Friday, June 2, 2006

Today's paddle comes after yesterday's rain. When I put-in at the dock I noticed the water was higher than it had been. In fact looking at the photo I'd say the water was about 20 cms higher than it had been. On a lake this large, that represents a tremendous amount of newly added water.
I hadn't gone very far when I saw my first person on water skis this year. I also found I didn't need to wear my neoprene gloves. The water was noticeably warmer. Then it hit me. The newly added rain water being warmer and lighter was sitting on the heavier, colder water down below. With little wind, there had been almost no mixing of the lake and rain waters. Not only that, but it's possible that the lake had gone through it's years 'turn over', something which occurs each spring about this time.
What that means is that as the ice melts and the resulting water warms up to 4°C, it gets heavy and sinks to the lake bottom displacing the water at the bottom, forcing it to the surface, hence the lake 'turns over', top water to the bottom, bottom water to the top. As the lake water continues to warm up, the warmer water ends up floating on top of the denser 4°C water. During the summer warming period, the body of warm water grows larger and larger, and goes deeper and deeper. You can actually determine how big it is by swimming down and suddenly entering the cold layer on which the warm water is floating. This cold water layer begins at the surface in the spring and gradually descends to about 10 meters in our lake by mid-summer.
The warm water in the lake today was mostly the result of the recent rain, but the appearance of water-skiers and swimmers indicates that the lake may have turned over as well. Summer is on it's way!

Another inch and those drinkers on the right there will be swimmers! Good thing I'm in my trusty kayak!

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