Guest Blog by Morgan Murphy, Canada Summer Jobs Student and Conservation Biology student at Trent University
Lake Simcoe is a hotspot for many fun summer activities. Swimmers, boat owners, and fishers alike can all agree that there’s something for everyone. But what we often take for granted after a great day on the water is the privilege of returning home to quality food and clean air. Aquatic organisms in Lake Simcoe can’t say the same. Phosphorus loading and road salt runoff have been affecting the health of sensitive aquatic life, and it only takes a small change in one species’ population to disrupt an entire ecosystem. This is why it is crucial that we protect the organisms that have been taking the hardest hits from pollution: plankton. Despite their size, these minuscule critters have the most potential to influence the food chain. Let’s take a deeper dive into Lake Simcoe ecology to better understand the importance of these microscopic powerhouses.
What are Plankton?
Plankton are microscopic organisms that exist in both salty and fresh water bodies. While some larger plankton species may be visible to the naked eye, a microscope is usually required to view the complexities of their structure. These tiny organisms are vital to lake health as they form the baseline of aquatic food chains. Plankton can be sorted into two broad categories: phytoplankton and zooplankton.
Figure 1: Freshwater phytoplankton (left) and freshwater zooplankton (right) under a microscope. Sources: https://www.sciencephoto.com/media/819654/view/freshwater-phytoplankton-light-micrograph https://www.biologyonline.com/tutorials/freshwater-communities-plankton
Phytoplankton are primary producers found at the very bottom of the food chain. Most phytoplankton are single celled plants, but the category also includes bacteria and protists. There are approximately 25,000 known species of phytoplankton, but some scientists estimate there are over 100,000. Through photosynthesis, phytoplankton rely on sunlight as their main energy source. Carbon dioxide, nutrient availability, temperature, salinity, and water depth can also influence phytoplankton abundance.
Zooplankton are small animals that feed on phytoplankton and other zooplankton. The zooplankton category encompasses an estimated 30,000 different species, which includes the larval stages of some mussels and fish. Lakes typically have around 40 native species of zooplankton, and they can often be found near the surface of the water feeding on phytoplankton that need access to sunlight. Similar to phytoplankton, the abundance of zooplankton is influenced by changes in salinity, pH, temperature, and nutrient levels.
What Risks are Plankton Facing in Lake Simcoe?
Both categories of plankton serve a distinct purpose in the ecosystem and have different responses to fluctuations in water quality in Lake Simcoe. Phosphorus loading can cause rapid increases in phytoplankton growth, and although this biomass is important for carbon cycling, too much algae in the lake is dangerous. High concentrations of phosphorus can cause toxic algae blooms, which leads to low dissolved oxygen levels, less sunlight availability for aquatic plants, and corrupt habitats for other aquatic life. These blooms can also cause a loss in species richness, meaning the number of individuals in each phytoplankton species decreases. Lake Simcoe has already seen cyanobacteria algae blooms this summer on the shorelines of Innisfil and Georgina, and there may be more to come.
The negative impacts that phosphorus loading has on phytoplankton also have an effect on zooplankton. Cyanobacterial algal blooms not only decrease phytoplankton richness, but also zooplankton richness. Studies have also shown that zooplankton species composition and dominance patterns change when cyanobacteria is abundant. These cascading effects lead to a decrease in proper ecological functioning and can change the dynamics within a food chain.
Increasing chloride concentrations at Lake Simcoe also have an effect on the health of zooplankton. Freshwater zooplankton cannot adapt to increased salinity, even when nutrient availability is high. Even below the current Canadian Water Quality Guideline for chloride concentration, significant declines in zooplankton species richness, abundance, and biomass are observed. Chloride concentrations in Lake Simcoe are on track to exceed the chronic exposure guideline by 2058 and have already been exceeded in some rivers near high traffic urban areas.
How Does This Affect Other Aquatic Species?
Zooplankton are a significant food source for most fish in Lake Simcoe. Some fish only feed on zooplankton in their juvenile stages, but smaller fish like lake herring rely on a steady supply of plankton throughout their whole lifecycle. Less abundance and diversity of zooplankton caused by salt means less prey for lake herring. This leads to smaller and less abundant lake herring that may also have trouble reproducing. Lake herring are prey for predator species like lake trout, which in turn feel the same effects when their food supply lessens.
In 2020, the Ministry of the Environment’s 10-year report on Lake Simcoe stated that populations of lake trout, lake whitefish, and lake herring are still at lower than ideal levels. Lake trout are being stocked at 100,000 fish per year and whitefish stocking is between 100,000 and 150,000 per year. As well, lake herring fishing was closed for 13 years up until 2015 to allow populations to recover. This is far from ideal as a healthy ecosystem is self-sustaining and doesn’t rely on human intervention to maintain healthy population levels.
Take Action
Declining water quality will only continue to affect both plankton and fish populations unless road salt usage and phosphorus loading are significantly reduced. If you want Ontario governments to protect Lake Simcoe from salt pollution, click here to send an email to your local representatives. You can also sign this petition to encourage the Minister of Transportation to use a salt alternative on the Bradford Bypass, highway 404, and other provincial highways. Finally, you can click here to ask five Ontario MPPs to develop a plan to reduce Lake Simcoe’s phosphorus pollution to 44 tonnes per year by 2030.
Sources:
https://www.sciencedirect.com/science/article/pii/S0048969722044345
https://www.doc.govt.nz/nature/native-animals/invertebrates/zooplankton
https://scec.ca/pdf/the_effects_road_salts.pdf
https://www.iisd.org/articles/zooplankton-and-fresh-water
https://earthobservatory.nasa.gov/features/Phytoplankton
https://www.doc.govt.nz/nature/native-animals/invertebrates/zooplankton
https://www.epa.gov/national-aquatic-resource-surveys/indicators-phosphorus
https://www.sciencedirect.com/science/article/abs/pii/S0048969720371369
https://www.ontario.ca/page/ministers-10-year-report-lake-simcoe
https://www.fishingsimcoe.com/fish-species