2020 Dead Zone Summer Update

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.

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.

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 peak of oxygen depletion typically occurs in July or August. Water temperatures are highest during these months and the days are longest accelerating the growth of phytoplankton that ultimately consumes all the dissolved oxygen. The dead zone is typically gone by late fall. Cooler air temperatures at that time of year chill the surface waters, while the deeper water remains warm and allows more mixing of the layers during storms. Cooler water also will hold more oxygen. The size and shape of the dead zone is variable from month to month during the summer.

From VIMS

This year our region experienced a long heat wave in July. The hot and still conditions were ideal for promoting hypoxia and resulted in an expanding Dead Zone throughout the month. Warmer waters hold less oxygen, and warmer surface waters can create a barrier to oxygen mixing into deep waters of the bay.

From VIMS

Hypoxia started later in the summer than in other recent years, peaked in late July, and decreased quickly with the passing of Hurricane Isais whose winds stirred up the Chesapeake Bay near the beginning of August. The outlook for the rest of the season changed with the increase in tropical storm activity impacting our area. Isais was followed by Laura. .

In the fall of each year, the Virginia Institute of Marine Science and Anchor QEA release a retrospective seasonal analysis of the severity of hypoxia in the Chesapeake Bay. The Annual Chesapeake Bay Hypoxia Report Card summarizes dissolved oxygen concentrations in the Bay as estimated by the team's 3-D, real-time hypoxia forecast model. We should see that report in two to three months. The modeling team also generates the same dissolved oxygen statistics for previous years for comparative purposes you can look at the past few years below.

In 2019, hypoxia decreased quickly in late August and early September due to the winds of Hurricane Dorian; however, the Dead Zone returned with the high temperatures in late September and early October until strong winds mixed the Bay water and ended the Dead Zone in the mainstem of the Bay for the year. Overall, the total amount of hypoxia in 2019 was estimated to be on the high end of the normal range for 1985 to 2018, and higher than in the recent past (see above); and as in 2018, hypoxia also lasted longer than in other recent years.