Lake Erie Grows More Susceptible to Harmful Algae, May Need Stricter Control MeasuresBy By Nora Macaluso
October 15, 2014
Oct. 15 — Cyanobacteria in Lake Erie have become increasingly sensitive to phosphorus in recent years, making the lake more susceptible to large, harmful algae blooms, according to a study from the University of Michigan and the National Oceanic and Atmospheric Administration.
The findings call into question the adequacy of current phosphorus-reduction targets.
“Our results suggest that current phosphorus loading targets will be insufficient for reducing the intensity of cyanobacteria blooms to desired levels, so long as the lake remains in a heightened state of bloom susceptibility,” lead author Daniel Obenour, research fellow at the University of Michigan Water Center, said in an Oct. 15 statement announcing the report, which was published Oct. 8 in the journal “Water Resources Research.”
Teams from the Great Lakes Commission, the Ohio Lake Erie Task Force and the International Joint Commission are looking at ways to reduce the amount of phosphorus entering the lake by 40 percent of its five-year average, following an incident this summer that led to a ban on drinking the water in Toledo, Ohio, because of contamination from the algae (2014 WLPM, 10/9/14).
The researchers said greater reductions may be needed because of the “increased sensitivity of the Lake Erie system.”
The IJC’s recommendation of a 37 percent cut in total phosphorus for Ohio’s Maumee River in spring, while an “ambitious” target, “will likely be insufficient,” the researchers said.
‘Significant’ Phosphorus Reductions Needed
“Predicting the size of algal blooms in Lake Erie is complicated science, but it is clear that significant reductions in phosphorus inputs are necessary to restore Lake Erie to health,” the IJC said in a statement e-mailed to Bloomberg BNA Oct. 15.
The commission said phosphorus loadings are one major cause of harmful algal blooms that can be controlled by humans.
“The IJC recommendations will help do that,” the commission said. “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.”
Don Scavia, director of the University of Michigan Graham Environmental Sustainability Institute, said that the problem will probably continue as long as the lake is in a heightened state of susceptibility.
Computer Modeling Studies Analyzed
The report analyzes computer modeling studies that use the amount of phosphorus entering Lake Erie in the spring to predict the size of late-summer cyanobacteria blooms, which have been increasing in recent years.
The total amount of phosphorus entering the lake “doesn’t fully explain” the increases in blooms during the period 2002 to 2013, the researchers said. Neither does the amount of dissolved reactive phosphorus, which is more readily absorbed by algae, or water temperatures in Lake Erie, which haven’t increased significantly, they said.
The spread of invasive zebra and quagga mussels, which don’t eat toxin-producing Microcystis cyanobacteria, could be a factor, the report said.
Recent U.S. Geological Survey studies in western Lake Erie suggest a decrease in zebra mussel numbers but an increase in quagga mussels and total mussel abundance over the last decade. Other possible explanations are increasingly calm summer weather conditions and a growing reservoir of Microcystis seed colonies at the bottom of Lake Erie, the researchers said.
The paper, “Using a Bayesian Hierarchical Model to Improve Lake Erie Cyanobacteria Bloom Forecasts,” was co-authored by Craig Stow and Andrew Gronewold of NOAA’s Great Lakes Environmental Research Laboratory in Ann Arbor, Mich. The project was funded by the Great Lakes Restoration Initiative, the U-M Water Center, the Cooperative Institute for Limnology and Ecosystems Research and NOAA and is part of a partnership between the university and NOAA’s National Ocean Service.
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