Wednesday, December 6, 2023

2023 Dead Zone December Update


At the end of November the Maryland Department of Natural Resources, Old Dominion University, and Virginia Institute of Marine Science announced that the dead zone in the Chesapeake Bay this year was the smallest since monitoring began in 1985. 

The “Dead Zone” of the Chesapeake Bay refers to a volume of hypoxic water that is characterized by dissolved oxygen concentrations less than 2 mg/L, which is too low for aquatic organisms such as fish and blue crabs to thrive. Within the hypoxic area life of the bay dies and a “Dead Zone” forms. The Chesapeake Bay experiences hypoxic conditions every year, with the severity varying from year to year, depending on nutrient and freshwater flows into the bay, wind, and temperature and season. Dead zones form in the warmer months.

The extent of each year’s dead zone is dependent on several factors, including how much nitrogen and phosphorus pollution enters waterways. High precipitation can contribute to the dead zone because it leads to more polluted runoff washing into rivers and streams. Precipitation was below average for most of 2023 delivering less pollution especially during the critical spring season.  

The spring-time nutrient supply to the Bay was relatively low and June was relatively windy, both of which may have contributed to June through August having a low amount of hypoxia. The Dead Zone remained at low to moderate levels throughout June, July, and into August. The Potomac basin has experienced unusual dryness, despite sporadic heavy rains.  Low stream flows carried less nutrients into the rivers. The cumulative deficit over the past 12 water year was around  6 inches in the basin as a whole.

from VIMS

Each year the Maryland Department of Natural Resources measures the actual dissolved oxygen at several points during the summer months in the Maryland portion of the Chesapeake Bay main stem and the size of the Dead Zone. While the Virginia Institute of Marine Science (VIMS), Anchor QEA and collaborators at UMCES, operate a real-time three-dimensional hypoxia forecast model using measured inputs that predicts daily dissolved oxygen concentrations throughout the Bay ( using the National Weather Service wind monitoring data.

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