Concerns over an oxygen-depleted “dead zone” that covers roughly 350 square miles of the Chesapeake in a typical year launched efforts more than a decade ago to control nutrient pollution throughout its 64,000-square-mile watershed.
So, will a dead zone the size of New Jersey in the Gulf of Mexico spur nutrient control efforts throughout the Mississippi River’s 1.2-million-square mile watershed?
It’s a question federal officials are seeking to answer. A group of agency officials and scientists recently released a report laying out the gulf’s oxygen problem and potential solutions.
An “action plan” to deal with the problem will be written sometime after the report’s Dec. 22 comment period closes. In the end, it may call for reigning in agricultural runoff and a range of other nutrient control efforts similar to those in the Chesapeake.
But the gulf — whose basin is large enough to hold 19 Bay watersheds — takes the same issues to a much grander scale: Fully 40 percent of the country drains down the Mississippi.
“In broad strokes, it’s the same set of problems and issues,” said Donald Boesch, president of the University of Maryland’s Center for Environmental Science, and a member of an editorial board that oversaw the completion of the gulf report.
“It should not be any great surprise that the system has changed that much off the Mississippi, just as it has changed in the Chesapeake and a lot of other areas of the world that are receiving greatly exaggerated nutrient inputs off the land,” Boesch said.
Nor, perhaps, should it be a surprise that Midwest farmers — thought to be the prime source of gulf nutrients — are skeptical about their role in causing a problem far downstream, and fear they could be targeted by nutrient control efforts.
The American Farm Bureau Federation has criticized recent gulf reports as biased, and expressed doubt that farmers could cut back on the use of fertilizers — as is suggested — without harming production. “Farmers today are producing more crops with less fertilizer, meaning they are more efficient and are leaving less nitrogen in the environment,” it said in its comments.
At first glance, the gulf may seem an unlikely place to have Chesapeake-like problems.
The Chesapeake is largely enclosed, allowing it to trap nutrients that fuel excessive blooms of algae. When the algae die, they sink to the bottom and are decomposed by bacteria in a process that depletes bottom water of the oxygen needed by fish and other aquatic species.
In an average year, about 350 square miles of the Bay’s deepest water becomes hypoxic — or has less than 2 milligrams per liter (roughly 2 parts per million) of oxygen. During 1993, which had the worst conditions observed in the Bay, nearly 1,500 square miles suffered from hypoxia. When hypoxia occurs, species that can move are squeezed into other areas, where the water has several times as much oxygen. Those that can’t move may die, or suffer other problems.
Unlike the Chesapeake, the gulf looks like a wide open body of water, rather than a big trapping zone. But in the case of the gulf, appearances are deceiving. While the gulf itself is huge, the Mississippi drains into a predominantly westward flowing stream of near-shore water. Half or more of all the nutrients flowing out the river are caught in that stream, and never make it off the continental shelf where they would mix in deep ocean water.
“Even though you have an unbounded system, the physics kind of conspires to keep the nutrients in play rather than just having them dilute and mix offshore,” Boesch said.
Lighter freshwater is on the surface of the westward flowing stream while saltwater is in the bottom. Sunlight striking the top of the nutrient-laden water spurs algae growth which — as in the Bay — sinks to the bottom and decomposes. But in the shallow water off the Gulf Coast, the bottom water is frequently remixed back into surface layers because of winds and intervening shoals, in effect, Boesch said, recycling nutrients to “fuel the fires of production.”
Also, because temperatures are warmer in the gulf, algae grow more rapidly and low-oxygen problems last longer than in the Bay. Low-oxygen conditions in the gulf can start in March; in the Bay, problems rarely begin before May.
And the hypoxic area is massive: Since 1993, the gulf dead zone has covered more than 4,000 square miles every year, hitting a maximum of 8,000 square miles this year — an area larger than New Jersey.
