The permeable sandy sediments of beach aquifers receive a high input of electron acceptors, such as oxygen (O2), as well as fresh organic matter through seawater infiltration, driving the biogeochemical turnover in the subterranean estuary. Here, we experimentally determined seasonal sedimentary O2 consumption rates of intertidal sediments along a transect in the seawater infiltration zone at Spiekeroog Island North Beach, Germany, and present the data together with measurements of organic carbon and grain sizes, oxygen concentration of pore waters and beach topography. The samples were taken down to 1 m depth during two-monthly sampling campaigns from May 2022 to April 2023. Preliminary investigations of O2 consumption rates took place in in March, June and August 2017. Sediment and porewater sampling procedures were carried out as described by Massmann et al. (2023). O2 consumption rates were determined in slurry incubations of the retrieved sediments using gas tight vials (Labco Exetainer® 12 ml) equipped with O2 sensor spots (Pyroscience, OXSP5). Incubations were carried out in the dark at in situ temperatures, and vials were mounted on a rotating wheel to mimic porewater advection. The sediment's total organic carbon content was determined in a CS analyser (Eltra CS 800). Additionally, the fine fraction of the sediment was washed out and the organic carbon content of the fine sediments was measured in a CHNSO analyser (Hekatech Euro EA). The grain size distribution of the sediments was detemined using dynamic image analysis (Sympatec QICPIC). The O2 concentration in the pore water along the transect was measured immediately after the sample was taken using a flow-through oxygen optode (Pyroscience, OXFTC). The data was collected to investigate the impact of seasonal inputs and filtration efficiency on the O2 consumption during seawater infiltration into the permeable sands of beach aquifers.
Sandy beaches are highly dynamic land-ocean transition zones. For two-monthly sampling campaigns from May 2022 to April 2023, the beach topography along a sampling transect in the seawater infiltration zone at Spiekeroog Island North Beach, Germany, was obtained using Digital Elevation Models (DEMs) derived from aerial imagery during drone flights and manual Real-Time-Kinematic (RTK) differential GPS-surveys. In December 2022, the data was obtained using differential GPS measurements (Stonex S9 III Plus GNSS) because of unfavorable conditions for drone flights. These measurements were carried out in connection with sediment and pore water sampling along the transect during the campaigns. The data was collected to investigate the impact of morphodynamics on the O2 consumption during seawater infiltration into the permeable sands of beach aquifers.
We collected sediment cores from the Janssand intertidal sand flat in Germany in April 2016, August 2016, and February 2017. All measurements were made in laboratory experiments using NOx (nitrate + nitrite) microbiosensors and oxygen microelectrodes. Cores were kept at in situ temperatures with a simulated day/night cycle and regular flushing with site seawater to simulate natural porewater advection during periods of inundation. We determined the depth of maximum microphytobenthos photosynthetic activity from steady-state oxygen profiles. We then flushed site seawater down through the core to measure net NOx and oxygen consumption rates at that depth. We measured potential denitrification rates at high spatial resolution by flushing acetylene- and nitrate-amended site seawater down through the core and measuring the accumulation of nitrous oxide using a microelectrode. Finally, we applied a range of realistic downward advective flows of seawater into sediment, in both the light and the dark, in both the spring and summer. We measured the depth to which NOx and oxygen penetrated over the course of several hours under these steady flow conditions using NOx microbiosensors and oxygen microelectrodes. from our study site, NOx always reached the depths of maximum denitrification potential, regardless of light availability or season.