Dataset: Soil physicochemical properties

Nine coastal wetland soil cores were collected in June 2018 from Barataria Bay, Louisiana, a shallow open water basin located west of the Mississippi River Delta.  Soil cores were collected along three transects, roughly 1 meter apart, that consisted of three points:  the coastal fringe (0 m inland), 1 meter inland, and 2 meters inland. Soil cores were collected in polycarbonate tubes via the push core method to a depth of 150 cm, and field-extruded into 15 separate 10-cm intervals. Soils were stored  in polyethylene bags on ice and immediately transported back to the laboratory, where they were kept at 4 °C until sample analysis was complete. 

This dataset includes analyses of biogeochemical properties, organic matter fractionation, and stable isotope signatures. 

Moisture Content and Bulk Density: A subsample of soil was dried using a gravimetric oven at 70°C for 3 days or until a constant weight was achieved. Dried soils were ground using a SPEX Sample Prep 8000M Mixer/Mill (Metuchen, NJ). 

Total Carbon and Nitrogen content:  %C and %N were  determined using a Vario Micro Cube CHNS Analyzer on dried, ground subsamples.

Organic Matter Content: Dried, ground sub- samples were used to determine percent organic matter using the loss- on-ignition method, where soils were burned at 550°C in a muffle furnace for a total of 3 hours

Extractable Nitrate, Extractable Ammonium, Extractable Soluble Reactive Phosphorus:  2.5 grams of wet soil (both from the field and from the bottle incubation) were placed into 40 mL centrifuge tubes and 25 mL of 2 M KCl was added. Samples were then shaken continuously on an orbital shaker for 1 hour at 25 °C and 150 rpm, then centrifuged for 10 minutes at 10 °C and 5000 rpm.  Following the centrifuge step, samples were immediately filtered through Supor 0.45 μM filters and acidified with double distilled H2SO4 to a pH of < 2 for preservation. Samples of Extractable nutrients  were then analyzed using an AQ2 Automated Discrete Analyzer (Seal Analytical, Mequon, WI, EPA methods 231-A Rev.0, 210-A Rev.1, and 204-A Rev.0).

Carbon and Nitrogen isotopes: Stable isotope analysis was performed at the Stable Isotope Mass Spectroscopy Laboratory, Department of Geological Sciences at the University of Florida.  Dried, ground subsamples from only the 1 meter inland cores were initially combusted on a Carlo Erba NA1500 CNS elemental analyzer.  Following the removal of oxygen and water from the sample gas, the stream was passed through a 0.7 m GC column (120 °C), which separated the N2 gas from CO2.  Effluent then passed into a ConFlo II system, and into a Thermo Electron Delta V Advantage isotope ratio mass spectrometer, where sample gas was measured in relation to laboratory reference gases.  Carbon isotope results are expressed in relation to Vienna PDB, in standard delta notation.

Cellulose, Hemicellulose, and Refractory Carbon: Dried, ground subsamples were subjected to sequential extraction with H2SO4, following Rovira and Vallejo (2002) and Oades et al. (1970), with modifications.  The first fraction is referred to hereafter as Labile Pool 1 (LP1) and consists of either plant- or microbially-derived non-cellulosic polysaccharides, including hemicellulose.  Labile Pool 1 was extracted by adding 20 mL of 5 N H2SO4 into a 50 mL flask containing 0.5 grams of soil.  The solution was heated for 30 minutes at 105 °C and subsequently allowed to cool.  Samples were then filtered through Whatman #41 filters to separate particulates from the solution, and then diluted to a final volume of 50 mL.  Labile Pool 2 (LP2), which consists of cellulose, was determined by adding 2 mL of 26 N H2SO4 to 0.5 grams of dried, ground soil.  Samples were shaken at 100 rpm for 16 hours, then diluted to a final concentration of 2 N H2SO4 with deionized water.  Samples were heated for 3 hours at 105°C, then filtered in the same manner as LP1.  Determinations of LP1 and LP2 concentrations were conducted by use of a Shimadzu TOC-L (Shimadzu, Kyoto, Japan).  The refractory pool was calculated as total soil C minus the sum of the labile pools.  All pools were normalized to total soil C content.