Dataset: Core biogeochemical properties, 2018-2019

Soil Sampling:
Eleven soil cores (~ 2 m deep) were collected 1 m inland from the marsh edge two marsh islands in Barataria Basin, Louisiana. A polycarbonate core tube (2.6 m x 7.6 cm diameter) was used to extract soil samples via the push core method. In addition, triplicate cores (50 cm deep) were collected using a piston corer from the estuarine bottom, at 25 m from the edge of a island at a water depth of 1 m. Soils were extruded in the field, sectioned into the 10-cm intervals and placed and sealed in zip-lock bags. Samples were stored on ice, immediately transported to Louisiana State University (LSU), and stored at 4 degrees C until analysis

Moisture Content:
Drying a subsample of soil using a gravimetric oven at 60 °C until a constant weight was achieved. Dried soils were ground using a mortar and pestle.

Bulk Density:
The bulk density of each sample was determined by calculating the total dry weight of the sample and then dividing by the volume of the 10 cm section of the core (384.85 cm3).

Organic Matter Content:
Dried, ground sub- samples were burned at 550°C in a muffle furnace for 4 h to determine percent organic matter using the loss-on ignition technique (Sparks, 1996).

Total Carbon:
Total Carbon content was determined on ground samples using elemental combustion system (Costech Analytical Technologies, Valencia, CA).

Carbon Density:
The volumetric concentration of the TC (g cm-3; carbon density) was determined by dividing the amount of TC in 10 cm section of the core by the volume of the 10 cm section of the core.

Labile Carbon:
The molecular complexity of the organic matter was determined from dried and ground soil subsamples through a H2SO4 extraction following Rovira & Vallejo (2002) and Oades et al. (1970) with modifications by Steinmuller & Chambers (2019). The organic matter was fractionated into two groups-1) Labile pool (LPC) consisting of plant or microbially derived non-cellulosic polysaccharides, hemicellulose, and cellulose and 2) Refractory pool (RPC) consisting of klason lignin, fats, waxes, resins, and suberins (Rovira & Vallejo, 2002). To extract LPC, 2 mL of 26 N H2SO4 was added to a flask containing ~0.5 g of dried and ground soil. The solution was shaken in an orbital shaker at 100 rpm for 14 h and diluted to a concentration of 2 N H2SO4 by adding 26 mL of nanopure water. The resulting solution was heated at 105 degrees C for 3 h, allowed to cool, filtered through Watman #41 filters, and then diluted to a final volume of 50 mL. The concentration of LPC carbon was determined using Shimadzu TOC (Shimadzu, Kyoto, Japan).

Refractory Carbon:
The amount of refractory carbon was calculated by deducting the labile pool of carbon from the total carbon content of the soil.

Total Nitrogen:
Total Carbon content was determined on ground samples using elemental combustion system (Costech Analytical Technologies, Valencia, CA).

Total Phosphorus:
A 0.2-0.5 g subsamples were weighed in 50 ml glass beakers and burned in a muffle furnace at 550 degrees C for 4 h. Total phosphorus was determined by acid digesting ashed samples following Andersen (1976) and analyzed colorimetrically using a SEAL AQ2 Automated Discrete Analyzer (SEAL Analytical Inc, Mequon, Wisconsin) with a detection limit of 0.002 mg P L-1 (USEPA 1993).

Total Inorganic Phosphorus:
Total inorganic phosphorus (TIP) was extracted from dried and ground samples following Richardson and Reddy (2013). Samples of 0.3-0.5 g were weighed in centrifuge tubes, and equilibrated with 25 ml of 1 M HCl for 3 hours in a longitudinal shaker, centrifuged for 10 minutes at 5000 g, and vacuum filtered through a 0.45 µm filter. The filtered solution was analyzed for TIP colorimetrically using a SEAL AQ2 Automated Discrete Analyzer (SEAL Analytical Inc, Mequon, Wisconsin) with a detection limit of 0.002 mg P L-1 (USEPA 1993).

Total organic Phosphorus:
Total organic phosphorus (TOP) was determined by difference of total inorganic phosphorus from total phosphorus.

