Chesapeake Bay Dead Zone Smaller Than Previous Years Due To Mild May Temperatures
BALTIMORE -- Researchers are predicting this summer's dead zone in the Chesapeake Bay will be smaller than the long-term average taken between 1985 and 2021, according to environmental staff.
The change in size is due to the below-average amount of water entering the bay from the watershed's tributaries this past spring, Chesapeake Bay Program staff said.
Program staff made the announcement alongside researchers from the University of Maryland Center for Environmental Science, the University of Michigan, and U.S. Geological Survey.
Decreased nutrient and sediment pollution from jurisdictions within the watershed also contributed to the smaller dead zone, staff said.
The dead zones consist of areas of low oxygen, known as hypoxic regions. This is where there are dissolved oxygen concentrations of less than two milligrams per liter— primarily caused by excess nutrient pollution flowing into the bay, staff said.
The lack of oxygen can lead to the loss of habitat for various types of marine life, including fish, blue crabs, oysters, and underwater grasses, according to researchers.
The reason the dead zone is smaller this year is likely due to a shorter period of summer hypoxia in 2022, staff said. That period began later this year than it has in the past several years.
For example, in 2021, 2019, 2018, and 2017, hypoxic conditions began in mid to late May, according to researchers.
But in 2022, hypoxia did not appear in the bay until early June. This may be due to cooler temperatures in May when compared to previous years, staff said.
The levels of pollution reaching the Chesapeake Bay each year vary due to the amount of spring rainfall, which flushes excess nutrients and sediment into the water through river flows, according to researchers.
Those levels also hinge on conservation practices implemented by various jurisdictions to reduce and manage pollutants in the water, staff said.
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 of the hypoxic conditions, according to researchers.
The amount of nitrogen pollution entering the Bay during spring 2022 was 22% lower than the long-term average and included 102 million pounds of nitrogen recorded at nine river input monitoring stations and 5.7 million pounds from treated wastewater, researchers said.
There was 5% less water flowing into the bay when compared to the long-term average, according to staff.
A bay-wide assessment of the 2022 dead zone will be available in the fall, staff said.