Effect of inlet morphodynamics on estuarine circulation and implications for sustainable oyster aquaculture.

The incidence of nutrient-induced hypoxia or anoxia-related mortality of aquatic species is becoming more prevalent in coastal systems worldwide. One such instance in an estuary of New Brunswick, Canada, resulted in the loss of approximately 75% of cultured oysters in certain farms. Field observations revealed that, although the occurrence of summer hypoxia in north Tracadie Bay was linked with anthropogenic stressors, changes in the morphology of one of the bay's inlets were likely to play a significant role in escalating the eutrophic conditions. However, adequate information on the circulation dynamics of Tracadie Bay was lacking. To address this knowledge gap, a high-resolution spatially explicit hydrodynamic model was developed for Tracadie Bay to evaluate the possible physical processes involved in the generation of hypoxia leading to oyster mortality. Further, the model was coupled with a volume advection-dispersion tracer module to track the dissemination of effluent. The model showed high skill in south Tracadie Bay in simulating water level elevations and slightly lower skill in north Tracadie Bay. Residual flow estimates revealed poorly-circulated stagnant areas, consistent with hot spots in sediment organic matter content. Findings from modeling scenarios based on past, present, and future inlet morphology suggest that inlets have strong consequences on intricate circulation patterns, renewal of water, and transport. Outcomes from this study will be of relevance for managing water quality and aquaculture practices. • Bay's flushing potential responds to inlet geomorphic setting. • Long water renewal time indicates poor flushing. • Stagnant areas coincides with hot spots of sediment organic content. • Feeble outgoing fluxes likely to escalate eutrophic conditions. [ABSTRACT FROM AUTHOR]