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Dead-Zone Report Card

Compare the annual severity of Chesapeake Bay hypoxia

Each year, the Virginia Institute of Marine Science and Anchor QEA, LLC release a retrospective seasonal analysis of the severity of hypoxia in the Chesapeake Bay. The Annual Chesapeake Bay Dead Zone Report Card—one component of the Chesapeake Bay Environmental Forecast System—summarizes dissolved oxygen concentrations in the Bay as estimated by the team's 3-D, real-time hypoxia forecast model. The modeling team also generates the same dissolved oxygen statistics for previous years for comparative purposes.

Download a printable pdf copy of the VIMS 2022 report card.

Report Card Metrics

The forecast and report card use multiple metrics to quantify and compare hypoxic severity:

  • Maximum Daily Hypoxic Volume (km3): The maximum volume of Chesapeake Bay water experiencing hypoxic conditions on any given day
  • Average Summer Hypoxic Volume (km3): The average volume of hypoxic water from June through September
  • Hypoxic Duration (days): The number of days in a given year between the first and last day of hypoxic conditions exceeding 2 km3 in volume
  • Total Annual Hypoxic Volume (km3 days): The total amount of hypoxia in the Bay for a given year, calculated by summing the hypoxic volume on each day
Synopsis for 2022

Springtime nitrogen inflows in 2022 were 22% below the long-term average, resulting in the prediction that the amount of hypoxia would be less than average. Cool and relatively windy conditions in the spring resulted in hypoxia in 2022 starting later in the year (June) than average, like the mild-hypoxia year of 2020. As summer arrived in 2022, moderate winds allowed hypoxia to increase through the beginning of August, resulting in a maximum size of the dead zone similar to the average historical size. This mid-summer peak is similar to what occurred in 2020 and 2021, but smaller than 2019, when hypoxia was quite severe. In 2022, hypoxia quickly decreased from the high in early-August and continued a downward trend until ending in late September to early October. The quick decrease in hypoxia resulted from cooler temperatures and stronger winds, both of which act to limit the amount of hypoxia in the Bay. Overall, the duration of hypoxia in summer 2022 was short and the total annual amount of hypoxia was relatively low, representing a relatively good year for hypoxic conditions in the Bay.

Springtime nutrient supply to the Bay suggested hypoxia in 2022 should have been somewhat better than average; subsequently, hypoxia was at the low end of the expected range in the total annual hypoxia, based on the 1985-2021 historical record, and water quality monitoring showed better than average conditions. This demonstrates how a relatively late onset followed by a quick decline from near-average maximum summer hypoxic conditions can result in a relatively low amount of total hypoxia in the Bay.
Summed Annual Estimates

Here we describe the severity of hypoxia as estimated by the forecast model. We define hypoxia as dissolved oxygen concentrations less than 2 milligrams/Liter (mg/L).