Washington Post - Joby Warrick
Lakes around the world are growing rapidly warmer, according to a new
scientific study that warns of potential consequences ranging from
depleted fisheries to harmful algae blooms that kill fish and
contaminate water supplies for cities large and small.
Hotter
freshwater lakes are yet another sign of global climate change, and
their increasing temperatures are happening at a faster rate compared to
the warming seen in the oceans and atmosphere, a team of scientists
report in the peer-reviewed journal Geographical Research Letters.
The
study is based on decades of measurements from 235 lakes that contain
more than half the world’s fresh water supply. On average, temperatures
are rising by about six-tenths of a degree Fahrenheit per decade, a
rapid increase by geological standards.
The results are a
“wake-up call,” especially for regions that rely on lakes for food and
drinking water, said Henry Gholz, a program director for environmental
biology at the National Science Foundation, which co-funded the research
along with NASA.
“Our knowledge of how lakes are responding to global change has been lacking,” Gholz said.
The
study, the largest of its kind, involved more than 60 scientists who
used temperature records as well as satellite data to gauge changes over
time, from Lake Tahoe on the California-Nevada border to the tropical
lakes of central Africa to partially frozen lakes in Scandinavia.
The
most dramatic increases were observed at far-northern lakes, which are
warming at an average rate of 1.3 degrees F per decade. But tropical
lakes also are warming rapidly, the researchers found. Only a small
number of warm-water lakes kept a constant temperature or cooled
slightly, a departure from the norm that scientists attributed to local
land-use changes such as reforestation that increased shade along the
shoreline.
Even small variations in temperature can impact fish and other wildlife,
the researchers found. Most significant for many areas was the greater
potential for harmful algae blooms, an explosive growth in populations
of microscopic plants that can strip oxygen from the water and kill
fish. Destructive algae blooms—such as the one in Lake Erie in 2014 that
contaminated the water supply for Toledo and other Ohio cities—already
are occurring more frequently worldwide.
Such
events are important because of the role played by lakes in sustaining
human populations in many parts of the world, said study co-author
Stephanie Hampton, a professor at Washington State University’s School
of the Environment.
“Lakes are important because society depends
on surface water for the vast majority of human uses—not just for
drinking water, but manufacturing, energy production, irrigation and
crops,” Hampton said. “Protein from freshwater fish is especially
important in the developing world.”
A separate report earlier
this month predicted the number of severe algae blooms would double over
the next century because of a combination of warmer temperatures and
increased pollution. By 2115, disruptive events like the one in Toledo
will be commonplace rather than exceptional, according to a team of U.S.
researchers using climate and watershed models to project future
trends. The scientists discussed their findings at the American
Geological Union meeting in San Francisco.
Even reducing the
amount of nutrient pollution that feeds algae growth—including
fertilizers and human and animal waste—will not be enough to prevent
destructive algae blooms if warming trends continue, said Noel Aloysius,
a post-doctorate researcher at Ohio State University’s Aquatic Ecology
Laboratory who presented the findings.
“Our assessment of climate
reveals less winter snow, more heavy spring rains and hotter summers,”
Aloysius said. “Those are perfect growing conditions for algae.”
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