I scanned a few websites to see what they were saying about ice. Here are a few things, which mostly aren’t true:
‘An ice-capped pond is prevented from enjoying the normal gas exchanges between the water and atmosphere‘.
As yesterdays measurements on my pond show, exchange with the atmosphere is not necessary for keeping high oxygen levels. So, although its true that ice will stop the exchange of gases, this doesn’t reallly matter.
‘The biggest enemies of your pond and its inhabitants are algae in the summer, fallen leaves in autumn and ice in winter‘.
Three myths for the price of one!
‘….freezing can threaten the survival of aquatic animals as it prevents oxygen diffusion from the air into the water. Holes should be opened in the ice to allow oxygen into the pond, and for toxic gases to escape. A good way to do this is to place a bucket of hot water onto the ice.’
More of the same. I rather doubt that a small hole in the ice would actually make much difference to the amount of oxygen getting into the pond anyway because diffusion of oxygen into still water is an extremely slow process.
‘Another important reason not to let your pond ice-over is because the oxygen levels in the pond water can drop to dangerous levels.’
Well, as we saw yesterday, oxygen levels actually rose to unprecedented levels during ice cover. It will be very intgeresting to find out how general this phenomenon is.
And to finish with, one from the Environment Agency of England and Wales:
When winter arrives, your main concern is going to be the pond freezing over. In really harsh conditions, a couple of weeks of freezing weather will cause the pond to freeze up to a depth of 15cm. If this happens, the fragile ecosystem of the pond can change dramatically. At least one opening should be made in the ice as there is a danger of oxygen levels dropping if the pond is completely frozen over.
And some more added later: from a book called ‘The Pond Book’ (not ours at Pond Conservation, I hasten to add!)
‘Ice is a poor conductor of heat’ – well we did that one the other day. Ice is actually a good conductor of heat.
But on the positive side – ‘…if a snowfall occurs light will be blocked out of the pond…‘ is true and really can lead to a drop in dissolved oxygen concentrations as photosynthesis, which produces the oxygen under the water, is stopped.
I’d be interested to hear from anyone who has 15 cm of ice on their pond – perhaps in the north of England, or Scotland (it doesn’t count if you live somewhere really cold!). Come on guys – time for some feedback!