EM – Changing weather patterns mix the size and duration of the annual dead zone in Chesapeake Bay


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November 30, 2021

by Rachel Felver, University of Michigan

The Chesapeake Bay Program and its partners, including the University of Michigan, today released information on the state of the 2021 “Dead Zone” in Chesapeake Bay. While last year the dead zone was the second smallest observed since 1985, this year’s rating paints a more complex picture of the bay’s health.

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This year’s assessment confirms the earlier forecast of a slightly below average dead zone due to lower spring precipitation and less nutrient-rich runoff that flow from the watershed into the Chesapeake.

“While a below average river runoff in spring results in a smaller dead zone than predicted in July, calm winds, increased rainfall, and near-record warm temperatures in August and September made the dead zone larger and longer than usual, “said University of Michigan aquatic ecologist Don Scavia, a member of the research team.

Throughout the year, researchers track oxygen conditions in bays using a variety of methods. Oxygen and nutrient levels are measured as part of the Chesapeake Bay Monitoring Program, a bay-wide collaboration that includes watersheds, multiple federal agencies, 10 academic institutions, and more than 30 scientists.

Among these institutions is the Maryland Department of Natural Resources, the Virginia Department of Environmental Quality, and Old Dominion University made nine cruises between May and October to investigate summer hypoxia on the bay. The results of each surveillance voyage can be found on the Eyes on the Bay website for the Maryland portion of the bay and the VECOS website for the Virginia portion.

Scientists at the Virginia Institute of Marine Science, working with Anchor, use QEA Computer models combined with local weather information to produce real-time, daily estimates of the size of the dead zone during the summer. Based on the nine monitoring cruises conducted between May and October 2021, the Maryland Department of Natural Resources found that the dead zone in 2021 was only slightly below average.

On the other hand, the model simulations showed of the Virginia Institute of Marine Science and Anchor QEA that the dead zone was slightly larger than average, largely due to the duration of the dead zone in 2021. However, both estimates suggest a near-average dead zone for that year.

“The Monitoring hypoxia and other water quality and habitat conditions in Chesapeake Bay provides valuable data to assess and improve the health of the bay, “said Mark Trice, director of water quality informatics for the Maryland Department of Natural Resources.

” Maryland and its partners of the Chesapeake Bay Program are working to meet the goals of reducing nutrient and sediment pollution e.g. u achieve that will provide improved habitat for iconic species like crabs, oysters and rockfish while promoting a robust economy that supports these bay’s resources, “said Trice.

Since 2007, a model developed by the University of Michigan is being used used to forecast the volume of summer hypoxia for the Mainstem des Chesapeake based on the amount of nitrogen pollution that poured into the bay from the Susquehanna River from January to May. The model is based on data from the Chesapeake Bay Program, the Maryland Department of Natural Resources, the Virginia Department of Environmental Quality, and the U.S. Geological Survey.

“The general consistency between the various methods used to determine the size of this summer’s dead zone is reassuring,” said Marjy Friedrichs, research professor at the Virginia Institute of Marine Science. “The relatively average size of the dead zone despite warmer summer temperatures is evidence of the success of management measures that have resulted in nutrients being reduced in the bay.”

Weather conditions play a large role in the size and duration of the annual Dead zone. It is believed that below-average river runoffs due to the lower spring rainfall that brings nutrients and sediments to the bay may have played a role in the below-average dead zone identified during surveillance voyages conducted from May to July.

Due to calm, However, with increased rainfall and warm temperatures in late summer 2021, the conditions were perfect for the dead zone to be larger than in previous years. For example, temperatures in August and September were recorded as the fifth warmest in Maryland since those months began, according to the National Oceanic and Atmospheric Administration.

Despite the short-lived high winds and cool temperatures that came with the passage of the remains of the hurricane Ida were connected, the dead zone in September remained above average throughout the month and well into October. Overall, the 2021 dead zone lasted longer than 89% of the zone recorded over the past 36 years.

“While this year’s complex seasonal dynamics resulted in a smaller July dead zone than predicted, the summer average and overall annual forecast were pretty much what the Underscores the value of tracking and predicting longer term conditions, ”said UM’s Scavia, professor emeritus at the UM School for Environment and Sustainability.

Nutrients can primarily enter the bay via tributaries in the watershed. Higher river flows bring an increased nutrient load into the bay. Despite lower runoffs in the spring of 2021, the US Geological Survey reported that the average for the water year (measured October 1, 2020 through September 30, 2021) was higher than normal, with runoffs averaging 84,880. the bay flowed into cubic feet per second, which is above the long-term average of 79,000 cubic feet per second. Estimates of the river and nutrients entering the bay can be found on the U.S. Geological Survey.

The dead zone is an area of ​​little to no oxygen that forms in deep bays when excess nutrients, including nitrogen and phosphorus, enter the water through polluted runoff and feed on naturally occurring algae. This drives the growth of algal blooms, which eventually die and decompose, removing oxygen from the surrounding water faster than it can be replenished. This creates deoxygenated – or hypoxic – conditions at the bottom of the bay. Plants and animals often cannot survive in this environment, which is why the area is known as the “dead zone”. “This year’s estimate of the Chesapeake’s ‘dead zone’ illustrates the challenge between the management measures of the Chesapeake Bay program and climate change, that leads to increased rainfall and increased river flows, ”said Michelle Price-Fay, acting director of the Chesapeake Bay program office for the Environmental Protection Agency. “While the long-term trend is towards a reduction in hypoxia due to management measures across the river basin and catchment area, warming from climate change is a headwind that can increase the duration and extent of hypoxia.”

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