Today’s post comes from Emily Wright, a Discovery Leader at Grundy Lake Provincial Park. The park is surrounded by three crystal-clear lakes, and that rich biodiversity inspired Emily to take us on an aquatic tour of Ontario’s lakes and some of the complex life cycles contained within, from hard-working microbe clean-up crews to feisty Largemouth Bass.
Cannonballing into a refreshing lake, casting a line hoping for the “big one,” dipping your paddle into serene waters, or simply enjoying the shifting lights dancing across the water’s surface on a sunny day…
Lakes offer us a plethora of enjoyment, both invigorating as you take a brisk swim, or peaceful and relaxing as you watch a sunset turn the waters from blue-green to wine red.
Not only are lakes beautiful, but fresh, clean water is essential to our everyday lives! Lakes are reservoirs for rain and groundwater, and — along with wetlands — they are responsible for collecting, filtering, and cleaning the very water we drink, bathe, and cook with.
Thus our lives are fundamentally intertwined with these pockets of freshwater. The health of our lakes directly reflects on our own health, and yet we rarely glimpse the complex and intricate systems that keep them clean, healthy, and enjoyable for all.
Let’s dive beneath these still waters, descend through the various layers of life, and discover how a giant “puddle” is able to feed, clean, and support such a vast array of wildlife…and us!
Forests of green: the critical role of aquatic plants and life in the littoral zone
We’ll start near the surface of the water, along the shores, where sunlight gently filters down, flickering across swaying aquatic plants.
This “littoral zone” is where plants flourish. Here they have ample sunlight to give them energy, while still staying rooted in the soil below. Plants are a lake’s integral base, and serve many important roles in keeping waters clean and healthy.
100% organic water filter
Plants work as filters, taking up excess nutrients and storing them in their stems, leaves, and roots. Some are even capable of extracting small amounts of toxic hydrocarbon compounds or man-made chemicals, such as fungicides, pesticides, and antibiotics.
Others can bind heavy metals such as mercury, boron, uranium, and arsenic. Unassuming duckweed has been shown to be able to take up compounds such as lead, cadmium, and even petroleum products to an extent!
While the amount of contaminants currently being input into natural systems cannot be completely removed by plants in the current ecosystems (especially as many native aquatic plants are being removed by well-meaning landowners, or outcompeted by invasive species), they can and do work hard to make the waters safer for swimming, fishing, and drinking.
Plants serve as shoreline buffers. Their complex root systems hold onto dirt.
Stems and leaves slow waves, protecting shores from extensive erosion. This also improves water clarity, as slowing the waves allows detritus and dirt to settle on the bottom.
Source of energy
Almost all the energy in a lake starts with plants (along with algae) converting sunlight into oxygen and sugars. Plants are eaten by snails, insects, and other invertabrates, which are eaten by small fish, which then feed large fish, and maybe even a loon or osprey! Or maybe you!
Without the conversion of sunlight into energy by plants, the rest of the ecosystem would quickly collapse.
Plants in the littoral zone, also provide the perfect nursery for fry (baby fish)!
Plant stems and leaves provide places for the tiny fish to hide from predators, and big fish are rarely found in the shallows.
Tiny bass, pike, sunfish, and many others hatch from their nests and huddle among the waving fronds. Here they snack on smaller creatures, such as daphnia and other zooplankton (an overarching term for any very small animals and insects).
Danger in the shallows
While being safe from larger fish, the shallows are by no means a danger-free zone.
We mostly know dragonflies to be master hunters of the skies. Their childhood, however, is spent in the warm muddy shallows of the lake.
Here they lie in wait, ready to ambush unsuspecting prey with a unique jaw (called a labium) that snaps out to grab a passing minnow, insect, or even a tadpole!
These shallow waters are home to many other hunters stalking between the weeds. Some chase down their prey like the Giant Diving Beetle. Others lie in wait like water scorpions, their long front legs stretched out, not unlike Preying Mantises, waiting for a hapless insect to swim by.
Hunters become the hunted
While you may be concerned for the fish in the lake (considering many of these insects love to snack on fry), these same insects and their larvae are tasty meals for the bigger fish too.
Sunfish, catfish, and perch gobble up insects of all sorts, and where the forest of plants ends in the shadows of the depths, bass, pike and catfish grab any stragglers that venture too far from the safety of the shallows.
Into the open: life in the limnetic zone
Now we can follow these larger fish into the open waters: welcome to the limnetic zone.
Here, while the top layer of the water has ample sunlight, the water is far too deep for plants to root.
Instead the sun basks phytoplankton, tiny photosynthesizing (converting sunlight to energy) algae.
Just as there are many species of plants, there are also many species of algae!
While too small to see without a microscope, many are beautiful shapes and colours, and all of them convert sunlight and carbon dioxide into energy and oxygen for the lake.
Below this sunny (photic) zone, the light dims and darkens, until very little, if any light reaches into the depths. Here, dead things collect. Dead algae, fish, and plants all eventually descend into the deep and rest in the thick mud.
Here, bacteria get to work breaking the dead matter down, back into base nutrients, and cycling those nutrients back to the shallows via underwater currents. This completes part of the lake’s cycle.
We are part of a cycle
Every component within a lake, whether it’s
- the largest fish keeping smaller ones in check
- aquatic plants and algae providing food and oxygen
- insects, the essential go between for plants and fish
…each species is part of the bigger whole.
Humans, too, are a part of this community (ecosystem). We rely on and enjoy clean water for drinking, recreation, and eating, and yet our actions often endanger this same system.
Pesticides, herbicides, microplastics, and pharmaceuticals are in our sewage, road, lawn runoff, and stormwater. Managing and removing the plants providing energy and cleaning our waters; in many ways we are affecting our community, and not in a good way.
We can however, learn to be better. We can begin to see these connections between us and nature, and through that, have a greater appreciation and desire to protect the biodiversity that sustains us.
Next time you are out kayaking on one of Ontario’s pristine lakes, take some time to reflect on its complex ecosystem, from the smallest oxygen-producing algae, to the voracious Northern Pike, all lying beneath the waves.
“We cannot protect something we do not love,
We cannot love something we do not know,
And we cannot know something we do not see.
Or hear. Or sense.”
— Richard Louv