Rabiger-Völlmer, Johannes; Schneider, Birgit; Westermann, Henriette; Fischer, Markus Lothar; Zielhofer, Christoph (2024): Ahr river overbank sediments: grain sizes, carbonates and soil organic parameters (Mayschoß-Transect, core Ahr2022-1_1, Ahr2022-1_2, Ahr2022-2_1, Ahr2022-2_2) [dataset]. PANGAEA, https://doi.pangaea.de/10.1594/PANGAEA.973867 (DOI registration in progress)

Four sediment cores from the Mayschoß floodplain (Ahr) were analysed for grain size, carbonates and soil organic parameters. For this purpose, the freeze-dried samples were sieved (2 mm) to remove large organic matter and the samples were separated into fine (< 2mm) and coarse (> 2 mm) fractions. For the grain size analysis, the fine fraction (< 2 mm), sieved samples (10 g) were left overnight in 35% hydrogen peroxide (H2O2). The samples were then heated to remove organic matter. In addition, the samples were dispersed by a 10 ml solution of 0.4 N sodium pyrophosphate (Na4P2O7) and ultrasonicated (45 min). The sand fraction was separated by dry sieving (classes: coarse sand: 2000 - 630 µm, medium sand: 630 - 125 µm, find sand: 200 - 125 µm and finest sand: 125 - 63 µm). X-ray granulometry (XRG, SediGraph III 5120, Micromeritics) was used to measure the fine fraction (coarse silt: 63 - 20 µm, medium silt: 20 - 6.3 µm, fine silt: 6.3 - 2.0, coarse clay: 2.0 - 0.6 µm, medium clay: 0.6 - 0.2 and fine clay < 0.2 µm). The coarse fraction was divided into two classes (2-10 mm, > 10 mm) by dry sieving. The roundness of gravels (> 10 mm) was also determined (> 10 mm rounded, > 10 mm sub-rounded, > 10 mm angular). The carbonate content of the fine fraction was determined using the Scheibler method. A pre-test is therefore carried out to determine the sample quantity. The more carbonate is contained, the smaller the required sample quantity. During the measurement, a defined amount of 10 % hydrochloric acid (HCL) is then added to the sample and the outgassing of the resulting CO2 is measured. The amount of HCL can be used to calculate the amount of dissolved calcium carbonate (CaCO3). For further geochemical analysis, the samples were pulverised and homogenised using the Retsch vibrating mill MM 200. The content of total carbon, nitrogen and sulphur of the fine fraction was analysed using the vario EL cube (Elementar). For this purpose, the ground fine soil sample was mixed with tungsten oxide (WO3) in a ratio of 1:3 and wrapped in tin foil for analysis. Due to the higher accuracy, the sulphur values of the X-ray fluorescence spectrometry (XRF) were included in the data set. The samples (8 g) were pressed into uniform pills with a carbon-based binder using a Vaneox press at 20 t for 2 min. Elemental analysis was performed in a He atmosphere using a Spectro Xepos energy dispersive XRF spectrometer. The complete XRF dataset including errors, reproducibility and security of the measurement is also available on Pangaea. Finally, the inorganic and organic carbon as well as the C/N and C/S ratios were calculated. The surface elevation was extracted from Brell et al. (2023).