When it comes to the restoration of the Chesapeake Bay, one could say it is a bottom-up operation.

That is, efforts aimed at restoring the Bay's productivity are focusing first on bottom dwelling organisms with the expectation that improving their lot will result in better habitat for fish and other Bay creatures.

While underwater plants, worms that crawl through sediment and clams that live at the bottom of the Chesapeake are not what typically come to mind when one thinks of the Bay's bounty, they serve as key indicators of the Bay's health.

And this year, these largely unheralded organisms are moving front-and-center as Bay managers re-examine a pollution reduction goal set in 1987.

The question looming before scientists and policy makers is this: Will a 40 percent reduction in nutrients entering the Bay result in enough oxygen for aquatic life to breathe? And will it allow enough light for submerged plants to grow?

That goal, set by the Bay Executive Council — comprising the governors of the three Bay states, the EPA administrator, the District of Columbia mayor and the chairman of the Chesapeake Bay Commission — was based on a computer model that indicated such a cut in nitrogen and phosphorus entering the Bay would result in increased oxygen in the water and increased habitat for important aquatic plants.

This year, scientists and managers — armed with a new state-of-the-art computer model — are re-evaluating that goal. They hope to determine whether those reductions can be met by the year 2000 (the original target date) and whether they will indeed improve the Bay's habitat.

Two of the key indicators that will tell them whether they are on the right track are the levels of dissolved oxygen in the Bay and the amount of submerged grasses. A reduction in nutrients should increase the amount of both.

A supercomputer operated by the Army Corps of Engineers in Vicksburg, Miss., will run various scenarios — what the Bay would be like if the entire watershed is forested, what would happen with a 40 percent nutrient reduction, what would happen with just a 40 percent phosphorus reduction or just a 40 percent nitrogen reduction, and so on — to see if those indicators improve.

People have been known, in some quarters, to hug trees to save them.

No one has suggested hugging submerged aquatic vegetation — called SAV by scientists and Bay managers — but perhaps they should. Probably no other organism serves as a better indicator of water quality.

Though the Bay contains about a dozen species of submerged plants, their numbers in recent decades declined markedly, bottoming out in 1984 at about 37,000 acres. That has increased modestly to about 50,000 acres today, but that's still only about one-tenth of the area they once covered.

With the plants have gone fish habitat and waterfowl forage. Grass beds serve as spawning grounds and forage areas for fish, crabs and other Bay species. And the loss of the grasses has played a role in the demise of duck populations, which have fallen 70 percent to 80 percent since the mid-1950s. The decline of the grasses has even caused the Bay's canvasback ducks to switch from being herbivores to carnivores, now opting for shellfish rather than grasses.

Researchers working on a report called the "SAV Synthesis" — a summary of the conditions needed for the survival of submerged plants — have determined the most important factors governing the survival of submerged plants.

The parameters include: nitrogen; phosphorus; total suspended solids; chlorophyll; and light attenuation (a measure of sunlight received).

"The most important factor is light attenuation," said Linda Hurley, a biologist with the U.S. Fish and Wildlife Service who chairs the workgroup writing the SAV Synthesis. "The other parameters influence light attenuation."

Like other plants, submerged vegetation needs nutrients to survive and once the plants in the Chesapeake's large underwater beds absorbed huge amounts of nutrients from the water. But in past decades, the plants were — in effect — overfertilized.

Nutrients spurred the growth of excess algae which began to cloud the water above the plants. Some types of parasites settled on the leaves of the plants themselves.

As the water clouded, plants had to live in shallower and shallower water.

And as the plants died off, there were fewer of them to perform another job of submerged vegetation: filter sediments out of the water. As a result, turbidity increased, further clouding the water.

As scientists determine the water quality parameters within which the plants can survive, people using the computer model will be able to estimate the amount of habitat — areas with enough light — that can be restored by various management actions, such as adjusting the percentages of phosphorus or nitrogen they may seek to control.

