Pacific oyster (Crassostrea gigas) stocking density as a regulator of nitrous oxide emissions: connecting sediment biogeochemistry and microbial functional genes

Abstract

Bivalves play a key role in regulating the biogeochemistry of coastal systems, particularly by enhancing nitrogen recycling in sediments. However, the impact of these processes on sediment nitrous oxide (N₂O) emissions—a potent greenhouse gas—remains poorly understood, limiting our ability to develop effective mitigation strategies. This study investigated N₂O fluxes at the sediment–water interface in a 120 day land-based enclosure experiment with Pacific oysters (Crassostrea gigas) at four stocking densities and a control group. The results showed that sediments consistently acted as N₂O sources, with the highest stocking density exhibiting significantly greater N₂O fluxes due to increased particulate organic carbon (POC) and nitrogen (PON) deposition. Oyster aquaculture significantly altered sediment biogeochemistry, and random forest modeling identified pore water nitrate as a strong predictor of N₂O flux. The nirK gene abundance increased while nosZ gene abundance decreased in the highest stocking density group, resulting in an elevated nir/nosZ ratio. Structural equation modeling further indicated that oyster density indirectly increased N₂O flux by altering pore water physicochemical properties. Although local environmental conditions modulate N₂O fluxes, this study elucidates how stocking density drives N₂O emissions via biogeochemistry and microbial pathways, highlighting that managing stocking density is a key consideration for mitigating the climate footprint of aquaculture.

Keywords

N₂O fluxes / Oyster / Sediment–water interface / N-cycling genes

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RIGHTS & PERMISSIONS

The Author(s), under exclusive licence to Ocean University of China