Ice and oxygen: the end of the story (for now)


After the ice melted on the pond I carried on with the oxygen measurements to see if levels went down to the pre-ice levels.

And they did.

So now we are back to the oxygen level that’s about right for the present temperature – 5 degrees C – around 12 or 13 milligrams of oxygen in each litre of water (just a little higher than in November probably because the water is a bit colder now, and oxygen dissolves better in cold water than warm water).

When something new and unexpected happens contrary to what most people would have expected, its interesting to see whether it has been reported before.  If it has, you can be much more confident that this is something real, and not some kind of fluke or even a simple mistake.

And there is one example reported by American lake ecologists a couple of years ago of the phenomenon – not in a garden pond, but at least we know that it has been seen somewhere else before, which suggests its a real phenomenon.

You can read a summary of the scientific paper describing this work here, though to read the whole thing you will need access the archive of the journal which requires a subscription.


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3 Responses to “Ice and oxygen: the end of the story (for now)”

  1. Pond Story: making a new clean water wildlife pond « The Garden Pond Blog Says:

    […] of you who read the blog will know that in my first shallow pond oxygen levels rose during the ice cover this winter to double the normal […]

  2. brian Says:

    I read with interest your article on oxygen levels in frozen ponds. Although in your tests this may have been the case what happened with other chemical levels? Did the toxins inncrease also because they could not be vented to the ait or did these drop? The reason I ask this is because I put a pond into my garden last year (april time) and it established a good selection of wildlife inhabitants quite quickly. It had also a waterfall fed from a pump thrrough a uvbiological filter. The pond is about 2.5m x 1.5m maximum and was doing very well up until late autumn when I started having problems with the pump so I turned it off at the beginning of winter thinking it was not necessary. At this time most of the plants started dying back leaving very little to grow through the winter. As you know we had a very severe winter and when the pond froze over I broke the ice as recommended. On one occasion when the weather was particularly bad I could not easily break the ice. This lasted for several days and eventually the ice was just too thick even by pouring boiling water onto it. Once the thaw finished and I started preparing the pond for the coming spring I noticed there was about 30 frogs and even some of the fish dead in the pond. Not frozen in the ice but lower in the bottom and between plant pots etc. The only conclusion I could come to was the toxins built up because of the ice cover over a prolonged period. Do you agree or could there be any other reason? I have not had any more die since and there are frogs, newts and fish in it now.

  3. Jeremy Biggs Says:

    In answer to Brian….

    What happened to you happened to a lot of other people last winter – which as I’m sure you know was one of the worst we’d have for a while.

    In our ponds we measured oxygen and that was clearly implicated in deaths of fish and frogs. Frogs are happy at low dissolved oxygen levels in the cold but can only stand a few days with no oxygen. Goldfish tolerate zero oxygen for longer but even they succumb eventually.

    So far we haven’t measured the other ‘toxic gases’: ammonia, methane, CO2 – so can’t rule them out completely. However, these will often be kept in check when there is oxygen about – so the rise of these gases will probably coincide with lack of oxygen.

    It looks like when ponds are reasonably well-oxygenated in winter there should be few deaths of pond animals.

    But it’s important to say that we are far from knowing all the details of this problem at the moment.


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