15N labeled phytoplankton was continuously pumped for three days into 30.5 cm diameter mesocosms containing\u00a0 10 cm of sediment and 20 liters of overlying water. Three mesocosms contained oysters twelve 7-cm long oysters (O1, O2, O2) and three mesocosms had no oysters and served as controls (C1,C2,C3). Mesoscosms were flow through with a 0.3 day residence time and open to the atmosphere. N2O and\u00a015N2\u00a0were measured during the phytoplankton addition period.
\nWater samples for N2O analysis were collected with a peristaltic pump through a syringe needle directly into 12 ml exetainer that had been flushed with N2 and preserved with KOH to a pH above 12. Approximately six ml sample was collected. N2O concentrations in the headspace were measured on a GC-ECD.\u00a0 Water samples for 15N2 samples were collected with a peristaltic pump through a syringe needle directly into 30 ml serum bottles that had been flushed with He and preserved with KOH to a pH above 12. \u00a0 Approximately eight ml sample was collected. 15N2 was analyzed by GC - Isotope Ratio Mass Spectrometry (IRMS). 15N-Phyto sample was collected by GFF 0.7um filtration of phytoplankton stock solution.
Open Mesocosm Oyster 15N2 and N2O
N2O concentrations were calculated from N2O\u00a0 calibration curve and corrected for N2O solubility in the aqueous phase using the Bunsen coefficient. 15N2 was normalized to air and air saturated water standards and reported in the delta notation. 15N Phyto enrichment is reported in at% 15N.
\nBCO-DMO Processing:
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