Farm fertilizer runoff wreaking havoc

‘Nitrogen pulse’ impacting Mississippi River, worsening Gulf of Mexico’s dead zone

Orlan Love
Published: August 4 2013 | 5:30 am - Updated: 28 March 2014 | 6:35 pm in
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The world’s strongest man opening and dumping bag after bag of nitrogen fertilizer into the Mississippi River could not begin to keep up with the stream of nitrogen flowing this spring from the Iowa River into the main conduit to the Gulf of Mexico’s dead zone.

A near-record pulse of nitrogen, driven by last year’s drought and this spring’s record rainfall, has been leaving Iowa farm fields, bound for ecological and economic damage in the gulf and along the way, according to researchers studying the phenomenon in the watershed of the Cedar and Iowa rivers.

A real-time nitrate gauge near Wapello, 20 miles above the Iowa’s confluence with the Mississippi, was recording 25 kilograms (55 pounds) of nitrate per second during the first week of June, said Amy Burgin of the University of Nebraska School of Natural Resources, one of several scientists studying the nitrate pulse.

It is a prime example of innocents downstream paying for actions upstream in the same watershed, said Burgin, the lead researcher on the project, which also involves scientists from Coe College and the University of Iowa.

Nitrogen pulse

After the 2012 drought, in which crops fell far short of using all the applied nitrogen, Burgin, an Iowa native and Coe College graduate, and Terry Loecke, her husband and research colleague, suspected that Corn Belt rivers would transport a major nitrogen pulse this year. In October, they applied for a $200,000 National Science Foundation grant to document and study the pulse, and they received their approval within six days.

“We knew that (the excess nitrogen) had to come out, and we wanted to find out how climate and precipitation would affect the timing and magnitude of the pulse,” said Loecke, a University of Nebraska biogeochemist and Manchester native.

“Once it started raining, it came out all of a sudden,” said Burgin, who grew up in the south-central Iowa town of Lacona.

“We would have had high nitrate levels this year, even if farmers had not applied nitrogen for this year’s crop,” said project collaborator Marty St. Clair, a Coe College chemistry professor who has been monitoring water quality in Lime Creek, a Cedar River tributary, for the past 12 years.

Scientists on Monday completed their annual measurement of the gulf dead zone, which encompassed 5,800 square miles — about twice the size of last year’s dead zone but well short of the 8,561 square miles predicted by the National Oceanic and Atmospheric Administration.

Much of the 2013 nutrient load is still en route to the Gulf, said Larry McKinney, executive director of the Harte Research Institute for Gulf of Mexico Studies at Texas A&M University — Corpus Christi.

Pollution dangers

Excess nitrogen and phosphorus pollution primarily from agricultural sources throughout the basin stimulates the growth of algae, which deprives gulf waters of oxygen as it decomposes on the bottom.

Fish and other mobile aquatic life can move, but organisms rooted to the bottom “don’t have a prayer,” said Paul Montagna, a scientist at the Harte Research Institute.

“Shrimp and crabs are somewhat mobile and try to escape but often can’t,” Montagna said.

McKinney, who has been diving in Gulf waters since the 1980s, said it is pathetic to see aquatic animals climb whatever structure is available, seeking more oxygen-rich water farther from the bottom, before they finally suffocate.

Montagna said the shallow northern gulf waters are an important commercial fishery, whose greatest dead zone economic losses are associated with shrimp.

“The boats working near the dead zone harvest less shrimp and have to go farther afield,” he said.

Some boats sit idle each year because they can’t afford additional fuel costs or don’t want to infringe upon other boats’ home waters, McKinney said.

Gulf residents “are not resentful of Midwest farmers, but they understand the hypoxia issue and want to see it resolved,” he said.

Mississippi threat

Though less dramatic than manure and chemical spills, nitrogen and phosphorus pollution also degrades waters throughout the Mississippi River Basin and its tributaries, threatening wildlife and recreation as well as the safety of drinking water.

The Environmental Protection Agency requires nitrate in drinking water be kept at less than 10 milligrams per liter to avoid potential human health problems, especially for infants and pregnant mothers.

