By PAMELA WOOD, Staff Writer
There are two dreaded words that pretty much sum up all that's wrong with the Chesapeake Bay: dead zone.
Though scientists say the term is something of a misnomer, it conjures a relatively accurate picture of what's going on below the surface of the bay.
The dead zone is a vast stretch of oxygen-deprived water that can't support fish, crabs, shellfish or even little worms. The root cause of the dead zone is nitrogen and phosphorus pollution that comes washing off the land.
"It's kind of the ultimate measure of our combined impact of nutrient runoff from all the watershed of the Chesapeake Bay," said Dr. William Dennison, a water quality expert at the University of Maryland Center for Environmental Science. "It's a bit of a report card on the health of the ecosystem."
When the Chesapeake Bay Foundation's John Page Williams goes searching for the dead zone, he doesn't have to look farther than the fish finder on his Boston Whaler.
The little screen shows fish swimming around near the surface. Farther down, there's not a fish in sight this time of year, he said.
"What you see on the screen is just empty space. That's what a dead zone looks like on a fish finder," said Mr. Williams, who works as a naturalist for the nonprofit foundation and lives along the Severn River.
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Sophisticated instruments confirm the less-scientific fish finder. Out on the Round Bay section of the Severn this week, members of the Severn Riverkeeper Program dipped meters in the water that told the same tale. In many spots, barely any dissolved oxygen was registering.
"This is the third year we've been out here and it's the third year we've seen the dead zone," said Dr. Pierre Henkart, a medical researcher who volunteers as monitoring coordinator for the riverkeeper program.
'Not the life we like'
So what exactly is the dead zone?
The dead zone is the end result of an equally ominous-sounding process called eutrophication.
When nutrients like nitrogen and phosphorus, which occur naturally, flow into the water at unnaturally high levels, it touches off a series of events.
Plant life, namely algae or phytoplankton, thrive on the nutrients. But the blooms of algae block light from reaching underwater grasses. And when the algae die, they are decomposed by bacteria, a process that sucks oxygen out of the water.
Hot air and lack of wind makes the problem worse.
While fish, crabs and the like can't survive in the oxygen-depleted water, certain bacteria do.
"It really is a misnomer," said Dr. Dennison said. "It is not dead … It's teeming with life, it's just not the life we like."
The dead zone is not exactly toxic or harmful to humans. But for fish and crabs and shellfish, it's like being trapped in a room with no air. Some animals can swim out, like fish and crabs. Oysters can survive short bouts of low oxygen, but they can't escape it by moving the way fish or crabs do.
When marine animals can't escape, the result can be fish kills (mass die-offs of fish) or crab jubilees (when crabs scurry toward shore in search of oxygen).
Rockfish, shad, perch and clams need at least 5 mg oxygen per liter of water, spot can survive at 2 mg/l, crabs need 3 mg/l and worms need 1 mg/l.
Healthy water has 5 mg/l or more of oxygen. Dissolved oxygen is considered low, or hypoxic, below 2 mg/l. The water is truly dead, or anoxic, when the levels drop to 0.2 mg/l.
There are other negative effects of the low oxygen.
The water has a "toxic byproduct" of hydrogen sulfide. That's the rotten-egg odor that you can smell in water pulled up from the depths of the bay or rivers. And it can be harmful to the few people who are brave enough to dive into the bay's deepest waters.
Also, oxygen helps keep harmful nutrients that are trapped on the bay's floor to stay there. When there's no oxygen, those nutrients - especially phosphorous - escape and contribute to the whole harmful cycle all over again.
"It kind of creates a runaway situation," Dr. Dennison said.
How bad is it?
The multistate Chesapeake Bay Program tracks the dead zone in the main stem of the bay, from Maryland to Virginia.
As of the latest set of data from late June, a zero-oxygen zone snakes in a long, narrow line from the Bay Bridge down to mouth of the Potomac River. It's mostly in the bay's deepest depths. But low-oxygen zones surround the dead zone and branch out toward the rivers.
As the summer stretches on, the dead zone typically gets worse.
In all, during most summers, roughly 40 percent of the bay's main stem does not have adequate oxygen levels.
"It marks off whole, big sections of the bay that can't support the kind of life we want," Dr. Dennison said. "It's shrinking the healthy part of the bay."
Or as Mr. Williams puts it: "It's habitat taken away. It's like giving up 40 percent of your house."
In addition to the main section of the bay, the dead zone is showing up in the rivers, too. Just as the Severn Riverkeeper Program has been documenting that river's dead zones for three years, other local groups and state agencies have tracked oxygen problems on other rivers.
Fixing the problem
While the dead zone is persistent, some say there's hope that things could eventually be turned around. Nearly everything that's being done to help the health of the bay - from planting trees to fixing sewage plants - will help the dead zone problem.
"We need to understand that it's not all hopeless. This isn't all doom and gloom," said Mr. Williams of the bay foundation. "There are some very good things in the pipeline to deal with this."
Nitrogen and phosphorus are the main drivers of the process that results in the dead zone. Those nutrients come from farms, urban and suburban stormwater runoff, sewage plants and air pollution.
So, as sewage plants are modernized, as farmers better manage their fertilizer, as old stormwater pipes are fixed, the amount of nitrogen and phosphorus reaching the Chesapeake Bay should decrease.
But more needs to be done, Mr. Williams said. Governments and individuals need to continue to find ways to reduce nutrient pollution.
"Individual efforts add up, there's no doubt about that. Rain barrels, rain gardens - those are really important," he said. "The advocacy side of it is important, too. Let elected officials know that you care about clean water and healthy rivers."
(Revised August 2008)