The dataset was used to map the spatial information of the subsurface to build an accurate representative stratigraphy for calculating the carbon storage of the initially degraded peats in a small valley system of the Alpine Foreland in Bavaria; the Loosbach valley at Pestenacker, an UNESCO world heritage site of Late Neolithic wetland occupation. In detail, we used geophysical prospection methods (Electromagnetic Induction and Electrical Resistivity Tomography) to map the distribution and thickness of peat deposits, and conducted direct push sensing and driving core drilling to ground-truth the geophysical data and to sample bulk material for subsequent carbon analysis in the laboratory.
Electromagnetic induction (EMI) was measured with a CMD-Mini Explorer (GF Instruments s.r.o., Brno, Czech Republic) in May 2018 and June 2019. We used the vertical dipole (VDP) at coil spacings of 0.32 m (VDP1), 0.71 m (VDP2) and 1.18 m (VDP3). With the existing coil spacings, effective penetration depths of 0.5 m (VDP1), 1.0 m (VDP2) and 1.8 m (VDP3) could be achieved. According to the manufacturer, 70 % of the signal originate from above these depths. The EMI sensors measured the apparent electrical conductivity (ECa, in mS/m). Measurements were taken by carrying the instrument about 0.2 m above the ground while being directly connected to D-GPS (Leica GPS1200) for positioning. The acquisition rate was five measurements per second. Data quality was checked by measuring a reference line before and after each measurement. The maximum offset of the EMI values between the two time points was 1.5 mS/m. We corrected the data and removed the reference lines and single outliers.
The data set contains the EMI data with an intercoil spacing of 0.71 m (VDP2) and 1.18 m (VDP3). The measured values of the VDP1 (coils spacing of 0.32 m) could not be used due to a high signal-to-noise ratio.
The Electrical Resistivity Tomography (ERT) data were acquired by using a PC controlled DC resistivity meter system (RESECS, GeoServe, Kiel, Germany) in June 2019. We measured two transects with an electrode spacing 0.5 m. For both transects (transect A with a total length of 158 m, transect C with a total length of 103 m) we applied a Wenner alpha configuration. The coordinates and the height of the electrodes were measured with a D-GPS (Leica GPS1200).
The data set was used to predict soil organic carbon and soil moisture in the vertical as well as horizontal domain, i.e. volumetrically, by using a weighted conditioned Latin Hypercube Sampling design for selecting the calibration samples and the geophysical covariates derived from electromagnetic induction (EMI) and a gamma-ray spectrometer with different intercoil spacings and, thus, different penetration depths and footprints of the signal. The study site is an agricultural field of 58 ha about 70 km north of Leipzig, Saxony-Anhalt, Germany. Present soil types are Gleysols and Gleyic Cambisols consisting of alluvial loam (loam and clay)over Holocene sediments of fluvial sand (LAGB, 2014).
The geophysical measurements were recorded with three EMI sensors (EM38-DD, Geonics Limited, ON, CA; CMD-Explorer and CMD-Mini-Explorer, both GF Instruments, CZ) and a gamma-ray spectrometer (GS CAR, GF Instruments, CZ) in August 2016. EMI sensors measure the apparent electric conductivity (ECa in mSm-1). All EMI sensors captured 5 records s-1 in any dipole orientation. The gamma-ray spectrometer is equipped with a 4l NaI(Tl)-crystal and automatic peak-stabilization to measure the concentration of potassium (40K), uranium (238U) and thorium (232Th). The device has 512 channels with an energy range from 100 keV to 3 MeV. Measurements were captured every 5 seconds. 40K, 238U and 232Th were measured as counts per second. The concentration of 40K (in %) and 238U and 232Th (both in ppm) was calculated corresponding to the decay rate at specific energy levels. The concentration of 40K, 238U and 232Th was used to calculate the dose rate (nGyh 1; IAEA, 2003).
For determination of soil organic carbon, the samples were dried at 40 °C for 24 h, sieved (<2 mm), ground and root fragments were removed. Total carbon was determined with dry combustion using an ELTRA CHS-580A Helios analyser (ELTRA GmbH, GER). Soil moisture was measured gravimetrically with drying at 90 °C for 24 h.