The rains come and water the spring shoots of another bounteous Midwestern corn crop in Ohio, Indiana and Michigan. The rains also wash phosphorus off farm fields and into creeks, streams and rivers. The waters flow into the shallowest of the Great Lakes—Lake Erie, which is just 18 meters deep on average and far shallower on its western edge. All that phosphorus doesn’t just help crops grow. When it reaches the lake it fuels the growth of mats of bright green algae, turning the water the color of pea soup. Such Microcystis cyanobacteria bear poisons, at least 80 different varieties of a toxin dubbed microcystin. And when the shallow waters deliver an algal bloom down to the right water intake pipes, an entire city like Toledo is left without water.
“Most water treatment plants are watching for the toxin,” says Don Scavia, environmental engineer, director of the Graham Environmental Sustainability Institute at the University of Michigan and an expert on such harmful algal blooms. “The options when it occurs are to treat it—very expensive—or to shut down.”
Such dangerous blooms are becoming more common, affecting all 50 states, according to the U.S. Environmental Protection Agency. Just last year a township near Toledo had to shut down its water supply due to a similar bloom. And such blooms are not confined to freshwater. Offshore, similar algal blooms create dead zones; microbes consuming dead algae use up all the available oxygen in the water, killing slow-moving and sessile sea life. Such dead zones are on the rise not just on the U.S. seaboards and interior waters but worldwide. The annual ocean dead zone at the mouth of the Mississippi River covered an area roughly the size of Connecticut this year, after reaching Massachusetts-proportions in 2013. Freshwater blooms like the one that shut down Toledo’s drinking water cost the U.S. hundreds of millions of dollars each year, and also occur in countries such as Brazil and China.
Warmer summertime temperatures, more powerful rainstorms and longer growing seasons—all conditions expected to strengthen as climate change continues—will only make conditions even more hospitable for such cyanobacteria, some of the oldest life on Earth. The algae have been blooming earlier and lingering later in recent years. And ecosystem changes in Lake Erie may be contributing to the problem. “The zebra and quagga mussels in Lake Erie might also be important because they do not eat theMicrocystis species, favoring their growth over others,” Scavia notes.
The bloom that shut down water supplies for Toledo is just getting started, though the tap water is now drinkable again. It will persist into the fall, likely peaking in September. And such blooms are not confined to Lake Erie: similar blooms have happened in Green Bay on Lake Michigan and Lake Huron’s Saginaw Bay.