Different continuous freshwater contributions to submarine groundwater discharge at a coastal peatland, southern Baltic Sea

• Published in: Isotopes in environmental and health studies Vol. 61; no. 1; pp. 42 - 60
• Main Authors: Jenner, Anna-Kathrina, Saban, Rhodelyn, Ehlert von Ahn, Cátia M., Roeser, Patricia, Schmiedinger, Iris, Sültenfuß, Jürgen, Reckhardt, Anja, Böttcher, Michael Ernst
• Format: Journal Article
• Language: English
• Published: England Taylor & Francis 02.01.2025; Taylor & Francis Ltd
• Subjects: Baltic Sea; Biogeochemistry; Climate change; Coastal waters; coastline; coasts; Deuterium - analysis; Discharge; Environmental Monitoring; Estuaries; Fresh water; Fresh Water - analysis; Fresh Water - chemistry; freshwater; Geologic Sediments - analysis; Geologic Sediments - chemistry; Groundwater; Groundwater - analysis; Groundwater - chemistry; groundwater dating; Groundwater discharge; Groundwater runoff; Helium; hydrochemistry; Hydrology; Isotope composition; Lances; long-term observation; North Sea; Oxygen Isotopes - analysis; Peatland; Peatlands; Pore water; porewater; River flow; rivers; Runoff; Salinity; Salinity effects; Seawater - analysis; Seawater - chemistry; sediments; Stable isotopes; Submarine groundwater discharge; Surface runoff; Surface water; Surface-groundwater relations; temperate climate; Tritium; water isotopes; Water Movements; Baltic Sea; North Sea; groundwater dating; coastline; hydrochemistry; water isotopes; long-term observation; porewater; temperate climate; Peatland; Submarine groundwater discharge; Baltic Sea
• ISSN: 1025-6016; 1477-2639; 1477-2639
• DOI: 10.1080/10256016.2024.2422864

The impact of freshwater sources like surface river runoff and submarine groundwater discharge (SGD) on coastal waters is currently in focus of intense debate and investigation. One of the ongoing challenges in SGD research is the characterization and quantification of the freshwater endmember contributions to the subsurface mixing zone and their influences on element balance and biogeochemical transformations. Long-term investigations of the sediment porewater composition provide characterization and understanding of the physical, hydrological and biogeochemical processes controlling the substance exchanges. In this study, we focus on the hydrochemical and stable isotope (δ 2 H, δ 18 O) compositions of sediment porewaters along the coastline of a southern Baltic Sea peatland. Coastal surface water and groundwater dynamics were monitored at two coastal sites using 5-m-long stationary lances over a 5-year period. The vertical compositional gradients were used to extrapolate to zero-salinity (ZS) components applying a binary mixing model on the salinity and water isotope composition. The results characterize a subterranean estuary (STE) with three potential mixing endmembers: two fresh groundwaters and the brackish Baltic Sea. Tritium-helium ( 3 H- 3 He) porewater dating gave ages of more than about 20 years for the freshwater components. The ZS components were compared with other SGD sites along the southern Baltic Sea and North Sea and highlight the importance of local SGD studies for a proper groundwater endmember characterization as basis to understand hydrological and biogeochemical developments at the land-ocean continuum in times of current climate change.