Microbial DNA sequencing reveals nutrient pollution and climate change reinforce lake eutrophication

Lake 227 of the Experimental Lakes Area.
Photo Credit: Rebecca Garner

The algal blooms increasingly seen in Canadian lakes have been linked to both nutrient pollution from agricultural runoff and climate change. However, a new Concordia-led study using DNA sequencing of lakebed microbes reveals that these two drivers amplify each other in ways that profoundly affect the health of lake ecosystems.

Using records and samples from the International Institute for Sustainable Development Experimental Lakes Area (ELA), a group of 58 lakes in northwestern Ontario designated freshwater research facilities, the researchers paired environmental monitoring data dating back more than five decades with paleogenetic reconstructions from lakebed microbes dating back more than a century.

By sequencing DNA found in lake sediments, the researchers got insight into past algal communities’ composition and compare them to communities today. This provided critical insight into how those communities changed over decades.

“The sediment DNA archives gave us a chronology of these lakes’ history,” says lead author Rebecca Garner, PhD 2023, and currently a postdoctoral fellow at the University of California, Berkeley. “This is the first study to show that we can reconstruct the community dynamics of that ecosystem and dramatically expands the diversity of microorganisms that we were able to study.”

The study was published in the journal Environmental Microbiology.

Rebecca Garner: “This is the first study to show that we can reconstruct the community dynamics of that ecosystem and dramatically expands the diversity of microorganisms that we were able to study.”
Photo Credit: Courtesy of Rebecca Garner/Concordia University

A double threat

The researchers examined sediment samples from five lakes in the ELA. Three had been fertilized by phosphorous and other nutrients and two were unmanipulated.

Samples from the fertilized lakes revealed rapid and dramatic changes in the algal communities, resulting in persistent blooms. These algal blooms are a clear indication of eutrophication, a process in which excessive nutrients fuel algal growth that consumes the lake’s oxygen, killing off fish and making the lake unsafe for recreation.

The unfertilized lakes had no such evidence of sudden change. However, there was evidence of gradual algal community growth around 1980, when regional air temperatures began to show sharp and sustained rises.

Using statistical modeling techniques, the researchers were able to see how algal communities were changing in response to fluctuations in nutrients and climate. They found that the strongest responses occurred when both nutrients and climate were affecting the ecosystem.

This contrast in algal community response shows that eutrophication is exacerbated by the combined effects of pollution and warming on the ecosystem. Together, these factors act to prime the ecosystem to become more unstable and more vulnerable to stresses brought about by climate change.

“This works expands on the monitoring work done at the ELA by adding an ancient DNA component to it,” says Garner’s thesis supervisor and co-author David Walsh, a professor in the Department of Biology in the Faculty of Arts and Science.

“Using this new methodology allows us to look further back in time and to get a broader view on the community that is changing in the water column. It demonstrates that there is a synergistic interaction occurring between climate change and nutrient addition that is leading to more rapid responses within the microbial community. We would not have seen that without the paleogenetic approaches.”

Contributing researchers include Zofia Taranu at Environment and Climate Change Canada, Scott Higgins and Michael Paterson of the IISD Experimental Lakes Area and Irene Gregory-Eaves at McGill University.

Funding: Funding was provided by the Natural Sciences and Engineering Research Council of Canada, the Fonds de recherche du Québec—Nature et technologies, the Canada Research Chairs Program and Mr. Stephen Bronfman.

Published in journal: Environmental Microbiology

Title: Eutrophication and Warming Drive Algal Community Shifts in Synchronised Time Series of Experimental Lakes

Authors: Rebecca E. Garner, Zofia E. Taranu, Scott N. Higgins, Michael J. Paterson, Irene Gregory-Eaves, and David A. Walsh

Source/Credit: Concordia University | Patrick Lejtenyi

Reference Number: eco093025_01

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