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• All in the Numbers

It’s not been a banner year for the world’s water bodies.

Off of the California and Oregon coasts, federal regulators issued an unprecedented ban on commercial and recreational salmon fishing through the remainder of the year. While the National Marine Fisheries Service points the finger at a lack of nutrient-rich deep ocean upwellings caused by ocean temperature changes, most biologists say it goes deeper than that and includes such factors as agricultural pollution.

A professor in the Midwest warns that the Lake Erie ecosystem—the predominant of all of the Great Lakes in terms of the fishing economy—is being threatened by such factors as harmful algal blooms, aquatic invasive species, a dead zone, sediment loading, and nutrient loading attributable to phosphorus and nitrogen from point and nonpoint sources, or sewage and agriculture.

To the east, a scientist points out that nearly 90% of the Chesapeake Bay and its tidal tributaries have insufficient levels of dissolved oxygen. Maryland and Virginia have announced substantial restrictions on commercial and recreational fishing for crabs because the population is so low.

And to the south, scientists say that the Gulf Coast dead zone this year will extend west into the Texas area, primarily because of high discharges from the Mississippi River and the high concentration of nitrate it contains.

Dead zones are everywhere: the US Atlantic, the Gulf and Pacific coasts, the Caribbean, Central and South America, Europe, the Middle East, and Africa.

Water bodies suffering from hypoxia and thus dubbed dead zones exist in all parts of the world, says Robert Diaz, professor of marine science at the College of William and Mary’s Department of Biological Sciences/Virginia Institute of Marine Science.

Furthermore, their numbers are increasing; Diaz estimates nearly 400 dead zones this year.

“The number is rising for a couple of reasons,” says Diaz, who recently wrote a paper for the World Resources Institute titled “Eutrophication and Hypoxia in Coastal Areas: A Global Assessment of the State of Knowledge.”

“One is that people are looking for [dead zones] more, so we’re finding more of them. But I think it’s also due to our systems going lower in oxygen through time,” says Diaz.

Although natural processes lower oxygen levels in some areas throughout the world, most of the European and American dead zones are being driven by eutrophication in coastal systems.

Eutrophication occurs when water becomes rich in dissolved nutrients from sewage or fertilizers. As a result, oxygen-depleting plant life grows, decomposes, and consequently harms other organisms.

In some dead zones, the cause is clearly related to sewage and population centers, while others are related to agricultural land runoff.

“A lot of the dead zones off of the west coast of South America and Africa are actually naturally driven oxygen minimum zones and upwelling areas,” says Diaz. “The one off Oregon’s coast that started about six years ago also is driven by oceanographic processes, but it may be related to shifting wind patterns and climate change—but what causes the climate to change?”

Diaz surveys a map of the United States, listing dead zones and the reasons they exist.

There’s the Providence River area in Rhode Island, which includes Narragansett Bay; dead zones there are linked to Providence’s population centers. Long Island Sound’s dead zones are attributable to a combination of population, sewerage, and some agricultural runoff.

To the south in the Chesapeake Bay, causes are linked not only to agriculture and population, but also to air deposition, causing eutrophication when air pollution is deposited directly onto the surface of the water or onto the land, reaching water through runoff.

In the Pamlico Sound area off of the coast of North Carolina, agricultural runoff accounts for most of the dead zones.

To the south near the Charleston, SC, area, dead zones are most likely due to land development, Diaz says.

“In the Gulf of Mexico, [dead zones] seem very clearly linked to what goes on in the Mississippi Basin, and that’s the primary agricultural region for the US. The dead zone there fluctuates very predictably with nutrient loadings from the river,” he explains.

“Then you go around to some areas in Corpus Christi, Texas—there’s a dead zone there that could be related to sewage. Some small areas in Galveston Bay seem to be linked with population and development. On the West Coast in Puget Sound, there’s Hood Canal, which is like a fjord and is very prone to low oxygen. It’s probably population development in the watershed that’s driving that.”

Weather fluctuations, such as extreme rainfall that flushes more pollutants than normal into a water body, and also extreme drought that reduces inflows and concentrates harmful substances in certain water bodies, can also lead to dead zones.

“When you look at what creates a dead zone, the biggest thing you need from a physical, oceanographic point of view is a stratified water column,” says Diaz. “Somehow, you have to isolate the bottom water from the surface water; it’s the mixing in the surface that oxygenates the bottom. If you have high stratification due to either lots of freshwater runoff or high temperatures, then you isolate the bottom water, and oxygen goes down.”

