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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

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2024

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Vol. 66 (1)

111-138

EN

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.

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Benthic diffusive fluxes of organic and inorganic carbon, ammonium and phosphates from deep water sediments of the Baltic Sea

Lengier Monika, Szymczycha Beata, Brodecka-Goluch Aleksandra, Kłostowska Żaneta, Kuliński Karol

Oceanologia

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2021

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No. 63 (3)

370--384

EN

In this study, Baltic Sea sediments, as a source of dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), ammonium (NH4+), and phosphates (PO43-), were investigated based on samples obtained in 2017 and 2018, shortly after a sequence of inflows from the North Sea that occurred between 2014 and 2017. Two different data sets (I and II) were used to assess benthic diffusive fluxes and thus elucidate both the temporal conditions at the time of sampling (data set I) and the diffusion potential of the sediments (data set II). The estimated fluxes were characterized by a high spatial variability within the whole Baltic Sea and ranged between −0.01 and 3.33 mmol m−2 d−1 for DIC, −0.02 and 0.44 mmol m−2 d−1 for DOC, −40.5 and 1370.1 µmol m−2 d−1 for NH4+, and −5.9 and 60.9 µmol m−2 d−1 for PO43-. The estimated benthic diffusive fluxes indicated a high potential for DIC, DOC, NH4+, and PO43- release from Baltic Sea sediments. The high O2 concentrations in the water column of the Gulf of Bothnia together with major Baltic inflows (MBIs) bringing oxygenated seawater to the Baltic Proper and to some extent the Eastern Gotland Basin regulate the amounts of chemicals released from the sediment. Our study showed that a sequence of inflows has greater impact on the diminution of diffusive fluxes than does a single MBI and that the sediments of the Baltic Proper, even under the influence of inflows, are an important source of C, N, and P (159 kt yr−1 for DIC+DOC, 6.3 kt yr−1 for N- NH4+ and 3.7 kt yr−1 for P-PO43-) that should be considered in regional budget estimations.

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Significance of nutrient fluxes via submarine groundwater discharge in the Bay of Puck, southern Baltic Sea

Szymczycha Beata, Kłostowska Żaneta, Lengier Monika, Dzierzbicka-Głowacka Lidia

Oceanologia

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2020

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No. 62 (2)

117--125

EN

In this study, we collected submarine groundwater discharge (SGD) and seawater samples at six sites in the Bay of Puck, in the southern Baltic Sea, in order to estimate the nutrient distribution in groundwater affected areas. In addition, we estimated nutrient fluxes via SGD, including both fresh SGD (FSGD) and recirculated seawater SGD (RSGD), to the entire Bay of Puck. Phosphate (PO43−) concentrations varied significantly among study sites and seasons, while both ammonium (NH4+) and nitrates (NO3−) concentrations varied only seasonally. The N:P ratio indicated P limitation in most of the samples. The estimated seasonal and annual loads, via SGD, of both dissolved inorganic nitrogen (DIN; 9303 t yr−1) and PO43− (950 t yr−1), were the most significant source of nutrients to the Bay of Puck, and notably higher than quantified before (FSGD nutrient loads of 50 t yr−1 and 56 t yr−1 for DIN and PO43−, respectively). The SGD fluxes reported here indicate some of the highest rates of sediment-water fluxes reported in the Baltic Sea. These results suggest that SGD (both FSGD and RSGD) should be considered as source of chemical substances to the marine environment.

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Hydrogeochemistry and magnitude of SGD in the Bay of Puck, southern Baltic Sea

Kłostowska Żaneta, Szymczycha Beata, Lengier Monika, Zarzeczańska Dorota, Dzierzbicka-Głowacka Lidia

Oceanologia

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2020

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No. 62 (1)

1--11

EN

This work reports the hydrogeochemistry of submarine groundwater discharge (SGD) in the Bay of Puck, southern Baltic Sea. To understand the seasonal and spatial variability of SGD, groundwater and seawater-based SGD samples were collected in several sites in November 2017, March 2018, May 2018 and July 2018. Additionally, a vertical, one-dimensional, advection-diffusion model was used to estimate SGD in each site. The obtained results ranged from to 1.8 ×10-7 L cm-2 s-1 to 2.8 ×10-7 L cm-2 s-1 and depended on both: short-timescale factors (wind direction and monthly precipitation) and long-timescale factors (total precipitation and large-scale sea level variations). The calculated rates were further extrapolated to the entire Bay of Puck and ranged from 16.0 m3 s-1 to 127.7 m3 s-1. The estimated SGD fluxes were significantly higher than results including only the freshwater component of SGD. In the Baltic Sea the importance of SGD, as a source of water and accompanying chemical substances, is still neglected, however, the present findings indicate that locally SGD can be higher than rivers runoff.