죽음의 구역 오염이 수십 년의 작업에도 늘어나다

Image: NASA Science Earth

HERMANN, Mo. – The Missouri River stretches more than a quarter-mile from shore to shore here, its muddy water the color of coffee with a shot of cream.

The river carved this valley hundreds of thousands of years ago, and in the 1830s, it deposited the German settlers who founded this city. Today, visitors who sip local wine in hillside gazebos can gaze down at the water and imagine being on the Rhine.

For two centuries, Hermann has been known for the Missouri River – and now the river is making Hermann known for an unexpected reason: It is a hot spot for nitrate.

Washing off farms and yards, nitrate is largely responsible for the Gulf of Mexico’s infamous “dead zone.” Nitrate and other nutrients from the vast Mississippi River basin funnel into the Gulf, sucking oxygen out of the water and killing almost everything in their path.

The pollution is one of America’s most widespread, costly and challenging environmental problems, according to the U.S. Environmental Protection Agency.  Sewage treatment plants along the rivers already have spent billions of dollars, and some farmers now use computers to apply fertilizer with pinpoint precision.

But after three decades of extensive efforts to clean it up, nitrate along the rivers is getting worse. In Hermann, the levels in the Missouri River have increased 75 percent since 1980, according to U.S. Geological Survey research published last year.

The pollutant continues to pour into the rivers, and ultimately the Gulf, at a growing pace. And no one – at least yet – has figured out exactly why.

1,247 miles downstream
Hermann is an ideal place to start unraveling the mystery. There are no big factories here, no major sewage treatment plants, and not even much of the intensive row-crop agriculture sometimes blamed for heavy runoff. Rather, this small city looks like something out of a German fairy tale. Churches, shops and red-brick houses line tidy streets. Vineyards dot the rolling hills. Tourists arrive via Amtrak train to hear oom-pah bands at Oktoberfest and dine on bratwurst with sauerkraut.

How could Hermann be responsible for increasing the pollution that creates a dead zone 1,247 miles downstream?

The answer is Hermann is merely a microcosm of an immense problem involving 31 states and more than 76 million people.

Hermann sits roughly in the center of the vast Mississippi River basin, which drains 1.24 million square miles stretching from the Rockies to the Appalachians.

The Missouri River, as it rushes past Hermann’s churches and shops, carries the residue of life upstream. Rain washes excess nitrogen and phosphorus, along with other pollutants, from farmers’ fields, cities, factories, cars and suburban lawns into ditches, streams and tributaries, and finally to the river itself. The “Big Muddy” joins the mighty Mississippi just north of St. Louis, then makes a sharp right turn and rushes past the soaring St. Louis Arch on its way to the sea off Louisiana.

When the nutrient-rich water empties into the Gulf far downstream, it triggers a biological phenomenon with deadly results. The nutrients serve as an all-you-can-eat buffet for hungry algae. The phytoplankton population booms and then dies, sinking to the bottom, where bacteria decompose the organisms and use up precious oxygen in the process. The resulting low-oxygen environment – also called hypoxia – is so toxic that all animals must flee or die. 

Hypoxia drives away shrimp, crabs and fish and kills creatures such as worms at the bottom of food chains.

“There is die-off, a loss of ecosystem diversity,” said Nancy Rabalais, a marine ecologist and director of the Louisiana Universities Marine Consortium in Chauvin, La. “If you have continuous year-after-year hypoxia, some animals won’t be able to recruit back into the area.”

Rabalais has been mapping hypoxia for almost 30 years. Her research helped spawn a state/federal task force, which set a goal of cutting the Gulf’s dead zone almost in half, to about 1,930 square miles, by 2015. 

Yet the dead zone keeps growing fatter, like an obese patient unable to shed weight. Last year it was 6,800 square miles – more than triple the goal.

“We’re a long way from the target now – a very long way,” she said. “When that target was set, it didn’t seem impossible, but it’s just getting harder and harder.”

In addition to the 75 percent increase at Hermann, nitrate levels have increased 76 percent since 1980 along the upper Mississippi River at Clinton, Iowa, according to the USGS research. In all, nitrate runoff in the entire basin increased 9 percent over the past 30 years, and much of that increase came from the watershed upstream of Hermann and Clinton.

“This the first time anyone has been able to show the actual concentrations have either not changed or actually increased when we’re supposed to be reducing the loads,” said Don Scavia, a professor of environmental sustainability at the University of Michigan in Ann Arbor who studies the dead zone.

 “Whatever conservation practices have been put in place are not enough,” he said.

The corn theory
One theory is that more fertilizer is washing into the watershed because corn acreage has skyrocketed. But urban runoff, livestock and other sources could play a role, too.

“These are really large watersheds with a lot of things happening – changes in crop patterns, livestock use, human population,” said Lori Sprague, a USGS hydrologist based in Denver who was lead author of the nitrate study. “All of those things changewater quality.”

