The Mystery of the Purple Buse

Buse Lake in Barnhartvale is one of the few in the world that is magenta clear through

Where on the planet could you go to find an entire lake that has a magenta colour from top to bottom? Well, probably much fewer than 10 places as a matter of fact. They are exceedingly rare and seldom does the entire depth of the lake turn colour. But you could go to Buse Lake in Barnhartvale to see this spectacular natural phenomenon. In fact, you should go there and take your camera.

This is where I was on a sunny October day sitting in a small boat inhaling the rather disagreeable and strong hydrogen sulphide aromas coming from the lake. This "rotten egg" smell is one that virtually all human beings agree as being quite unpleasant. I was floating on a lake that looked like some sort of weird pink grapefruit Kool-aid mix as locals drove by and honked in laughter.

They probably thought we were angling in this fishless place. I was with Heather Larratt, an aquatic biologist from Kelowna as we watched the dials of her test instrument measure the chemical conditions of this very rare condition. "No dissolved oxygen" in the entire water column she said. "In 30 years of studying lakes, I have never seen a bacteria bloom like this," said Heather. From the colour and smell, she was pretty sure that we were dealing with one or more forms of purple sulphur bacteria that only live in lakes where there is no oxygen in the water.

They actually photosynthesize the hydrogen sulphide produced by a different species of bacteria that breaks down other sulphur-bearing compounds in the lake. People are very sensitive to the hydrogen sulphide smell as we can smell it in concentrations as low as parts per billion. But our sense fatigues and we get used to it as we know from days when our pulp mill reminds us of its presence. All of this is happening in a lake that has other properties akin to water on the moons of Jupiter. With this bacterial bloom, you can only see about 3 centimetres into the water of Buse Lake due to the abundance of the pinky purple pigment in the bacteria. And the colour goes right to the bottom of the lake which is only about 3 metres deep.

This was all starting to make sense now, as various people had told me that the colour was due to a bloom of algae. But I was puzzled and could not understand how our common blue-green algae could give this colour. So a little detective work was in order. After asking Heather to come over to do some basic measurements, I spoke to Bob Grace, a retired aquatic biologist from the Ministry of Environment. He indicated that some type of sulphur bacteria were present but they had not been identified during a water analysis last year. Heather and I took samples that are currently being analyzed by a lab in Vancouver in hopes that they can identify the exact species responsible.

Pictures sent to Brian Heise at Thompson Rivers University caused a "buzz" around the Science building, as scientists and students alike marvelled at the colour. Perhaps we may see some local research to further characterize the ecology of this rather special condition. While the bacteria themselves are not rare in the world, they like sulphur rich waters and having the populations build up to numbers that cause the entire lake to turn colour is ..... well, it is just very unusual indeed.

Mahoney Lake in the South Okanagan has a related condition but the bacteria live in a thin layer (chemocline) near the middle and can give a purple hue to the lake at times. But they do not occur throughout the water column. It has been well-studied because it is one of few lakes whose layers of water do not mix during the year, resulting in low oxygen conditions deep in the lake where the bacteria live.

Buse Lake is also different than the somewhat more common pink-red lakes in California and elsewhere that are very salty and support a brine-loving bacteria that turn them bright. These lakes have high concentrations of sodium chloride (table salt) and support other types of highly adapted bacteria called halophytes.

So why Buse Lake? Well, we don't know the answer just yet. It is a shallow lake with almost no in- flowing water for most of the year. Buse Creek no longer enters the lake and water from snow melt has been low for a number of years. There is no outlet and the lake has been getting smaller due to evaporation during the summer. Climate change may also be a factor in reducing the inflow and increasing the rate of evaporation. The colour was noticed last year and may become an annual event. Prior to this, it was quite unpredictable during late summer and may have happened once every 10 years or less.

Today, the lake is conserved within Buse Lake Protected Area, along with a very rare and tiny brine fly that was reported to live there. Whether it is surviving in these conditions we don't know.

So take a drive east of the golf course along the Barnhartvale Road. You won't miss the lake and if it is a sunny day, the colours will be much brighter. This is a world class rarity that should not be missed.

Rick Howie is a biologist with an interest in all manner of wildlife and smelly lakes.

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