A One-In-A-Thousand Lake In Gatineau
Today we find out why Pink Lake in Gatineau Park is a one-in-a-thousand phenomenon.
EPISODE NOTES
TRANSCRIPT
Today we’re heading into Gatineau Park in Quebec to visit a very strange place. One of only twelve like it in Canada.
It’s called Pink Lake. You might notice… it’s not pink. In fact it’s famous for being a vivid blue-green at certain times of year. Its contradictory name comes from the Pink Family who settled nearby in 1826. But that’s not even the weirdest thing about it. Because Pink Lake is also a meromcitic lake.
Most lakes are Holomictic: that means that the water near the surface and deeper down, mixes.
Polymictic lakes mix frequently - they’re often shallow enough that wind alone can churn their water.
Dimictic lakes mix because of seasonal temperature change. For most of the year the warm water stays at the top and the cool water stays at the bottom. But in the fall and spring it equalizes at 4 degrees celcius, and the water mixes freely.
And in some climates you can also get monomcitic lakes where that temperature equilibrium only occurs once a year.
And then you have very rare examples like Pink Lake where the water layers never mix. It’s estimated about one in a thousand lakes are meromictic. We’ve only found twelve so far in Canada.
In the case of Pink Lake, it’s because it has a small surface area, a bowl-like shape, it’s protected from the wind on all sides by steep hills, and its twenty meter depth is enough for two distinct layers and a transitional ‘chemocline’ in the middle.
So, what effect does that actually have? Well, the only time water comes in contact with the air and absorbs oxygen is at the surface. If the water is sealed off below, it loses that oxygen and becomes hypoxic.
The surface layer can have 10mg per litre or more of dissolved oxygen. But the bottom layer of a meromcitic lake can have less than 1mg per litre. The bottom 7 meters of Pink Lake are a dead zone.
This has a couple of consequences. For one, it stops almost all organic activity, which means anything that falls into this zone is almost perfectly preserved. Core samples from the bottom of Pink Lake can track climate conditions going back 10 centuries. Core samples from McKay Lake, another meromictic lake in Ottawa, revealed a mass die-off of Hemlock trees 4800 years ago and, even crazier, radioactive fallout, still preserved in the sediment layers from nuclear weapons testing in the 1950s and 60s that had drifted all the way to Canada.
The other consequence of the hypoxic lake bottom is that animals and plants can’t venture below the chemocline layer.
But in a crazy twist of fate, the oxygen in the rest of the lake is also being threatened. In fact its beautiful colour is a consequence of the amount of algae in the water, which results in oxygen depletion in a process known as eutrophication.
That usually takes thousands of years. But Pink Lake got so popular that we have been speeding it up. Park staff have installed a boardwalk and planted 10,000 trees to reduce erosion that promotes algae growth. Swimming, pets and even just throwing stones into the lake is forbidden, to keep the eutrophication process on a more natural timeline.
So, this rare lake with its oxygen-free bottom now risks losing all its oxygen. But Pink Lake actually has an even weirder coincidence.
I said plants and animals can’t venture below the chemocline. And that’s true… but some life doesn’t depend on oxygen.
In the lower reaches of Pink Lake, occupying a sliver of space where the light still reaches but below the oxygen rich layer, is a type of prehistoric, anaerobic bacterium. It gets its energy from photosynthesis but rather than using oxygen as a catalyst it uses sulphur, still available near the bottom of the lake.
They’re called purple sulphur bacteria. But I don’t think it’s a stretch to say… they look… pink.
So by total coincidence, the incredibly rare circumstances at Pink Lake, named arbitrarily for the Pink family… mean it has pink in it after all.
And next time, we’ll learn about the other most fascinating inhabitant of this endlessly fascinating lake.