U.S. Water News Online
CLEVELAND -- Researchers think zebra mussels may be causing
a low-oxygen ``dead zone'' in the central basin of Lake Erie.
A team of 17 government and academic scientists was scheduled to
leave Cleveland for a week aboard a federal research vessel to
conduct experiments and gather water and soil samples on the
Researchers are finding that the thumbnail-size zebra mussel clam
and the newly arrived quagga mussel are altering the food chain and
habitat in the lake.
``What we're seeing is a complete change in the ecosystem,'' said
Gerald Matisoff of Case Western Reserve University, the U.S. research
team project leader.
The working cruise continues research started last summer into the
cause of high levels of phosphorus and algae and low levels of
Canadian researchers have been conducting similar studies.
High levels of phosphorus are believed to be behind a dead zone
that occurs in the central basin of Lake Erie between spring and
fall. Colder, more dense water stays at the bottom and cannot be
replenished with oxygen by moving to the surface, creating a harsh
Scientists have focused on three theories on what's causing the
high phosphorus levels: climate, increased phosphorus releases from
farms and sewage treatment plants and internal changes in the lake.
Matisoff said no theory has been ruled out. However, the strongest
evidence points to changes caused by mussels.
They filter particles from the water and release smaller ones that
sink and decompose in deeper water. Their actions and presence have
altered the food chain because they have replaced tiny animal and
plant life that once floated in the water.
By removing that small animal and plant life, the mussels have
also made the water clearer. Light now penetrates deeper, allowing
algae to grow at deeper levels.
Scientists also are finding that the zebra mussel is no longer the
dominant mussel. The quagga, which lives in lower temperatures and
deeper waters, is now dominant.
The research could lead to changes in policy that govern the Great
Lakes but it's too early to say what that could be, said Herb Gray,
Canadian chairman of the International Joint Commission that oversees
water resources shared by the two nations.
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