Poison Paradise: Is climate change making toxic algal blooms worse?

Article: Ho, J. C., Michalak, A. M., & Pahlevan, N. (2019). Widespread global increase in intense lake phytoplankton blooms since the 1980s. Nature, 1-1. https://doi.org/10.1038/s41586-019-1648-7


Algal blooms are not a new environmental threat. Algal blooms are large growths of algae in that can happen in both bodies of fresh and salt water. Algal blooms not only ruin the prospect of a nice day at the beach or on the lake, but can also be toxic for animals that live in these environments and for humans who might rely on these freshwater systems for their drinking water. Algal blooms can occur due to a number of factors including changes in temperature or sunlight, as well as due to influxes of nutrients from runoff carrying fertilizer or sewage. Recognizing the number of factors that can contribute to algal blooms and the potentially devastating effects when they do occur, scientists have done a lot of work to better understand the causes and effects of algal blooms (find out more about some of that work highlighted in previous Envirobites).

An algal bloom that occurred in Lake Binder in Iowa. Photo Credit: Dr. Jennifer L. Graham, U.S. Geological Survey (CC BY 2.0)
If you seek a new way to monitor lake conditions

One growing concern is how the impacts of climate change could affect the causes of algal blooms in lakes across the globe. While there have been studies focused on specific regions or short time frames (season, for example), getting an idea of how climate change has been impacting the water quality of lakes across the world has been challenging. Assessments of algal blooms and water quality have traditionally relied upon water samples collected from the impacted lakes, which means that there is not a lot of data available, especially data that were taken over a long period of time to see how things might have changed. In a new study led by Jeff Ho from Stanford University and the Carnegie Institution for Science, a team of scientists used a new method to look at algal blooms that have occurred in lakes across the globe over the past few decades. The scientists used photos taken by satellites to track algal blooms in 71 large lakes around the world.

A large algal bloom in Lake Erie that occurred in 2011 can be seen as a green patch in the lake in an image captured by another NASA satellite Image Credit: NASA Earth Observatory (CC BY 2.0)
Oops, it happened again: Global trends in lake algal blooms

When the scientists looked at data trends, the team found that the intensity of algal blooms increased between 1984 and 2012 in 68% of the lakes. Only a small number of the lakes (8%) experienced a decrease in the intensity of algal blooms. The scientists then compared these trends in algal bloom intensity with trends of potential causes of algal blooms, including fertilizer use, temperature, and precipitation. There was no consistent relationship between any single one of the drivers and the algal bloom trends. The scientists hypothesized that this was due to how each lake is different and thus changes in factors like fertilizer use or temperature might have different impacts in each lake. However, the lakes where the intensity decreased experienced less warming than compared to the other lakes where algal bloom intensity increased or did not change.

Gimme more nutrient management: More action may be required to counteract impacts of climate change

Thanks to this new method for studying algal blooms, this study showed that, in general, algal blooms have been worsening in freshwater lakes around the world. While there was no single factor driving this increased intensity across all the different lakes, the only lakes where there was decreased algal bloom intensity were lakes that did not experience much warming. Thus, while climate change is probably not directly driving increases in algal bloom intensity, it could be making things worse by counteracting improvements in other areas. For example, even if there have been decreases in fertilizer use, we might not be seeing a decrease in the intensity of algal blooms due to the increase in temperature from climate change. To help see fewer toxic algal blooms, communities and land managers will likely need to consider this additional impact of climate change and take more drastic action to address other causes of algal blooms such as limiting fertilizer use and preventing sewage from entering runoff.


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Jeannie Wilkening

Jeannie Wilkening

I am currently a PhD student in Environmental Engineering at UC Berkeley where my research focuses on ecohydrology, which means I look at interactions between ecosystems and the water cycle. Before coming to Berkeley, I did my undergraduate in Chemical Engineering at University of Arizona and an MPhil in Earth Sciences at University of Cambridge, where my research focused on biogeochemical cycling in salt marshes. When I'm not in the lab, I enjoy knitting, hiking, watching too much Netflix, and asking strangers if I can pet their dog. Twitter: @jvwilkening

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