Testing water for sign of life in `dead zone'

Bay: Scientists are studying dissolved oxygen levels to see if marine animals could survive in the Chesapeake.

July 18, 2004|By Rona Kobell | Rona Kobell,SUN STAFF

ON THE CHESAPEAKE BAY -- The summer "dead-zone" patrol has begun.

For the next several months, scientists will be monitoring the Chesapeake Bay and its tributaries to see if there's enough oxygen in the water to sustain healthy populations of marine life.

The results so far: Dissolved oxygen levels in the bay have gone from abysmal last July to about average.

"Right now, there's not a heck of a lot going on out there," said Amy Imirie, a research technician who has been testing bay waters for 15 years. "It's very, what I would call, boring."

The bay could use a dull summer. At this time last year, low levels of dissolved oxygen turned about 40 percent of the water in the bay's main stem into a so-called dead zone. This year, tests are showing that 28 percent is deprived of oxygen. That's not great, but it's about what scientists expected.

Water in a dead zone is desperately low on or devoid of dissolved oxygen needed by all aquatic animals -- from the lowliest worms to strapping rockfish. As oxygen levels plummet, fish and other mobile creatures flee, leaving bottom dwellers to smother and turning a rich estuary into a biological desert.

Fueled by nutrients and sediment flushing off farms and developed shorelines, dead zones emerge and grow in coastal waters in the hot still days of summer and shrink in autumn as waters cool and accommodate more oxygen. One of the largest and best-known dead zones is in the Gulf of Mexico, where nutrients from the mouth of the Mississippi River spawn an oxygen-starved area the size of New Jersey.

In the Chesapeake Bay last summer, record heavy rains were culprits. They washed huge amounts of sediment and nutrients into the estuary, sucking dissolved oxygen levels out of the deep channels in Maryland and south to the mouth of the York River in Virginia.

Too early to tell

As the state research vessel cruised this month from Havre de Grace to Sandy Point State Park -- past new homes, industrial plants, busy highway bridges and other structures that affect the bay-- Maryland Department of Natural Resources scientists said it's too early to draw conclusions about the bay's summer health.

But the fact that the scientists are not yet reporting zero-oxygen conditions in Virginia bay waters and are seeing healthier dissolved oxygen levels in Maryland suggests the bay may be stabilizing after last summer's woes.

"Right now, this is kind of what we've been expecting," said Bruce Michael, director of DNR's Tidewater Ecosystem Assessment Division. "The good thing is, it hasn't moved all the way down into Virginia."

Scientists don't like to refer to "dead zones" because such areas are not devoid of all life. After all, bacteria and other microbes still live there.

Instead, researchers say water is "hypoxic," which means its dissolved oxygen levels are low, or "anoxic," which means the oxygen has been depleted.

The bay draws dissolved oxygen from the atmosphere, microscopic plants called phytoplankton and underwater grasses. When the system works properly, phytoplankton and bay grasses take in sunlight and carbon dioxide and release oxygen.

But excess nutrients -- particularly nitrogen and phosphorus discharged by sewage treatment plants and flowing from farms -- upset the process.

Nutrients fertilize the water, spurring algal blooms that, along with sediment, block sunlight. That leaves the bay's other organisms competing for dissolved oxygen -- a tough fight when the bottom bacteria use most of it to decompose the excess algae.

Compounding the process in summer are warm waters that create a barrier between the bay's freshwater on top and saltwater on the bottom, cutting off the bottom's dissolved oxygen supply. Cold water holds more oxygen than warm water.

`McDonald's diet'

David Jasinski, a University of Maryland water-quality data analyst, said excess algae compound the bay's problems by overloading stressed filter-feeding shellfish.

"We're overfeeding the bay too much. It's on a McDonald's diet, basically," Jasinski said.

The junk-food infusion has produced troubling sights for Imirie and other researchers.

A few weeks ago, the Potomac River's algal blooms were so intense that the beach looked as if it had been covered in fluorescent paint. One recent day, Imirie was testing an anoxic water sample that smelled like rotten eggs. And on a cruise last month, researchers found water so filled with sediment it looked like chocolate milk.

This year's rains have been about average so far, but the bay is still struggling with last year's over-fertilization.

The Chesapeake Bay Foundation expressed concern last week that Virginia tests showed low-oxygen levels throughout the York River and other tributaries.

DNR scientists found algae blooming on the Maryland side in February and March -- much earlier than usual. And Larry Simns, president of the Maryland Watermen's Association, said the so-called "bad water" problem seems worse than it did last year -- especially around Tilghman Island.

All that is disturbing to scientists like Scott Phillips, Chesapeake Bay Coordinator for the U.S. Geological Survey, who nonetheless took comfort that this month's cruise was better than last year's.

"Right now," he said, "average is not good for the bay."

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