UPDATED: Keep up to date with the discussion about freezing ponds on Jeremy Biggs' garden pond blog.
Many of Britain’s 3 million garden pond owners will be wondering 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 new research undertaken by Pond Conservation suggests that most garden ponds and their wildlife will be OK during the big freeze 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.
Why does this happen? Even 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.
So what should people do to look after their ponds?
- Don’t worry too much. Your 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.
- Don’t 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 SAFTY FIRST - TAKE GREAT CARE NOT TO STEP ONTO THE POND ICE IN CASE YOU BREAK THROUGH .
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”.
Notes to editors:
1.Pond Conservation is the national charity dedicated to protecting the wildlife of ponds, lakes and rivers. We run a wide range of survey, research and practical projects, lobby policy makers to increase the protection for freshwaters and help the public and others to make and manage ponds.
2.Ponds are important freshwater habitats: there are roughly 500,000 ponds in Britain and they support more endangered freshwater plants and animals than either rivers or lakes.
3.There are at least 3 million garden ponds in Britain. Although putting in a pond is often said to be the best thing you can do for wildlife in the garden, so little is known about what actually lives in garden ponds that much of the advice given to people about their ponds is misleading or wrong. Pond Conservation is currently running a range of projects to help people improve the design of wildlife garden ponds.
4.Ponds are amongst our most threatened habitats: government data show that 80% of ponds in England and Wales are in poor or very poor condition. At present, ponds enjoy much less protection than other freshwaters, despite their importance.
