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.
During seawater circulation in permeable intertidal sands, organic matter degradation alters the composition of percolating fluids and remineralization products discharge into surficial waters. Concurrently, coastal seawater nutrient and organic matter composition change seasonally due to variations in pelagic productivity. To assess seasonal changes in organic matter degradation in the intertidal zone of a high energy beach (Spiekeroog Island, southern North Sea, Germany), we analyzed shallow pore waters for major redox constituents (oxygen (O2), manganese (Mn), iron (Fe)) and inorganic nitrogen species (nitrite (NO2-), nitrate (NO3-), ammonium (NH4+)) in March, August, and October. Surface water samples from a local time series station were used to monitor seasonal changes in pelagic productivity. O2 and NO3- were the dominating pore water constituents in March and October, whereas dissolved Mn and Fe were more widely distributed in August. Seasonal changes in seawater temperature as well as organic matter and nitrate supply by seawater were assumed to affect microbial rates and respective pathways. Pore water and seawater variability led to seasonally changing constituent effluxes to surface waters. Mn, Fe, and NH4+ effluxes exhibited their minimum in March (3; 2; 7 mmol d-1 per meter shoreline, respectively) and reached their maximum in August (41; 159; 99 mmol d-1 per meter shoreline, respectively). Furthermore, the intertidal sands switched from being a net dissolved inorganic nitrogen (DIN) sink in March (-62 mmol d-1 per meter shoreline) to a net source in August (99 mmol d-1 per meter shoreline). In conclusion, we demonstrated the necessity of seasonal flux evaluations.
This dataset was acquired to investigate the sources and sinks of dissolved organic matter in a high-energy beach subterranean estuary on Spiekeroog Island, German North Sea. The North Beach sampling location is approximately at 53°46'45N, 7°42'40E. Data were collected during a total of five sampling campaigns in the period of September 2016 - September 2019, spanning over all four seasons. The samples collected were from beach porewaters, seawater, and groundwater from the islands' freshwater lens. Pore water samples were collected with push-point lances (10-100 cm depth), seawater samples with bottles in the surf zone, and groundwater samples from inland monitoring wells (4-40 m depth). Samples were filtered onsite and preserved for storage (acidification for dissolved organic carbon, dissolved organic nitrogen, and trace metals, and poisoning with HgCl2 for dissolved nutrients). In situ data were collected, including temperature, salinity, oxygen concentrations (instrument: WTW Multi 3430), and humic-like fluorescent DOM (instrument: Turner Aquafluor). Laboratory analyses were conducted within a week of sampling and included spectrophotometry for nutrients, ICP-OES for trace metals, and TOC-VCPH analysis for DOC and TDN. Acidified subsamples were desalted and concentrated by solid-phase extraction, then analyzed on via ultra-high resolution Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS on a 15T Bruker solariX XR.