The Case of the Little Freeze-resistant Pond

On a sunny day near the end of January, I was walking in a pathless area of the floodplain in Eliza Howell Park when I came across a small pond in a dip in the ground, a little body of water that was unfamiliar to me.

What was most remarkable about the pond or pool was that it was not ice-covered. Other standing bodies of water that are not part of the flowing river had already been frozen over for weeks at this point. Before February it had not been a very cold winter, but cold enough to freeze non-running water.

I checked to see if the water was moving at all; it did not appear to be. There were some deer tracks near the water, but not many and it did not look as though the pond was a watering hole, at least at this tine of the year. I was curious and decided to come back for another look on a different day.

In the next visit, I realized that the pond, which I had stumbled upon the first time, was not easy to relocate. I needed to walk through thick understory growth.

Fortunately, I was able to follow my own tracks in the snow from a couple days before.

The pond was that day roughly 15 feet long and 5 feet wide. I could see nothing like bubbles or rising water suggesting that it was spring-fed (which could account for its remaining open).

Though the water looked clear, I was beginning to wonder whether it might be contaminated and a potential risk to the environment. When I got home, I emailed contacts in several different organizations seeking information about the possibility of getting the water tested.

On the next visit, the pond looked basically unchangedI, though we had now had several consecutive days of sub-freezing temperatures. I filled a small glass jar that I had brought with the clear water.

I left the jar on the floor of our unheated detached garage and the next day the water in the jar was frozen almost completely solid. Apparently there is not something in the water that acts as an “antifreeze.”

By this point I was getting responses to my inquiries. From the Michigan Nature Association came the suggestion that ground water might be seeping to the surface, despite the fact that no spring activity was visible to me.

Now that I know that the water removed from the site did definitely freeze, this explanation makes good sense to me. Ground water in this region is reportedly over 40 degrees F when it emerges from the ground. A regular supply of “warmer” water would keep much of the pond unfrozen, though I would expect freezing to occur at the pond edges, especially when the air temperatures in consistently below freezing.

In my most recent visit, such edge icing is noticeable.

So the puzzle is probably solved and I likely do not need to be concerned about contamination entering the river the next time it floods.

And I now know where to find a small, hidden, sunken pool of water to observe and to see what it attracts in the different seasons.

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