Enzyme Activities (β‑glucosidase, β‑xylosidase, and alkaline phosphatase):
Extracellular enzyme assays were performed within 48 hours of the sample collection to determine the activity of β‑glucosidase, β‑xylosidase, and alkaline phosphatase. Soils from the triplicate marsh and estuary cores were analyzed. Marsh soils were analyzed on a 30 cm depth interval from the surface to the depth of 160-170 cm. The estuary cores were analyzed on alternate depths from the surface to 40-50 cm depth. Enzyme Assays were performed using fluorescent substrate 4‑methylumbelliferone (MUF) for standardization and fluorescently labeled MUF-specific substrates (German et al., 2011). A soil slurry was created adding ~1 g of moist soil to 40 mL of deionized water and shaken on an orbital shaker for 1 h at 25 degrees C and 150 rpm. Fluorescence was measured at excitation/emission wavelengths 360/460 on a BioTek Synergy HTX (BioTek Instruments, Inc., Winooski, VT, USA) both immediately after substrate and sample were added and 24 h later to determine a rate of enzyme activity.

Potentially mineralizable nitrogen (PMN) and phosphorus (PMP):
Soils from triplicate marsh and estuary cores (same depth interval as enzyme activity) were incubated following White & Reddy (2000) to determine PMN and PMP rates. Four sets of samples were assigned a time of 0, 2, 5, and 10 days of incubation at 40 degrees C. For zero-day sample, field-moist soil (~5 g) was weighed into 40 mL centrifuge tubes with 25 mL of 2M KCl added, shaken on an orbital shaker at 150 rpm and 25 degrees C for 30 min, and centrifuged at 4,000 g for 10 min at 10 degrees C. Each sample was vacuum-filtered through 0.45 µm membrane filters, acidified to a pH of <2 with sulfuric acid, and stored at 4 degrees C. For 2, 5, and 10 days samples, field moist soil (~10 g) was weighed in to a 40 mL glass serum bottle and sealed with rubber septa and aluminum crimp. Head space was evacuated until -75 kPa, purged with N2 gas for 10 min, and 15 mL of N2 purged filtered site water was then added through a syringe to create a slurry. The serum bottles were incubated at 40 degrees C and shaking at 120 rpm in an Incubated Shaker (IS-971, Jeio Tech Lab Companion, Daejeon, Korea). On the designated day, samples were removed from the incubator, added with 25 mL of 2M KCL using a syringe, and placed in a shaker for 30 min. Then samples were transferred to 40 mL centrifuge tubes and centrifuged at 5,000 g for 10 min at 10 degrees C. Each sample was vacuum-filtered through 0.45 µm membrane filters, acidified to a pH of <2 with ultrapure concentrated sulfuric acid, and stored at 4 degrees C. Each sample was analyzed for extractable ammonium (NH4+) and soluble reactive phosphorus (SRP) colorimetrically using a SEAL AQ300 Automated Discrete Analyzer (SEAL Analytical Inc, Mequon, Wisconsin) with a detection limit of 0.01 mg N L-1 and 0.002 mg P L-1 (USEPA, 1993). The PMN and PMP rates were determined by regressing NH4+ and SRP concentrations over incubation time.

Extractable Ammonia and soluble reactive phosphorus (SRP):
Field-moist soil (~5 g) was weighed into 40 mL centrifuge tubes with 25 mL of 2M KCl added, shaken on an orbital shaker at 150 rpm and 25 degrees C for 30 min, and centrifuged at 5,000 g for 10 min at 10 degrees C. Each sample was vacuum-filtered through 0.45 µm membrane filters, acidified to a pH of <2 with sulfuric acid, and stored at 4 degrees C. Each sample was analyzed for extractable ammonium (NH4+) and soluble reactive phosphorus (SRP) colorimetrically using a SEAL AQ300 Automated Discrete Analyzer (SEAL Analytical Inc, Mequon, Wisconsin) with a detection limit of 0.01 mg N L-1 and 0.002 mg P L-1 (USEPA, 1993).