Jon Cranfield

The big pond thaw survey 2011

In snow news, the big pond thaw survey 2011, the garden pond blog, Wildlife on December 1, 2010 at 11:47 am

Pond Conservation is running its big thaw survey again this winter after a successful survey in 2010 – you can see the results here http://www.pondconservation.org.uk/bigponddip/bigpondthawresults2010

I am going to monitor my small garden pond this winter and I will be reporting back to the survey through the online form

From the survey some interesting results were collected and pretty much provided evidence that the usual advice about ponds may not be the best advice

From the results and other research by Pond Conservation

the following advice has been given in relation to amphibian deaths in ponds due to ice

What can we do to reduce amphibian deaths during cold spells?

What are the practical implications of the survey for creating and managing garden ponds so their inhabitants can survive in the cold winter months?

There are several suggestions we can take from all the findings so far:

1. Ponds shouldn’t be too deep for their area. Shallow ponds – less than 30 cm (1 foot) are more likely to have higher oxygen levels in the water which helps amphibians, so a good pond shape is wide and shallow – a saucer rather than a tank.

This is the exact opposite of much of the standard advice, which says that ponds ‘should be deep to protect them from freezing solid’. In fact, we know that most ponds didn’t have more than more than a few centimeters of ice, even during the very coldest days of the 2009-10 winter – so ‘freezing solid’ isn’t the problem.

2. A large build-up of leaves and sediment on the pond bottom is probably not good news – almost certainly because this de-oxygenates water. This is especially a problem in ponds which are small and deep.

3. Having plenty of plants in the pond throughout the winter is a good way of improving oxygenation. Underwater plants, including mosses (which don’t die-back in winter) are ideal, although it’s worth remembering that algae, both filamentous and unicellular (the sort thatcolour the water pea-green) also produce oxygen.

4. There isn’t any evidence that making holes in the ice, or breaking the ice, can prevent amphibian deaths. This is not surprising, as most amphibians hibernate at the bottom of ponds. Oxygen diffuses very slowly into still water, at about 2 millimeters a day! So it takes over 6 months for surface oxygen to reach the bottom of a 50 cm deep pond.

5. BUT – If you have a pump, and you think the pond might have low oxygen levels, it is worth making a surface hole and keeping the pump running so that the water is stirred up – this can move oxygen from the surface to deeper waters. A shallow pond with lots of underwater plants won’t need a pump.

6. If the pond freezes and then snow falls on top of the ice, clearing some snow off the ice to make a ‘sunlight-hole’ can help. But this is only likely to work if your pond has lots of underwater plants (or algae) which can then oxygenate the water.

http://www.pondconservation.org.uk/bigponddip/bigpondthawresults2010

The first frozen frogs have been reported through this last round of snowy weather http://thegardenpondblog.org.uk/2010/11/30/oh-dear-the-first-frozen-frogs/

I hope that I can assess the numbers of invertebrates that have died over the frozen period – I will also be seeing whether the pond freezes solid as it is only 20cm deep!

 

 

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