Saturday, August 20, 2011

Pink Lake (or a short lesson in meromictic lakes)

I went for a hike today with a friend of mine around Pink Lake in the Gatineau Park. I hadn’t done this trail before – which is an easy 2-km loop around the water. In order to protect the delicate ecology of this lake, the trail is very well-maintained with lots of boardwalk sections and wooden steps.

One distinctive aspect of the lake is that is one of 16 meromictic lakes in North America. In most lakes, water mixes completely during spring and fall - due to such things as water density and air temperature and wind - evenly distributing nutrients and oxygen. But in meromictic lakes, the waters of different levels of the lake don’t mix.

Pink Lake is in a uniquely sheltered position with steep hills all around it protecting it from the wind and bowl-like shape with a small surface area. Because the waters do not mix, the bottom 7 metres have no oxygen in which thrive an anaerobic prehistoric bacteria which uses sulphur instead of oxygen.

Apart from the anaerobic bacteria, nothing can survive at the bottom of the lake. So anything which sinks into the depths of Pink Lake will not decompose. This is a historian’s dream since analysis of the 10,000 year-old sludge in the bottom of the lake can reveal such thing as the history of the surrounding ecosystems and the changing levels of lead in the air.

Another distinctive thing about Pink Lake is that it’s fed only by runoff water. Like most of the surrounding lakes, it was once part of the Atlantic Ocean which left pockets of water behind when it retreated, most of which desalinated in the course of about 30 years since they are fed by rivers and streams. But Pink Lake took more than 3,000 years to desalinate – a process so slow that the stickleback, a salt-water fish was able to evolve and adapt.

One interesting thing about the sticklebacks is their unusual mating behaviour. Males construct a nest from vegetation held together by secretions from their kidneys and attract females to their nests. The female will lay her eggs inside the nest after which the male fertilizes them and guards them until they hatch.

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