Every summer, a massive green-algae blob colonizes western Lake Erie. Last year’s bloom ranked among the biggest ever, blanketing 700 square miles—an area 1.5 times bigger than Los Angeles. The shoreline of Toledo, Ohio, “smelled like a sewer,” according to one reporter.
Poisoned water is only one of the consequences of the excess farm fertilizer that ends up in lakes. Another is accelerated climate change. A new paper—by a team that includes researchers from the EPA and the University of Minnesota—finds that algae-riddled lakes are much bigger emitters of the potent gas methane than was previously known. Methane is a greenhouse gas with about 30 times the heat-trapping effect of carbon.
All told, they found, methane from the world’s lakes emits methane equivalent in greenhouse effect to about 20 percent of all the carbon dioxide from fossil fuels burned globally—about twice the level of previous assumptions. And they directly tied these emissions to algae blooms. “The greener or more eutrophic these water bodies become, the more methane is emitted, which exacerbates climate warming,” the study’s lead author, University of Geneva researcher Tonya DelSontro, said in a press release. The paper found that even modest increases in eutrophication over the past century could add methane to the atmosphere equivalent in greenhouse gas terms to 13 percent of the world’s current fossil fuel combustion.
And there’s a feedback loop at play. Excess phosphorus from farms provides the nutrients that feed the algae, but they need warm water to thrive. There’s strong evidence (see this 2017 Tufts paper) that climate-related warming trends are helping make harmful algae blooms bigger and more frequent. In other words, algae-ridden lakes contribute massively to climate change—and climate change makes lakes more hospitable to algae blooms.
Meanwhile, last week, after years of pushing for voluntary solutions to Lake Erie’s algae woes, the Ohio EPA declared Lake Erie “impaired”—a move advocates hope will eventually lead to regulations that slow the flow of algae-feeding fertilizer into the lake. The state has established a goal of reducing phosphorus flows by 40 percent by 2024; in a report released Monday, the agency acknowledged that the state’s policies “haven’t moved the needle” on runoff reduction, despite “significant taxpayer and private dollars spent on incentives and voluntary nutrient reduction programs.” I have more on agriculture’s role in the plight of Lake Erie here and here.
Tom Philpott has been at MoJo since 2011. His award-winning writing on food politics has appeared in numerous publications, and he was a cofounder in 2004 of Maverick Farms in Valle Crucis, North Carolina. He is currently based in Austin, Texas.
Climate Desk is a journalistic collaboration dedicated to exploring the impact—human, environmental, economic, political—of a changing climate. The partners are The Atlantic, Atlas Obscura, CityLab, Grist, The Guardian, High Country News, HuffPost, Medium, Mother Jones, the National Observer, New Republic, Newsweek, Reveal, Slate, Undark, Wired.