This of course does not immediately translate into more ducks or fish. But it would be a strong indication that the cleanup is moving in the right direction — as long as the water quality conditions run through the computer are actually achieved. "The levels (in the SAV Synthesis) are strictly for the plants," Hurley said. "But based on past experience and intuitive knowledge, when you have healthy SAV beds, you have healthy habitat for other species as well."

Like people, animals, birds, worms and other living things on the Earth¹s surface, many — though not all — of the creatures that live in the Bay require oxygen to survive.

But while the air we breath contains about 210,000 parts per million of oxygen, the organisms living on the bottom of the Bay need only a fraction of that — only a few parts per million.

But in recent years, not even that has been available in certain parts of the Bay during much of the summer. When the oxygen levels drop, aquatic species must move if they can. Those that can't, die.

Juvenile striped bass will die in water when oxygen levels drop to 3.5 ppm. Adults will die if it drops to 2 ppm. Blue crabs die at 0.5 ppm; and adult yellow perch at 1.5 ppm.

Near the Bay surface, where the water interacts with the air, and where submerged plants give off oxygen as a by-product of photosynthesis, there is plenty of oxygen — on the order of 6 to 14 ppm.

The exact amount of oxygen water can hold is limited by natural factors. Colder water can hold more oxygen than warm water. Fresh water can hold more than salt.

Salt water from the ocean, being denser, tends to settle toward the bottom of the Bay, while fresh water is on top.

Normally, these waters gradually mix as they circulate in the Bay. But during the spring — and sometimes the summer — heavy rains increase the rate of fresh water flow into the Bay which results in an invisible barrier forming between the fresh and salt water, called a pycnocline, preventing the mixing of oxygen.

Nutrients promote the growth of algae blooms which die, fall to the bottom of the Bay, and decompose. The process of decomposition draws the oxygen out of the water.

The bottom becomes hypoxic — containing low quantities of oxygen — or even anoxic — that is, no oxygen at all.

While hypoxic and anoxic conditions generally originate in the Bay's deepest parts, low oxygen areas can literally 'slosh' around the Bay, being pushed by storms or strong winds. The resulting low oxygen conditions can reach coastal habitat areas and tributaries, and can last for hours or even days — long enough to kill or stress many aquatic species.

As a result, a large amount of the Bay's bottom may be subject to hypoxic or anoxic conditions during a given year. Studies done for the Maryland Department of the Environment found that from 1984 to 1990, hypoxic conditions of less than 2 ppm ranged from 40 percent to 70 percent in Maryland's portion of the Bay. The actual amount of hypoxia in a given year was largely tied to the amount of freshwater flow from tributaries.

Because of such variations, it may be years before there is a clear trend toward improvements on the oxygen front.

Some scientists suspect that the degree to which nutrient reductions can increase oxygen levels is limited because natural factors play such a large role in the equation.

"That doesn't mean to say that we [people] haven't made it worse," said Anna Shaughnessy, a scientist with Versar ESM Operations, a firm which has a contract with Maryland and the EPA to do water quality studies in the Bay. "I suspect we've made it worse. It's just that there's a tremendous amount of natural variation."

Closely linked to that issue is whether hypoxic and/or anoxic conditions in the Bay are natural. Some scientists believe they are, and that periods of low oxygen levels will exist no matter what nutrient management efforts are taken. Others believe that severe hypoxic or anoxic events may not be normal — that the clearing of land has increased water flows into the Bay and added nutrients which are major contributing factors to the problem.

"The fact there's naturally low dissolved oxygen in the deep trough isn't really relevant," contends Mike Hirshfield, senior science adviser with the Chesapeake Bay Foundation, who has worked with living resource issues connected to the 1991 re-evaluation process. "What we want to know is how much more good water we can get."

'Good water' might be defined as water with enough oxygen for aquatic species to live in. Or, perhaps as water that has healthy 'benthic communities.' Benthic organisms, or 'benthos,' include bottom-dwelling organisms such as worms, clams, oysters and blue crabs.

Many type of benthos serve as food for other species. Like submerged plants, benthos are good indicators of water quality: Most, like clams and oysters, can't move if the oxygen runs out — they are left to die.