A large study of children in Iowa and Texas, published in late June, found that babies whose mothers consume nitrates in drinking water have a higher risk of spina bifida, cleft palate and other birth defects.

May nitrate readings reached record levels in the Raccoon River (24 milligrams per liter) and the Des Moines River (18 milligrams per liter), both water sources for the Des Moines water plant, which has spent more than half a million dollars this year to operate its treatment facility.

“Both rivers were above the EPA limit for about 90 consecutive days,” said Water Works General Manager William Stowe, who said the plant’s denitrification apparatus, the nation’s largest, costs about $7,000 per day to operate.

The Environmental Protection Agency has ordered Iowa and 11 other states in the Mississippi River basin to reduce their contributions of nitrogen and phosphorous to the gulf dead zone.

Reduction plan

After extensive research by state agencies and Iowa State University, Iowa responded last year with a science-based but strictly voluntary plan to assess the nutrient load in Iowa waterways and reduce it by 45 percent, with most of the burden falling upon agriculture.

Environmental groups contend the Nutrient Reduction Strategy provides little incentive for farmers to limit fertilizer applications or to take land out of production to create wetlands, buffer strips and other conservation practices that can keep nutrients out of waterways.

“We have repeatedly called on state leaders to set clear, measurable goals for reducing Iowa’s contribution to the dead zone,” said Ralph Rosenberg, executive director of the Iowa Environmental Council.

The Iowa plan, he said, “does not currently explain how this will take place, when it will take place, and when many stakeholders — those who drink from Iowa’s waters or fish or canoe — will know that progress is being made.”

Stowe described the plan as “completely unrealistic” and “a non-starter for us.”

Progress toward the plan’s goals will not be made in flood years following droughts, sai another study collaborator, University of Iowa geologist Adam Ward.

“For me, the big conclusion (of the Iowa-Cedar nitrate study) is how weather interacts with human management decisions. When you plan for normal weather and get the worst, you get negative results with social consequences,” he said.

The nitrate load, calculated by multiplying the concentration by the volume, has reached the second highest level on record for the combined Cedar and Iowa rivers, second only to the persistently rainy summer of 1993, according to Burgin.

Nitrate levels

Most of the nitrogen leaves farm fields dissolved in water flowing through tile drainage systems, Loecke said.

“We’ve recorded it coming out of tile lines at 40 milligrams per liter this year,” he said.

Ward said he has recorded nitrate readings above 30 milligrams per liter at his three test sites on Clear Creek, which empties into the Iowa River at Coralville.

The Cedar River reached one of its highest recorded nitrate levels, 18.5 milligrams per liter, upstream from Cedar Rapids, but the city’s drinking water, which is drawn from a series of wells, has consistently tested well below the EPA limit.

Cedar Rapids Water Department spokeswoman Megan Murphy said this year’s annual spring rise in nitrogen levels came earlier and went higher than usual.

The city draws water from more than 45 wells that are fed by Cedar River water that is first filtered naturally through the river bank, where microbes break down nitrogen.

“The bugs were not fully active in early spring, when nitrate levels started climbing,” she said.

To compensate, the city increased its well monitoring and mixed water from wells with lower nitrate levels — a routine that diverted staff but did not add to overall operating expenses, she said.

Treatment changes

If high nitrate levels become the norm, Cedar Rapids may have to adjust its treatment procedures, Murphy said.

Burgin said the peak nitrogen flow at the Wapello gauge, 25 kilograms (55 pounds) per second, lasted about three days in early June. A smaller peak, about 44 pounds per second, occurred in mid-May, she said.

“For about the past 100 days, we’ve had a consistent (baseline) load of 8 to 10 kilograms of nitrogen per second at that same site,” she said.

This year’s nitrogen load at that site is about double what it is in a normal year and 10 times greater than it was in last year’s drought, Burgin said.

“In comparison to the longer-term record, we have not yet quite reached the total (nitrogen) load of 1993, but as of July, we were closing in on that record,” she said.

Burgin said this year’s nitrogen load almost equals the record, even though there is much less water in Iowa streams and rivers than in 1993.

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