Phosphorous Fed Algae Bloom Threatened Toledo's Tap Water

Aug 5, 2014
Originally published on August 5, 2014 8:47 am
Copyright 2014 NPR. To see more, visit



The weekend water emergency in Toledo is over, as least for now. Yesterday, Toledo's mayor took a big sip of H2O for the cameras, as he declared his city's water supply safe. But Toledo is located near the shallow, flat, western basin of Lake Erie, which still faces the threat of toxic algae blooms. The algae are fed by phosphorous, mainly from fertilizer running off from farmland. And we want to better understand this. Our colleague Linda Wertheimer spoke to a watershed specialist named Steve Davis. He works with the U.S. Agriculture Department's field office in Lima, Ohio. For one thing, he said farmers are not necessarily using too much fertilizer.

STEVE DAVIS: Farmers apply about 40 to 48 pounds per acre of phosphorus on average. That is the amount that replaces the nutrients that are taken out of the soil and away from the farm when corn is hauled to market. So we're not losing excessive amounts per acre, compared to, even, other areas in the country. But we have so many acres draining into one spot.


Now, as I understand it, one of the problems is that fertilizer is spread in pellets. And those pellets sometimes just sit up on top of the ground and roll right into watershed.

DAVIS: That's somewhat true. Fertilizer is spread in pellets. It's put on in a variety of ways. Sometimes it's broadcast. If it's broadcast right before a rain, certainly, it can be washed off. And especially if it's broadcast on frozen and snow-covered ground, there's a much higher chance of it moving. And that is a very bad practice. But surveys actually show that fertilizer use rate is declining in the basin and has been declining for the past 10 years. So farmers are doing a better job than they used to of putting on the right amount. We need to make it get it put on the right place. And, you know, a lot of the scientific information shows that the amount of phosphorous that is lost per year is directly related to the amount of precipitation we get. And as we have had more extreme events and more precipitation events in the past years, we have had more runoff and more algae bloom.

WERTHEIMER: If you just need to reduce the amount of fertilizer that is lost by a relatively small amount, how are you going to do that?

DAVIS: Number one would be the amount of fertilizer the farmer uses.

WERTHEIMER: And consider if they can cut back on that?

DAVIS: Yeah, can they cut back on that? Second line of defense would be, are they putting it on in the proper method? Third thing we have been looking at and promoting is what we call the precision nutrient management, which involves going over the field and mapping it with a GPS unit and taking soil samples that are referenced to satellite locations in their field. And then when the producer, the farmer, the fertilizer dealers spreads fertilizer, they link to that satellite. And as their machine goes across the field, it puts five pounds on in this place and 20 pounds on in that place and zero in the third place. And it actually changes the amount of fertilizer that the farmer puts on, on the go, as they drive back and forth across the field. That is further targeting fertilizer so we get it only where we need it, in the amount we need it. And this practice is growing fast.

WERTHEIMER: Steve Davis is a watershed specialist, who works at the U.S. Department of Agriculture. Mr. Davis, thank you very much.

DAVIS: Thank you. I appreciated being on the show. Transcript provided by NPR, Copyright NPR.