Geochemical investigations of submarine groundwater discharge, river outflow, and benthic diagenesis in the coastal Baltic Sea

Medientyp: E-Book; Hochschulschrift

Titel: Geochemical investigations of submarine groundwater discharge, river outflow, and benthic diagenesis in the coastal Baltic Sea

Beteiligte: Ehlert von Ahn, Cátia Milene [VerfasserIn]; Böttcher, Michael Ernst [AkademischeR BetreuerIn]; Kersten, Michael [AkademischeR BetreuerIn]

Körperschaft: Universität Greifswald

Erschienen: Greifswald, 16.12.2022

Umfang: 1 Online-Ressource (PDF-Datei: 279 Seiten, 36586 Kilobyte); Illustrationen (farbig), Diagramme (teilweise farbig), Karten (farbig)

Sprache: Englisch

Identifikator:

Schlagwörter: Ostsee > Biogeochemie > Grundwasserstrom > Flusswasser > Benthos > Diagenese > Isotop

Entstehung:

Hochschulschrift: Dissertation, Mathematisch-Naturwissenschaftliche Fakultät der Universität Greifswald, 2023

Anmerkungen: Literaturverzeichnis: Seite 218-227. - Literaturangaben

Beschreibung: Ostsee, Geochemie, Isotop, Grundwasser, Diagenese

The exchange of water and dissolved elements between the continents and the oceans occurs via different routes in the hydrological cycle, such as rivers, atmospheric exchange, and submarine groundwater discharge (SGD). In addition, the elemental fluxes in the coastal waters may strongly depend on benthic water-solid-microbe interactions close to the sediment-water interface. It is becoming increasingly recognized that SGD can impact diagenesis and act as a source of water and dissolved substances for coastal ecosystems. The qualitative and quantitative assessment of SGD is still challenging as it requires the identification of suitable geochemical tracers for the complex hydrological and biogeochemical processes in the subterranean estuary. In this study, geochemical analyses were combined with geophysical, hydrological, and biological investigations to gain insights into the mechanisms driving SGD in coastal waters. In addition, onshore ground and surface waters were evaluated to identify the processes controlling the potential end member. The surveys were performed along the Baltic Sea coast: Warnow River and Wismar Bay in Germany, the Gulf of Gdańsk and Puck Bay in Poland, and Hanko Bay in Finland. The results suggest that the analyzed surface water system was strongly impacted by seasonal variations, while SGD displayed a much more stable composition throughout the year. New areas of SGD were also identified along the Baltic Sea. It was also observed that anthropogenic coastal infrastructures could promote SGD affecting the water balance and the benthic fluxes. At other sites, the SGD was associated with natural structures such as pockmarks. The stable isotopic composition of the fresh component of SGD was close to the meteoric water at most sites; however, old groundwaters from distinct aquifers were identified. Combining all sites, SGD showed high variability, ranging from near 0 to up to 300 L m-2 d-1, and the saline SGD was more dominant than the fresh component. The fluxes obtained at one site were even higher than the surface runoff. SGD was higher on sandy sediments, but the elemental fluxes were relatively low. Despite low SGD at muddy sites, interfacial elemental fluxes, enhanced by intense diagenesis in the top sediments, resulted in higher chemical fluxes to the water column. The sediment porewater gradients at the SGD impacted sites suggest that the advective upward flow of groundwater increased the elemental fluxes across the sediment-water interface. Therefore, the dissolved substances of SGD are partly impacted by the processes in the soil zone and aquifer during groundwater development, and partly impacted by the early diagenetic process in the surface sediments. Overall, this study shows the importance of SGD for the biogeochemical cycles of coastal waters. Moreover, 6 it can be concluded that a combination of interdisciplinary approaches can provide a better understanding and assessment of SGD in a specific environment. Although all the studies presented here are local, the methodology and results presented in this thesis can be replicated and thus provide assistance in other coastal areas.

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