THE MOBILITY AND RETENTION OF DISSOLVED ORGANIC MATTER IN PERMEABLE SEDIMENTS OF A HIGH-ENERGY SUBTERRANEAN ESTUARY

Permeable sandy aquifers beneath high-energy beaches are potent biogeochemical reactors with high respiration rates. Besides contributing to nutrient and trace metal fluxes, little is known about their role as sinks or sources of dissolved organic matter (DOM). We explored DOM-solid phase interactions by analyzing the molecular composition of water- and acid-leachable sedimentary DOM down to 24m in a subterranean estuary (STE) on Spiekeroog Island, German North Sea, using fluorescence spectroscopy and FT-ICR-MS. We also examined the coprecipitation of DOM and Fe³⁺ (oxy)hydroxides in STE porewaters containing reduced Fe²⁺ after exposure to air. For both sediment treatments, ~10% of total organic carbon was leachable as dissolved organic carbon (DOC). Water leachates contained aliphatic, nitrogen-rich compounds indicative of marine origin, while acid leachates were more variable, including oxidized aromatic and labile compounds, likely from both terrestrial and marine sources. Fe-DOM coprecipitation induced molecular composition changes, but DOC removal was within analytical uncertainties, and molecular fractionation varied across sampling periods. Thus, DOM-Fe coagulation at redox zones of deep beach STEs may be low and influenced by transport-driven changes in porewater chemistry. Overall, terrigenous DOM is preferentially retained in sediments, while the labile fraction is more mobile. We suggest that in deep beach STEs, organo-mineral interactions are more important in governing DOM dynamics than infiltrating sea- and groundwater.

Presentation Preference: Oral

Primary Presenter: Kojo Amoako, Carl von Ossietzky Universität Oldenburg (kojo.amoako@uol.de)

Authors:

Kojo Amoako, Research Group for Marine Geochemistry (ICBM-MPI Bridging Group), Institute for Chemistry and Biology of the Marine Environment (ICBM), Carl von Ossietzky Universität Oldenburg, 26129 Oldenburg, Germany  (kojo.amoako@uol.de)

Anja Reckhardt, Research Group for Marine Isotope Geochemistry, Institute for Chemistry and Biology of the Marine Environment (ICBM), Carl von Ossietzky Universität Oldenburg, 26129 Oldenburg, Germany  (anja.reckhardt@uol.de)

Magali Roberts, Research Group for Marine Isotope Geochemistry, Institute for Chemistry and Biology of the Marine Environment (ICBM), Carl von Ossietzky Universität Oldenburg, 26129 Oldenburg, Germany  (magali.roberts@uol.de)

Rena Meyer, Research Group for Hydrogeology and Landscape Hydrology, Institute for Biology and Environmental Sciences, Carl von Ossietzky Universität Oldenburg, 26129 Oldenburg, Germany  (rena.meyer@uol.de)

Simone Brick, Research Group for Benthic Microbiology, Institute for Biology and Environmental Sciences, Carl von Ossietzky Universität Oldenburg, 26129 Oldenburg, Germany  (simone.brick1@uol.de)

Thorsten Dittmar, Research Group for Marine Geochemistry (ICBM-MPI Bridging Group), Institute for Chemistry and Biology of the Marine Environment (ICBM), Carl von Ossietzky Universität Oldenburg, 26129 Oldenburg, Germany  (thorsten.dittmar@uol.de)

Hannelore Waska, Research Group for Marine Geochemistry (ICBM-MPI Bridging Group), Institute for Chemistry and Biology of the Marine Environment (ICBM), Carl von Ossietzky Universität Oldenburg, 26129 Oldenburg, Germany  (hannelore.waska@uol.de)