What difference does a hole in the ice make?

Check out Jane’s interesting observation’s in today’s comment.

She has kept the ice open in both 2009 and 2010 winters.

Last year, no problem.

This year: amphibian mortalities.

I suspect the harsh weather is the problem here: the longer the ice cover, the more oxygen levels are reduced, until frogs simply run out of oxygen. The icy weather went on for much longer this year than last.

But we are still largely in the realm of speculation. For example, what, if any, is the role of ‘toxic gases’ in this. Do ice holes make any difference at all? Could they let air-breathing creatures get to the surface for a vital gasp of air? Are frogs running out of fat reserves before running out of oxygen? How are the other animals surviving all this? Would it be better just to run the pump, even in a wildlife pond?

All of these are hot questions with no definite answer yet.

And the differences between one pond to another are likely to be tremendously important too. There’s probably not going to be a one rule fits all answer.

The quick and the dead

The quick: this frog has spent the last month in my pond. But if there's enough oxygen, common frogs (Rana temporaria) can survive under ice a lot longer than this.

I had a good look at what was in the ponds today, now that all the ice has finally gone.

I was pleased to find two frogs: the one above about two thirds-grown (I took it out of the pond for this bad photo) and one full-sized adult. Both were quite lively.

Both, I’m 95% certain, have successfully survived in the bottom of the pond, under the ice.

The dead: this Emperor Dragonfly larva, which I found in the new pond today, was probably killed by being frozen solid.

Not so lucky was my fully grown Emperor Dragonfly larva, which I found today in the shallow half  (2 inches) of the new pond. I was very fond of this animal – I knew it was the only one in the pond, having netted it earlier in the autumn in the detailed surveys of our ponds, and I’d been keeping a special eye out for it. It was the fifth species of breeding dragonfly in the garden.

In this case it was in the wrong place at the wrong time: I’ve no doubt it would have survived in the slightly deeper water, only 20 cm, of the new pond’s main basin.

And this depth of water was fine for my Broad-bodied Chaser dragonfly larvae in the old pond. They were safe, happily lurking in about 25 cm of water in the ‘deep’ part of the pond, amongst the leaves and mosses, with no sign of any casualties.

As well as the dragonflies, the old pond still has plenty of mayflies, backswimmers, large red damselfly larvae – I even saw an adult Brown Diving Beetle (nice picture here) which I guess must have overwintered in the pond.

Obviously, many other people’s animals have not been so lucky as mine. Perhaps because of this, there’s been a terrific response to the request Pond Conservation put out earlier this week for information about the effects of snow and ice on ponds – the Big Pond Thaw survey. I will start posting some of the results, and commenting on specific questions, soon. Thanks to everyone who has sent back forms.

Oxygen in the ponds: it’s going on up

[Click the graph for a clearer picture].

Pretty crazy weather here in Abingdon: snowed today so new pond now has slush on top of ice.

Old pond ice has now melted.

Oxygen in the old pond has gone up remarkably over the last couple of days, peaking yesterday and now dropping down a bit. 20 milligrammmes of oxygen in each litre of water is as high as my meter goes!

The new pond is back to the level when it first iced over, around its normal value.

The big test now is to see how the snow cover – and associated very low oxygen levels (for this pond) – affected animal life in the pond.

After the thaw

Sadly we’re getting quite a few reports of dead frogs, and also dead fish too.

It’s very reminiscent of this time last year when the blog was just starting and one of the first big events was people reporting the loss of their beloved frogs.

I will be trying to answer questions as quickly as possible as well as getting together information about what is really causing the losses.

For everyone who can bear to do it, it would be very useful to hear what the state of your ponds was like during the Big Freeze by completing the simple ‘Big Pond Thaw‘ survey.

We’re interested both in ponds with animal deaths, and those where things seem OK.

You can submit the information quickly on-line here.

We trying to find out more about the kinds of ponds most vulnerable to this problem so that, as far as possible, we can help people avoid the problem in the future.

Pictures of ponds would also be very helpful: you can either send them direct to me (jbiggs@pondconservation.org.uk) or upload them as part of the Big Pond Thaw online form.

The Big Pond Thaw survey

Pond Conservation is launching today the Big Pond Thaw survey, asking people to help us gather more information about the condition of ponds during the Big Freeze.

