After discovering the movement of Stack No. 4, in early 2019, Mosaic alerted officials, and then began to pump water out of the pond. Managing water is a juggling act; the campus often holds more than a billion gallons in total, spread across various cells and reservoirs, which grow and shrink thanks to rain and evaporation and pumping. Quickly, the company began to dig a new pond. By May, Mosaic asked for permission to use aerators that would spray droplets of wastewater into the air, speeding up evaporation by increasing surface area. The Louisiana Department of Environmental Quality—which confirmed some facts for this story but otherwise declined to comment—denied this request, though in September the company submitted a revised application for the required permits. Then, in December, Mosaic asked for permission to treat the water and dump it directly into the Mississippi. Both applications are still pending, according to the company.

Mosaic says the company had made “significant progress” on the issues facing the gypstack. “Lateral movement of the north slope of the gypstack continues to slow, and there has been no offsite impact, nor is any expected,” Callie Neslund, a public-affairs official, wrote in an email. “The safety of our community, employees and the environment remains our focus.”

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Once the finished fertilizer leaves a processing plant, it enters the supply chain, where it travels from warehouse to farm store to field. Some of this phosphorus is absorbed by plants, which are then absorbed by animals, including humans—and thus the rocks of the earth become a part of our corporal selves. (One study estimates that people who eat meat also, in this way, eat some 25 pounds of rock a year.) Farmers have other options for phosphorus fertilizer—manure and guano and bone meal, even human urine. But phosphate rock is so ubiquitous that organic farms use it in unprocessed form, too. Within the industry, there is a standard talking point: there is no way to feed the world without mining this rock.

U.S. farmers dump more than four million tons of phosphorus onto their fields each year, far more than plants successfully absorb. By some estimates as much as 40 percent washes into rivers and lakes and oceans, where it can feed massive algal growths. These, too, can have dire consequences: this summer, every beach in Mississippi was closed for days or weeks due to the presence of cyanobacteria. In 2014, an algal bloom on Lake Erie turned the tap water in Toledo, Ohio, undrinkable. This is one more geography of phosphorus, dispersed across the nation, though its extent is hard to map. We know the problem has affected waterways in every state, and costs us billions of dollars each year. Because warmer temperatures promote algal growth, the situation may worsen as the climate warms.