In June, federal scientists predicted a bigger-than-average oxygen-deprived dead zone in the Chesapeake Bay this summer, and it turns out they were right.
Researchers with the Virginia Institute of Marine Science who study bay hypoxia announced Monday that the total amount of dead zones this summer was the worst since 2014, and a 10 percent increase over last year.
This, despite a drop in the overall duration and maximum extent of dead zones compared with 2016.
“The time period from beginning to the end was just a little shorter than usual,” said VIMS marine biologist Marjorie Friedrichs in a phone call Monday. “But the peaks — when it was bad, it was really bad.”
VIMS, based in Gloucester Point, has used a real-time, three-dimensional forecast model since 2014 to gauge various hypoxia metrics in the bay, including volume and duration, the average summer volume and the cumulative or total amount in a given year, generated by adding up each day’s hypoxic volume.
Tallying up the daily volume, researchers estimated there were 919 cubic kilometers of hypoxia during 2017. This is larger than the 833 cubic kilometers in 2016, 757 cubic kilometers in 2015 and 918 cubic kilometers in 2014.
Hypoxia occurs when large amounts of nitrogen — mostly from farm fertilizers — is swept into the vast watershed, typically by rain events, and ends up in the bay.
There, it fuels explosive growths of algal blooms in the Chesapeake and its major tributaries. As the blooms decay, they suck up oxygen from the water column and create dead zones that are lethal to blue crabs, striped bass and other marine life.
The concentration of dissolved oxygen in ocean water is typically between 7 and 8 milligrams per liter, said VIMS. Anything below 4 milligrams will begin to affect marine organisms.
Waters with less than 0.2 milligrams are called anoxic and can’t support most forms of life; those with no measurable dissolved oxygen are hypoxic.
In June, NOAA warned that heavy rains in the northern part of the watershed from January to May spelled trouble for the bay this summer, sweeping even more nitrogen than usual into the waterways that feed the estuary.
Much of that nitrogen came from the Susquehanna, the bay’s biggest tributary and a notoriously polluted river running through New York, Pennsylvania and Maryland before it hits the Chesapeake.
Robert Magnien, director of NOAA’s Center for Sponsored Coastal Research, said at the time that “great strides” have been made to reduce nutrient pollution in the watershed — but not enough.
“More work needs to be done to address nonpoint nutrient pollution from farms and other developed lands to make the bay cleaner for its communities and economic interests,” Magnien said.
According to VIMS, the early spring loads were but one factor in this year’s dead zone activity.
Also in play were relatively strong winds in the first half of May, which delayed the onset of hypoxia compared to previous years. In June, hypoxia increased “very rapidly” and peaked unusually high at mid-month.
Windy periods kicked up in late June through August, dropping the overall amount of hypoxia from earlier peaks created in part by record-breaking temperatures of 100-plus degrees in mid-summer.
VIMS operates its baywide forecast model with Anchor QEA, a Seattle-based scientific and engineering consulting firm where managing scientist Aaron Bever is a VIMS graduate.
Their report comes on the heels of a report from Maryland released last month that found that, at least for a portion of Maryland’s mainstem of the bay, dissolved oxygen levels were better than average for late August.
But the Maryland Department of Natural Resources cautioned that its results were incomplete due to bad weather conditions, which precluded assessing the bay south of the Potomac River to the Virginia state line.
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