Study says snow flushes pollution to Lake Erie 'dead zone'

[GLF]

Snow melting in yards and in the fields of northern Ohio's farms is a leading culprit in creating the low-oxygen "dead zone" in the central basin of Lake Erie, researchers have found.

Four of the 10 snowiest winters to hit the region have occurred since 2000. While summer storms also wash fertilizer into the lake, it's those big winter snowmelts that deal the heavier blow.

"We always knew weather was important but were not able to document it," said Gerald Matisoff of Case Western Reserve University, who headed a U.S. team of Lake Erie researchers. "Now we're seeing a connection."

Scientists are finding that oxygen levels in the lake rise and fall depending on how much phosphorus entered the lake the previous year, Matisoff said. How much phosphorus enters the lake depends on the weather.

The findings by the international team of researchers will be presented at a Great Lakes conference that starts today in Windsor, Ontario.

Storms flush phosphorus into drainpipes, creeks, then rivers and finally into Lake Erie. Once there, phosphorus causes extreme growth, especially in algae.

As algae and other organic matter decompose in the water, they suck oxygen from the water, which creates an area devoid of fish, worms and clams on the bottom of the lake between spring and fall.

This in turn hurts commercial and recreational fishing.

The loss of oxygen shows up first in the central basin, an area between Huron and Erie, Pa., because of its characteristics.

The central basin is not as deep as the eastern end of Lake Erie, which has a thick layer of oxygen on the bottom.

It is not as shallow as the western basin, which receives oxygen from natural wind mixing.

Scientists have seen phosphorus concentrations in the lake at the highest levels since the early 1970s.

Adding to the problem are zebra mussels, which first appeared in the late 1980s, and their more dominant cousin, the quagga mussel.

They are thumbnail-size shellfish from foreign waters that are altering Lake Erie's food web and bolstering the dead zone.

Normally, phosphorus in the lake would bind to a solid, sink to the bottom and be buried under the mud, said Dave Culver, a professor of biological sciences at Ohio State University and part of the research team.

But the mussels eat the algae and secrete nitrogen in the form of ammonia and phosphorus in the form of phosphate. That keeps the phosphorus re-circulating.

It's also bad news because the mussels are a source of ammonia and phosphates that Lake Erie did not have before, Culver said.

"We're a lot better off than we were 30 years ago," he said. "But it appears to be getting worse. A lot of convenient things [that] we can fix have been fixed. That's why I'm concerned."

During the 1970s and 1980s, state and local governments spent billions of dollars to improve sewage treatment plants, which were the No. 1 source of phosphorus in the Great Lakes. Phosphates were removed from detergents.

By the mid-1980s, Lake Erie phosphorus had been cut to 12,100 tons yearly, which was believed to be an acceptable level.

Then the zebra mussel arrived. Since then, phosphorus levels have gone up.

Zebra and quagga mussels have disrupted the food web as well.

Tiny phytoplankton, the start of the food chain that once hung in the water column, are being removed by the mussels. That allows sunlight to penetrate deeper, stimulating growth near the bottom.

More of the aquatic life in Lake Erie has moved to the lake bottom, where the mussels are, research has proven.

"Clear water where you can see real deep does not necessarily mean things are better," Matisoff said.

Researchers estimate that two-thirds or more of the phosphorus entering Lake Erie comes from runoff during storms.

"We will need to focus some of our land management issues toward trying to keep the soil on the land and the nutrients on the land," Matisoff said.

The team of 27 government and academic researchers has written more than 20 papers on their work, which started in 2003.

They will be published in the Journal of Great Lakes Research in June, he said.