Lake Erie is increasingly plagued by toxic algae blooms each summer, and a new study suggests how climate change and mussels, of all things, may be to blame.
On Thursday, the Columbus Dispatch reported on the new research and computer modeling, which show neither rising water temperatures nor runoff from fertilizers and sewage — the traditional causes cited — fully account for the blooms. According to the paper, published in Water Resources Research, climate change may be providing cyanobacteria — the toxic blue-green algae that’s been invading the lake — a competitive edge over other species of algae.
On top of that, invasive species of mussels which were transported to the Great Lakes in the 1980s by ocean shipping may also be killing off the other beneficial species of algae while avoiding the cyanobacteria, again giving them more room to spread.
“When you have these calmer weather conditions, the cyanobacteria can rise to the surface and create scum layers that shade out other species of algae, which makes cyanobacteria more dominant in the water,” said Daniel Obenour, who was the lead author of the study while still at the University of Michigan Water Center, though now he hails from North Carolina State University.
Climate change also contributes to the rising water temperatures and the phosphorous runoff from agricultural fertilizer and sewage treatment plants. The Earth’s natural cycles plow the vast majority of the additional heat from global warming into the oceans and other major water bodies.
Climate change is also projected to increase the severity of rainfall and flooding in the Great Lakes area over the next few decades. That can overwhelm the infrastructure in many major cities, especially the older ones where stormwater and sewage are handled by the same systems, pushing the nutrients from the sewage into the lakes where the cyanobacteria can feed off it. Runoff from the increased rainfall also carries fertilizer from farms and agricultural areas through the surrounding watersheds, ultimately bringing them to the Great Lakes as well.
“While analyzing all of the factors involved in the algae threat is important, it is imperative to act now on the factors we can influence,” Hugh McDiarmid Jr., a spokesman for the International Joint Commission, a U.S.-Canadian agency, told the Columbus Dispatch. The group has called for a 46 percent reduction in phosphorous and fertilizer runoff in Lake Erie’s western and central basins, and a 37 percent reduction for the Maumee River watershed which flows into the lake near Toledo, Ohio.
In 2013, the Ohio Phosphorus Task Force recommended a 40 percent reduction in the phosphorus washing into the northwestern Ohio watersheds that feed Lake Erie. And an international commission called the Lake Erie Ecosystem Priority recently provided 16 specific ideas — including wetland restoration, pollution filtering, biodiversity support, and other policies — to help with the reductions in phosphorous. So far, however, they remain recommendations only.
Don Scavia, a University of Michigan environmental engineer who contributed to Obenour’s study, said the research shows even those cuts may not be enough on their own. “The caution of this paper is that if there’s a continuing trend and if it gets more sensitive, loads may have to be reduced even more than we’re targeting now,” he said.
This past summer, the algae blooms forced 400,000 people in and around Toledo to avoid their tapwater for two days after toxins from the cyanobacteria were found in the water supply. Lake Erie is also suffering from larger and larger seasonal deadzones, as algae blooms consume all the oxygen in the surrounding water and kill off fish and other marine life.
Other places in the United States where the blooms have been spotted include Lake Okeechobee in Florida, California’s Klamath River, the Cheney Reservoir in Kansas and Sodus Bay in New York. Though how precipitation and temperature changes from climate change, and the presence of invasive species will affect the blooms in each case remains an open question.