Ice on the ponds

Like more or less everyone, I imagine, my ponds are iced over.

So it’s time to take a close look at pond oxygen levels again.

The green bars show the oxygen levels in the New Pond over the last month or so, compared with today - the first measurement under the ice. With clear water and a bit of underwater plant growth, levels seem to be holding up. On the other hand, the red bars of the Old Pond show that levels were already low earlier in the autumn - presumably because of the duckweed cover - and now under the ice, levels are getting very low indeed.

In the New Pond, there’s a reasonable amount of oxygen: the water is clear and there’s presumably pretty good light penetration – so far we’ve only had the very lightest dusting of something you’d barely call snow.

The Old Pond on the other hand is pretty thick with duckweed, is rather turbid now and, for the last 3 or 4 months, has had much lower oxygen levels than this time last year. The main difference between then and now is that the String Moss is much less abundant (it was severely knocked back by the large number of tadpoles we had this year), and the duckweed has really got going.

And presumably because of the lower light penetration and lack of underwater plants, oxygen levels are pretty low now. Having been around the 4 or 5 milligrammes of oxygen in each litre of water all autumn – already quite a lot lower than the New Pond – under the ice oxygen is getting down to just 1 or 2 milligrammes.

That’s a bit worryingly low.

It will be interesting to see how this plays out.


One Response to “Ice on the ponds”

  1. jonspond Says:

    Hi jeremy – I have been looking at the ice coverage on my small pond –
    The ice is getting thicker, I have noticed the mayfly larvae are coming to the underside of the ice – I thought these were dead but they are moving to the depths of the pond during the course of a day.

    see photos

    I am now getting good photos of these creatures under the ice – air pockets are forming. Is this going to help the animals under the ice?

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