Limiting Dead Zones

How to curb river pollution and save the Gulf of Mexico

Second of two parts. Part I: “Dead Waters

RIVER OF NITROGEN. Map quantifies nitrogen in commercial fertilizer, in kilograms per square kilometer per year, that farmers apply to their fields throughout the Mississippi River watershed. Typically, 15 percent of the total drains into rivers that feed the Gulf of Mexico. S. Norcross, adapted from USGS
SUBMERGED. This central Illinois wetland, formerly a cornfield, is designed to remove nitrate from water. It’s the prototype of a for-profit “nutrient-farming” system. Wetlands Initiative
TABLED. Temporarily covering the lower holes in this drainage-control box effectively raises the height that water must reach before it drains from a field into a stream. The drainage carries nitrate pollution. L.C. Brown, The Ohio State University

Every second, the mighty Mississippi gushes another 4.5 million gallons of water into the Gulf of Mexico. Along with the water come nitrate and other pollutants. In the Gulf and other large bodies around the globe, plant nutrients—especially nitrate—have created coastal dead zones. The nutrients fertilize the growth of algae, which soon die, settle to the seafloor, and decay. Bacteria feeding on the algal corpses consume so much oxygen that the water becomes unsuitable for most forms of life.

In the face of an increasing number and persistence of dead zones worldwide (SN: 6/5/04, p. 360: Dead Waters), some researchers are trying to stem the flood of plant nutrients into rivers and eventually seas. The U.S. government limits major releases of nitrate into the environment because high concentrations of the nutrient can be toxic to wildlife and even people.

Low, diffuse nitrate emissions, such as farm runoff, remain largely unregulated, even though this nutrient concentrates in waterways, where it can severely damage water quality and aquatic organisms’ health.

Without new regulations, U.S. attempts to reduce low-level nitrate pollution—and reverse the trend of increasing dead zones—must rely on voluntary efforts by farmers and others whose activities also contribute to the problem. Therefore, financial carrots must be incorporated into the programs.

A variety of projects, especially in the United States and Europe, are beginning to test novel approaches to reducing nutrients in the waters that eventually drain into coastal seas. Pilot programs in the Midwest focus on farming because that activity sends the most nitrate via the Mississippi into the Gulf of Mexico.

Some programs are simple, such as just encouraging cuts in fertilizer use, observes Doug Daigle in the New Orleans office of the Mississippi River Basin Alliance, a nonprofit group representing 150 organizations along the river. Other projects are more creative, even “visionary,” he says, such as changing crop choices or expanding or creating wetlands. But the important thing is to start putting these programs in place, he contends, because the problem of coastal hypoxia, “should be reversible”—if society doesn’t wait too long.

“It’s kind of like we’re playing roulette,” he says. In most venues, such as the Gulf of Mexico, “we haven’t seen really pervasive damage to fisheries yet.” But if present trends continue, that should happen over time, he notes. “So, it’s like we’re in a race to avoid some crash.”

As with disease, he argues, practicing preventive medicine is always easier and less expensive than coping with the ravages of illness. So, Daigle hopes that these voluntary programs can kick-start a new conservation ethic that will protect coastal waters in the Gulf and elsewhere from the ecosystem devastation that nutrient overenrichment can foster.

Fertilize less

According to the National Oceanic and Atmospheric Administration, nitrate releases throughout the Mississippi River watershed—some 1.2 million square miles encompassing all or parts of 31 states and two Canadian provinces—have to be cut nearly in half from current amounts to significantly shrink the annual Gulf dead zone. In many recent years, that hypoxic zone has been about the size of New Jersey.

The U.S. Geological Survey, which monitors the nation’s waters, reports that quantities of nitrate in the Mississippi increase from north to south as tributaries add their loads. For instance, in Royalton, Minn., near the Mississippi’s headwaters, some 930 tons of nitrate pass between the river’s banks in a typical year. At Clinton, Iowa, the river moves about 81,800 tons of nitrate annually. By Memphis, just below the inflow of the Missouri and Ohio Rivers, the annual nitrate flow reaches some 1 million tons per year. Amounts in recent years have been roughly triple those in the 1950s to 1970s.

