There’s something lurking in Lake Erie, and it’s killing off life across vast portions of its waters. Algae, in massive blooms, has over the years created “dead zones” in the Great Lake, the 11th largest lake in the world. And it’s a monster of our own creation.
Lake Erie, surrounded by farmland and industry in Ontario, New York, Pennsylvania, Ohio and Michigan, is just one of the lakes in North America affected by algae blooms, albeit the most profoundly. The problem, which is spreading across the globe, is the product of nutrient-rich runoff from intensifying agricultural practices — the application of fertilizers in particular.
“The problem is sometimes the way we operate on the landscape can actually drive an imbalance in that wonderful tight little cycle that is life,” says Dr. Kevin McCann, a professor at the University of Guelph, who studies the structure and function of food webs, with a focus on aquatics systems. “In aquatic systems, this has actually happened a lot, unfortunately, because of the production of food.”
Here’s how algae blooms happen
Phosphorous and nitrogen, the major nutrients in fertilizers, are used to make crops grow. The nutrients that aren’t absorbed by the crops are carried into drainage ditches during rainfall, and eventually into streams, rivers and lakes. This fuels overproduction of benthic algae. These “blooms” grow so fast that algae-consuming creatures can’t devour them fast enough. The algae then dies, drops from the water column and falls to the bottom amongst the sediment. That’s when bacteria takes hold of it and consumes all the oxygen. No oxygen means no life, and that means dead zones — pockets of water with extremely low concentrations of oxygen.
“The super imbalances that we’re seeing, like massive dead zones, are absolutely human-driven.”
“We’re not doing [agriculture] very naturally if you think about it,” says McCann. “If you did it naturally you would do things where you didn’t actually impact the natural nutrient dynamics on the landscape. The super imbalances that we’re seeing, like massive dead zones, are absolutely human-driven.”
Rinse, repeat, recycle
Then there’s the problem of internal loading. Humans have a history of putting phosphorus into lakes from farming and other activities. It settles into the mud at the bottom. Oxygen keeps the mud-bound phosphorous at bay. However, when oxygen concentrations in the water are depleted, the phosphorous is released into the water. That causes more algae blooms to grow, then die, sink to the bottom, further deplete oxygen levels and rinse, repeat, recycle.
“There’s this horrible positive feedback loop that happens with more phosphorous, more algae, more dead zones and so on, and that’s actually difficult to quantify,” says Dr. Neil Rooney, who researches ecosystem science and biodiversity at the University of Guelph.
When you factor in invasive species introduced by ballast water, like zebra mussels, which clear the water column and let light penetrate deeper, and add the effects of climate change, Lake Erie is in big trouble. Indeed, its dead zones grow bigger year by year, and are having a significant impact not only on the commercial harvesting of fish, but on the entire food chain.
“[Dead zones often occur] where we commercially harvest things we eat,” says McCann. “Basically, the production of one food enters into a system and can actually kill the production of other food we use — fish, crabs, things like that. There are whole sets of food chains that emerge from that lower reach of the water. There’s a ton of fish production down there that’s literally killed.”
Governments are beginning to take note. The Ontario Ministry of Agriculture, Food and Rural Affairs has programs to educate farmers about best management practices with respect to fertilization use. Fertilizer Canada works with stakeholders to promote efficient and responsible nutrient use. And the University of Guelph is continuing its research work on sustainable agricultural systems.