Saginaw Bay 'dead zone' may explain muck problems

Jeff Kart By Jeff Kart The Bay City Times
Follow on Twitter
on July 23, 2009 at 8:20 AM, updated July 23, 2009 at 11:46 AM

Lake Huron's Saginaw Bay may have something bad in common with Lake Erie --- a dead zone, or area with little or no oxygen for fish and other aquatic creatures.

Terry Birdsley of Chesaning holds a walleye that he caught in Saginaw Bay Wednesday morning. A dead zone in the bay could have an impact on the fishery.

Researchers with the National Oceanic and Atmospheric Administration, in the second year of a five-year study on Saginaw Bay stressors, are speculating that problems with intensive algal growth and shoreline muck may be related to a dead zone in a deep spot of the bay.

"Saginaw Bay's not all that deep, for the most part, but there may be pockets where we're accumulating dead algae or pseudofeces from the mussels," said Craig Stow, a NOAA scientist based in Ann Arbor.

Pseudofeces refer to material that zebra or quagga mussels expel without digesting.

A dead zone would have implications for how nutrients recycle in the bay, making phosphorus inputs from wastewater overflows and other sources more readily available for algae growth, Stow explained.

"At very low oxygen conditions, phosphorus tends to dissolve more readily in water," he said.

This can cause phosphorus trapped in sediment to be recycled back into the water.

"What's generally referred to as a dead zone is usually the area on the bottom, of very low oxygen levels, that tends to occur because the water doesn't always mix completely from the surface to the bottom" due to temperature differences, Stow explained.

A map of surface water temperatures in Saginaw Bay, which may help researchers find a dead zone, or low oxygen area, that's spurring algal growth.

According to a U.S. Environmental Protection Agency Web site on the Lake Erie dead zone, "Aquatic creatures need oxygen in the water to live.

"Sometimes, however, conditions exist in which the dissolved oxygen in the water is used up by organisms faster than it can be replaced from the air. If all the oxygen gets used up, the organisms will suffocate.

"The configuration of the Central Basin of Lake Erie is partly responsible for the problem, but too many nutrients (especially phosphorus) from human activities is also a major factor."

NOAA researchers have been working in the Saginaw Bay and along the shoreline for the last month, said Scott Peacor, associate professor with the Michigan State University Department of Fisheries and Wildlife.

The researchers are trying to determine exactly where benthic, or bottom-dwelling, algae that washes up on beaches is growing, and what type of algae is most prevalent in the bay.

"They're out on boats and scuba diving," Peacor said.

He was working in foot-deep muck in shallow water at the Bay City State Recreation Area on Tuesday.

"As far as muck goes, in most places in the Great Lakes is cladophora," Peacor said.

"We have cladophora in Saginaw Bay, but there's also a second type of algae called spirogyra. We're actually not sure if they're both contributing to the muck or if it's mostly spirogyra."

Spirogyra has different nutrient and light needs to grow, but not much is known about the aquatic plant, he said.

Stow said NOAA researchers are discussing ways to dig deeper into the dead zone idea.

The agency recently acquired new equipment that allows for measuring low oxygen conditions.

But those conditions usually occur at the peak of summer, when the weather's the warmest. Dead zones can appear and reappear, as they do in Lake Erie.

"Conditions so far have been pretty cool up here," which is making it hard to plan for pinpointing a dead zone in the bay, Stow said.

Finding a zone will require looking in deeper areas of the bay or those with weak currents where material or organic matter might accumulate, such as a large, visible surface mat of algae.

Stow said he's not sure what impact a dead zone would have on the Saginaw Bay fishery.