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FairfaxNews'Dead zone' again lower than average in Chesapeake Bay

‘Dead zone’ again lower than average in Chesapeake Bay

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Researchers from the Chesapeake Bay Program, the University of Maryland Center for Environmental Science, University of Michigan and U.S. Geological Survey are predicting this summer’s “dead zone” in the Bay to be smaller than the long-term average taken between 1985 and 2021.

The reasons include the below-average amount of water entering the Bay from the watershed’s tributaries this past spring, as well as decreased nutrient and sediment pollution from jurisdictions within the watershed.

Compared to the previous 36 years, this year’s Chesapeake Bay hypoxic volume, or “dead zone,” is predicted to be 13 percent lower than average, up slightly than a year before.

Areas of low oxygen, also known as hypoxic regions, can result in the loss of habitat for various types of marine life, including fish, blue crabs, oysters and underwater grasses.

“The fact that hypoxia in the Bay is once again forecasted to be lower than the long-term average is clearly a positive sign for Bay restoration, said Dr. Marjy Friedrichs, a research professor at the Virginia Institute of Marine Science.

A Bay-wide assessment of the 2022 dead zone will be available this fall. For the past three years, the dead zone has been forecasted to be lower than the long-term average – and in all cases, the forecasts proved accurate when compared to data collected throughout the summer.

In 2022, summer hypoxia also began later than it had in several previous years. In 2021, 2019, 2018 and 2017, hypoxic conditions began in mid to late May, but in 2022, hypoxia was not apparent in the Bay until early June. This late start is largely due to cooler temperatures in May when compared to other years.

The levels of pollution reaching the Chesapeake Bay each year vary due to the amount of spring rainfall impacting river flows, which flushes excess nutrients and sediment into the water, as well as conservation practices implemented by jurisdictions to reduce and manage those pollutants.

Although different types of nutrients contribute to the annual dead zone, it is the amount of nitrogen that enters the Bay during spring that is a key driver in how hypoxic conditions can vary from year-to-year. The amount of nitrogen pollution entering the Bay during spring 2022 was 22 percent lower than the long-term average.

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.

The hypoxia forecast model, enhanced in 2020, is based on the monitoring of nitrogen pollution and river flow at the nine river input monitoring stations along the Appomattox, Choptank, James, Mattaponi, Pamunkey, Patuxent, Potomac, Rappahannock and Susquehanna rivers. Together, the U.S. Geological Survey, in partnership with Maryland and Virginia, monitor nitrogen pollution and other important pollutants, flowing into the Bay from 78 percent of the watershed.

In the area not monitored by these stations, additional pollution reported from wastewater treatment plants are also included in the model.

“This summer is shaping up to be similar to 2020, when hypoxia conditions were relatively good compared to the long-term average and the recent past,” said Dr. Aaron Beyer, managing scientist at Anchor QEA. “We will have to wait and see how weather during the summer of 2022 impacts the total amount of hypoxia, but the Bay is off to a promising start to the summer.”

Each of these models and forecasts are supported by the most up-to-date river flow and nutrient inputs from the U.S. Geological Survey. Scientists at the Virginia Institute of Marine Science, in collaboration with Anchor QEA, produce daily real-time estimates of hypoxia volume that show levels beginning later in 2022 when compared to recent years, consistent with monitoring data.

Funding for the models has come from the National Oceanic and Atmospheric Administration and data used by the models are provided by the U.S. Geological Survey, Maryland Department of Natural Resources, Virginia Department of Environmental Quality and Chesapeake Bay Program.

The “dead zone” is an area of little to no oxygen that forms when excess nutrients, including both nitrogen and phosphorus, enter the water through polluted runoff and feed naturally-occurring algae. This drives the growth of algae blooms, which eventually die and decompose, removing oxygen from the surrounding waters faster than it can be replenished.

Plant and animal life are often unable to survive in this environment, hence the name “dead zone.”

While pollution levels are a key component, weather conditions also play a role in the size and duration of the annual dead zone. Heavy rainfall can lead to strong river flows entering the Bay, which carries along increased amounts of nutrient and sediment pollution.

Above-average spring freshwater flows to the Bay, along with hot temperatures and weak winds in the summer, provide the ideal conditions for the dead zone to grow larger and last longer.

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