Dataset: Concentrations of phospholipid-linked fatty acids (PLFAs)
Deployment: Plum_Island

The three ponds are located in the high marsh (1.43-1.46 m above North American Vertical Datum of 1988) of the Plum Island Ecosystems – Long Term Ecological Research (PIE-LTER) site. Surface sediments were collected weekly for TOC, TN, δ¹³C, and δ¹⁵N (June 25-August 13 and November 11-25, 2014). Cores (5 cm diameter x 2 cm deep) were collected from three 1 m² quadrats placed at random locations along two crisscrossing transects in each pond. Sediments were combined in combusted glass vials to form composite samples and stored (-80 ℃) until analysis. Lipid biomarker compounds were extracted using a modified Bligh & Dyer (1959) method (Spivak and Reeve 2015). Sediments were extracted with a methanol : chloroform : phosphate buffer saline mixture (2:1:0.8, v:v:v) using a microwave-accelerated reaction system (MARS6); samples were heated to 80°C for 10 min with continuous stirring. Samples were then partitioned and the organic phase removed. The total lipid extract was concentrated under N₂ and samples were eluted on silica gel columns with chloroform, acetone (F1/2), and methanol (F3) (Guckert et al. 1985). The F3 (phospholipids) was dried under N₂ and saponified with 0.5 M NaOH at 70°C for 4 h. Saponified samples were acidified and extracted 3 times with hexane. The extract was methylated with acidic methanol (95:5 methanol:HCl) and heated overnight at 70°C to form fatty acid methyl esters (FAME). Samples were analyzed with an Agilent 7890 gas chromatograph with the effluent split ~70:30 between a 5975C mass spectrometer and a flame ionization detector. Compounds were separated on an Agilent DB-5 ms column (60 m, 0.25 mm inner diameter, 0.25 μm film). FAME concentrations were quantified using methyl heneicosanoate as an internal standard. FAs are designated A:BωC, where A is the number of carbon atoms, B is the number of double bonds, and C is the position of the first double bond from the aliphatic ‘ω’ end of the molecule. Iso- and anteiso refer to whether the methyl group of branched compounds is attached to the penultimate or antepenultimate carbon atom.