Fertilizer applied to crops is the greatest contributor to the pollution that has created a Gulf of Mexico dead zone. Farmers find that, other than water, fertilizer is the primary limiter of growth in most plants. So, to avoid the possibility of any decreased productivity, they typically apply more fertilizer than their crops need, observes agronomist Brian Brandt of the American Farmland Trust’s Agricultural Conservation Innovation Center in Columbus, Ohio.

For any given area, U.S. Department of Agriculture extension agents provide an estimate, called the agronomic rate, of how much fertilizer is needed in a typical year. For instance, a county agent might advise that farmers apply 150 pounds of nitrate per acre of planted corn. However, every 4 or 5 years, rainy weather creates an environment in which plants could grow even better with an extra 40 pounds or so of nitrate.

Since farmers apply fertilizer at planting, when they can’t yet know how the season’s weather will pan out, most apply the extra fertilizer every year. If the extra rain doesn’t materialize at the right time, the excess fertilizer remains in the soil until after-harvest rains wash it into nearby streams.

Conservation groups are looking for ways to convince farmers to limit fertilizer applications to the agronomic rate. Brandt’s center has undertaken a no-risk solution: low-cost insurance to corn growers.

Policyholders fertilize virtually all of their acreage at the agronomic rate. In a few small patches, however, they apply as much extra fertilizer as they wish. At harvest, if these overfertilized patches have outperformed the other fields, the farmer is compensated for the diminished yield on the less-fertilized plots.

Although the insurance would cost about $8.50 an acre, Brandt explains that it spares farmers from buying extra fertilizer, which costs around $18 per acre.

The federal government approved the plan as a pilot program, but insurance companies have been reluctant to join in and only a few farmers are participating, says Brandt.

With that in mind, his organization is teaming up with the farm-services company Agflex of Carroll, Iowa, to offer the program in a warranty form that can be offered by companies that don’t handle traditional insurance. The program would still compensate growers for yield losses associated with fertilizing at the agronomic rate.

Friendly competition

The nonprofit Sand County Foundation of Madison, Wis., is beginning to test various strategies to evaluate “which one gives us the biggest bang for the buck in reducing nitrogen discharges to the environment,” explains Alex Echols, a Washington, D.C., consultant to the project.

Echols contends that current antipollution efforts often fail because they focus on compliance with laws and adoption of environmentally oriented programs, rather than on results. “So, the Sand County Foundation decided to instead set performance goals,” such as nitrate-runoff limits for farms, and test how best to meet them, he says.

Among the competing technologies is a practice called controlled drainage. Ordinarily, farmers in the upper Midwest install porous pipes below their fields to carry away excess water and keep fields from being soggy in the spring. Usually, the open pipes continuously funnel their outflow through a primary drainage pipe to a stream. In controlled drainage, a control box is inserted near the final outlet, and farmers can insert boards into it to temporarily raise the outlet’s elevation. This raises the height that the water table must reach before the field will drain.

Controlled drainage can keep more water in the ground during crop germination and growth and limit nitrate washout before planting and after harvest.

“We’re hoping it’s going to produce higher yields in income to farmers as well as higher environmental quality,” Echols says. The Sand County Foundation plans to measure the farms’ nitrate washout, taking costs into account.

The foundation is also testing crop diversification—moving away from reliance on corn-soybean rotation cycles. The ideal would be to restore “perenniality” to the agricultural landscape, says Steve Morse of the University of Minnesota, Twin Cities.

Fields that had been planted with corn and other traditional row crops often lie bare from October until June, a period when they can produce “heavy concentrations of nitrogen runoff,” he says. Indeed, he notes, studies show that the nitrate concentration in runoff from a field planted with row crops is more than 20 times as much as that from one that’s fully covered year-round with plants—be they pasture grasses or a succession of seasonal cover crops, such as red clover and white rye.

The goal is to create acreage that performs all year long in some fashion. This differs from the agricultural strategy in which fields lie fallow to recover their productivity.

Morse has just launched a consortium of universities and conservation groups that will investigate the potential profitability of new perennial-cover options that might entice corn and soybean farmers.

Development of wetlands is another strategy being investigated by the Sand County Foundation and other conservation groups. Bogs, swamps, marshes, and other soggy environments provide a host of benefits, not the least of which is that they can convert nitrate to nitrogen gas, permanently removing this pollutant from water.

