- Research
Could microorganisms in our waterways serve as early indicators of lake health?
Photo : Christophe Langevin
How do you determine the health of a lake? By looking at the clarity of the water? The density of microscopic algae? The presence of urban or agricultural waste? These are all helpful indicators, certainly. But while most can be used to monitor lake quality and detect problems, few can be used to take preventive action.
Lake eutrophication, caused by an overload of nutrients, is already a recurring problem in Quebec. And as the repercussions of the climate crisis and human activity continue to grow, identifying early indicators of changes in lakes could help preserve them.
Professors Jérôme Comte and Isabelle Laurion of the Institut national de la recherche scientifique (INRS) are looking to do just that. More specifically, they are searching for markers that could predict how a lake may be affected by environmental stress, i.e., by rapid changes in certain chemical (e.g., eutrophication), physical (e.g., dams), and biological (e.g., invasive species) characteristics. For these aquatic ecosystem specialists, it’s microbial populations that are the key.
“Microbes are at the very heart of how lakes function. They are involved in recycling nutrients and carbon—in short, everything that supports life. At the same time, they are also the first organisms to react to a change in the water. ”
Professor Jérôme Comte, who specializes in microbial diversity and function.
“So, the question is: can changes in certain populations of microorganisms warn us about an imminent deterioration in lake health?”
Developing a lake identity map
In Quebec, lakes are already well classified based on their productivity. The classification ranges from oligotrophic lakes, which have very clear water, to eutrophic lakes, which have cloudy water loaded with nutrients and microscopic algae. Lakes naturally move between stages as they age, and this comes with a gradual change in the microorganisms they host. In recent decades, however, these changes have accelerated, largely due to human activity. What’s more, bacteria vary not only from one type of lake to another, but also seasonally within the same lake. The challenge, then, is to identify which changes are caused by human activity.
“The first step is to characterize the microbiomes of these different lakes,” explains Professor Laurion, an expert in aquatic ecology.
Photographie du dispositif expérimental. Photos : Christophe Langevin
“We need to know how they change with natural, seasonal, or other variations, and only then will we see how much of the variability in microbial diversity comes from climatic and anthropogenic disruptions.”
Professor Isabelle Laurion, an expert in aquatic ecology
To do this, the research team based at the INRS Eau Terre Environnement Research Centre focused on lakes that had already been well characterized through the Ministère de l’Environnement et de la Lutte contre les changements climatiques, de la faune et des parcs’ (MELCCFP) Réseau lacs témoins program. The program monitors the chemical and biological dynamics of representative lakes in different regions of Quebec over several years in order to identify potential changes in condition.
“The idea is to start by finding the typical profile for each category of lake,” explains Christophe Langevin, a Ph.D. student in water sciences at INRS and head of the project partly funded by the MELCCFP’s Osmoz program. “To do this, we will take water samples and extract the microbial DNA. After that, targeted sequencing can be used to create a microbial identity card of the lake. Sampling has taken place from May to October every year since 2020, which will give us seasonal and inter-annual variability.”
Once they have this identity card in hand, the researchers hope to find signs that are precursors to lake degradation in the variations. “The advantage of the microbiome is that it reacts quickly,” continues the Ph.D. student. “With classic variables such as chlorophyll a or phosphorus in a lake, by the time their concentration exceeds a certain threshold, it’s already too late. Knowing which microbial population changes ahead of a cyanobacteria bloom, for example, would allow us to know what is going to happen before there’s any visible deterioration.”
The secrets of microbial resilience
The other advantage of characterizing the microbiome is that it can predict whether a lake will be resilient in the face of environmental change.
To determine this resilience, the researchers also perform experiments in mesocosms to test how a microbial community reacts to physical and chemical changes associated with eutrophication. “Over time, we want to see whether the microbes will remain and simply experience population changes, or whether some may disappear while others take on a much larger role,” explains Professor Comte. “If we see a change coming in the trophic stage of a lake linked to increased phosphorus inputs, for example, and we implement measures to reduce these inputs and bring the lake back to a lower level of productivity, will the microbial communities return to the initial state?”
The team hopes to answer these questions sometime in 2025.
