float new theory on algae
U.S. Study. Plant-eating organisms might explain density
Researchers in the United States are investigating alternate
theories that could explain why blue-green algae blooms
have been growing in Lake Champlain and Missisquoi Bay.
The consensus in Canada and the U.S. is that high levels
of the toxic algae are caused by phosphorus seeping into
the lake from neighbouring farms and communities.
But a professor at the University of Vermont says there's
more to it than that.
"The phosphorus concentrations have not increased,
although the blooms have, so that tells me there's something
else," said Mary Whatzin, who is heading a study
on blue-green algae.
She said a reduction in "grazers" - organisms
that eat the algae - may be why the plant's density has
increased in Lake Champlain, which separates Vermont and
New York and whose northern tip is in Quebec.
That tip - Missisquoi Bay - has seen high levels of cyanobacteria,
or blue-green algae, in recent years, a result of shallow
depth, phosphorus deposits and southern winds that push
floating algae cells north of the border.
All the bay's beaches were closed after the Montérégie
public health department issued warnings to avoid all
contact with its water because of high levels of the toxic
If ingested, the algae can be harmful to humans.
No health advisories have been issued for the U.S. part
of Lake Champlain, but water is tested every week, Whatzin
Last year, Vermont and Quebec signed an agreement for
the gradual reduction of phosphorus seeping into the lake
It was determined that 60 per cent of phosphorus deposits
comes from the U.S. and 40 per cent from Canada.
But Gregory Boyer, a biochemist at the State University
of New York in Syracuse, said the accumulation of phosphorus
in the lake over decades makes the amount that is currently
being deposited almost irrelevant.
"I don't think phosphorus is the only issue,"
Phosphorus deposits have been drastically reduced in
Lake Erie, yet that body of water is still experiencing
problems with algae density, he said.
Boyer cited three popular theories to explain the conditions:
a loss of predators that eat the algae, predators that
eat anything but the blue-green algae, or predators that
produce nutrients that feed the plant.
In Lake Champlain, scientists have been looking at zebra
mussels, an exotic shellfish that was introduced to the
body of water in the early 1990s, as one of the organisms
that has affected the balance in the ecosystem.