A fish suffocated in the Lake Erie algae bloom in August 2011, near Pelee Island, Ontario. (Photo Credit: Tom Archer)
Harmful algal blooms getting worse
Tuesday, April 02, 2013, 23:00 (GMT + 9)
The largest harmful algae bloom in Lake Erie's recorded history was likely caused by the confluence of changing farming practices and weather conditions that are expected to become more common in the future due to climate change.
Rather than an isolated, one-time occurrence, Lake Erie's monumental 2011 algae bloom was more likely a harbinger of things to come, according to University of Michigan researchers and colleagues from eight other institutions.
The interdisciplinary team explored factors that may have contributed to the event and analyzed the likelihood of future massive blooms in the lake.
"Intense spring rainstorms were a major contributing factor, and such storms are part of a long-term trend for this region that is projected to get worse in the future due to climate change," said aquatic ecologist Donald Scavia, director of U-M's Graham Sustainability Institute. "On top of that we have agricultural practices that provide the key nutrients that fuel large-scale blooms."
|Cup of fouled water, scooped from Lake Erie during the algae bloom and, map of the Lake Erie algae bloom in September 2011, covering the lake's entire western basin (Photo Credit: Tom Bridgeman/Michigan Sea Grant)
A paper summarizing the team's findings was published in the journal Proceedings of the National Academy of Sciences.
The researchers found that a series of intense spring rainstorms and runoff events resulted in record-breaking levels of phosphorus, a nutrient in crop fertilizers that also fuels rampant algae growth, washing into western Lake Erie.
That set the stage for an algae bloom that covered about 2,000 sqmi by the time it peaked in early October 2011. That's more than three times larger than any previously observed Lake Erie algae bloom, including blooms that occurred in the 1960s and 1970s, when the lake was famously declared dead.
The 2011 spring storms included one that dumped 2 in of rain over Ohio's Maumee River basin in 24 hours on 26 May and 6.8 in total for the month of May 2011—more than 20 per cent above the long-term monthly average. The Maumee is a primary tributary to western Lake Erie, and it drains an agricultural watershed where corn, soybeans and wheat are grown.
In their study, the researchers used 12 computerized climate models to determine if rainstorms like the May 2011 events are more likely to occur in the future. The models, which incorporate the anticipated effects of human-caused climate change due to the buildup of heat-trapping greenhouse gases, showed that the frequency of spring rainstorms that drop more than 1.2 in is likely to double in this region by the end of the century.
"The models do predict an increase in extreme springtime precipitation events, and that's driven by an increase in greenhouse gases," said Steiner, an associate professor in the Department of Atmospheric, Oceanic and Space Sciences.
Once the 2011 Lake Erie bloom formed, unusually warm water temperatures and calm winds created ideal conditions to promote summer algae growth.
"All of these factors are consistent with expected future conditions," the 29 authors of the PNAS paper wrote.