The concentration and isotopic composition of soil carbon and nitrogen were measured from select archived soil cores originally collected for the NSC01 dataset using an isotope ratio mass spectrometer coupled with an elemental analyzer. These soil cores were collected from the lowlands (25 cm depth) of four experimental watersheds in 1982, 1987, 2002, 2010, and 2015. The four experimental watersheds are 001d, n01b, 020b, and n20b.
Location of Sampling Stations: Soil were sampled along the LTER vegetation transects in the lowlands of 001d, n01b, 020b, and n20b.
Frequency of sampling: Five sampling periods (1982, 1987, 2002, 2010, and 2015)
Variables measured: C concentration, N concentration, δ13C, and δ15N
Field methods: An Oakfield Soil Sampler, with a coring diameter of 3/4" (19.05 mm) was used to obtain soil to a 25 cm depth. All samples were stored at 5-10oC until they could be processed. The samples were sieved through a #5 U.S.A. Standard Testing sieve (4 mm opening). All visible rocks and large root fragments are subsequently removed from the sieved soil. Sorting takes approximately 20 minutes for each composite sample. Locations of Archived Soil Samples: 1982, 1987, 2002, 2010, 2015 -Bushnell Annex 121.
Laboratory methods: Dried soil samples were ground and homogenized using a Wig-L-Bug amalgamator. Samples were packed at 4 mg in pressed tin capsules and analyzed via continuous flow on a ThermoFinnigan Delta Plus isotope ratio mass spectrometer via a Conflo II interface with a CE 1110 elemental analyzer. The isotopic ratio of samples was calculated using delta notation as:
δ = [(Rsample/Rstandard)-1)]*1000
where R is the ratio of the heavy to light isotope for the sample and standard, respectively. For carbon, the laboratory working standards were calibrated relative to the international standard VPDB, while for nitrogen, the laboratory working standards were calibrated relative to the international standard atmospheric air. The within-run variability estimated as the SD of working standards was always <0.05‰ for carbon and <0.10 ‰ for nitrogen, and the between-run variability, estimated as the difference between the measured value of a working standard and its long-term calibrated value, was always <0.05‰ for carbon and < 0.15‰ for nitrogen.
For additional metadata information see: http://lter.konza.ksu.edu/sites/default/files/DC.pdf
For additional methods information see: http://lter.konza.ksu.edu/sites/default/files/MM.pdf