Zebra Mussels Get Second Billing To Quagga In Lake Erie
August 6, 2002 at 4:24 PM EST - Updated July 12 at 4:00 AM
CLEVELAND (AP) - A cousin to the better-known zebra mussel may be the main reason oxygen levels are dropping in Lake Erie.
Researchers said the quagga -- thumbnail-size clams -- and zebra mussels are causing high phosphorus levels that are creating a low-oxygen "dead zone" in the center of the lake. Both mussels release phosphorus as a waste, but the quagga releases more.
Just nine years ago, the zebra mussel outnumbered the quagga 100 to 1.
Scientists studying the lake have found that the quagga, which arrived in Lake Erie about a decade ago, outnumbered the zebra mussel 10 to 1 in samples taken last week off South Bass Island near Sandusky.
"This astounded us," said David A. Culver, a professor at Ohio State University who is part of a research team trying to figure out why low oxygen levels in Lake Erie's central basin have returned.
Culver spoke Monday at a hearing held by U.S. Sen. George Voinovich to investigate Lake Erie's low-oxygen "dead zone."
Scientists said the lake remains healthy, but they are seeing high levels of phosphorus.
"We thought we had it all figured out," Culver said. "But to have phosphorus and algae increase, that makes us concerned we'll lose all the progress we have made."
During the 1970s and 1980s, state and local governments spent billions of dollars to improve sewage treatment plants and reduce phosphorus releases in the Great Lakes.
Culver said the quagga, a cousin to the zebra mussel, may be a leading culprit for the dead zone, a term scientists have used to describe an area between Erie, Pa., and Lorain.
Phosphorus in fresh water serves a nutrient for the growth of algae. Decomposition of algae or any other organic material, such as matter released from sewage-treatment plants, sucks oxygen from the water.
If oxygen is used up, fish will not go there or will die.
"If the central basin were deeper, there wouldn't be a problem," said Jeffrey M. Reutter, director of the Ohio Sea Grant College Program.
Scientists do not know why the quagga has replaced the zebra mussel. However, the quagga survives at deeper depths and spawns in colder weather.
This summer, a team of 27 researchers from 18 institutions is studying the dead zone for the U.S. Environmental Protection Agency.
Federal funding, which helped sewage-treatment plants make improvements, will not be easy to come by, Voinovich said.
"From the testimony submitted for today's hearing, I am very concerned we may be on the edge of sliding behind rather than moving ahead," he said.
(Copyright 2002 by The Associated Press. All Rights Reserved.)