Lake Mendota is suffocating. That’s according to a new study published this month in the scientific journal Hydrology and Earth System Sciences.
In a normal summer, lakes such as Mendota can develop “dead zones,” an oxygen-deficient layer deep beneath the surface. According to the study, climate change and the resulting longer summer weather are prolonging the lifespan of dead zones.
In Lake Mendota, that dead zone can linger for up to sixty days each summer.
Robert Ladwig is a postdoctoral researcher at UW-Madison’s Center for Limnology and a co-author on the study. He says that prolonged dead zones can have serious consequences on bottom-dwelling fish — who can find their habitable range narrowed, or in some cases, totally eliminated.
“And in the worst case, you can have these huge dying off events of fish,” he says.
The threat of lingering dead zones isn’t just an issue in Mendota — Ladwig says that the issue can afflict most lakes in temperate climate zones. But, the problem is particularly pronounced in lakes near urban centers and farming operations, where there’s no shortage of fertilizers and other chemical nutrients.
That’s because certain nutrients nurture algal blooms, which help drive dead zones. When blooms die, they sink to the bottom of a lake and suck out the surrounding oxygen as they decompose.
Ladwig says local leaders can help mitigate the dead zone issue by reducing the amount of fertilizer and chemical nutrients that flow into area lakes.
“So we can’t really mitigate climate change locally. The only thing we can do is to reduce nutrients [in Lake Mendota]. So less nutrient means less algal blooms every summer,” he says.
Local leaders are working on reducing algal blooms. Dane County is piloting a new technology to suck algae off lake surfaces, keeping local beaches safe as well. As of last July, that cleaning system was being tested on the shoreline at Mendota County Park, with a goal to expand the technology on beaches across Dane County in the future.