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.
These fetid growths appear on lakes throughout the country and
world. They’re known as “harmful algal blooms” because they
generate toxins called microcystins, which when ingested cause
nausea, vomiting, diarrhea, severe headaches, fever, and liver
damage. “Pets and livestock have died from drinking water
contaminated with microcystins,” the US Environmental Protection
Agency reports. In the summer of 2014, the city of Toledo, which
draws its water from the western end of Erie, had to warn
residents not to drink or even bathe in tap water for days after
it became tainted with microcystins. (The city has launched a
$500 million project to upgrade its water-filtration system,
partially in response to the microcystin threat.)
 Algae-riddled lakes are much bigger emitters of the potent gas
methane than was previously known.
Where do these green blobs come from? In short, we create them.
In land upstream from the lake, farmers apply phosphorus as
fertilizer for their corn and soybean crops. Every year, a
portion of it leeches into the lake, where it fertilizes algae
instead—a process called eutrophication. While Erie’s west-side
drainage basin has been planted in millions of acres of farmland
for decades, the state’s regulators have documented that the
amount of biologically active phosphorus entering the lake each
year spiked in the 1990s and has remained high ever since. The
reason may be linked to the boom in no-till soybean farming that
started in the 90s, as a 2017 paper by researchers from the
National Center for Water Quality Research suggests
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.
Algae-ridden lakes contribute massively to climate change—and
climate change makes lakes more hospitable to algae blooms.
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. |
