Climate change impacts will just not be limited on change in weather or rise in temperature. Global warming’s adverse effect on freshwater systems can lower nutrition and increase toxicity at the base of the food web too, according to a team of researchers from Dartmouth College and the Swedish University of Agricultural Sciences.
Their research, published in Scientific Reports, focused on the effects of warming water temperatures and browning—a discoloration of water caused by increased dissolved organic matter—using controlled outdoor environments known as mesocosms.
“Climate change scenarios predict increases in temperature and organic matter supply from land to water,” said Pianpian Wu, a postdoctoral fellow at Dartmouth and lead author of the study. “For the first time, we used manipulated mesocosm systems to test the effects of warming and browning.”
Under the expected climate scenario of more warming, changing precipitation patterns, and higher levels of dissolved organic matter, the study looked at the fate of nutritious polyunsaturated fatty acids and toxic methylmercury in the food chain.
The research found that a combination of warmer, browner water resulted in the higher transfer of methylmercury from water to phytoplankton at the base of food web. Lower concentrations of essential polyunsaturated fatty acids in phytoplankton were also observed.
Long-chain polyunsaturated fatty acids—such as omega-3 and omega-6—support the growth and survival of animal and plant life by providing energy and by regulating immune systems. Methylmercury is a form of mercury that is easily absorbed by living organisms and acts a potent neurotoxin.
“The reduction of polyunsaturated acids at the end of the mesocosm experiment with both warming and browning effects was concerning,” said Wu, who began the research as a PhD candidate at the Swedish University of Agricultural Sciences.
“This study shows that the food quality at the base of aquatic food webs deteriorates with climate change,” said Kevin Bishop, professor at the Swedish University of Agricultural Sciences and the senior researcher of the study. “The research is important because it places food web investigations within the context of active global change processes.”
While previous research on browning and warming has been conducted in natural environments, this is the only study to rely entirely on controlled mesocosm environments.
“The use of mesocosms to investigate questions related to ecosystem effects of climate change is particularly important,” said Celia Chen, research professor at Dartmouth and a co-author of the study. “The effects of factors such as temperature and browning can be tested individually and in combination while controlling other environmental conditions. Mesocosms also eliminate the need to travel long distances for field investigations.”
The study was conducted at the WasserCluster Lunz research facility outside of Vienna using lake water from Lunzer See in Lower Austria.
Martin Kainz and Katharina Winter, from WasserCluster Lunz- Biologische Station; Fernando Valdés, Uppsala University; Siwen Zheng and Rui Wang, Tongji University; and Brian Branfireun, Western University all served as co-authors of the study.
