Eastern oyster (Crassostrea virginica) filtration, biodeposition, and sediment nitrogen cycling at two oyster reefs with contrasting water quality in Great Bay Estuary (New Hampshire, USA)

• Published in: Biogeochemistry 2015, Vol.122 (1), p.113-129
• Main Authors: Hoellein, Timothy J, Zarnoch, Chester B, Grizzle, Raymond E
• Format: Article
• Language: English
• Subjects: Algae; Ammonium; ammonium compounds; Anaerobic respiration; anaerobiosis; Animal populations; argon (noble gases); Biogeochemistry; Biogeosciences; carbon; chlorophyll; Cores; Crassostrea virginica; Denitrification; Earth and Environmental Science; Earth Sciences; Ecosystems; Environmental Chemistry; Environmental conditions; environmental factors; Estuaries; Eutrophication; Feeding rates; filtration; historic sites; isotopes; Life Sciences; Mollusks; nitrates; nitrogen; Nitrogen cycle; nutrients; Organic matter; Oysters; Phytoplankton; Reefs; Sediments; Water column; Water quality
• ISSN: 0168-2563; 1573-515X
• DOI: 10.1007/s10533-014-0034-7

Benthic deposition of carbon (C) and nitrogen (N)-rich oyster biodeposits may increase denitrification, or anaerobic respiration of nitrate (NO₃⁻) to di-nitrogen gas (N₂). However, environmental drivers of C and N dynamics in oyster biodeposits and reef-adjacent sediments require clarification. In July 2012, we collected intact sediment cores adjacent to and 15–20 m away from two oyster reefs (Crassostrea virginica) in Great Bay, New Hampshire, USA: one reference site and one site with cultural eutrophication. We also measured seston, chlorophyll a, and in situ oyster feeding and biodeposition. Cores were incubated in continuous-flow chambers where inflow water received¹⁵N-ammonium (NH₄⁺),¹⁵NO₃⁻, or no isotopes (control). We quantified fluxes of dissolved nutrients and gasses (oxygen,²⁸N₂,²⁹N₂,³⁰N₂, and argon) after 24 h. Finally, we measured size-fractionated sediment organic matter. At the eutrophic site, abundant phytoplankton in the 5–28 µm size range was correlated with enhanced oyster feeding rates and biodeposit quality (lower C:N). This site had greater denitrification rates in reef-adjacent cores relative to distal cores. Low production of²⁹,³⁰N₂in¹⁵NH₄⁺amended cores suggested water column or biodeposit NH₄⁺were unlikely to be converted to N₂. At both sites, reef-adjacent cores had more shell and higher²⁹,³⁰N₂production with¹⁵NO₃⁻addition relative to distal cores, suggesting direct denitrification enhancement near reefs. Oysters likely increased sediment N₂production via high quality biodeposits (eutrophic site), and NO₃⁻diffusion via structural complexity of reef-adjacent sediment (both sites). Overall, results suggest oyster-mediated ecosystems services may be expected to vary with environmental conditions.