2020 Dead Zone Update

Overall, the total volume of the 2020 Dead Zone in the Chesapeake Bay was the second lowest since 1985 and was estimated to be considerably lower than in the Last several years. 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.

If your will recall, in mid-June, the EPA Chesapeake Bay Program, United States Geological Survey, University of Maryland Center for Environmental Science and University of Michigan scientists released their prediction for slightly smaller than average 2020 Dead Zone. This prediction was based on slightly less than average water and nitrogen flows into the bay from January – May 2020. The actual Dead Zone was smaller than they predicted.

At various times each summer the Maryland Department of Natural Resources measures the dissolved oxygen 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 input of that predicts daily dissolved oxygen concentrations throughout the Bay (www.vims.edu/hypoxia) using the National Weather Service wind monitoring data.

"The average hypoxic volume of the eight 2020 summer cruiseswas 0.63 cubic miles, compared to a historical summer average from 1985-2019 of0.84 cubic miles. During 2020, every cruise except the one in late July hadbetter than average oxygen conditions for its time period. The most recentmonitoring cruise conducted in September found no hypoxic waters in theMaryland mainstem of the Chesapeake Bay. "The September cruise normally occurs mid-month but was delayed a week due to several days of high winds which, along with cool September temperatures, contributed to the increase in oxygen in the deeper bay waters. Similarly, no hypoxia was observed in Virginia Chesapeake Bay mainstem waters in September. 

Crabs, fish, oysters, and other creatures in the Chesapeake Bay require oxygen to survive. Scientists and natural resource managers study the volume and duration of bay hypoxia to determine possible impacts to bay life. Each year from May to September, the Maryland Department of Natural Resources computes these volumes from data collected by Maryland and Virginia monitoring teams during twice-monthly monitoring cruises. Data collection is funded by these states and the Environmental Protection Agency’s Chesapeake Bay Program. Bay hypoxia monitoring continues throughout the year.

From the VMIS 2020 Bay Report Card:

“Springtime nitrogen inflows in 2020 were 17% below the long-term average, resulting in the prediction that the amount of hypoxia would similarly be slightly less than average... cool windy weather helped mix and aerate Bay water in the spring, resulting in hypoxia beginning later than in previous years. As summer arrived, weak winds and very high temperatures allowed hypoxia to increase considerably, resulting in a very large dead zone in late July... In 2020, hypoxia decreased quickly in early August in response to Hurricane Isaias; however, hypoxia returned in early September until stronger winds and cooler temperatures prevailed, ending hypoxia in the mainstem of the Bay earlier than in previous years. Overall, the total amount of hypoxia in 2020 was estimated to be considerably lower than in the recent past, with hypoxia both starting later and ending earlier, as was also seen in periodic ship based observations of dissolved oxygen.”

Despite the fact that the rain fall was above average in the region, and an extended heat wave struck the area in July the hypoxia was below average. This could be an indication that the Chesapeake Bay pollution diet is working, or an indication that the large number of storm that passed through the region bringing strong winds and cooler temperature were the controlling factor.