Vario micro cube

The chemicals used in this work were obtained from suppliers and were used without purification. NMR spectra in solution were recorded by using a Bruker DPX 300 and 400 spectrometer. Elemental analyses were performed with an Elementar Vario Micro Cube (Elementar Analysensysteme GmbH, Langenselbold, Germany). An air condenser (FindenserTM, SUPER air condenser, Radleys) was employed in the catalytic reactions instead of a water condenser. The infrared spectrum was recorded using with a Shimadzu 4300 spectrometer (Shimadzu, Kyoto, Japan).

We dried and reweighed soil samples at 60 °C for 48 h to determine the moisture content. Soil pH was measured by pH meter 3151i (Xylem incorporation GmbH, Hessen, Made in Germany) in soil suspension with a ratio of 1:2.5 (w/v). Total carbon (Ctot) and nitrogen (Ntot) content were determined from 60 °C dried soil sample (8–10 mg) using an Elementar Vario Micro cube (Elementar, Langenselbold, Germany) and expressed in percentage. The carbon to nitrogen ratio (C/N ratio) was calculated by dividing Ctot with Ntot. The dissolved organic carbon (DOC) and dissolved nitrogen (DN) were analyzed by mixing soil: water in a 1:5 ratio (w/v) and shaking on an orbital shaker (150 rpm) for an hour and the filtered soil solution (10–15 mL) was used for LiquiTOCII (Elementar, Germany) and expressed in ug g⁻¹ dry weight of soil.

The ¹H (400 MHz) and ¹³C NMR (100 MHz) spectra in acetone-d₆ were recorded with a Varian (Agilent) 400 spectrometer (Agilent Technologies, Santa Clara, CA, USA), internal standard was tetramethylsilane (TMS). Chemical shifts (δ) are reported in ppm. Elemental analysis was performed on a CHNS analyzer “Elementar Vario MICRO cube” (Elementar Analysensysteme GmbH, Hanau, Germany). The melting point was determined on a Boetius table. The progress of the reaction and the purity of the synthesized compound were monitored by TLC on ALUGRAM^® SIL G UV₂₅₄ plates (MACHEREY-NAGEL GmbH & Co. KG, Düren, Germany), and a hexane–ethyl acetate–acetone (2:2:1) mixture was the eluent.

Sediment source samples were sieved to < 63 µm in the field to facilitate direct comparison to the target sediment samples^{29 (link),105} . Sediment source samples were air-dried and ground for further analysis (Fig. 6c). All sediment samples (sources and target) were analysed in the laboratory for their chemical properties, including total carbon (TC) and total nitrogen (TN) content^{21 ,106 (link)} and major and minor elemental geochemical constituents^{32 (link),106 (link)} as potential sediment tracers. For TC and TN concentration a sub-sample of 15 mg was wrapped in tin capsules and combusted in an elemental micro-analyser (Elementar vario MICRO Cube, Elementar Analysensysteme GmbH, Langenselbold, Germany) at 950 °C. A handheld XRF spectrometer (Bruker Tracer IV-SD, Bruker, Kennewick, WA USA) that uses energy dispersive X-ray fluorescence (EDXRF) was employed to determine the following major elements: Al₂O₃, CaO, Fe₂O₃, K₂O, MgO, Na₂O, P₂O₅, SiO₂ and TiO₂ and trace elements: Ba, Cr, Cu, Mn₂O₃, Nb, Ni, Pb, Rb, Sr, Y, Zn and Zr. For this analysis, a sub-sample of 500 mg was placed onto a thin film to measure trace elements at a setting of 40 kV and 15.7 µA and major elements at an excitation of 15 kV and 35 µA under vacuum with Helium gas. For each sample the mean of three replicates was used for further analysis (Fig. 6d).

A topographic survey was completed on a 20 m × 20 m grid within the 20-ha plot using an Electronic Total Station (Sokkia SET-4120). Three topographic variables, including mean elevation, mean convexity and mean slope, were calculated for each 20 m × 20 m quadrat [9 , 18 , 45 ]. These topographic data were used to do habitat classification. Mean elevation ranges from 304.2 m to 602.8 m, with nearly 300 m difference in elevation in the plot. Mean convexity ranges from -5.8 m to 6.9 m, and mean slope varies from 13.8° to 50.3°.
For edaphic variables, 1,292 soil samples covered the whole 20-ha plot at high resolution were collected by both regular and random sampling schemes (S1 Fig). The soil samples were air-dried for more than 30 days, and then were passed through a 0.149 mm sieve. Each sieved soil sample was divided into two subsamples. One subsample of 10 mg was used to analyze total C and total N by elemental analyzer (vario MICRO cube, Elementar, Germany). Another sub-sample of 350 mg was used to analyze total P using flow-injection autoanalyser (SAN++, Skalar, Netherlands). Soil pH of each soil sample was determined by Metterler Toledo pH meter (1:2, H₂0). For simulating heterogeneous environment in spatial point pattern analysis, standard block kriging was used to obtain three topographic and four soil variables for every 5 m × 5 m quadrat [46 , 47 ].