It’s based on last year’s Big Pond Dip format and aims to find out more about ice and snow cover on ponds during the freeze, how people managed their ponds and whether there have been any fish or amphibian deaths.

There’s a copy of the form here, and you can upload the results at the Pond Conservation website here.

As is clear form what’s been happening over the last month or so with my own ponds there’s still masses to learn about what makes ponds tick, not just in winter.

Our aim with the Big Pond Thaw survey is to collect information that will help to improve the pond creation and management advice available. At present, almost everything about managing garden ponds is still mainly a matter of guesswork.

It would be great to hear from everyone who’s posted about fish and amphibian deaths on the blog.

But it’s also really important to hear about ponds where there don’t appear to be any problems so far.

24 hours of air and pond temperature

I thought I’d share this nice looking 24 hour plot of air and pond temperatures. [Click the graph to get a clearer picture].

The green line is the slightly warmer new pond – out in the open, and in full sun.

The blue line, the shady, cooler, old pond.

Red lines are air and ground temperature.

During the warm middle of the day you can see the ponds very slightly warming up.

Both ponds are still completely ice-covered, except for a small sheltered area under bushes on the old pond.

Under the ice, oxygen zooms up on a sunny day

Yesterday, Sunday, was a bright sunny day here in Abingdon.

Both ponds responded with significant rises in dissolved oxygen, with parts of the old pond reaching 16 milligrammes of oxygen in each litre of water, which is supersaturated (that is, the water has more oxygen than its theoretical 100% capacity). [Click the graph to see a better quality image].

Both ponds were covered in ice again all day so oxygen trapping may be occurring.

Also, it was noticeable that the better vegetated old pond has gone higher than the rather barer new pond.

Effects of the big freeze on ponds

Sadly, as you’ll have seen from the comments, there are beginning to be reports of dead frogs now that ponds are thawing.

UPDATE: And newts to.

This also happened last year in the shorter freeze we had in January 2009 (see this post, for example, and especially the comments that follow it).

I’ll be posting more about this over the next day or two, and doing my best to answer questions, so keep an eye on the blog.

In a special extension of The Big Pond Dip survey, we at Pond Conservation will also be seeking your help to tell us more about what happened to your pond during the freeze.

Given that we know so little about what makes ponds tick, both in the garden and in the countryside, this information will help us improve pond design and management in the future.

I should say, for those who expected the Big Pond Dip results to be available by now, they are coming soon – but we’ve been focusing on the more urgent icy pond information first!

The start of the thaw

Red lines: air temperature. Green lines: new pond. Blue lines: old pond

Air temperatures have reached 7 C in the sun today.

The ponds are very slowly responding.

The graph above shows the air temperature clearly (thick and thin red lines) but the signals from the radio tranmitters in the old pond (blue) and the new pond (green) are rather intermittent.

I think the probes may be just too far from the house to be completely reliable.

Despite this minor technical problem, you can still see the difference between the two ponds.

The old pond, which is shaded by a tall hedge and house-high trees and never get direct sun except in the middle of the afternoon in the height of summer, is cooler than the new pond.

Out in the open, the new pond has reached 1.8 C below the ice. The old pond is still down at 1.3 C.

After a nippy night both ponds are still almost completely ice-bound.

Clearing the snow

On Thursday I cleared the snow from the old pond

On Thursday I tried a final experiment: clearing the snow from the old pond.

There appeared to be an instant response: from a level of around 4 milligrammes of oxygen in the morning it rose to over 8 by the evening.

Click the graph to get a clearer picture

I made a second hole in the old pond at the same time – the black line with open square on the graph.This hole was over the area of the pond with the densest moss cover – so potentially the area of greatest oxygen use and oxygen production.

Before clearing the snow it was 2.3 milligrammes of oxygen per litre of water. By the evening it had also risen considerably, reaching just over 8 milligrammes of oxygen in each litre of water, shown by the dashed red line with triangles symbols on the graph.

At the same time the new pond – which still had its snow cover – continued to fall.

Next day (yesterday, Friday) the snow all melted so the experiment didn’t go on for as long as I would have liked.

With water standing over an inch of ice, now the increase has slowed in the old pond, and with no snow cover the new pond has also begun to recover.

It will be interesting to see what happens next as the ice melts completely.