In the Gulf of Mexico, which has the largest dead zone in the US, the zone shrinks during drought conditions, Diaz says. “It’s not that clear in a place like Chesapeake Bay, where it’s a smaller system—more confined—and the area or volume of hypoxia is weakly associated with the freshwater runoff,” he adds. “But typically, water conditions lead to less stratification, which leads to less hypoxia.”

The second-largest dead zone in the United States is in Lake Erie in the Great Lakes. “That’s a stratified water body, but it’s temperature stratification and it’s on the order of 10,000 square kilometers,” says Diaz.

The causes are rooted in nutrients, he notes. “Phosphorous is more important in the Great Lakes than it is in the Gulf of Mexico. You have a reservoir of nutrients in the lake because [although] there has been tremendous nutrient management in the Great Lakes since the early 1970s, it really hasn’t improved the way managers thought it would.

“A lot of it has to do with the residual memory of the system and all of the pollutants that it built up in the sediments,” Diaz continues. “It’s going to take a long time before they actually work their way out of the system. What you are seeing there is a store of nutrients in the sediments that keep being recycled and creating low oxygen, much to the dismay of the managers who thought they’d have it under control by now.”

The third-largest dead zone is in the Chesapeake Bay. “About 25% of the nitrogen that enters the bay is air and is from whatever puts nitrogen in the air—burning fossil fuels, cars,” says Diaz. “The rest is split between agriculture and sewage.”

Each region has scientists working diligently to identify dead zones and their causes.

The Largest Zone—and Growing
The Gulf of Mexico was the first area to be named a dead zone by Nancy Rabalais, dubbed the “Queen of the Dead Zones” in the scientific community. She’s a professor and executive director of the Louisiana Universities Marine Consortium.

Her husband, R. Eugene Turner, is a professor with the Coastal Ecology Institute and Department of Oceanography and Coastal Sciences in the School of the Coast and Environment at Louisiana State University.

In studying the Gulf of Mexico’s hypoxia, Turner says, “What I expect this year is that there’ll be a pretty large [dead] zone in the summer. I don’t know what the impact of the storms are going to be until we measure it.”

Although the nitrogen in the large discharge emanating from the Mississippi River has been diluted a bit, “there’s a lot of farmland that’s been added,” he says. “Last year it was 19%, and it may be down to only half of that this year, but it’s got a lot of nitrate in it—more than we usually have. So we have a high concentration and a high discharge.” This situation explains the expansion of the dead zone into the Texas Gulf region, adds Turner.

Hypoxia takes on a different twist in its definition among various regions. “We use an operational definition of two milligrams per liter oxygen on the bottom layer—what’s close to the sediment,” says Turner, adding that this is a definition accepted by the fishing industry. “The reason we use that is because that’s about the time when about anything that can get out of there will leave. The fish and shrimp can’t be found in there.

“It’s driven by the reaction of the organisms; if you get even lower than that, then other things start to happen,” Turner says. “Animals can’t leave, so they get stressed. But maybe they’ll revive if it doesn’t go any lower. And at some point, if there’s no oxygen, the whole area—even bacteria—will get wiped out, although there will always be some bacteria that won’t be.”

The predominant cause of runoff problems leading to dead zones in the Gulf region is agricultural fertilizing practices, Turner says: “Particularly corn, which uses about two-thirds of the fertilizer in the US. It is the dominant crop in the watershed.”

And it has become even more dominant: from 2006 to 2007, the area in the US dedicated to corn production increased to 90 million acres in response to the demand for ethanol.

Hypoxia is not the only concern in the Gulf region; the accompanying water-quality issues are also a concern, Turner says. The organic matter that takes up oxygen causes hypoxia. “But some of that organic matter isn’t burned up all in that year and is stored in the sediment, so in the following year, that legacy effect is adding to the hypoxia potential,” he explains. “That means there’s more hypoxia for the same amount of oxygen loading each year, and it builds up.”

Nutrients in Lake Erie
At the Stone Laboratory and the Ohio Sea Grant College Program, researchers are working with federal and state agencies to develop new techniques to remove microcystin, a toxin from algae, at water treatment plants; determine the sources of phosphorus entering Lake Erie; and determine the role of nitrogen in the process, among other measures.

“It is very important that we succeed in these efforts to allow Lake Erie to remain the most productive of the Great Lakes and Ohio’s most valuable natural resource,” writes Jeffrey Reutter, the director of the program and laboratory.

Lake Erie also is an immense economic resource in the region, supporting a charter fishing fleet in Ohio of about 800 licensed captains, accounting for approximately 40% of all the licenses in the Great Lakes.