Farm fertilizer and livestock manure are the two biggest sources of total nitrogen in the Missouri River watershed, together responsible for 70 percent, according to 2011 USGS data.  A 2008 study of the entire Mississippi River watershed had similar findings, with agriculture contributing 70 percent of the nitrogen and phosphorous that ended up in the Gulf.  Scientists in 2009 also reported a direct correlation between intensive crop production, particularly corn, and nitrate-nitrogen levels in rivers.

Nationally, consumption of nitrogen fertilizer has tripled since the 1960s, surging to 12.3 million tons in 2010, according to USDA data.  The amount of nitrogen applied as farm fertilizer grew 18 percent between 1987 and 1997, according to a 2006 USGS study.

It sounds clear-cut. Many farmers, however, tell a different story.

In the Bootheel area of southern Missouri, farmer Mike Geske grows about 2,000 acres of corn, cotton, rice and soybeans near Matthews, Mo. The land lies flat as a plate, the northernmost reaches of the fertile Mississippi delta.

Geske, a third-generation farmer, said when he first started farming in the 1970s, he would lay a thick dose of fertilizer on his fields in the spring. “Anhydrous ammonia was so cheap, we put on 80 to100 pounds extra,” he said.

Today, he applies fertilizer three or four times throughout the year so plants can use it as they need it. He said he uses 20 to 25 percent less fertilizer these days, yet he gets 25 to 30 percent more bushels of corn per acre. He credits better seed technology and careful management of nutrients in the soil.

Farther upstream, Ron Hardecke raises crops, hogs and cattle on 2,000 acres in Owensville, Mo., about 35 miles south of Hermann. He said he carefully monitors his nitrogen use.

“Sometimes it’s portrayed we’re out here dumping fertilizer for fun,” he said. “But if you pay the bill, why, you don’t use more than you need.”

Nationwide, farmers are getting more grain out of their fertilizer, according to the National Corn Growers Association. Nitrogen use has decreased 38 percent in terms of pounds per bushel of corn, said Rod Snyder, director of public policy for the trade group.

Nevertheless, corn farmers are using as much fertilizer per acre as ever on their high-yielding crops, according to federal data. on average, farmers applied 58 pounds of nitrogen per acre to corn crops in 1964.  By 1985, that number had grown to 140 pounds per acre, where it remained in 2010.

In addition, more acreage is being planted as corn prices boom, according to U.S. Department of Agriculture data.  In 2012, farmers planted 96 million acres of corn – the highest level in nearly 70 years, and up nearly 22 percent from a decade earlier.

“The primary cause [of nitrate pollution] is row crop agriculture, and the primary culprit of that is corn. That’s being exacerbated by the fact that corn is expensive right now. People are taking areas out of conservation and putting them into corn production,” said Matt Rota, science and water policy director for the New Orleans-based Gulf Restoration Network.

Farmers use many methods to reduce runoff: planting cover crops, adjusting the amount of fertilizer and when it’s applied. Such conservation practices in the Upper Mississippi River basin reduce nitrogen loss by an average of 18 percent per acre, according to a USDA report. 

But the same report found that only 14 percent of cropland consistently had good nitrogen management.

“What we are showing is how bad the problem would be if there were no conservation,” said Lee Norfleet, a USDA soil scientist. “If there is an uptick, it would be a lot worse if a lot of (conservation) practices had not occurred.

In addition, Norfleet said, it takes time for farmers to adapt to the changing genetics of corn, which needs less nitrogen now. Farmers who don’t adjust could end up over-applying nitrogen at the rate of 23 pounds per acre.

Other sources of nitrate also may have increased.

The Missouri River basin, which includes the cities of Denver, Omaha and Kansas City, grew by more than 1.3 million people between 1990 and 2000, now reaching more than 11 million people.

In addition to crops, “there’s also animal feeding operations, sewage treatment plants. Petrochemical industries discharge into water. And then urban runoff,” Rota said.

Home use of fertilizer for yards and gardens nearly doubled between 1987 and 1997, although it was just 1 percent of the total nitrogen, according to the USGS nationwide study. Nitrogen from manure increased almost 5 percent and nitrogen from the atmosphere, largely from the burning of fossil fuels, increased 13 percent.

Reliable data on another urban source of nitrate, sewage treatment plants, are not available. And while septic systems are responsible for about 12 percent of the nitrate in the Missouri River watershed, there is no data on whether it has increased.

None of this information provides definitive answers about what is driving the increased contamination of the river. Nitrogen applied to the ground may never reach the Gulf, depending on weather patterns, vegetation, waterway conditions and many other factors.

“There isn’t clear evidence to support the hypothesis that it’s ag or urban or wastewater treatment plants,” Sprague said. “We don’t have a good understanding of how these things have changed over time.”

A foot soldier in the war
The Missouri River has been monitored at Hermann since 1844, which makes it a good place to observe changes in the river.

USGS water quality technician Kelly Brady is a foot soldier in the war against hypoxia. He takes water samples once a month that end up being used in the recent USGS study.

On a recent trip, the Missouri River looked deceptively smooth, but Brady knew it could quickly turn deadly. on average, 88,500 cubic feet of water – enough to fill an Olympic-size swimming pool – slip past here every single second. If water were oil, the volume of the entire BP oil spill could pass by in five minutes.

