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Smaller-than-average dead zone predicted for Chesapeake Bay

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Seagrasses

Algae blooms kill off seagrasses and cause “dead zones” in the Chesapeake Bay. Scientists are predicting a smaller-than-average summer dead zone for the Bay in 2020.

ANNAPOLIS — Researchers from the Chesapeake Bay Program, the University of Maryland Center for Environmental Science, University of Michigan and U.S. Geological Survey announced June 17 that they are forecasting a slightly smaller than average Chesapeake Bay “dead zone” this year, due to reduced rainfall and less nutrient-rich runoff flowing into the Bay from the watershed this spring.

Hypoxic and anoxic regions, areas of low and no oxygen, respectively, are caused by excess nutrient pollution flowing into the Bay. Compared to the past 34 years, this year’s Chesapeake Bay hypoxic volume, or “dead zone”, is expected to be 9% lower than average, while the volume of water with no oxygen is predicted to be 4% lower than average. The predicted volumes are smaller than the dead zone in 2019, a year with exceptionally high freshwater flows and nutrient pollutants entering the Bay.

“The river flows and nutrient loads were closer to average conditions in spring 2020. The more normal spring flows, along with the nutrient reduction efforts of the Chesapeake Bay Program, should result in smaller amounts of hypoxia this summer compared to 2018 and 2019, when near-record levels of spring rains washed more nutrients into the Bay,” said Scott Phillips, co-chair, Scientific Technical Assessment and Reporting Workgroup, Chesapeake Bay Program.

Although different types of nutrients contribute to the annual dead zone, it is the amount of nitrogen that enters the Bay from January-May that is a key driver in how hypoxic conditions can vary from year-to-year.

In spring 2020, the Bay received a slightly below-average amount of nitrogen pollution (17%) compared to the long-term average.

Overall, nitrogen loads entering the Bay included 111 million pounds recorded at nine river input monitoring stations and 7.3 million pounds from treated wastewater.

“The hypoxic forecast is a critical component to tracking progress of our Chesapeake Bay restoration efforts. Dissolved oxygen levels are a key indicator of Bay health as sufficient oxygen is needed to support our iconic Chesapeake species such as oysters, crabs and fin fish. The forecast brings attention to our continued need to implement our nutrient reduction strategies. We look forward to working with our Bay Program partners to monitor and report on hypoxic levels throughout the summer,” said Bruce Michael, director of Resource Assessment Service, Maryland Department of Natural Resources.

Throughout the year, researchers measure oxygen and nutrient levels as part of the Chesapeake Bay Monitoring Program, a Bay-wide cooperative effort involving watershed jurisdictions, several federal agencies, 10 academic institutions and over 30 scientists. Among these institutions, the Maryland Department of Natural Resources and Virginia Department of Environmental Quality conduct 8-10 cruises between May – October, depending on weather conditions, to track summer hypoxia in the Bay. Results from each monitoring cruise can be accessed through the Eyes on the Bay website for the Maryland portion of the Bay and the VECOS website for the Virginia portion. Estimates of river flow and nutrients entering the Bay can be accessed on the U.S. Geological Survey’s website. A Bay-wide assessment of the 2020 dead zone will be available this fall.

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