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Frogs, ponds and winterkill

by Kate Bradbury


One of Kate's frogs. Photo taken by Julie WatsonIn January I blogged about 'winterkill', after letters, emails and blog comments flooded in from gardeners who'd found dead frogs in their ponds. One commenter, Wishful Thinker, suggested I blog about winterkill before winter, so people can take action to prevent it happening again. So I have:

Winterkill can happen when ponds freeze over for a long period. Noxious gasses build up and literally suffocate any frogs which happen to be there. Frogs (usually males) often choose to spend the winter lying dormant at the bottom of ponds, where they slow down their metabolism and breathe through their skin. They can survive if the pond freezes over, but only if it has oxygenating plants growing in it (plants can still photosynthesise and produce oxygen under ice), or it has very little leaf litter. If there aren't sufficient oxygenating plants in the pond, or it contains too much leaf litter (which releases noxious gases as it breaks down), or snow covers the surface and prevents the plants from photosynthesising, gases can build up and kill the frogs.

To prevent winterkill you need to create a hole in the ice so noxious gasses can leave the water. I shouldn't need to do so this year, as two feral pigeons have taken to having a daily bath in my pond. I doubt this will please my frogs, but there's no danger of any ice forming if they continue splashing about in it. If you don't have pigeons to do the job for you, Froglife suggests doing the following: place a plastic ball in the pond before it freezes over and remove it once a layer of ice has formed. If the pond has already frozen, make a hole by leaving a pan of hot water on the surface, allowing the base of the pan to melt the ice. Froglife also warns against smashing or pouring hot water on the ice, or adding chemicals (particularly salt). All of these methods can cause serious damage to pond life.

Adding oxygenating pond plants will help maintain oxygen levels in the pond, even under ice. Autumn is a great time to give the pond a clear out, removing leaf litter and other debris. This will keep your pond healthy for frogs, toads and other pond life, and hopefully ensure our frogs make it through the winter, ready to give their populations a good boost in spring.

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