Vermont farms have built up a massive phosphorus surplus – one that is growing at an estimated 1,500 tons per year – as farmers continue to import large quantities of animal feed and fertilizer, a new University of Vermont study says.

The study is the first to estimate the build-up of agricultural phosphorus in Vermont, which is the largest contributor to phosphorus pollution. It finds the state has accumulated between 1,000 and 4,500 tons of surplus phosphorus annually for nearly 90 consecutive years, creating a nearly 240,000-ton “legacy” that hinders phosphorus-reduction efforts.

“These findings reveal the magnitude of Vermont’s phosphorus problem – and show that our efforts to deal with it need to consider the phosphorus entering our state, and not only the part that washes into our rivers and lakes,” says lead author Michael Wironen, a PhD researcher at UVM’s Gund Institute for Environment, and the Rubenstein School of Environment and Natural Resources.

“We have been building up phosphorus in our farm soils for nearly a century, but still import it by the truckload,” he says. “That makes it harder to reduce runoff.” The study was published in the journal Global Environmental Change.

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