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“Legacy P” Poses Long-Term Challenge To Water Quality

Scott Gordon WisContext

Phosphorus is one of the most important components in the ongoing struggle to balance agricultural prosperity with water quality. When farmers fertilize their fields with this essential nutrient, plants use some, with precipitation carrying excess amounts into nearby bodies of water, fueling algal blooms that can kill fish and and endanger drinking water quality.

But phosphorus that lingers in the soil, sometimes for decades, is troublesome as well.

What scientists call “legacy phosphorus” — or “legacy P,” a common abbreviation — exists in a sort of nutrient limbo.

Agriculture Phosphorus

Phosphorus can easily bind to soil particles, a state in which plants don’t usually access it. The nutrient generally must be in water plants take up in order for them to use it. Moreover, as farmers spread more fertilizer, new quantities of phosphorus are made available to crops. But as land erodes or heavy rains hit fields, some of that older phosphorus will make its way into streams, rivers, lakes and ultimately groundwater. In coming decades, greater quantities of legacy phosphorus could get flushed into water sources due to climate change, which is projected to increase heavy precipitation events in the Midwest.

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Dead Zone grows in Gulf of Mexico

The dead zone in the Gulf of Mexico, which is believed to have been around since the 1970’s, is now an estimated 6,474 square miles of water unable to support marine life.

Government and independent scientists believe nutrient runoff is the main cause of the dead zone.  Pollutants such as nitrogen and phosphorus flow into the gulf of Mexico by way of the Mississippi River and its tributaries.

mississippi-meets-gulf

For many, the ethanol industry and the government’s 2005 Renewable Fuel Standard carry a lot of the blame.  Since the governments introduction of the Renewable Fuel Standard in 2005, acreage of U.S. land to farm corn and soy beans has grown by 16.8 million and over 1.2 million acres of grassland has been lost.

Flooding in 2015 and earlier this year washed away tremendous amounts of pollutants that had accumulated on land during the prolonged drought. The sources of much of these nutrients were cornfields, 40% of which are dedicated to producing ethanol, which fuel companies are compelled by Congress to blend with gasoline.

dead-zone

NOAA officials estimate the Dead Zone costs the nation’s seafood and tourism industries $82 million a year. And it likely will get worse, scientists believe. The gulf produces about 40 percent of the nation’s seafood, which includes offshore species such as shrimp and red snapper. And Louisiana is second in seafood production to Alaska, according to The Nature Conservancy.

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Turning Phosphorus in Wastewaster into Fertilizer

Chicago officials boast that the Stickney Water Reclamation Plant is one of the world’s largest sewer treatment plants, handling the waste of 2.3 million people.

The Stickney Water Reclamation is the biggest single source of phosphorus in the entire region that drains into the Mississippi River. Combined with other sewage plant releases a state task force concluded that these plants are responsible for about half of the phosphorus pollution in rivers that drain into the Mississippi.

Stickney Water Reclamation Plant

The need for more aggressive and widespread action is especially acute in Illinois, which by most estimates is the largest contributor of phosphorus and nitrogen pollution to the Gulf of Mexico.

Gulf Pollution

A new $31 million project will help to reduce that pollution by diverting wastewater through three reactors that use catalysts to form tiny, nutrient-rich “pearls” for the fertilizer industry. The district estimates the equipment will produce up to 10,000 tons of slow-release fertilizer a year and reduce the Stickney plant’s phosphorus discharges by about 30 percent.

More still needs to be done, but this project is a good start.

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