A new study out Monday seems to confirm an unpleasant reality: Potentially toxic algae blooms in the world’s freshwater lakes have become more intense over the last 30 years. And while climate change may not be the only reason why blooms have gotten worse, rising temperatures are likely making it harder for lakes to recover from them.
For their study, researchers from Stanford University and NASA used data from the Landsat 5 near-Earth satellite, which orbited and took pictures of the Earth’s surfaces for nearly 30 years until it was decommissioned in 2013. Then they used a computer algorithm borrowed from Google Earth Engine to identify algae blooms in the world’s largest lakes.
“Better data are available for more recent years, from instruments such as MERIS and MODIS,” study author Anna Michalak, a senior researcher at Stanford’s Carnegie Institution for Science, told Earther via email. “The goal here, however, was to get the longest possible record using a single approach both across time and across a large number of lakes worldwide.”
Overall, they studied algae trends in 71 large lakes located across 33 countries on six continents. They found that in 68 percent of the lakes, the peak summertime intensity of blooms got worse, while the intensity of blooms only decreased in a 8 percent of lakes during that same time. The same pattern was true for a particularly dangerous type of algae made of bacteria called blue-green algae, which can be toxic to wildlife, pets, and people.
The findings, published in Nature Monday, provide more evidence that toxic blooms really are becoming more widespread across the globe and “counter the hypothesis that increased reporting of toxic blooms is instead a byproduct of increased scientific attention,” the authors wrote.
While there seems to be a link between climate change and these blooms, though, the relationship is complicated. Michalak and her co-authors didn’t spot a consistent association between warming temperatures and the chance of more intense blooms across lakes globally. What that likely means, Michalak said, is that algae blooms can be affected by many different factors, depending on an individual lake’s environment. And while these factors can include temperature, it can also include rainfall or fertilizer use nearby.
“However, one consistent finding is that only lakes that warmed less (or actually cooled) were able to sustain gains in water quality,” she added.
In other words, even if climate change isn’t making blooms in one particular lake more common, it’ll still make trying to manage them a nightmare for scientists and governments across the world. Already, the authors noted, algae blooms in the U.S. are thought to cost the country $4 billion annually, thanks to the damage they can cause to an area’s drinking water, agriculture and tourism industry. They also can be deadly, as a wave of pet deaths over the summer linked to blue-green algae demonstrated this year.
One key takeaway from the study, Michalak said, “is that tackling climate change will also benefit us in many other ways, such as safeguarding water quality.
“A second takeaway,” she added, “is that water management strategies need to take into account the fact that temperatures and rainfall are changing. Doing so will increase the chance of success of those strategies.”