A new study done by Canadian researchers takes a look at nitrates in ground water in the Mississippi Basin and finds bad news. If we stop using nitrogen fertilizers today, there will still be a three-decade legacy of excess nitrogen in water—and there’s a lawsuit right now that will decide who will foot the bill.

Nitrogen fertilizers are incredibly important. The ability to keep nitrogen from being depleted from the soil, despite years of agriculture, has saved billions of lives. This doesn’t mean that using the fertilizers doesn’t have consequences. A new study published in the journal Environmental Research Letters shows how long-term those consequences will be. Researchers from the University of Waterloo showed that nitrogen fertilizers have caused nitrates to accumulate in the Mississippi River Basin, and that they won’t be clear for decades.

Nitrates are simple molecules that combine three oxygen atoms with one nitrogen atom. They are not, on their own, harmful to adults. They’re routinely added to meats during the curing process. Many doctors suggest that pregnant women should stay away from cured meats for the length of their pregnancy, because when nitrates lose one oxygen atom they become nitrites.

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Nitrites can cause something called “blue baby disease.” Babies affected by this disease have much of their hemoglobin replaced with methemoglobin—which can take up oxygen but can’t release it into tissues. Babies’ digestive systems, which aren’t as developed as adults’ digestive systems, are more likely to reduce nitrate to nitrite, which means any public water system needs to be low in nitrates.

Water that lies just under the surface of the soil in the Mississippi Basin is low in nitrates. Get between 25 and 100 centimeters down, and the nitrate level rises sharply. The chemical leaches into wells and public water reservoirs. This is not just a seasonal rise, increasing when rains wash fertilizer into rivers, but a slow accumulation over decades—and it’s one that won’t subside for decades more. The researchers predict that it will take 30 years for nitrogen levels to return to normal, even if nobody uses nitrogen fertilizers again after today.

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This is not just an abstract problem. Someone will be hit in the pocketbook over this nitrogen accumulation, and there’s already a lawsuit going on to see who it will be. The Des Moines Water Works recently filed a lawsuit, demanding that three counties upstream pay for the millions of dollars it will have to spend for the next few years to make sure that it can meet federal standards when it comes to nitrates in the water supply.

Exactly who is at fault depends on who is asked. Some claim that farmers are using too much nitrogen fertilizer and that drainage systems, which make more land arable by washing excess water away, increase nitrate levels. Others claim that drainage systems don’t do much damage and that the increase in nitrates comes from nitrogen-producing bacteria in the soil. What’s for sure is that someone needs to pay to make water safe, and that they will need to do so for decades. But who?

[Environmental Research Letters]