochemical investigations of pore and surface waters, and was supported by nearshore groundwater and river surveys. Acoustic investigations identified areas of disturbance that may indicate zones of preferential SGD release. The composition of porewater and the differences in the bay's surface waters disclosed SGD as common phenomenon in the study area. Regional SGD was estimated through a radium mass balance. Local estimation of SGD, based on porewater profiles, revealed highest SGD fluxes at the sandy shoreline, but relatively low elemental fluxes. Though SGD was low at the muddy sites corresponding elemental fluxes of nutrients and dissolved carbon exceeded those determined at the sandy sites due to intense diagenesis in the top sediments. SGD appears to be sourced from different freshwater endmembers; however, diagenesis in surface sediments substantially modified the composition of the mixed solutions that are finally discharged to coastal waters. Overall, this study provides a better understanding of the SGD dynamics in the region by a multi-approach and emphasizes the need to understand the processes occurring at the sediment-water interface when estimating SGD.

Plastic contamination of sandy beaches along the southern Baltic – a one season field survey results

Mazurkiewicz Mikołaj, Martinez Paula Sancho, Konwent Weronika, Deja Kajetan, Kotwicki Lech, Węsławski Jan Marcin

Oceanologia

2022

No. 64 (4)

764--780

The subject of this study was microplastics (>32 µm), large micro-/macroplastics (>2 mm) and plastic litter (visible by naked eye) contamination on sandy beaches and in coastal waters along the Polish coast of the Baltic Sea. Microplastics were studied with particular attention, with simultaneous observations in the water and across the beach. Other data was intended to serve as a background and as possible sources of microplastics. Most of the microplastics found were fibers <1 mm long, with blue fibers dominating, followed by transparent, red and green ones, both in sand and water samples. The concentration of microplastics on the beach sand ranged from 118 to 1382 pieces kg−1, while in coastal waters from 0.61 to 2.76 pieces dm−3. As for large micro-/macroplastics and plastic litter, there was no dominant litter along the coast. The amount of large micro-/macroplastics ranged from 2 to 124 pieces m−2 (or from 0.13 to 44.30 g m−2). Regarding plastic litter, on average between 0.03 and 6.15 litter debris m−2 were found (or from 0.007 to 4.600 g m−2). The study confirms that plastic pollution of the Polish coastal zone is a significant problem comparable with both the rest of the Baltic Sea and other seas and oceans. Similar color-based composition of microplastics among all studied sites suggests that they may have a common source, while the contamination of large micro-/macroplastics and plastic litter (both amount of particles and their composition) along the Polish coast is highly site-specific and may be influenced by various local factors.