As rainy spring weather washes phosphorus off farmfields, a series of new filters in northwest Ohio’s Defiance County are working to catch the nutrient — before it gets into the streams and waterways that feed Lake Erie.
The project is part of a broader effort to prevent harmful algal blooms there.
“If we can just get to, say, 20% of the high phosphorus fields, that will be a big success and will have a big impact on removing the phosphorus that gets into Lake Erie,” said Matt Fisher, vice president of the Lake Erie Foundation.
The nonprofit has installed five filters in the past couple of months and is monitoring their effectiveness.
How do the filters work?
The phosphorus filters work like giant sieves, Fisher said.
They’re about 20 by 30 feet wide and around 12 feet deep, depending on the size of the area they serve.
“The fields drain into those filters on one side, flow through a series of pipes and media, and exit with what has turned out so far to be very clean water,” Fisher said.
About a month in, he says the filters are removing nearly all of the dissolved reactive phosphorus from the farm runoff they’re collecting.
What makes the filters a useful tool?
There’s been a big push in recent years to teach farmers about nutrient application and employ practices like cover crops.
Those are helpful strategies, Fisher says, but these new phosphorus filters are useful for capturing phosphorus in “legacy fields” where the nutrient has been accumulating over many decades.
“About 9% of the fields are responsible for 35%-plus of what runs off into the Maumee,” Fisher said. “So we want to find as many of those 9% as we can, and try to work with leaders of the agriculture community to put filters in those places to try to catch as much dissolved reactive phosphorus as we can.”
The filters are expensive: Fisher says each one costs about $10,000.
But because they should last for about a decade and cover large areas, Fisher finds the solution encouraging.
He’s hopeful more will be added across the region, and that they’ll work to help keep Lake Erie clean.
