Appropriately, for the first (official) day of spring

Hi Jeremy,

Just thought I would give you an update on our pond.

After burying about 30 frogs that had died [during the cold weather] I am overjoyed to report that at the moment there are probably about 50 young adult frogs having a whale of a time in the pond laying frog spawn, so hopefully all is not lost and it is a joy to see.

Carole

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FOOTNOTE: We will be publishing the results of the Big Pond Thaw survey on Monday or Tuesday this week. Jeremy

Is removing half the water in the pond, followed by a rainwater top-up, likely to be good for wildlife?

Joe asked in the comments what I thought about half-changing the water in a pond – something that’s pretty widely recommended.

Well….removing half the water and topping up with rain water should reduce pollutant levels, but whether it reduces them enough to make a difference might be another matter.

Nutrients, in particular, need to get down to a pretty low level to be ‘safe’ for wildlife: if the half dilution didn’t get down to that level the benefits might not be as much as you’d hope.

As so often, at the moment the problem is that no-one has carefully observed the effects on wildlife in ponds where this kind of water change has been done, so it’s hard to give anything other than a tentative answer.

And because a lot of nutrients can be locked up in sediments and plants (a re-released into the pond) there’s a good chance you’d need to combine water changing with regularly removing plant material and sediments to have a chance of success.

But to be honest, at the moment we’re all a bit in the dark about how effective a technique this would be.

But before yuo get to gloomy remember that, even if the pond does have some management problems it’s still going to have a lot of life in it – it’s just that it may not reach it’s full potential.

If you’re worried, one thing we can do is have a look at the pond conductivity – send us a sample and we can check whether watr changes might be a good idea or not.

It’s frog city out there

UPDATED: 9.0 am 21 March 2010. There are now another 17 clumps in other parts of the pond away from the main spawn patch.

It’s a common phenomenon for frog numbers to build up quickly in new ponds.

This has certainly happened in my ‘old’ pond, filled in April 2007.

In 2007 we were too late for the frog breeding season.

In 2008 we had 2 clumps of spawn.

In 2009 we had four – and a huge number of tadpoles which stripped the pond bare and turned the water green for a while.

This year the frogs have really gone for it.

The tape measure is pulled out to 1 metre

There’s a one metre wide patch of spawn which, using the graph below, is equivalent to about 50 clumps which means 50 female frogs (each female lays one clump of spawn).

And there are a few more clumps away from this main patch.

To work out how many spawn clumps you estimate the area of the spawn patch in square centimetres – a patch 1 m diameter is roughly 7500 square centimetres.

On the graph you read up from 7500 on the horizontal axis until you cross the middle line of the graph – and then read back to the vertical axis to estimate the number of clumps.

So that means we’re heading for somewhere between 50,000 and 100,000 tadpoles in the pond (there are usually 1000-2000 eggs in a clump).