Pamela Wood – The Capital
Pierre Henkart runs a water quality monitoring program for the Severn Riverkeeper Program. On the river this week, he found dangerously low oxygen levels in deep water, such as this reading of 0.02 milligrams of oxygen per liter of water — too low for fish, crabs and shellfish.
It has happened again.
Like clockwork each summer, the waters of the Chesapeake Bay become starved of oxygen, leaving vast stretches of the water inhospitable to fish, crabs, oysters and even tiny worms.
And this summer’s oxygen-deprived "dead zone" – which already has appeared – could be one of the worst ever.
"We’re going to have one of the worst years," said Bruce Michael, director of the Resource Assessment Service at the Maryland Department of Natural Resources.
Much of the dead zone is our own doing.
People who live in the bay’s watershed send nutrients coursing into the water through septic systems, sewage discharge, fertilizer runoff and stormwater runoff.
The nutrients fuel the growth of algae blooms. And when the algae die, the decomposition process sucks oxygen out of the water.
That process is intensified this year due to Mother Nature. Heavy spring rains and strong flow of the Susquehanna River have brought nutrients into the bay and rivers more quickly and in larger amounts.
Scientists at the University of Michigan have crunched the numbers and predict the sixth-worst dead zone in the bay this summer.
At its worst, the dead zone will stretch somewhere between 8.6 cubic kilometers and 11.1 cubic kilometers, according to the University of Michigan prediction by Donald Scavia and Mary Anne Evans.
Michael said the dead zone already is apparent in the deepest part of the bay’s main stem – a trench that runs down the middle.
"We are seeing this dead zone from Baltimore Harbor to the Potomac," he said.
While water near the surface generally has plenty of oxygen, by the time you get to the bottom, there’s none at all.
River dead zones
The same phenomenon happens in many rivers, too.
On the Severn River this week, volunteers with the Severn Riverkeeper Program came up with painfully low numbers while doing their regular water testing.
They put small meters into the water and read out the depressing numbers: oxygen levels as low as 0.01 and 0.02 milligrams per liter of water.
Most fish and hard clams need 5 or 6 milligrams of oxygen per liter of water. Blue crabs need 3 milligrams of oxygen per liter of water and worms need at least 1 milligram per liter of water.Pierre Henkart, who runs the Severn monitoring program, pointed out people crabbing on the Sherwood Forest docks.
"All these people could have much better crabbing if there were more clams and worms," he said.
Henkart produces a detailed report each year with the oxygen trends at the 15 stations his team monitors. He worries that statewide and baywide reports don’t fully reflect the oxygen problem in the Severn.
The state has one automated monitoring station in the Severn, near the Route 50 bridge. Henkart said that station often shows better oxygen levels than further up in the river.
The riverkeeper program on the West/Rhode rivers in south county also has spotted oxygen deprivation this year.
Chris Trumbauer, the West/Rhode Riverkeeper, said dissolved oxygen has been dropping the last few weeks in deep waters at 29 sites on the rivers.
Trumbauer said it’s sometimes difficult to explain the problem of low oxygen, because you can’t actually see the dead zone. Oxygen-starved waters can look perfectly lovely at the surface.
"A lot of times, people don’t pay attention to the oxygen problem unless it comes with 50,000 dead fish with it," he said.
Even when fish aren’t going belly-up due to oxygen deprivation, fishermen and crabbers often know when a dead zone is forming. Fish and crabs will leave an area when the oxygen drops, in search of better water – leaving nothing left to catch for dinner.
The story is the same in the South River, where Riverkeeper Diana Muller keeps an eye on the water for the South River Federation.
The dead zone started earlier and is more intense than most years, Muller said.
"We have not had good bottom dissolved oxygen at all," she said.
Muller traces the South River’s problem to late winter and spring rains that flushed nutrients and sediment into rivers and the bay. The rains also mean that the river is less salty than normal, which may drive away crabs and fish that crave saltier water.
Michael, from the DNR, said it’s likely that the bay’s dead zone will never go away completely, even as all of the states around the bay continue to try and reduce pollution.
The geography of the bay makes it so the deep areas will always have less oxygen, he said.
But it is possible to bring those oxygen levels up, so more aquatic life will survive.
"We’re hoping to see improvements over time," he said.