Dataset: FTIR Spectra

Soil cores were collected from three sites within the Plum Island Ecosystems - Long Term Ecological Research (PIE-LTER) domain (MA, USA; 42.74° N, -70.85° W). A core liner was fitted with a gasketed piston and placed on the sediment surface and pushed down into the marsh subsurface, ensuring that the soil column did not compact during collection.

The sites had similar elevations (1.41 - 1.51 m North American Vertical Datum of 1988 [NAVD88]) and salt marsh grass communities, dominated by Spartina patens, S. alterniflora, and Distichlis spicata. Permanently inundated ponds within each site had comparable depths (0.24 - 0.30 m) but varied in size (643 - 7,149 m²) and age (40 - 53 years) (Spivak et al., 2017; Spivak et al., 2018).

Soil cores were split lengthwise and sectioned into 1, 2, or 5 cm sections, with higher resolution in the top 30 cm. Soil water content (%) and bulk density (g/cm³) were determined gravimetrically after drying to constant mass (60°C). Samples were sieved (1 mm) to remove root material and homogenized with a Retsch Mixer Mill 200.

Samples were run on a Bruker Vertex 70 Fourier Transform-Infrared Spectrometer (Bruker Optics Inc., Billerica, MA) outfitted with a Pike AutoDiff diffuse reflectance Accessory (PIke Technologies, Madison, WI) and data were obtained in diffuse reflectance mode at a 2cm-1 resolution. Raw spectra were transformed using a calculated two-point linear tangential baseline using Unscrambler X (Camo Software, version 10.1, Woodbridge, NJ) (Bulseco, 2019).