In 2014, an algal bloom in Lake Erie caused authorities to turn off tap water
As the climate changes, dead zones in lakes and oceans could increase in size, while toxic algal blooms and "red tides" could become commonplace, according to a new study. The paper, published Thursday in the journal Science, suggests increased rainfall will cause more nitrogen from fertilized fields to enter waterways around the world.
What they found: All told, the total nitrogen runoff is expected to increase by 19% for the continental US, and other regions around the world are vulnerable as well.The impacts of this increase are predicted to be especially strong in the Northeast and Midwest U.S., India, China, and Southeast Asia.
Why it matters: "When we think about water sustainability, it's not just enough to think about the quantity of water. It's also the quality of water," Anna Michalak, an earth scientist at the Carnegie Institution for Science, in Stanford, California, and an author on the study, tells Axios. Nitrogen runoff can destroy lakes and cause toxic algal blooms that close beaches, kill animals and shut down fisheries, causing massive economic damage.
What they did: Past studies have shown that the size of dead zones in areas with high fertilizer application is best explained by rainfall. To see how climate change might impact runoff, the scientists used 21 of the same climate models used by the IPCC in their climate change reports to predict where rainfall would go up or down. They gave each model one vote, and overlaid the averages with known data about fertilization.
Sound smart: Eutrophication is when an excess of nutrients in water causes plant overgrowth. Those plants die, and the decomposition uses up all the oxygen in the water, essentially suffocating it. It's caused massive dead zones in bays and lakes around the world.
There's hope: To offset the 19% increase in nitrogen runoff, there would need to be a ⅓ reduction in total ground-based fertilizer application. But there are ways to change farming practices that might help mitigate some of the impacts ("Farmers want their fertilizer on the fields, not in the rivers," says Michalak) and researchers are cautiously optimistic: simple things like using compost and rescuing nitrogen from sewage can have a big impact, and genetic engineering is helping to create nitrogen-fixing crops.
The bottom line: The impacts of climate change, especially when considered on a hundred-year scale, can be hard to fathom. But the effects of nitrogen runoff are very tangible. Says Michalak: Large algal blooms like the ones currently happening in Lake Erie "aren't caused by a perfect storm. They're a harbinger of what we might see in the future."