Denitrification Capacity of a Natural and a Restored Marsh in the Northern Gulf of Mexico from 2014-02-27 to 2015-02-26 (NCEI Accession 0223379)

Additional sampling and analyzing information from submitter:

The marsh platform elevations were measured at the beginning of the study with a Trimble NetRS GPS receiver and are reported relative to the NAV 83 (conus) datum, region 16N. In June 2014 triplicate cores to a depth of 10 cm were collected. Dried sediments were ground with a mortar and pestle and percent carbon and nitrogen contents of the sediments were measured on a Carlo Erba elemental analyzer.

In June 2014 triplicate cores to a depth of 10 cm were collected. Dried sediments were ground with a mortar and pestle and percent carbon and nitrogen contents of the sediments were measured on a Carlo Erba elemental analyzer.

Five cores (9.5 cm, 24 cm Height) were collected bimonthly during low tide at each site to a depth of 20 cm. Cores tubes were pushed into the marsh soil within patches of J. roemerianus at the natural and restored marsh sites within 5 cm of the vegetation base taking care not to include aboveground vegetation in the core. Belowground biomass was removed from each core by rinsing the cores and drying the material retained on a 2 mm sieve to dry weight at 60 degrees Celsius.

At the natural marsh, aboveground vegetation was harvested bimonthly (n = 3) by placing 0.25 m2 quadrants over a patch of J. roemerianus and collecting the vegetation. Stems were dried at 60°C to a constant weight and aboveground mass per area was determined. Because the restored marsh is part of a public education and outreach center, vegetation could not be harvested frequently. Therefore, stems of J. roemerianus at the restored site were harvested at one time and individual stem heights were measured and dry weights recorded. A height versus mass vegetation regression was fit to this log transformed data (y = 1.33 × −2.48, R2 = 0.94) and used to estimate above- ground biomass from stem densities and heights in 0.25 m2 quadrats during bimonthly surveys (n = 3).

Sediment Chl-α content was determined for samples collected in triplicate with a cut off syringe (I.D. 1.3 cm) to a depth of 1 cm. Sediments were freeze dried and extracted for 24 h in 90% acetone. Concentrations were determined fluorometrically and normalized per gram dry sediment.

Porewaters from a depth of 10 cm were collected approximately biweekly during high tide from each sipper and along with triplicate surface water samples were glass fiber filtered (GF/F, 0.7 μm pore size) and nalyzed for dissolved inorganic nutrients. Nitrate, nitrite. Ammonium, and phosphate were measured on a Skalar SAN+ Autoanalyzer. Triplicate cores (2.6 cm ID) from the top 10 cm of sediments were collected biweekly at each site for analysis of total sediment extractable NH4 . One gram of homogenized sediments was weighed into 50 mL centrifuge tubes and extracted for 10 h with 10 mL of 1 M NaCl (Smith and Caffrey 2009) on a shaker table at 60 rpm. Samples were then centrifuged at 4500 rpm for 10 min and the supernatant was GF/F filtered and frozen prior to analyses as previously described.

Triplicate cores (2.6 cm ID) from the top 10 cm of sediments were collected biweekly at each site for analysis of total sediment extractable NH4 . One gram of homogenized sediments was weighed into 50 mL centrifuge tubes and extracted for 10 h with 10 mL of 1 M NaCl (Smith and Caffrey 2009) on a shaker table at 60 rpm. Samples were then centrifuged at 4500 rpm for 10 min and the supernatant was GF/F filtered and frozen prior to analyses as previously described.

The five bimonthly cores were capped underwater avoiding air bubbles and inflow and outflow tubing was connected to each core. Filtered site water (GF/F) spiked with sodium 15N-nitrate to a final concentration of 50 μM flowed through each core for 24 hr with a peristaltic pump at a rate of 2.5 mL per minute. Each core contained a magnetic stir bar suspended from the caps that stirred the overlying water. Water samples for NH4 Flux, NO3 Flux, and PO4 Flux were collected after 24 hours. Water samples were filtered through GF/F and frozen. NH4 and PO4 concentrations were measured on a Skalar SAN+ Autoanalyzer. NO3 concentrations were determined with a combination of VCl3 reduction as described in Schnetger B, Lehners C (2014). At the same time as nutrient flux samples, triplicate samples from the inflow and outflow line of each core for analysis of nitrogen gas isotopes were collected in 12 mL Exetainers by overflowing the volume of the vial twice and then preserving the samples with 250 μL of 50% w/v ZnCl2. Samples were capped and stored underwater until analysis for nitrogen gas isotopes on a membrane inlet mass spectrometer.