ANNAPOLIS — Researchers from the Chesapeake Bay Program, the University of Maryland Center for Environmental Science, University of Michigan and U.S. Geological Survey announced Tuesday that they are predicting this summer’s dead zone to be smaller than the long-term average taken between 1985 and 2021.
This is due to 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.
Areas of low oxygen, also known as hypoxic regions, are often considered to have dissolved oxygen concentrations less than 2 mg/L (milligrams per liter) and are primarily caused by excess nutrient pollution flowing into the Bay. These regions can result in the loss of habitat for various types of marine life, including fish, blue crabs, oysters and underwater grasses.
Compared to the previous 36 years, this year’s Chesapeake Bay hypoxic volume, or “dead zone”, is predicted to be 13% lower than average. This is similar to last year, when the hypoxic volume was predicted to be 14% lower than the average. 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.
A 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.
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.
“Dissolved oxygen levels are a key measure of Bay health, as sufficient oxygen is needed to support vital fish, crab and oyster populations, as well as a healthy ecosystem. The forecast brings attention to our continued progress towards implementation of nutrient reduction strategies to improve oxygen conditions,” said Mark Trice, water quality program manager with the Maryland Department of Natural Resources.
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% 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. There was 5% less water flowing into the Bay when compared to the long-term average.
A Bay-wide assessment of the 2022 dead zone will be available this fall.