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Healed
once, Lake Erie in relapse
Chicago Tribune -
10/18
Lake
Erie, once so polluted and putrid that it was irreverently called
"the place where fish go to die," is now often cited as
a worldwide model for ecosystem recovery.
But on
the 30th anniversary of the Clean Water Act Friday, legislation
inspired in part by Lake Erie's near-death in the 1960s,
scientists say parts of the Great Lake are dying once again.
Mysterious
dead zones, or areas without oxygen, have returned to about half
of the lake's central basin. Yellow perch and prized walleye
populations declined in the 1990s. Meanwhile, avian botulism, also
present in the 1960s, has killed thousands of water birds,
including common loons and ring-billed gulls.
Decades
ago, the problem was chemical pollution, primarily phosphorous
from sewage, detergent and fertilizer. Today, despite controls,
the phosphorous is back and scientists suspect the culprit is
biological pollution, due in part to changes wrought by invasive
species such as the zebra mussel and the round gobie.
Shallow
and vulnerable to stress, Erie is the warmest and most
nutrient-enriched of the five Great Lakes.
"To
have the area occasionally become anoxic [oxygen-starved] is
something we expect," said Jeffrey Reutter, director of the
Ohio Sea Grant Program who has been researching Lake Erie since
1971.
"What
we're seeing is the lake is anoxic very early [in summer] and the
area covers a greater distance. It's a trend in the wrong
direction and becoming worse."
The
dead zones in Lake Erie are a bit counterintuitive--they occur
because there is too much life. When too many nutrients like
phosphorous are in the water, algae grows maniacally. Algae blooms
are followed by a die-off, and as the material decays, it consumes
oxygen like a forest fire. No fish, plants or insects can live in
oxygen-free zones.
Located
in depths below 40 feet, the dead zones are ominously spreading
east in the middle of the lake from the Lake Erie Islands toward
Erie, Pa., during the summer months.
Lake
Erie's central basin has been running out of oxygen more rapidly
than ever, partly because of its flat geography and average depth
of 60 to 80 feet.
The
fish that can leave the area do. Everything else eventually
suffocates.
The
Clean Water Act, which limited phosphates and supplied more than
$80 billion to upgrade sewage treatment plants, largely solved the
problem of chemical pollution.
But in
the mid-1990s, the U.S. EPA's Great Lakes National Program office
discovered that phosphorous levels and dead zones had both
increased.
To
figure out why, a team of researchers led by Gerry Matisoff,
chairman of the department of geological sciences at Case Western
Reserve University, and Jan Ciborowski of the University of
Windsor began a two-year, $2 million study in June.
Their
working theory is that zebra mussels and the related quagga
mussels, which have a maddeningly efficient ability to filter
debris and extract zooplankton, use phosphorous in a different way
than other species.
Zebra
mussels, which were first documented in Lake Erie in 1988 and
probably arrived in U.S. waters in the ballast water of ships,
established a strong presence in the early 1990s, when scientists
believe most of the ecosystem changes occurred.
"We
think [invasives] might have interrupted the natural process of
carbon and phosphorous cycling and how the ecosystem interacts
with their chemistry," said Matisoff, who spent most of the
summer on the EPA's research vessel, the Lake Guardian.
As
mussels vacuum organic matter out of the lake, they expel the
phosphorous their food contained into the bottom of the lake. This
helps the algae grow, and the algae drain the oxygen from the deep
water. As material decomposes, it consumes oxygen and is not
replenished until fall, when temperature changes cause the lake
water to mix.
But the
lake's variability from year to year is a major problem for
scientists trying to understand the processes at play. Round
gobies, a newer invasive species, are now eating zebra mussels,
and no one is sure what impact that will have. In addition,
underreported phosphorous levels and climatic change could be
exacerbating the situation.
Phosphorous
loads are supposed to remain below 11,000 metric tons per year to
keep Lake Erie healthy, but scientists, thinking Lake Erie was
rebounding, relaxed their monitoring efforts in the 1990s as
funding dwindled.
David
Dolan, a professor of natural and applied sciences at the
University of Wisconsin Green Bay, determined that phosphorous
levels spiked in 1997 at 17,000 metric tons but are now below the
target level.
The
phosphorous increases are probably related to the amount of
rainfall the basin receives and how much fertilizer makes its way
from sewers and farms to streams and into lakes, said Dolan, an
environmental statistics expert.
Climate
change might be another factor. When the lake was recovering,
water levels were rising, but since 1997 the water level has
dropped by 3 to 4 feet, reducing the oxygen reservoir, Reutter
said. With less water, it's more difficult to keep the phosphorous
level down.
Should
Lake Erie grow worse, the effects on the region and its
billion-dollar fishery could be huge.
The
lake also supplies drinking water to 11 million people. When
blooms of blue-green algae die and sink to the bottom, they
release chemicals that smell foul, taste musty and can be detected
in tap water.
"We
know Cleveland is the poster child of what goes wrong when you
don't pay attention to the lakes and rivers," Mayor Jane
Campbell told Great Lakes commissioners at their annual meeting
this week, as she called for help with a billion-dollar sewer
improvement project.
"Now
we're trying to turn it around to be the poster child for the
solution."
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