Lake Erie is starting to resemble a giant bathtub.
Last week, the western basin of the Great Lake recorded a surface temperature of 29 degrees Celsius—a staggering number considering Ontario’s cool spring. The average temperature across the lake has reached 26 degrees Celsius, rivalling July 2013, the warmest year recorded for Lake Erie’s surface temperature.
“In mid-June, we were running about two degrees Celsius below the 30-year average,” says Mike McKay, the director of the Great Lakes Institute for Environmental Research at the University of Windsor. “Within a month, mid-July, we’re a good two and a half to three degrees Celsius above the 30-year average.”
It’s difficult to parse out how much the heightened temperature is due to long-term climate change versus the current heatwave Southern Ontario is experiencing, but McKay says that Great Lake water temperatures have been trending warmer over the last several years.
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Erie, in particular, tends to have larger temperature swings because it’s the shallowest of the Great Lakes, allowing its water to warm and cool quickly.
This prolonged heat, however, could be having serious effects on the lake’s ecosystem. Last week, McKay received a notification from the National Oceanic and Atmospheric Association (NOAA), a U.S. federal agency that monitors the Great Lakes, stating that it had identified a hypoxia event in Lake Erie.
A hypoxia event is when there’s low oxygen concentration in the water. The surface layer of water absorbs oxygen from the atmosphere, but due to its warm temperature, it doesn’t descend and mix with deeper waters. This means the deeper water doesn’t have as much oxygen.
The lack of oxygen can kill species important to the food chain, such as invertebrates that can’t escape the hypoxic water. McKay says he’s heard from a Toledo, Ohio-based research group that they’ve already seen several dead amphipods floating in the water.
During summer months, a hypoxia event is common in Lake Erie’s central basin where the water is deep, but it doesn’t often happen in the western basin where waters are shallower.
“We got this large expanse of hypoxia throughout the western basin Wednesday, Thursday, and it’s persisting,” says McKay. “That’s where we start worrying about some ecosystem-wide consequences.”
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The hypoxic water could also impact municipalities that get their drinking water from Lake Erie. McKay says hypoxic water isn’t necessarily dangerous to humans, but because it has elevated levels of iron and manganese it could look yellow coming out of the tap. “You might have a lot of concerned consumers,” he says.
Another consequence is that hypoxic water can mobilize phosphorus buried in sediment. Phosphorus is one of the main causes of blue-green algae, a toxic bacterium that cause skin irritations and mild respiratory issues in humans.
Phosphorus tends to get into the lake through fertilizers and agricultural run-off, some of it settling on the lakebed. A lot of the phosphorous comes from the Maumee River in Northwestern Ohio, which drains into Lake Erie. Usually, precipitation sweeps the phosphorus into the lake, but since Southern Ontario had a dry spring, the NOAA predicted that Lake Erie’s algae bloom would be mild this summer, only a three out of 10.
But McKay points out that this prediction didn’t account for a hypoxia event, which can fuel algal blooms. They’re already forming in the western basin around Sandusky Bay in Ohio.
“Usually, these blooms will start in July and then persist until September, October,” he says. “They require a combination of warmer waters, which we’re getting, and available nutrients to continue to promote their growth. So, I expect that will speed up with the warm waters we’re seeing and maybe with this additional phosphorus making its way into surface waters.”
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