In a paper Reutter wrote addressing the situation in January, he points out that Lake Erie, the southernmost of the five Great Lakes, annually produces more fish for human consumption than the other four Great Lakes combined.

That comes as a result of it being the most shallow of the Great Lakes at 210 feet deep. It is also the warmest, and the one receiving the most nutrients from agricultural and sewage sources. It also receives more sediment.

In contrast, the watersheds around the other four Great Lakes have extensive forest ecosystems.

Lake Erie receives 80% of its water from the Detroit River, 10% from precipitation, and 10% from the rivers and streams surrounding it.

The Maumee River, which drains an extensively farmed area, is the largest tributary to the Great Lakes, with the Detroit River considered to be a connecting channel, although it brings in only 3% of the flow to Lake Erie, with the rest of the Great Lakes system fed by many small tributaries.

In contrast to the small flow percentage, the Maumee River brings in more sediment to Lake Erie than all of the tributaries contribute to Lake Superior, which, at a depth of 1,333 feet, contains 20 times more water than Lake Erie.

Lake Erie is divided into three basins:

• The shallow Western Basin near Sandusky, OH, with an average depth of 24 feet and an irregular bottom
• The deep Eastern Basin near Erie, OH, with an irregular bottom
• The moderately deep Central Basin between the two, with an average depth of 60 feet

The Western Basin is the warmest during the summer and receives the most nutrients and sediment. When Lake Erie stratifies during the summer, the thermocline—the transition layer above which the water is warmer, and below which the temperature decreases rapidly—normally forms at a depth of about 45 to 50 feet. The Western Basin seldom has a thermocline, and the cold bottom layer, or hypolimnion, beneath the thermocline in the Central Basin is thin—about 10 feet.

If Lake Erie is consequently too productive from receiving too many nutrients, it is likely the dissolved oxygen in the Central Basin hypolimnion will be used up during the summer, creating an area of anoxia—the dead zone.

This changes the chemistry within the hypolimnion, causing it to move from an oxidizing environment to a reducing environment, which allows phosphorus and metals in the sediment to dissolve into the water.

“I would argue that the most important problems facing the Lake Erie ecosystem right now are harmful algal blooms (HABs), aquatic invasive species (AIS), the dead zone, sediment loading, and nutrient loading (phosphorus and nitrogen from point and nonpoint sources or sewage and agriculture),” Reutter writes.

The dead zone is a Central Basin issue. HABs are a Western Basin issue and a significant human health issue (Microcystis sp. is a form of blue-green algae that produces the toxin microcystin and requires warm, nutrient-rich water that is found in the Western Basin).

While Microcystis is native to Lake Erie, it rarely became a dominant species prior to 1996, according to Reutter. Since 1996, it has been blooming each year in late summer with blooms starting in Maumee Bay and Sandusky Bay where phosphorus levels are highest and the water is warmest—common requirements of blue-green algae.

“It also appears that zebra and quagga mussels are serving as catalysts,” Reutter adds. “When the mussels suck in Microcystis in their normal filter feeding process, they stop filtering, spit it out, and then resume filtering. In so doing, they remove the things that compete with Microcystis, allowing it to bloom.”

While eliminating the dead zone and HABs are admirable goals, the latter is most critical and practical, says Reutter.

“Eliminating the dead zone is likely to require very large reductions in the amount of phosphorus entering the lake,” he explains. “As climate change causes the lake to become warmer and water levels to go down, oxygen will be used more quickly and the Central Basin hypolimnion will become thinner (less volume) and contain less oxygen.

“Therefore, it will likely become impossible to reduce phosphorus loading enough to eliminate the dead zone,” Reutter adds. “Furthermore, we are finding evidence that the dead zone may have existed for hundreds of years simply due to the shape of Lake Erie.”

HABs directly affect human health, and reducing nutrient loading enough to eliminate them is much more feasible action, Reutter says.

“This will also reduce the magnitude of the Central Basin Dead Zone, for much of this blue-green algae floats out of the Western Basin and into the Central Basin where it sinks to the bottom and consumes oxygen as it is decomposed by bacteria,” he writes. “If we produce less algae, there is less to be decomposed and use oxygen in the dead zone.”

Grim Outlook for the Chesapeake Bay
The news in the Chesapeake Bay region is poor, reports Beth McGee, a senior water-quality scientist for the Chesapeake Bay Foundation. Recent reports show that nearly 90% of the bay and its tidal tributaries had insufficient levels of dissolved oxygen.

