Ice increases oxygen levels in my garden pond

Oxygen levels in my pond roughly doubled when ice covered the pond over the last few days in January. The November values show the typical winter levels. On each day, am indicates measurements made in the morning; pm measurements made in the afternoon (morning is usually lower than afternoon). In January - the line on the right - when ice covered the pond, oxygen levels roughly doubled.

The last few days of ice cover on my pond has revealed something both interesting and surprising about oxygen in garden ponds.

It has shown that ice cover can increase the amount of oxygen in the water – the exact opposite of what most advice on the web suggests will happen.

The graph above shows the oxygen level before ice cover a couple of weeks ago – around 10 milligrammes of oxygen in every litre of water – and how it has roughly doubled after about 10 days of ice cover.

How does this happen?

It’s all down to the ice. Photosynthesis goes on as long as its light and there are plants to do the photosynthesis. In my pond there are algae growing on the pond bottom, quite extensive beds of mosses under the water, and microscopic, free-floating, planktonic algae in the water. The water is also clear, letting light through to the plants, so there’s plenty of photosynthesis producing oxygen.

Normally the excess oxygen simply leaks into the atmosphere – but with a cover of the ice the oxygen is trapped – it can’t get out of the pond and the water becomes supersaturated with oxygen.

Of course, if you have a small pond with a lot of decaying organic matter in the bottom its still possible that there be de-oygenation of the water. But I think this is the first time that anyone has ever noticed that ice can increase the oxygen levels in a garden pond.

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5 Responses to “Ice increases oxygen levels in my garden pond”

  1. Should I break the ice on my pond? « The Garden Pond Blog Says:

    […] UPDATE: Ice cover doubles pond oxygen level. See latest. […]

  2. Pond Gardening and Pond Habitat Says:

    […] Ice increases oxygen levels in my garden pond […]

  3. linda butler Says:

    Following the freezing weather and long period of ice on our pond (approx. 100 feet in diameter), we are noticing lots of what appears to be the beginning of a serious growth of blanket weed! So, it looks like a lot was going on under the ice for those couple of weeks and that an abundance of oxygen may be making itself known. It also appears that the water level has dropped…

    Normally, we get some blanket weed during the summer. This is our first siting of it in Feb!

  4. dean jones Says:

    my pond was iced over during the bad weather we’ve had can’t find any problems with the pump as the water flow is ok and can’t see any reason why the water level has dropped as the pond is double lined so i don’t think there’s a leak my pond is 4m x 3m by 3m deep do you think i should top up the pond when the weather breaks i’ve only been keeping goldfish 4 a few months i started with 80 and only lost 5 since i’ve started is that good lost a few through white spot the pond has been treated since lost only 1 through bad weather my brother in law has lost 5 he’s been keeping them 4 about 15 years.

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