Abstract
In spring and summer of 2019, the two openings of the Bonnet Carré Spillway represented an unprecedented change from natural modes of variability to an engineered diversion in a coastal system. The abundance of river discharge diverted by this event has an unknown potential for impacts on water quality and coastal dynamics in this region. Using a combination of data from shelf hydrographic surveys and a mooring site during the event, the dissolved oxygen dynamics on the shelf are investigated. Extensive of areas of hypoxia on the shelf were observed throughout the summer study period with high variability in both space and time. Of particular interest was a regularly occurring mid-water column dissolved oxygen minimum, which in one incidence was hypoxic and had lower dissolved oxygen levels than bottom waters. Furthermore, time series data of bottom dissolved oxygen from June through September were highly correlated with changes in bottom temperature, revealing a significant connection to upwelling/downwelling events and the presence or absence of hypoxia on the inner to mid-shelf. The results of this study are expected facilitate the development of more effective mitigation and adaptation strategies in response to current and predicted changes in coastal oceans.
