Frontiers in Marine Science (Jun 2023)

The DynaDeep observatory – a unique approach to study high-energy subterranean estuaries

  • Gudrun Massmann,
  • Gudrun Massmann,
  • Grace Abarike,
  • Kojo Amoako,
  • Felix Auer,
  • Thomas H. Badewien,
  • Cordula Berkenbrink,
  • Michael Ernst Böttcher,
  • Michael Ernst Böttcher,
  • Michael Ernst Böttcher,
  • Simone Brick,
  • Iris Valeria Medina Cordova,
  • Jairo Cueto,
  • Thorsten Dittmar,
  • Thorsten Dittmar,
  • Bert Engelen,
  • Holger Freund,
  • Janek Greskowiak,
  • Janek Greskowiak,
  • Thomas Günther,
  • Gabriel Herbst,
  • Moritz Holtappels,
  • Hannah Karen Marchant,
  • Hannah Karen Marchant,
  • Rena Meyer,
  • Rena Meyer,
  • Mike Müller-Petke,
  • Jutta Niggemann,
  • Katharina Pahnke,
  • Dietmar Pommerin,
  • Vincent Post,
  • Anja Reckhardt,
  • Magali Roberts,
  • Kai Schwalfenberg,
  • Stephan L. Seibert,
  • Stephan L. Seibert,
  • Christopher Siebert,
  • Nico Skibbe,
  • Hannelore Waska,
  • Christian Winter,
  • Oliver Zielinski,
  • Oliver Zielinski

DOI
https://doi.org/10.3389/fmars.2023.1189281
Journal volume & issue
Vol. 10

Abstract

Read online

Subterranean estuaries are connective zones between inland aquifers and the open sea where terrestrial freshwater and circulating seawater mix and undergo major biogeochemical changes. They are biogeochemical reactors that modify groundwater chemistry prior to discharge into the sea. We propose that subterranean estuaries of high-energy beaches are particularly dynamic environments, where the effect of the dynamic boundary conditions propagates tens of meters into the subsurface, leading to strong spatio-temporal variability of geochemical conditions. We hypothesize that they form a unique habitat with an adapted microbial community unlike other typically more stable subsurface environments. So far, however, studies concerning subterranean estuaries of high-energy beaches have been rare and therefore their functioning, and their importance for coastal ecosystems, as well as for carbon, nutrient and trace element cycling, is little understood. We are addressing this knowledge gap within the interdisciplinary research project DynaDeep by studying the combined effect of surface (hydro- and morphodynamics) on subsurface processes (groundwater flow and transport, biogeochemical reactions, microbiology). A unique subterranean estuary observatory was established on the northern beach of the island of Spiekeroog facing the North Sea, serving as an exemplary high-energy research site and model system. It consists of fixed and permanent infrastructure such as a pole with measuring devices, multi-level groundwater wells and an electrode chain. This forms the base for autonomous measurements, regular repeated sampling, interdisciplinary field campaigns and experimental work, all of which are integrated via mathematical modelling to understand and quantify the functioning of the biogeochemical reactor. First results show that the DynaDeep observatory is collecting the intended spatially and temporally resolved morphological, sedimentological and biogeochemical data. Samples and data are further processed ex-situ and combined with experiments and modelling. Ultimately, DynaDeep aims at elucidating the global relevance of these common but overlooked environments.

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