U.S. Water News Online
INDIANAPOLIS -- Fertilizers are the largest source of nitrogen in the White River watershed, according to a report released by the U.S. Geological Survey (USGS).
"Based on our estimates of the total input of nitrogen into the watershed, 61 percent is from fertilizer, 19 percent from farm animal wastes, 17 percent from rainfall, and 3 percent from municipal sewage-treatment plants and industrial discharges," said Jeff Martin, principal author of the report.
Martin said that both surface water and groundwater in the White River watershed are, with few exceptions, well within the range of federal safe drinking water standards.
But current levels of nitrogen are a concern, he said, because if its role in stimulating growth of algae in lakes in Indiana and in estuaries like the Gulf of Mexico. When the algae die, they use up oxygen. Nitrogen in runoff from the corn-belt states has been implicated as the primary cause of a 7,000 square-mile zone of low oxygen in the Gulf of Mexico.
"Fish and shrimp can't live in this zone, which is one of the largest oxygen-deficient zones in the world," said Martin.
The White River study, undertaken from 1993 - 1995, was one of about 60 watershed studies conducted across the country as part of the National Water Quality Assessment Program. The USGS, said Martin, hopes these studies will provide "policy relevant information" to regulators, who may be better able to implement more regionally specific approaches to environmental regulations by gleaning scientific information from these reports.
"One of the most important questions", said Martin, "was how much of the pollution in this watershed is non-point source pollution? Our study found we are getting way more nitrogen from rural non-point source pollution than from anywhere else."
Martin said researchers measured slightly more than 1 ton of nitrogen going into the river basin from sewage treatment plants and other urban sources, but found the total amount of nitrogen came to approximately 5.1 tons per year per square mile of watershed in the White River basin. "[That means] over 4 tons of nitrogen were coming from somewhere else," he said.
These sources, Martin explained were from fertilizer, animal waste, and rainfall. This conclusion was confirmed, he said, by analyzing water from two separate branches of the White River: one near greater metropolitan Indianapolis where the greatest concentration of the state's population resides, and one adjoining sparsely populated rural areas.
The nitrogen levels were far greater in the branch passing through rural areas than urban areas, said Martin, leading to the conclusion that urban areas are contributing proportionately less nitrogen than rural areas.
But the results were different when it came to phosphorous, he said. The study found about 20 percent more phosphorous in urban watershed areas than rural.
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