The Press Newspaper
Researchers at Bowling Green State University are preparing for the next phase of a study that could help answer more questions about the so-called dead zone in Lake Erie.
Michael McKay, Ph.D, and George Bullerjahn, Ph.D., observed an algae, Aulascosiera islandica, in pockets floating under Lake Erie ice in February, 2007 and determined the plankton sometimes made up as much as 80-90 percent of the biomass in samples they collected.
Their next step is to try to determine whether the diatoms – a single-celled algae with a hard shell – get eaten by zooplankton and other organisms rather than die and sink to the bottom of the lake.
“If it turns out that most of these diatoms end up on the lake floor, they would provide a large source of organic carbon for bacteria to decompose, which would consume oxygen,” Dr. McKay said. “If this decomposition happens mainly when the water warms up and stratifies – forming a warm upper layer and a cold lower layer in the summer months – and not during the frigid winter months, it has to be contributing to the dead zone.”
The two are conducting their research through the Ohio Sea Grant program and plan to use Sea Grant funding to collect data for the next two winters.
Environment Canada will also use its icebreaker to deploy sediment traps that will sit on the bottom of the lake during the coldest months of the year in an effort to determine if the diatoms are sinking to the lake bottom.
Preliminary data should be available by next summer.
The study concludes there is a connection between the two phenomena and that the sediment plume, in fact, creates a perfect incubator for the blue-green algae.
Bridgeman and graduate student Justin Chaffin collected Microcystis samples during a large bloom that took place in August and September, 2008. Through testing, they verified that muddiness in the water acts as a protective shield for the cyanobacteria, particularly when the water is mixed by breezes blowing across the lake,
Because Microcystis has the ability to regulate its buoyancy, more than 90 percent of the cyanobacteria can be found at the surface on calm days, further shading other varieties of algae. However, bright sunlight will actually damage the blue-green algae, regardless of the amount of mud in the water.
“On calm, sunny days, Microcystis floating on the surface became damaged quickly, showing loss of up to 50 percent of photosynthetic capacity in samples collected between 10 a.m. and 2 p.m.,” Chaffin said. “Even after 2 to 5 hours of recovery time in the dark, traveling to the lab for testing, much of this damage was still unrepaired.”
The study also determined that the Microcystis had plenty of nitrogen but were still phosphorus deprived; indicating that phosphorus levels determine how much the blue-green algae will grow.
The researchers said the result underscores the importance of determining the source of the phosphorus that has plagued Lake Erie for decades, in addition to limiting the amount of sediment that gets into the river by implementing erosion controlling management practices.
The Ohio State University’s Ohio Sea Grant College Program is a part of the National Oceanic and Atmospheric Adminstration Sea Grant, a network of 30 programs.