Big freeze could boost oxygen levels of garden ponds
Last updated 14/01/2010 12:59:30
Big freeze could boost oxygen levels of garden ponds
The big freeze may be causing havoc for many, but it could benefit millions of garden ponds across the UK, according to conservation experts.
Research by Pond Conservation, the national charity dedicated to protecting the wildlife of ponds, lakes and rivers, suggests that most garden ponds and their wildlife will be just fine if just left to their own devices.
And most surprising of all, if ponds have clear water and plenty of pond weeds, oxygen levels can actually go up during the freeze – the exact opposite of what is traditionally believed.It's reassuring news for the estimated three million garden pond owners in the UK, who may be worried whether they should break the ice on their ponds to protect wildlife.
Standard advice has always been that, to safeguard garden pond wildlife during freezing weather, you need to make a hole in the ice to ‘allow oxygen into the pond'. But Pond Conservation explains that under ice, plants continue to photosynthesis, producing oxygen. With a covering of ice the oxygen is trapped in the pond and, if the ice cover lasts for long enough, oxygen levels will rise.So if garden ponds have lots of underwater plants or algae, oxygen levels can nearly double in the coldest weather.
Dr Jeremy Biggs of Pond Conservation said: "In the longer term, if you want to make a pond that will naturally maintain high oxygen levels in winter, make sure that the pond has plenty of underwater plants - even algae will do - and is shallow. Around 20-30 cm maximum depth is good.
"Shallow ponds are better lit than deep dark ponds so can produce more oxygen for their volume. Ideally, also keep the pond water as clean and unpolluted as you can to help the submerged plants flourish."
So what should people do to look after their ponds? A pond is unlikely to freeze solid and there's a good chance it will have enough oxygen for the animals in the pond - dragonflies, damselflies, mayflies, water beetles, hibernating frogs and the rest - to survive.
The advice is not to bother to make a hole in the ice: there's little evidence this makes any difference to the amount of oxygen in the pond. This is because oxygen diffuses so slowly into still water – about 2 millimetres a day – so it takes over 6 months for oxygen to diffuse to the bottom of a 50 cm deep pond.
If there is lots of sediment or leaves in the bottom of the pond - and you also have fish - you do need to get oxygen into the pond. To do this you need to stir the water in some way so that de-oxygenated water is constantly brought into contact with the air. Running a pump or fountain, if you have one, should do the trick.
If the pond is covered with snow, brush as much snow off as possible. Snow blocks the light and will stop underwater plants from producing oxygen. In these conditions, oxygen levels can go down a lot. But Pond Conservation says safety is most important – take great care not to step onto the pond ice in case you break through.
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