Turquoise Mystery Lake - Part 2 of 2
Last time, we visited a strange mediterranean-coloured lake in rural Quebec to find out where it’s strange colour came from. Turns out, it’s a vibrant example of a ‘marl lake’ suffused with calcium carbonate. So today, we’re going to look at what that distinction means for both the residents of the lake and for us. For a long time, marl lakes were big business. And some enterprising animals have found ways to make their extreme environments incredibly useful.
EPISODE NOTES
I almost went to Marlbank in Tweed, Ontario to shoot some footage of the abandoned Marlworks Cement Factory. It was a cool two and a half hour drive, and recent photos made it seem pretty accessible - it was even called out in some lists of ‘best ghost towns in Ontario’. But other sources warned that the ruins were now on private property. An obsessive google mapping and squinting at satellite photos wasn’t letting me see exactly where I’d park, where the ruins actually were, how to get there, or if I’d be tromping through someone’s back yard. All this with the awareness that this would at best represent 10 seconds in the final video, I eventually abandoned the whole idea. Big thanks go to the Hastings County Archives for digitizing and uploading these photos in the 1960s that appear in the episode, saving me a long drive and a trespassing charge.
TRANSCRIPT
Last time, we explored a pair of lakes in rural Quebec - one pretty nondescript, its neighbour an electric Mediterranean blue, and asked: what? why?
Turns out the showier of the two is a dramatic example of a Marl Lake. It’s defined by extreme amounts of calcium carbonate sediment covering just about everything and precipitating in the water which, under certain conditions and temperatures, reflects and scatters light to give it this otherworldly colour.
That Marl is most likely arrived here as glacial till in the last ice age.
Now, we’re gonna see what that all means for the plants and animals who can take advantage of these unusual lake - including us.
Because marl used to be big business. Its natural mix of calcium carbonate and clay was perfect for the production of ‘portland cement’, the most popular type of cement in the world.
And the glacial action of the last ice age in the Great Lakes region gave it a ton of marl deposits, making it a hub of cement production.
You’ll still find places named for it, like Marlbank in Tweed, Ontario. Home to the Beaver Portland Cement Company of Canada.
They produced cement from marl deposits in the area like in Dry Lake that would be used in the Panama Canal and the Quebec Bridge… which… infamously collapsed in 1907 but not because of the cement.
Anyway, looking down from above Marlbank, you can still see the way the marl has been scraped out of the lake.
And this is why we use marl for so long in cement production - it’s just sitting there in big deposits ready for us to scoop it out.
But if you visit today, the Marl Works cement factory in Marlbank looks like this.
As mining technology improves there’s a tipping point where quarrying limestone directly for cement becomes easier and cheaper than digging up marl.
And quarrying limestone has the benefits of consistency and standardization. Marl could be mixed with any number of things depending on the lake.
Plus, there’s a big conservation concern - I mean, look at this lake again. Marl deposits are found in fragile wetland habitats and scouring the lake severely disrupts them, to put it mildly.
Which at last brings us back to the ecology of the marl lake itself. As you can imagine, life in this kind of extreme environment can be tricky.
Plants and animals who live here need to be OK with highly alkaline water and minimal productivity.
Two plants that are OK with that are chara and water bullrush. The latter is responsible for 79% of the biomass in marl lakes.
Then you have insects like water striders who can be abundant at the surface.
They provide food for some hardy fish species: northern pike, yellow perch, sunfish and trout are all able to thrive in the specific conditions here. And they can take advantage of the unusually clear water when hunting.
As can diving birds who hunt the fish.
But one creature who is especially well suited is the humble crayfish.
Nocturnal little crustaceans who are known for being able to put up with harsh environments, they love a marl lake.
Like the fish, the clear water can help them find food and avoid predators.
They can also burrow into the marl for protection.
But the biggest benefit to crayfish specifically is all that calcium carbonate floating around them.
Crayfish, like the vast majority of larger crustaceans, have a hard shell exoskeleton for protection. They need to grow that shell and then need to regularly moult and regrow it as they mature.
And doing all that requires a lot of, drumroll, calcium!
So crayfish in marl lakes are completely surrounded by exactly the building material they need for strong, healthy shells.
This is especially useful for younger crayfish. The time before they’ve had a chance to grow their first shell is when they’re the most vulnerable, and marl lakes let them get there much faster.
Which is all to say: marl lakes like this one don’t exactly present a welcoming environment for most organisms. But - nature abhors a vacuum. Give it a set of extremes and it will respond with life that can take advantage of them. Give it a niche, and something will always swoop in to fill it perfectly.