Dataset: Sediment Core Biogeochemistry

These data were collected during 2018-2019 from a sandy subterranean estuary (STE) located in Gloucester Point, Virginia, USA (37.248884, -76.505324). In four seasons, a vibracore collected a sediment core roughly 100 centimeters (cm) in length from the mid-tide line of the beach during low tide. Cores were sectioned into ten-centimeter increments. Extractable nutrient concentrations in potassium chloride extracts were analyzed for NOx (nitrate + nitrite), nitrite, and ammonium with a Lachat autoanalyzer. Core sections were used in isotope tracer incubations with 15N-labeled substrates to measure potential denitrification and anaerobic ammonium oxidation (anammox) rates. Briefly, 1 gram (g) of the composited sediment from each 10 cm section was used in sediment slurry incubation experiments. Samples were incubated for 6, 12, or 24 hours in sealed, helium-flushed 12 milliliter (mL) exetainer vials (Labco) at the measured in situ temperature. Denitrification rate incubations were amended with 100 nanomoles ¹⁵NO₃⁻ (99 atm%, Cambridge Isotope Laboratories, Inc.), and ²⁹,³⁰N₂ products were measured using a gas bench isotope ratio mass spectrometer (IRMS, Delta V Plus, Thermo Fisher Scientific, Waltham, MA). To measure potential anammox rates, 500 nanomoles of ¹⁵NH₄⁺ (99 atm%, Cambridge Isotope Laboratories, Inc.) and 100 nmoles ¹⁴NO₂⁻ were added to the sediment slurries; the production of ²⁹N₂ was measured by IRMS. N₂ production rates were calculated using the methods described by (Song and Tobias, 2011). All incubations were conducted in duplicate.