Brady launched the work boat, a 26-foot sealed-hull aluminum skiff that he jokes looks like a gunboat out of “Apocalypse Now.” “It’s supposed to be unsinkable and self-righting, but I don’t want to try that out,” he said. “I like swimming, but I don’t want to do it on the job.”

The crew used a laptop, radar and high-precision GPS to find sampling locations. A crane hanging over the front of the boat dipped a Teflon-lined sampler into the water and hauled up several liters of water. Brady and his team processed the samples in mobile labs in the back of their trucks. These were put on ice and shipped to Denver for analysis.

Brady’s data are essential for keeping tabs on water quality. Dale Blevins, a USGS scientist emeritus who is an expert on the Missouri River, has studied historical nitrogen concentrations in the river in the past century. "It’s a cycle; it goes up and down," he said. "We’re in upward trend in one of those cycles and we’re about to bust out the top of where we’ve ever been before." Why? He’s not sure.

The total nitrogen concentration in the Missouri is not much different now than in the early 1900s, Blevins said. But most of that used to be organic nitrogen, whereas now, it's mostly nitrate, a form that many algae and other organisms can take in directly.

"It has reached almost its maximum concentration by time it reaches St. Joe," Mo., he said. "If you look at the location where the nitrate’s coming from, those are pretty much agricultural areas."

There is another possible explanation for the increasing nitrate numbers, a third view that blames neither today’s farms nor urban areas. The pollution could come from historic nitrogen deposits – the legacy of years of earlier excess that is just now showing up.

The USGS study found that a lot of nitrate poured into the river even when the water flow was low. one might expect heavy rain to wash nutrients off the land, but where did nitrate come from under dry conditions?

Sprague concluded groundwater was the source. Rain falls on the surface, percolates through the soil and drains out from days to decades later.

Norfleet, the USDA soil scientist, said nitrogen could stay in an aquifer for years before finally spilling into streams. “It’s kind of like having clogged arteries,” he said. “It’s going to take a while to clean those out.”

If groundwater really is responsible, it could take years for conservation measures to make a significant difference in the Gulf.

“Even if we stopped applying nitrogen now, the groundwater’s going to have a lot of nitrogen in it for 5 to10 years, or in some places, 20 to 30 years,” said Andrew Hug, an analyst with the Environmental Working Group who focuses on agriculture’s environmental impact. “It’s going to take a long time to fix this problem.”

Iowa farmers and Louisiana fishers
Up at the top of the watershed, Bill Northey spends a lot of time thinking about the Gulf’s dead zone. As secretary of the Iowa Department of Agriculture and Land Stewardship, he looks for science-based ways to maintain farm productivity while also reducing runoff to the waters below.

Iowa has 31 million acres in farmland, with 23 million of that planted to corn and soybeans, Northey said. Nine million acres of land is drained by tiles, underground drains that efficiently remove water from fields.

These drains also mainline nitrogen directly to streams. Underground nitrogen is “the most critical conservation concern” in the Upper Mississippi River Basin, said a 2010 USDA study of conservation practices.

Artificial wetlands can help get the nitrogen out. With the help of a federal conservation program, Iowa has built 70 shallow wetlands to filter tile-line water. “We’re seeing a 40 to 70 percent reduction in the amount of nitrogen coming out,” Northey said. “It’s pretty dramatic.”

The artificial wetlands are expensive, and they don’t work on every property. “We’re building five to 10 a year,” said Northey, a member of the federal-state hypoxia task force. “It would take building hundreds of years to get all of that.”

Scavia, with the University of Michigan, said significant changes are needed to shrink the dead zone – and quickly. The dead zone appears to be reaching a “tipping point” where the system is becoming increasingly sensitive to nutrient inputs, he said, and climate change exacerbates the problem as it warms water and increases intense storms.

Scavia’s solution? Fix the federal “farm bill,” which determines agriculture policy and subsidies. “It’s that difficult, and that simple,” he said. “It’s how much we incentivize producers. I believe farmers understand and do want to protect the environment.”

Voluntary methods are all well and good, said Rota, of the Gulf Restoration Network, but he wants to see enforceable standards as well. His group and others recently filed a lawsuit asking the EPA to set national criteria for nitrogen and phosphorus runoff.  “We need that minimum bar to start making progress,” he said, “because so far, we’ve only seen the dead zone trending bigger.”

The EPA has so far refused to set national criteria, saying the best approach is to work with states to develop their own standards and cleanup plans.

For his part, Northey said the first step is education. Through the task force, he has taken Iowa farmers down to the Gulf and brought people from Mississippi back up to see what Iowa farmers are doing.

The rivers forever link farmers in the Midwest and fishers in the Gulf.

“Maybe it doesn’t seem like it when you’re working on your farm on a cold November morning, but we are tied to those folks,” Northey said. “We are tied, up and down the river, all together.”

This article originally ran at Environmental Health News, a news source published by Environmental Health Sciences, a nonprofit media company.