Adaptive monitoring for change: Record low hypoxia in Chesapeake Bay in 2023

Seasonal hypoxia (dissolved oxygen [DO] levels ≤ 2 mg/l) poses a severe threat to coastal ecosystems globally, including the largest estuary in the United States, the Chesapeake Bay. This V-shaped drowned river valley features shallow flanks, where the deepest waters experience persistently low DO levels typically initiated during the spring and ending in late summer or early autumn. Reports on low DO conditions in the Chesapeake Bay date back over a century. Consistent annual records of summer hypoxic conditions have been available since 1985 based on routine data collected through the Chesapeake Bay long-term water quality monitoring program. In 2023, the Chesapeake Bay Program (CBP) reported a record low seasonal hypoxic volume (May to October) of 0.58 cubic miles, according to the Maryland Department of Natural Resources, and 0.52 cubic miles, as reported by the Virginia Institute of Marine Science. Both volumes are considerably below the long-term average of 0.97 cubic miles.

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