Dataset: Core Fluorescent Indicators, March and November 2017

Core samples were collected at five different distances from the island’s edge at three different transects on the island. These core samples were then broken down into 10 cm sections and these sections were then further divided into two subsets. The samples in the first subset were used for the soil physiochemical analysis. The samples in the second set were centrifuged to yield pore water samples that were spectroscopically analyzed (please see the sampling and analytical procedures for further details).

Sample Collection: Thirty cores, which were 0.5 – 1 m long, were collected on at three transects on the island with a manual push-coring method using an acrylic tube. At each transect, cores were extracted at 2 m inland, 1 m inland, 0 m inland (edge), 4 meters outland, and 8 m outland. Upon extraction in the field, each core was sectioned in 10 cm sections, sealed in polyethylene bags, and stored on ice during transportation back to the lab, where they were stored at 4 degrees C in the dark until analysis.

Surface water samples were collected 10 cm below the surface at the edge of the marsh and 16 m outland following the procedures in Haywood et al. (2018).

Soil Physiochemical Analysis: The 10 cm sections were homogenized and weighed prior to analysis to determine gravimetric moisture content, bulk density, percent organic matter, and total carbon.

Gravimetric Moisture Content: The entire 10 cm section (~30 g) was oven-dried at 60 degrees C until constant weight was achieved.

Bulk Density: The total weight of the dried 10 cm section of core was divided by the volume of the 10 cm section (385 cm3).

Percent Organic Matter: 1 g of the dried 10 cm section of core was ground using a mortar and pestle. It was combusted in a Thermolyne furnace (Thermofischer Scientific, Waltham, MA) at 550 degrees C for 4 hours. After cooling, the sample was weighed. The difference in weight following combustion determined percent organic matter.

Total Carbon: 8 mg of the dried 10 cm section of core was used to determine total carbon. These samples were placed into a Shimadzu Total Organic Carbon Analyzer with SSM-5000 A (Shimadzu, Columbia, MD) and combusted at 900 degrees C for 13 minutes.

Porewater Analysis: To remove pore water from the wet soil samples, samples were centrifuged at 2578 g for 10 min. The pore water was decanted and filtered through a 0.45-micrometer x 22-millimeter Nylon syringe filter. After filtration, the pore water was stored at 4 degrees C in the dark until analysis. To determine the dissolved organic carbon, a Total Organic Carbon Analyzer (TOC-L) (Shimazdu, Columbia, MD) was used. A Cary 100 Spectrophotometer (Varian Inc., Palo Alto, CA) was used to collect UV–Vis absorbance spectra, and a Spex Fluorolog-3 spectrofluorometer (HORIBA Scientific, Edison, NJ) was used to collect fluorescence, methods based on Haywood et al. (2018).