However, because well-drained crop soil can be twice as productive as wet soil, farmers have traditionally been among the most aggressive drainers of wetlands. Hydrologist Donald L. Hey of the Chicago-based Wetlands Initiative hopes to change that practice. He’s promoting the potential environmental and economical benefits of renewing or creating wetlands to soak up nitrate. He calls this approach “nutrient farming,” although the goal is to get rid of nitrate rather than to harvest it.

To create a nitrate-removing marsh, a farmer would smooth out a parcel of low-lying land and then flood it to a depth of about 2 feet. Pumps would control the flow of polluted water into and through the marsh to ensure prolonged contact between nitrate-laden water and denitrifying bacteria. These won’t be disease-breeding, bug-infested swamps, but open marshes that host fish and waterfowl, Hey says.

His group is currently studying 2,600 acres in north-central Illinois that were recently transformed from cornfields into a managed wetland (see Marsh Farming for Profit and the Common Good).

Who pays?

Hey projects that a nutrient farm could cost $5,000 a year per acre to operate. He proposes that upstream growers shouldn’t bear the cost of cleaning up their fertilizer runoff. Instead, he argues that the emissions credits purchased by other polluters—cities and industries—could indirectly subsidize farms and keep food prices low. Urban and industrial nitrogen wastes include sewage, fallout from automotive and power plant combustion emissions, and industrial releases.

The Environmental Protection Agency has devised an emissions-trading scheme for nitrate but hasn’t yet implemented it.

If corn growers do have to ante up for nitrate cleanups, Loni Kemp of the Minnesota Project in St. Paul points to an alternative financing source that will become available this summer: The Conservation Security Program within the 2002 U.S. Farm Bill offers farmers incentives to make investments in soil- and water-conservation projects. Subsidies can run up to $45,000 a year per farm.

Kemp notes that participating farmers “are going to have to sign a contract for 5 to 10 years, promising to implement a set of practices that solve a targeted problem,” such as cutting nitrate releases.

“We’d like the dominant farm policy to become one where we pay farmers for achieving [conservation] benefits” while they produce commodities. Kemp says.

All these ventures for controlling nitrate rely on voluntary participation, notes Paul Faeth, managing director of the Washington, D.C.–based World Resources Institute. The size of cutbacks necessary to make a dent in the Gulf’s dead zone is so large that “voluntary action is not going to solve the problem,” he contends.

He says that he’d like to see a federally mandated cap on nitrate emissions within each state. Those jurisdictions could then individually decide how to cut back nitrate pollution, including through an emissions-trading system that Faeth’s institute is brokering independently of the EPA.

If states exceed the cap on their emissions, he says, EPA should step in with mandatory rules on nitrate, as authorized by the Clean Water Act.

The institute’s approach would encourage states to target their conservation funds and pilot programs to areas offering the biggest returns, Faeth argues. Today, many such programs are available throughout a region, he says, but it simply doesn’t pay to put money for nitrate cleanup into sites well upstream of major nitrate sources. Yet “there’s significant political resistance to targeting,” he notes, because politicians want public money spread out broadly.

The cost of not targeting efforts is high, Faeth says. “Our own study and an Iowa study show that you can get 4 to 10 times the [nitrate-cleanup] performance for the same dollar investment if that money is targeted,” Faeth says.

Robert W. Howarth of Cornell University would also expand regulation of nitrate pollution. He notes that a committee of the National Academy of Sciences that he chaired 4 years ago found the nitrate-pollution problem so big that it recommended that even small sources of the pollutant be more stringently regulated.

For instance, Howarth would like to see EPA tighten controls on air pollution sources such as sport-utility vehicles and small trucks, which produce nitrogen oxide that in turn becomes airborne nitrate—and ultimately rains out into waterways.

Keep in mind, he warns, “two-thirds of coastal rivers and bays in the United States have some sort of degradation from nitrogen pollution—and it’s only getting worse.”

Part I: “Dead Waters” appeared in last week’s issue. Available at Dead Waters.

Janet Raloff is the Editor, Digital of Science News Explores, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer, specializing in toxicology. To her never-ending surprise, her daughter became a toxicologist.

More Stories from Science News on Earth