A dead zone may sound like something out of a zombie film, but it's all too real — an area in the water where there's not enough oxygen for aquatic creatures to survive. This year the Chesapeake Bay had the smallest dead zone on record, according to newly released data, a sign that long-running efforts to curb pollution are paying off.
Dead zones occur each summer in the Chesapeake, and scientists have measured their extent each year since 1985.
"It doesn't necessarily mean that everything is dead in there, so it's a little bit of a misnomer," explains Marjy Friedrichs, a professor at the Virginia Institute of Marine Science. "Basically, fish, crabs, and shellfish, all really can't survive there for any extended period of time because the oxygen levels are so low. So it's a region of very poor habitat for the animals in the bay."
Article continues belowThis year's dead zones in the bay were about half the size compared to last year, and nearly 5 times smaller than in 2019.
"This is really, really exciting news. We've been trying to reduce the size of this dead zone for decades in the bay," Friedrichs says.
Dead zones are caused by pollution flowing into the bay from sewage, agriculture, fertilizer on people's lawns, and other sources. This pollution is in the form of excess nutrients — too much nitrogen and phosphorus. These nutrients feed algae; when the algae die, they in turn are eaten by bacteria, which use up oxygen dissolved in the water, leading to a dead zone.
Many factors impact the size and duration of a dead zone, in addition to pollution levels, including temperature, precipitation, and wind. It can be difficult to tease out which of these are having the biggest impact in any given year, but reductions in pollution throughout the watershed appear to be playing a big role.
"What we see is when you have less nutrients in the system, you have a better habitat for things people care about — fish, crabs, and oysters," says Mark Trice, with the Maryland Department of Natural Resources.
Since 2009, efforts to cut pollution have led to an estimated 14.1% reduction in nitrogen flowing into the bay per year and a 13.4% reduction in phosphorus.
While these reductions are significant, they're not enough to meet the goal of restoring the bay by 2025, which has been embraced by all the states in the Chesapeake Bay watershed and the U.S. Environmental Protection Agency. Pollution reductions so far are only 51% of the target for nitrogen and 60% of the phosphorus target.
Joe Wood, Virginia senior scientist for the Chesapeake Bay Foundation, said the smaller dead zone this year was a "promising sign." But he says future pollution reductions may be more challenging.
"Our progress to date is largely because of these wastewater treatment plant upgrades," Wood says. "In the future, we're really going to need to deal with agriculture and stormwater pollution, which we've struggled to in the past. If we're going to be celebrating progress 30 years from now, it's going to require new approaches."
Technically speaking, dead zones are defined as areas in the water with less than 2 milligrams per liter of oxygen. Three organizations work on monitoring dead zones each year: the Maryland Department of Natural Resources, Old Dominion University, and Virginia Institute of Marine Science. These groups partner with the EPA's Chesapeake Bay Program, which oversees efforts to restore the bay.
Dead zones are also known by the more scientific and less sci-fi name, "hypoxic volume." Maryland researchers reported an estimated average of .52 cubic miles of hypoxic volume, while researchers in Virginia reported an estimate of .58 cubic miles — both well below the historical average of .97 cubic miles.
While nutrient pollution in the bay has been trending down in recent years, other factors are going in the other direction. Climate change is bringing warmer, wetter weather to the region — more rain flushes more pollution into the bay, while warmer water holds less oxygen, leading to larger dead zones. This year, those factors were mixed: while temperatures were above the historical average, there was significantly less rainfall than normal.
This story originally appeared on DCist.com
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