Studies of sediment cores indicate that gulf waters historically had little hypoxia, but conditions have worsened steadily since the 1950s. Over the same period, loads of nitrate have increased almost threefold, to about 2 billion pounds a year. (By comparison, the Bay gets about 340 million pounds a year.) Nitrate, and other forms of nitrogen, are the most important nutrients for spurring algae growth in saltwater.
The report said reductions of about 40 percent may be needed to return the gulf to conditions similar to those that existed before the 1950s, when nitrogen-based fertilizers became cheap and plentiful.
A 40 percent reduction from such a huge basin would be a massive task. Even the Chesapeake’s much-touted 40 percent reduction goal — because of the way it is defined — is actually only a 21 percent nitrogen reduction.
But the report also says that smaller reductions, in the range of 20 percent, could still yield significant water quality improvements and reduce the area affected by hypoxia. The most cost-effective ways of doing that, it says, is slashing the amount of nitrogen used as fertilizer by 20 percent, and restoring nutrient-absorbing natural areas, including 5 million acres of wetlands (about 8,000 square miles) and 19 million acres of streamside buffers in the watershed.
The report contends upstream residents should have reasons of their own to take action. Many rivers are impaired by high nutrient levels. And groundwater nitrate levels in parts of the Midwest exceed the EPA’s drinking water standards. Excessive nitrate levels can cause “blue baby syndrome” and is thought to be linked to ill effects in adults as well. Reductions in fertilizer use and environmental restoration programs should benefit local waterways and drinking water supplies as well as benefit the gulf, the report said.
But the report has received skepticism from upstream states and organizations. The Farm Bureau, for example, disputes a study that showed a 20 percent fertilizer reduction would reduce corn production by only 2.3 percent and have little impact on farm income. According to the bureau, that formula did not consider the fact that farmers from competing nations “would quickly fill any void [in the global corn market and United States] and farmers would lose both export markets and income.” And, along with others, the group questioned why it would be necessary to take “such precipitous actions when there has been no measurable impact on Gulf fisheries, nor is there likely to be in the foreseeable future.”
Indeed, persuading people to make such changes is compounded by a lack of convincing evidence that shows the “dead zone” is causing a problem. Gulf fish catches have been relatively stable despite the growing hypoxia problem, said Robert Diaz, of the Virginia Institute of Marine Sciences, who co-authored a report on the ecological and economic consequences of hypoxia in the gulf.
In part, he said, that is because most of the fish caught in the gulf are species that live in the water column, rather than bottom dwellers that would be more impacted by hypoxia.
Recent studies have suggested that this decade’s decline in the catch of brown shrimp — the gulf’s most economically important species — is related to the expansion of the dead zone during the same period. But Diaz said the evidence is not conclusive. While brown shrimp could be affected by hypoxia because they eat bottom-dwelling organisms, Diaz said, other factors may also play a role — such as the destruction of bottom habitat by fishing gear.
“I would like to say that brown shrimp were affected by the dead zone, but there is no way anyone could support that statement,” he said. “The strangest part of the hypoxia down there is that there are no obvious economic problems attributable to hypoxia.”
Nor are there obvious ecological problems, Diaz said. Unlike other areas with chronic hypoxia problems, the gulf hasn’t suffered major fish kills. And, possibly because of a general lack of long-term studies like those in the Bay, it’s difficult to show the ecology has been dramatically affected by hypoxia.
If conditions worsen, that could change, he cautioned. Though there are no “dead bodies” — fish kills — in the gulf, such problems are clearly associated with hypoxic conditions throughout the world and could begin turning up in the gulf as well. “This isn’t good, and the potential for it to be really disastrous is there,” he said. “But right now, there is little evidence of disaster. This lack of disastrous ecological and economic effects is what sets the gulf hypoxia apart from all the other coastal dead zones around the world.”
Persuading people to make nutrient reductions is further complicated because most of the pollution problem comes from far upstream: About 56 percent of the nitrate transported to the gulf enters the Mississippi above the Ohio River. And much of the rest comes from the Ohio. The main sources of nitrogen are from agricultural lands in Minnesota, Iowa, Illinois, Indiana and Ohio, according to the report.
