Skip to navigationSkip to content

June 15th 2021

Lac Hertel, an Invaluable Lab for Researchers

In Lac Hertel, these cyanobacterial — also called blue-green algae — blooms have become increasingly common over the past few decades. However, it is not clear why this is occurring. Generally, cyanobacteria growth is stimulated by excess nutrients, such as sewage, or agricultural runoff. However, neither of these nutrient sources are present in Lac Hertel. Other factors that could come into play are increasing temperatures, CO2 concentrations, and the increasing number of geese which could be enriching the lake by feeding on the surrounding fields and excreting their nutrient-rich waste into the lake. All these factors can interact to have unforeseen consequences on the ecosystem.

To understand of how these different effects and interactions affect Lac Hertel’s phytoplankton and zooplankton, researchers use a floating dock with a series of experimental units called “mesocosms”. Each mesocosm is a barrel that contains several hundred liters of lake water, to which any combination of treatments can be applied.

On land, we generally have a good intuition of the food webs around us. For example, trees are the primary producers that convert sunlight into biomass. Part of this biomass is consumed by rodents which are then predated by foxes, coyotes, or birds of prey. In a lake, on the other hand, the primary producers are not trees, but a group of microscopic organisms called phytoplankton. Phytoplankton are then consumed by zooplankton: tiny animals, only the largest of which could be spotted with the naked eye. Finally, small, and young fish feed on the zooplankton, whereas older, or larger fish tend to feed on insects or smaller fish. As the summer season progresses, slow-growing species of phytoplankton, called cyanobacteria, or blue-green algae, can begin to dominate a lake. Like old tree bark, which cannot be eaten by consumers, many cyanobacteria species form long strands which zooplankton cannot consume. Furthermore, several species of cyanobacteria can produce toxins, which can poison the water. They can also shade other species of phytoplankton by filling special organelles with gas, floating to the top of the water column, and preventing other species from accessing the sunlight that they require to grow. Of course, this causes problems for the rest of ecosystem.

Researchers use the mesocosms to understand of how these different effects and interactions affect Lac Hertel’s phytoplankton and zooplankton. Scientific papers have published detailed accounts of altered pH, nutrient concentrations, CO2 concentrations, temperatures, and various combination of thereof. An array of unpublished research, done by undergraduate students include experiments such as removing zooplankton, adding goose poop and cigarette butts. The mesocosms are small enough that the treatments do not affect the entire lake when the water is released back into it and allow enough replication for statistical analysis, but large enough to study phytoplankton and zooplankton in an environment that is much more like their natural environment than a laboratory.

By understanding the processes and factors affecting the food webs in Lac Hertel, we can learn not only about what is going on in this lake, but how other, similar lakes may behave in the face of a changing climate. This makes Lac Hertel an invaluable lab for researchers, and we hope to keep it as pristine as possible to allow us to continue learning from it.

Egor Katkov
PhD. Student and Mesocosm Researcher
Biology Department, McGill University

loading...

Newsletter

Subscribe to our newsletter

Follow us on
loading...