Dartmouth’s biology team is studying the “hidden” effects of climate

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by David Hirsch, Dartmouth College Organisms at the base of the aquatic food web may be invisible, but they are just as sensitive to climate change as other plant and animal species, according to a study published in Scientific reports.

“Climate change is causing food quality to deteriorate at the lowest level of the food web,” says Pianpian Wu, a postdoctoral fellow in Dartmouth and lead author on the study. “That means problems for the entire food chain from phytoplankton to humans.”

The study looked at two effects of climate change on water that researchers are likely to exacerbate in the coming years: warming and “tanning,” the discoloration caused by high levels of dissolved organic matter.

According to the study, a combination of warmer, browner water leads to greater transfer of toxic methylmercury from the water into the phytoplankton. The research also documented lower levels of essential polyunsaturated fatty acids in the organisms.

“The reduction in polyunsaturated acids is worrying,” says Wu, who started research as a PhD student at the Swedish University of Agricultural Sciences.

Fatty acids like omega-3 and omega-6 provide energy and regulate the immune system in animals and plants. Methylmercury is an easily absorbable form of mercury that acts as a powerful neurotoxin.

According to the study, fish and humans can be exposed to elevated levels of methylmercury because organisms lower in the food chain use more phytoplankton to make fat in their diet.

“People eat fish,” says Celia Chen, Research Professor of Life Sciences and co-author of the study. “Once we understand how the mercury and fatty acids in aquatic food webs react to climate change, we will learn about the risks embedded at the top of the food web.”

While previous research on tanning and warming was done in natural environments, this is the first study to rely entirely on controlled outdoor environments known as mesocosms.

The team used mesocosms – controlled outdoor environments – at their research location outside of Vienna, Austria. (Photo by Pianpian Wu)

The researchers used 24 isolated cylinders to test the effects of various degrees of warming and tanning under four different scenarios under sub-alpine conditions.

“It’s really cool to work with mesocosms,” says Wu. “We can test for various climate effects without having to travel long distances to the field.”

The study was carried out at the WasserCluster Lunz research facility outside Vienna, Austria. The lead researcher was Kevin Bishop, professor at the Swedish University of Agricultural Sciences.

Closer to home, Wu and Chen continue their aquatic food web research with a team that included undergraduate students. Previous research has examined how organic matter from freshwater can affect the mercury uptake of black fly larvae.

From left: Ella Dailey, Hartford High School; Ethan Rutledge, University of Massachusetts; Pianpian-wu; Nathan Giffard ’21; and Deedee E. Hernandez ’23. (Photo by Pianpian Wu)

“Dartmouth students are dedicated and hard working. Student participation in our research gives them direct experience researching environmental challenges that society will face for generations to come, ”says Chen.


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