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INDIANAPOLIS — Indiana is among a group of states considered the worst contributors to a nearly 8,000 square mile patch in the Gulf of Mexico that is inhospitable to marine life, according to research by the United States Geological Survey.
Animal manure and fertilizer flowing from Indiana and nine other states into the Mississippi River has significantly contributed to a seasonal "dead zone" -- an area that is so depleted of oxygen that most aquatic life cannot survive.
Along with Indiana, Illinois, Iowa, Missouri, Arkansas, Kentucky, Tennessee, Ohio and Mississippi were the worst contributors to the dead zone.
The nine states represented one third of the 31-state Mississippi River drainage basin, but were responsible for more than 75 percent of the nitrogen and phosphorous that deplete oxygen from the Gulf, killing fish, crabs, clams and shrimp.
The excessive amount of nitrogen in the Gulf was mainly caused by corn and soybean farming, and the overabundance of phosphorous was primarily caused by animal manure on pasture and rangelands, the survey said.
"Conventional thinking has been that the pasture and rangelands don't contribute as much as the cultivated cropland," said Richard Alexander, a research hydrologist and lead investigator on the study. "The thinking has been that the row crops would contribute more phosphorous."
The study found 37 percent of phosphorous delivered into the Gulf comes from animal manure on pasture and rangelands, followed by 25 percent from corn and soybean cultivation.
Corn and soybean farming accounts for 52 percent of nitrogen contributions.
Indiana was the third worst contributor of nitrogen at 10.1 percent and sixth worst of phosphorous at 8.4 percent among the states in the basin. Illinois was the worst offender for contributions of both nutrients.
"This is one more piece of strong evidence about the source of nutrients and about the serious action that should be taken to reduce the nutrients," said Nancy Rabalais, who serves as executive director of the Louisiana Universities Marine Consortium and researches the dead zone.
She said regulation may be difficult because the nutrients are coming from the land and atmosphere rather than pipelines.
Bruno Pigott, an assistant commissioner with the Indiana Department of Environmental Management's office of water quality, said the agency was reviewing the report but had been working on nutrient issues for years.
He said the sources of nutrients in groundwater were diverse -- including wastewater treatment plants and lawn fertilization as well as runoff from farming and other activities.
"We think there has to be a broad-based approach to reducing nutrients," he said.
Meanwhile, Pigott said, IDEM is using public funds to reduce pollutants to waterways and developing statewide criteria for nutrients.
The agency also has phosphorous limitations in place for wastewater treatment plants upstream of lakes, especially in the Great Lakes region, he said.
The high levels of nitrogen and phosphorous deposited in the Gulf cause a boom in the population of algae, which sucks up oxygen as it decays and creates a zone of hypoxia near the mouth of the Mississippi River.
The dead zone has grown as large as New Jersey in past years.
"That's a huge area not to have catchable fish and shrimp," Rabalais said.
The dead zone usually begins forming around March and breaks up when tropical storms and hurricanes move into the region around the fall.
Nutrients from industrial, urban and suburban areas also feed nitrogen and phosphorous into waterways that travel to the Gulf. Urban sources accounted for 12 percent of the phosphorous in the dead zone.
"They have a large local contribution, but when you look at it in the bigger watershed, their role is not quite as large as the other sources, the agricultural sources," Alexander said.
The dead zone was discovered in 1985 and has grown fairly steadily since then, affecting the fishing economy in the Gulf region. Last year the zone ballooned to the third largest size ever recorded, Alexander said.
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