“The bay is one of the only areas that has developed dissolved oxygen criteria that varies spatially and temporally through the bay and tidal rivers,” says McGee. “For example, at the bottom, they would allow a lower level of oxygen in terms of water-quality standards than they would at the surface, reflecting the natural system itself. The deeper levels naturally have lower levels of oxygen than surface waters do.

“In other words, in many areas of the country they want to see dissolved oxygen at five parts per million; in the bay, we’ve crossed that out by saying we would allow it to go as low as two parts per million in deep waters, but we expect it to be five or greater at the surface waters. When the EPA puts out the report, they’re basically comparing it to these time-varying dissolved oxygen standards.”

In the Chesapeake Bay, the predominantly serious areas of concern focus on the stem of the bay, says McGee.

“In any given summer, the dead zone can extend from near Baltimore south to about the mouth of the York River,” she says. “And a lot of the big river systems also have problems—the Potomac River in particular has a large dead zone. Almost all of our tidal rivers—particularly those on the western shore that are particularly deep—have a dead zone during the summer.”

The predominant cause of the Chesapeake Bay dead zone is too much nitrogen and phosphorous pollution, says McGee.

About 40% of the nitrogen coming into the bay is from agriculture, and some 20% comes from point sources, mostly sewage treatment plants, notes McGee.

Another large contributing factor is air, she adds.

“About a quarter to a third of the nitrogen pollution coming into the bay actually comes from the air, primarily from coal-fired power plants and automobiles,” McGee says. “Another small factor is urban stormwater and septic systems, but the top three sources of nitrogen pollution are point source, agriculture, and air.”

Weather is another factor influencing the size of a dead zone from year to year, McGee adds.

“If we get a lot of rain coming in the springtime, that tends to drive the system during the summer,” she says. “Regardless, because of all the manmade impacts on the bay, weather has an influence, but it has a bigger influence than it should because of the way we’ve altered the landscape.”

The impact on the ecosystem and the economies derived from it is immense, says McGee.

“Last summer, up to 90% of the water was basically off limits for aquatic life,” she says. “Animals that can move away from that water—like fish and crabs—are then concentrated in certain areas.”

One example of a fish that gets squeezed out is the rockfish.

“It doesn’t like really warm water, so in the summer it is trying to go to deeper waters where it is cooler, but what they find at the bottom where it is cooler is there’s no oxygen in the water,” says McGee. “They basically get squeezed between the warmer water at the surface that they don’t like and the cooler water at the bottom that they don’t like because of the low dissolved oxygen.

“Animals are stressed when they don’t have enough oxygen and are crowded into little spaces. We are seeing that in our fisheries. With our crabs, that certainly has been a factor.”

Economic Effects
The consequence of the dead zones’ impact on the environment has a ripple effect on the economy.

The restrictions on fishing for crabs in Chesapeake Bay will potentially force many watermen out of business, says McGee.

“And it’s going to have effects on the local community that the watermen live in, because the fishing industry is an economic engine,” she points out. “There are crab-picking houses and crab restaurants. It’s definitely going to have an impact on the economy. We rely on a lot of recreational fishing to bring tourist dollars into this region, and if our fisheries aren’t healthy, we’re going to start to see the impacts of that.”

It’s like a recurring nightmare in the region.

“It’s been a way of life,” notes McGee. “Chesapeake Bay used to be known for its oysters, and when the oysters were decimated by disease, water quality, and over-fishing, a lot of watermen switched over to crabs.

“This region is known for blue crabs, and if we don’t have that anymore, we lose more than just a fishery, we lose a way of life—something that has been an integral part of the culture in this region. They’ll be importing them from some other place in the world.”

Diaz says that it’s difficult to pin down the effects of dead zones on economies. However, he cites the example of economic loss encountered in Europe where hypoxia started in the 1980s in a 4,000-square-kilometer area between Sweden and Denmark that will no longer support a lobster fishery because the oxygen is so poor lobsters cannot survive.

“That’s a big loss, because if you’re going to be a fisherman, you have to go farther or move your boat,” Diaz points out. “I understand the same thing has happened in the Gulf of Mexico where hypoxia tends to draw the shrimp either near shore or off shore, but overall, the fishermen have to go farther distances to catch them, because they are not in the places where the oxygen is low.”

In the Black Sea during the 1980s, there was a complete collapse of commercial troll fishing affecting about 20 species of fish due to hypoxia, says Diaz.

