In the past three decades, submarine groundwater discharge (SGD) has been recognized as a major pathway for nutrients such as nitrogen, silicate, and phosphorous, and trace metals such as iron, from land to sea. SGD can fuel primary production and impact benthic community structures. Still, little is known about the modifications of groundwater at the sediment-water interfaces, as well as at redox and salinity gradients within the coastal aquifer, where fresh and saline groundwater mix (the so-called “subterranean estuary”). Our research project aims at understanding the modulation of SGD-derived compounds at such interfaces in the coastal beach aquifer on seasonal scales. Within the scope of BIME, we investigate a barrier island in the German North Sea (Spiekeroog) with regards to the dynamics and biogeochemistry of SGD. Our main study site, the northern beach of Spiekeroog Island, is a model example for a high-energy beach system with a mesotidal regime (mean tidal amplitude of 2.6 m) and large wave impact. In BIME, we have formed an interdisciplinary team which focuses on two biogeochemical “zones of interest” of the shallow subterranean estuary: the seawater infiltration zone and the highly diverse SGD exfiltration zones. The subterranean estuary is being investigated using a novel combination of hydrological (modelled and measured water fluxes and flow patterns), geochemical (nutrient, trace metal, and dissolved organic matter cycling), and microbial (community patterns and metabolic processes) perspectives.
The research topics are studied in tandem of, and through contributions by, teams from the Institute for Chemistry and Biology of the Marine Environment (ICBM), the Institute of Biology and Environmental Sciences (IBU), both at the University of Oldenburg, and the Max Planck Institute for Marine Microbiology (MPI) in Bremen.