“They’re 1,000 miles away,” Boesch said. “It’s like having one little Maryland and 30 big Pennsylvanias up the river saying, ‘Why should I worry?’”
In fact, about 90 percent of the gulf’s nitrogen comes from agricultural runoff, which has proved to be difficult to control both in the Bay watershed and other places around the world.
In the Bay, only about half of the nitrogen comes from agriculture. Much of the nutrient reductions made in the Chesapeake watershed have come from other sources, primarily wastewater treatment plants, which are easier to control. In the Mississippi watershed, though, less than 10 percent of the nitrogen comes from wastewater treatment plants and industry.
The scale of agriculture in the Midwest is dramatically different than that in the Bay watershed. Few counties in the Chesapeake region have more than half of their land in agriculture. In the Mississippi drainage, the majority of counties in some states have 90 percent of their land in agriculture. “And it is all farmed for high-fertilizer-demanding crops like corn,” Boesch said. “It makes our problem look like a piker.”
Boesch suggested that by using the “power of the purse” in how federal insurance and disaster relief programs dole out aid, some benefits could be reaped for the gulf without new layers of regulation.
He said federal programs that encourage the use of marginal farmlands — which the reports say are disproportionately responsible for nutrient runoff — could be restructured to encourage those areas to be taken out of production, and perhaps converted to wetlands.
And, if nutrient reductions are made, others will ultimately have to share in the burden, Boesch said. Although the reports discount the role of wastewater plants and atmospheric reductions, Boesch said the Chesapeake experience shows that reductions from almost all nutrient sources ultimately have to be considered.
“If you are trying to reduce things by 10, or 20 or 30 percent, you get into a game where 1 or 2 percent things matter, and you have to throw them all in,” Boesch said. “Also, there are equity issues.”
While the gulf may get cleaner over time, both Diaz and Boesch expressed doubt that a consensus will emerge in the Mississippi watershed to achieve the extent of nutrient reductions that may one day be reached in the Chesapeake.
“At the end of the day, public interest and public policy may require a higher level of environmental quality and improvement for the Chesapeake than what the consensus would lead to in the Gulf of Mexico,” Boesch said. “But that is part of public decision-making.”
Boesch noted that the cleanup of the Chesapeake could not likely be justified on the economic impact of low-oxygen areas on fisheries; many oxygen-depleted parts of the Bay are not important habitats.
But many nutrient-related problems besides hypoxia have been articulated. Nutrient-stimulated algae growth has turned the water murky over the years, and contributed to a 10-fold decrease in underwater grass beds which provide critical habitat for blue crabs, ducks, fish and many other species. Nutrients have contributed to the growth of undesirable algae species, which may have caused changes in the Bay’s food chain over the years.
“The economic impact of nutrient enrichment in the Chesapeake is probably not a lot compared to the cost of reversing it,” Boesch said. “But we know it does a lot of things that make the ecosystem function more poorly and with less resilience. It’s the same in the gulf.”
Probably more important, though, is that most of the Bay watershed population lives relatively close to the Chesapeake, and many have seen changes first-hand over time. Few people live near the area of the gulf that’s affected by hypoxia — that land is covered by vast wetlands and bayous.
“What’s different in the Bay is the connection of the people with the Bay,” Diaz said. “Most of them are pretty close to the Bay and have some sense of how what they are doing affects it. In the gulf, the majority of people in the watershed are completely detached.”
Lacking proximity, lacking a compelling economic argument, lacking proven ecological harm — only concerns — Diaz said the only argument likely to carry the day is getting enough people in the Mississippi basin to care about the gulf they way they worry about other far-off ecosystems. “It’s like the old growth forest,” he said. “Most of us will never see it, but we want it.”
The report, “Integrated Assessment of Hypoxia in the northern Gulf of Mexico,” is available on the Internet at: www.nos.noaa.gov/products/pubs_hypox.html