Even when the amount of oxygen increases, the fish habitat is effectively gone as there is no food.

Gradually, new benthos will move in, but the recovery process can be slow. The first benthos to return are likely to be more tolerant of the poorer conditions, but may not be the type of species that make good food. So a full recovery to a healthy benthic community may take a period of years.

"It's a natural succession process, sort of like turning an old field into a forest," said Fred Holland, a vice president at Versar ESM Operations.

The computer model being used in the 1991 re-evaluation effort will calculate in one scenario what levels of dissolved oxygen could be expected if the entire watershed was forested — an indication of the maximum amount of 'good water' that could be achieved.

The model may not be able to accurately predict levels of dissolved oxygen in tributaries, but if the dissolved oxygen levels in the Bay's deepest parts are brought up, that should translate into improvements elsewhere.

At this point, no one can say any of this would mean there would be more fish in the Bay. But it would improve their potential.

For example, anchovy eggs cannot hatch if dissolved oxygen levels drop below 3 ppm. If oxygen levels increased, more habitat area would be open to the anchovy. That, in turn, would create more forage areas for certain fish, such as spot and croaker.

"We don't know that that would provide more spot and croaker," said Steve Jordan, a biologist with the Maryland Department of Natural Resources. "But it would give them more opportunity."

Such improvements do not mean that species will come back in great abundances, though. Other factors can take their toll on living things in the Bay. Oysters, for instance, are a benthic organism. But their decline has been largely due to diseases — not oxygen levels. Better dissolved oxygen levels just improves their odds.

"It means I can knock that off my list of stresses that may be affecting that species," explained Rich Batiuk, of EPA's Chesapeake Bay Program office.

FROM studying the bottom dwellers — the submerged plants and benthic organisms — and those things that affect their survival, scientists have gained a new knowledge of factors that should trigger recovery of some Bay species.

The next step will be to test that by setting recovery goals — an objective recently called for by the Bay Program's Principals' Staff Committee, which advises the Executive Council.

Possibilities for goal setting may include such things as calling for a specific increase in the acreage of submerged aquatic vegetation beds, specific increases in the amounts of dissolved oxygen in certain parts of the Bay, or seeking healthy benthic communities — ones that are both productive and have a variety of species — in various areas of the Bay.

"That [goal setting] is a very difficult thing to do and there's a lot of people in the living resources community who don't want to do that," said Verna Harrison, an assistant secretary in the Maryland Department of Natural Resources and the chair of the Bay Program's Living Resources Subcommittee.

The setting of goals creates the potential of failure if the goals are not met. It also creates a situation that almost mandates certain amounts of money be spent if the goals are to be met.

"One of our risks, is that we set goals that are unachievable," Jordan said, "and that makes a lot of people nervous."

The goals, though, can also serve as concrete signs of success, and they can serve to bring together research efforts. For example, much of the information on dissolved oxygen and submerged grasses was 'synthesized' from various research projects in recent years to meet the information demands of the 1991 re-evaluation and the computer model.

"It's a big advance in the availability of knowledge," Jordan said.

The 1991 re-evaluation and the computer model will give a "big picture" indication of how far the 40 percent nutrient reduction goal will move the Bay toward recovery.

But all the answers will not come out of it.

"This is only the nutrient re-evaluation," Hirshfield said.

Other issues, he said, such as toxics — which can affect both benthics and plants — overfishing, destruction of habitat, and disease all can play major roles in species recovery.

"It's really tough to get people to focus on [those issues], because for so many people the Bay cleanup is nutrient reduction," Hirshfield said.

Other efforts under way in conjunction with the 1991 re-evaluation effort — such as an inventory of existing water conditions throughout the Bay and a report detailing the habitat requirements of specific Bay animals — will serve as a guides toward bringing local water quality to standards needed by plants and animals other than just submerged plants and benthos.

After all, the re-evaluation, by itself, won't bring back any species to its historic level. It will tell officials if they are on the right track — and give them an idea of what remains to be done to get where they want to be.

"It's important that people don't think the process ends in 1991," Harrison said. "It really just begins in 1991."