Seeing the photos from the record-breaking algal bloom on Lake Erie in 2011 was like déjà vu for me. I grew up in the Great Lakes region in the 1960s and 1970s and remember the days when Lake Erie was declared “dead.”
I later learned that the green scum that plagued the lake during summer months was a sign that the lake was actually overly alive. It gained its morbid reputation because when blooms of the tiny plant-like organisms die-off, the decomposition process consumes oxygen. In extreme cases, it creates an unpleasant, smelly mess and literally sucks the oxygen from the water.
With anoxic conditions like these, walleye pike and yellow perch alike turn belly-up and die or gasp for breath at the surface, unable to syphon oxygen from the water that flows through their gills.
This is what the surface of Lake Erie looked like west of the Erie Islands in 2004. Photo by Lisa Borre.
Algae gets a bad rap sometimes, a reputation not always deserved. Many varieties of algae are beneficial to lakes, providing the basis of the food chain that supports the entire ecosystem. Other types, like cyanobacteria, produce toxins that are harmful to humans and can even cause death to animals that consume it. Large blooms, even non-toxic ones, affect ecosystem health.
Too much phosphorus, an essential element for plant growth, is the usual culprit in triggering algal blooms in lakes. It washes into lakes from agricultural runoff, sewage treatment plants, lawn fertilizer, water treatment plants, and septic systems. At the right water temperature, the more phosphorus there is in the water, the more algal growth you get.
Lake Erie suffered from toxic algae blooms in the 1970s, but with a major effort to reduce phosphorus loading, the blooms disappeared for nearly two decades. By the mid 1990s, conditions began to deteriorate again. When I sailed across the lake in late summer 2004, an algae bloom stretched from the Erie Islands to the western shore.
Agricultural and Meteorological Trends Cause Massive 2011 Bloom
A recent forensic-like study of the 2011 bloom, published in the Proceedings of the National Academy of Sciences, gives new insight about possible causes of these extreme events.
The National Science Foundation awarded a five-year grant to a team of researchers to study the effects of climate-change induced extreme events on water quality and ecology in the Great Lakes system. “It was a coincidence that the project began in January 2011, and this perfect case study popped up out of nowhere,” a researcher at the Carnegie Institution for Science and principal investigator for the study, Anna M. Michalak explained to me.
Using a holistic approach, the team brought together high-tech tools and sophisticated statistical analysis to assess whether the record-setting algal bloom in Lake Erie was driven by an unfortunate combination of circumstances or is a sign of things to come. They concluded that trends in agricultural practices, increased intensity of precipitation, weak lake circulation, and quiescent conditions conspired to yield the massive bloom.
The main cause of the massive bloom was the confluence of long-term trends in nutrient management practices on farms and a changing climate, including more frequent extreme precipitation events. They study says these “are consistent with expected future conditions.” This means that unless something is done to reduce the input of nutrients from agriculture and other obvious sources or to stop changes in climate already underway, nuisance algal blooms are likely to become more common in the future.
Satellite photo of the Great Lakes showing the 2011 toxic algae bloom (light green) reaching into the central basin of Lake Erie. Source: NASA.
Michalak recommends that future management plans be guided by science like hers and her colleagues’ to mitigate impacts, but she doesn’t want her team’s findings to be misunderstood as placing the blame on farmers. “Farmers and land managers deserve due credit for implementing a variety of recommended conservation practices,” she told me, “and these have gone a long way to limiting soil erosion and reducing carbon loss.”
In 2011, severe spring rain events made it difficult for farmers to apply fertilizers without having the nutrients washed away immediately. Fertilizers are expensive. “It’s no more in a farmer’s interest to have fertilizers end up in the lake than it is for the environment,” said Michalak. She cited improved forecasting of spring storms to better guide the timing of fertilizer applications as one example where science and management could come together to address the problem.
As certain agricultural practices have increased in the region over the past ten years, so has the loading of “dissolved reactive phosphorus” (DRP), a form of “bioavailable” phosphorus that is readily available for uptake by plants, including nuisance algae. Although the total inputs of phosphorus have decreased since the 1970s, the loading of DRP from nonpoint sources has increased in recent years. Michalak says that reducing these loads will be key to restoring the lake again.