Scientists anticipate the growth of a “dead zone” in the Chesapeake Bay this year, spurred by the record 2018 rainfall, that is expected to span 2.1 cubic miles, one of the largest in recent decades.
A dead zone is an area of the water which has severely depleted oxygen levels, called hypoxia, or no oxygen at all, and is caused by excessive nutrient pollution, mostly from agriculture and wastewater runoff, according to the National Oceanic and Atmospheric Administration. Low oxygen levels can kill marine life and threaten near-bottom habitats in those areas.
The volume of water with no oxygen at all is predicted to be between 0.49 and 0.63 cubic miles during early and late summer, according to a release from the University of Maryland Center for Environmental Science, which worked with the University of Michigan to compile the report.
“The forecast this year reflects the high levels of precipitation that have been observed across the bay’s watershed,” report co-author Jeremy Testa of UMCES said in a release. “The high flows observed this spring, in combination with very high flows late last fall, are expected to result in large volumes of hypoxic and anoxic water.”
Last year, precipitation levels in Maryland peaked at the highest level in 124 years, according to data from NOAA. Rainfall washed in pollution to the watershed, fueling algae blooms, which consume oxygen as they decompose and subsequently push out or kill marine life there.
“It’s like overfertilizing your lawn,” Bruce Michael, director of the Resource Assessment Service at the Maryland Department of Natural Resources, said.
“Years with high amounts of rainfall, when we have excess nitrogen coming in, [algae blooms] create the low- or no-oxygen zones,” Michael said.
Researchers at UMCES and the University of Michigan expect the hypoxic area to be one of the largest in the past 20 years, according to a release.
The 30-year average maximum dead zone volume is 1.74 cubic miles, according to the release.
This spring, 102.6 million pounds of nitrogen washed into the headwaters of the Chesapeake Bay from the Susquehanna River, in addition to 47.7 million pounds of nitrogen coming in from the Potomac River, “well above long-term averages of 80.6 million from the Susquehanna and 31.8 million pounds from the Potomac,” the release stated.
The dead zone typically spans the deep channel of the bay, running from Baltimore’s Inner Harbor to the Potomac River inlet, in depths greater than 8 or 9 meters, Michael said.
“We experience dead zones every year, that’s a natural response” to changeable weather conditions, Michael said. “Our goal is to minimize and lessen the extent of those [zones], not only spatially but temporally. We’re gonna have a dead zone, but we want to have it in a shorter time period and at a smaller location.”
“The more nitrogen and phosphorous and sediment we reduce coming into the bay, the more oxygen there will be [to support] a healthy, vibrant bay with plenty of shellfish and clear, clean water,” he added.
Dead-zone monitoring is one indicator of the bay’s overall health. Other reports show that the long-term health of the bay is improving despite the extreme precipitation.
DNR conducts twice-monthly bay water quality monitoring cruises from June through August, assessing dissolved oxygen levels, and posts updates to the department’s Eyes on the Bay page on DNR’s website.