Cincinnati -- By now, most people have heard how zebra mussels can clog up water intake pipes. Some might even know that the zebra mussels are endangering commercially important native mussels in the Ohio River. But there will be no mistaking the next potential impact from the tiny invaders.
University of Cincinnati biologist Michael Miller says the mussels could indirectly cause the Ohio River to turn bright green.
Miller has studied the Ohio River and its tributaries since the 1970s. When he began his studies, tiny algae known as diatoms dominated the Ohio River. Today, 90 percent of all algae in the river during summer low-flow conditions are a single type of cyanobacteria (also called blue-green algae) known as Microcystis.
"Whether that dominance has come about due to zebra mussels, it's certainly there in 1996 and '97 in a big way," said Miller comparing the rise of zebra mussels in the Ohio River with the rise of Microcystis.
Miller collaborates with Miriam Steinitiz-Kannan, a biologist at Northern Kentucky University whose students regularly conduct genus-level counts of algae in the Ohio River. The two biologists also work with the Cincinnati Water Works to monitor the impact of Microcystis on drinking water purification.
Miller emphasized that there was no evidence of Microcystis breaking through the water works' filters and purification system, but noted that Microcystis can cause taste and odor problems with drinking water. So, their research is of high interest to utilities using the Ohio River as a drinking water source.
Instead, Miller expects the biggest impact from the Microcystis blooms to be an aesthetic one. Data indicates that zebra mussels don't eat or don't digest Microcystis while filtering just about anything else that comes their way suspended in the water. That helps explain why Microcystis is now dominant in the Ohio River.
Add up the overall filtering power of zebra mussels, and you get the big color change. "The average size zebra mussel in the Ohio River...can clear two a half liters a day," said Miller. "We've calculated that maybe 200 animals per meter squared could filter all the water at low flow in about a kilometer." Two- hundred animals is not a lot when it comes to zebra mussels on hard surfaces. They've been found clustered together with thousands of animals per meter squared.
In the short run, all that filtering clears up a shallow river or lake. The water becomes significantly clearer, but in deep, turbid rivers as sunlight suddenly reaches deeper and deeper into the water, the algae may bloom. Combine the energy from the sunlight with the nutrients contained in the treated sewage flowing through the Ohio River and the minerals released by the mussels themselves, and Miller says you have the conditions for a Microcystis bloom nobody could miss.
"When the light gets to two and a half to three meters, that's sufficient depth to make the entire river go green," said Miller.
It sounds strange, but the phenomenon has already occurred in three areas infested with zebra mussels: Saginaw Bay in Lake Huron, the western basin of Lake Erie and Sandusky Bay in northern Ohio.
Miller presented his data during the Ohio meeting of the
American Waterworks Association in Cincinnati Sept. 24. and will
present additional data to the Ohio River Basin Consortium
meeting Oct. 16 in Portsmouth, Ohio.