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Königshafen Submarine Groundwater Discharge Network (KiSNet)

Applicant Dr. Ulf Mallast
Subject Area Hydrogeology, Hydrology, Limnology, Urban Water Management, Water Chemistry, Integrated Water Resources Management
Term from 2019 to 2023
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 437385420
 
Final Report Year 2024

Final Report Abstract

The Covid pandemic had a significant impact on the project, necessitating a shift in approach from a method comparison framework involving all disciplines to a focus on a sequential campaign approach with careful planning and further measures such as the KiSNet seminar to support networking. The latter proved to be particularly valuable in increasing understanding of different disciplines, approaches and methodologies. Due to its effectiveness, it is planned to continue the seminar at a reduced frequency to further foster links within the KiSNet group. In terms of methodology, our sequential interdisciplinary approach to understanding groundwater discharge in the Bay of Königshafen yielded promising results. This included initial hydrogeological modelling, spatially continuous geophysical and remote sensing mapping, interdisciplinary integration to improve results, and validation by in-situ hydrological, physical and biogeochemical analyses. One aspect should be emphasised, as it was initially thought to be crucial: mapping does not require simultaneous application of different methods, as the SGD locations are consistent over different temporal scales, suggesting the feasibility of time-shifted application of methods. Our investigations revealed a previously unknown steep clay or silt structure that influences the hydrogeological flow behaviour and groundwater discharge in the bay. SGD sites were identified predominantly along the southern and southwestern coasts and showed temporal stability over three decades. Freshwater contribution was low, with SGD fresh estimated at 1 million m3/a, representing less than 0.4% of the annual water budget. Areas close to the shoreline exhibited the highest groundwater fluxes, while offshore discharge (up to 500 m from the coast) is potentially associated with subsurface clay structures and is therefore discontinuous and spatially confined to prominent features, highlighting the complex dynamics of groundwater flow in the bay. The Covid pandemic posed a significant and unforeseen challenge to the KiSNet project from the outset, disrupting its planning and requiring adaptive measures to sustain the networking efforts while maintaining the project's core objective of method comparison for submarine groundwater discharge (SGD) investigations. Another surprise was the initial perception of the Königshafen Bay groundwater system, which was thought to be a closed and clearly definable groundwater system with rather simple representable flow systems. This was the reason why it was chosen as a study site. Instead, it revealed a complexity beyond initial expectations. Questions remain about the connection between the surface ponds and the groundwater system, the volume of fresh groundwater originating from the freshwater lens, and the source of the radium concentration observed in the stream along the northern shoreline of the bay.

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