“We haven’t seen that in the US yet, but there probably are economic consequences, such as longer travel time and lower catches,” he says. “It’s tough.”

On the other hand, some evidence suggests hypoxia corrals species and makes them easier to catch, says Diaz. This became apparent with crabs in North Carolina following a series of hurricanes at the turn of the century.

“There was a large hypoxic event, and the crabs avoided it and moved downriver and congregated. They were easier for the fishermen to catch, so it actually depressed the population of crabs to the extent that it caused their numbers to drop,” he says.

The major economic and ecological consequences of the dead zones imply that “it doesn’t seem to be very good stewardship to have these zones the size of Massachusetts forming,” says Turner.

The damage to the shrimp industry is immense, he adds.

Dead zones force the shrimp crews to travel longer distances to find the shrimp against the current backdrop of higher fuel costs, which is the largest cost of doing business, notes Turner.

In their quest to keep looking for shrimp in areas not hit by hypoxia, shrimp-fishing companies have to cut back on their labor and other operating costs in order to have more money to spend on fuel.

“They are in a marginal economic existence as it is,” says Turner, adding that shrimpers’ numbers have decreased of late. “We don’t know how much of that is from the hypoxia.”

Water quality certainly is an issue, Turner says. “What’s driving the hypoxia is the nitrate concentration in the discharge, but the silica that’s delivered is also important, because it’s used by the diatoms [a type of phytoplankton]. When the ratio gets to be 1:1 or lower, you start to lose the food web that supports all those fisheries.”

It’s happened in European systems, Turner says.

“We’re right at the level at which the food web occasionally goes below that, and you can see the food web change,” he says. “If that happens in more than a month or two, it’s going to change all the fisheries. They would all be in serious trouble.”

The Role of Stormwater Management
Stormwater management plans can play a pivotal role in influencing dead zones, says Diaz.

“Any reduction in organic material or nutrients entering the system would be a relief, particularly in the Chesapeake Bay or even in the Great Lakes and Boston Harbor,” he says. “There were problems in the inner harbor that were due, for the most part, to people and sewage. Through intense nutrient management, Boston Harbor has completely turned around with collection of sewage and with the start of an ocean outfall in 2000. I understand that in the next year or two, they are going to have all of the stormwater drains running through the treatment plant, too. So, every bit helps.”

As for stormwater management, Turner points out that while the nitrogen load is what drives the size of a dead zone, “anything that stormwater management people can do to reduce the nitrogen load will be helpful.

“It’s not just an issue of at the end of the pipe, it’s also wherever the stormwater is discharging—the headwater quality issues,” he adds. “It’s definitely not a fair thing to pit farmers against the stormwater managers against the hypoxia. It’s really a general water-quality issue all over the world.”

Runoff reduction is important to alleviate the problem, Turner says.

Although 15% of the Chesapeake Bay’s total nitrogen pollution now comes from urban and suburban stormwater, McGee expects that number to grow as the region’s population grows.

“That’s also going to be expensive to retrofit. We not only need to be concerned with the existing stormwater and improving our existing best management practices around stormwater, but also, because we continue to develop in this region, we need to be conscious of new developments going in and forward-thinking in terms of how we manage our stormwater,” she says.

Looking ahead, McGee sees plenty of opportunities for municipal separate storm sewer systems (MS4s) to be treated like point sources. “They are given these permits in a TMDL [total maximum daily load]. They are considered part of the waste load allocation, not part of the load allocation, so one thing we’ve been working hard on in this region is to try to get the state’s environmental protection agency to put numeric limits in MS4 permits, which we think will then drive the reductions we need to get from MS4,” she says.

“That’s the way we can take advantage of existing regulations. We also think that, given that many of the activities related to new construction and development are also permitted activities, there’s room for both EPA and the state to be doing more to try to reduce pollution from that source.”

One of the vehicles to address the problem going forward will come through the nation’s Farm Bill, says Turner.

“The farm payments actually are the net gain for a lot of farms,” he says. “Their expenses are more than their profits, so the Farm Bill pays their profit. If you wanted to affect land use, you could direct where you wanted to pay the payments. This is an instrument to help direct land-use patterns.”

Corn is rough on soil, and runoff occurs easily, says Turner.

“It’s bare soil for three to four months, and any fertilizer you’ve used comes off,” he says. “It’s not a very effective sponge for applied fertilizer. But there are other plants that have perennial root systems, such as soy beans.”

To back out of the hypoxia situation will take a long time, says Turner. Additionally, it will require a sense of stewardship among farmers with respect to their business practices.