Changing agricultural practices and weather conditions are cited in a study as the likely causes of what is considered the largest harmful algae bloom in Lake Erie’s recorded history.
And the study by researchers at the University of Michigan and eight other institutions describes the 2011 algae bloom as a harbinger of things to come rather than an isolated occurrence.
“Intense spring rainstorms were a major contributing factors, 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.”
The researchers found that intense spring rainstorms and the resulting runoffs from farm fields resulted in record-breaking levels of phosphorus, a nutrient in agricultural fertilizer that contributes to algae growth, washing into western Lake Erie.
The study says those conditions set the stage for an algae bloom that covered about 2,000 square miles at its peak in early October 2011 – about three times larger than other blooms to occur in the lake, including those that occurred in the 1960s and 1970s.
“This event was caused by a complex combination of factors, and I think this paper really puts all the pieces together in a very clear and systematic way,” said Allison Steiner, atmospheric scientist at U-M. “We tried to think about this problem in a much more cross-disciplinary way than I think other people have thought about it before.”
The paper was published online last week in the journal, Proceedings, of the National Academy of Sciences.
That spring was particularly heavy in precipitation: 2 inches of rain fell over Ohio’s Maumee River Basin on May 26 and almost 7 inches fell during the month – more than 20 percent above the average.
The Maumee River is a primary tributary to western Lake Erie, draining an agricultural watershed of fields of corn, soybeans, and wheat.
In the study, researchers used 12 computerized climate models to determine if rainstorms such as those in May 2011 are more likely to occur in the future. The modeling incorporated anticipated effects of climate change due to the build-up of greenhouse gases that trap heat and projected the frequency of spring rainstorms that drop more than 1.2 inches would likely double in the region over the next 80 years.
When the 2011 bloom formed, higher than normal water temperatures and calm winds created ideal conditions to promote summer algae growth, the study says.
A bloom is the rapid accumulation of algae in a water body that can damage other organisms by producing toxins. The 2011 bloom was almost completely composed of toxic blue-green Microcystis algae, the study says, noting concentrations of mycrocystin, a liver toxin produced by the algae reached about 224 times World Health Organization guidelines.
As for agricultural practices, the study focuses on no-till planting – the planting of crops without plowing by inserting seeds into small holes through the stubble of a previous crop. While no-till reduces erosion, it leaves high levels of phosphorus-bearing fertilizer in the upper soil, making it more likely to be washed away by rain. Other trends are creating conditions for more run-off, the study says, including fertilizer being applied in the fall and surface broadcast application of fertilizer.
The study contends if there isn’t a significant shift away from those practices, run-off from agricultural land in the Maumee River watershed and other watersheds in the western basin will likely continue to provide the nutrients needed to produce large blooms in the lake.
Michael Moore, professor of environmental economics at U-M’s School of Natural Resources and Environment and a co-author of the study paper, said the emphasis on planting corn for ethanol production is also exacerbating the problem along with a decline in acreage reserved for conservation purposes.
“Corn is the crop on which phosphate-based fertilizer is most heavily applied,” he said.
Sandy Bihn, executive director of Lake Erie Waterkeeper, Inc., said studies of the 2011 algae bloom should also consider problems at the City of Detroit’s wastewater treatment plant.
“It continues to concern me that the assessments of the Lake Erie 2011 algae bloom fail to include the malfunctions at the Detroit wastewater plant that dumped over 20,000 tons of solids from the plant, and in addition a record 45 billion gallons of combined sewer overflows, of which an estimated 2 billion gallons was raw sewage,” she said. “The Thames River phosphorous algae inputs into Lake Erie. The Detroit River literally has three streams that flow to Lake Erie with the Detroit inputs hugging the Monroe shoreline and the Windsor/Thames inputs hugging the Ontario shoreline. There is also no discussion of what are known as internal loads - the sediments already in the bottom of Lake Erie that accumulated over the years. Some of us think the heavy rains in 2011 pushed the existing sediments east and combined with the 2012 drought resulted in very blue water in 2012.”
Steve Davis, a Natural Resources Conservation Service watershed specialist, questions whether no-till planting is contributing to the problem as much as the study implies.
“We know that agricultural run-off is a huge contributing factor,” he said. “The question in the scientific community is what percent each of the different management practices on the farms contribute.”
Fertilizer can be applied to no-till fields by methods other than broadcast, he said, and a large percentage of soybean fields don’t receive fertilizer.
“They put the fertilizer on for the corn and the soybeans in one application,” Davis said.
He concluded a five-year study in 2011 of the watershed and found that the percentage of fields continually planted with no-till is still small.
Pete Richards, senior research scientist at the National Center for Water Quality Research at Heidelberg University who participated in the study, said no-till’s effect is hard to measure.
“I think the role of no-till is mostly indirect, in that it tends to be accompanied by broadcast application of fertilizer onto the surface without incorporation, which leaves the fertilizer vulnerable to wash-off in successive rainfall events,” he said. “We currently don't have readily available equipment to get the fertilizer into the ground in a no till system. If we could get that fertilizer into the soil we'd be a lot better off.
“We also typically don't do true no-till, because tillage is usually used before corn. No-till proponents argue that the advantages of no till in terms of increased infiltration, reduced nutrient losses, and improved soil health are not achieved under this `rotational no- till’ system. This is obviously a pretty complicated business, and I'm not sure enough words could be devoted to it in our article to convey the message clearly. There is definitely not a unanimous opinion about the benefits or disadvantages of no till.”