Helen asks…

Helen: Could plants growing at the edge of the pond (e.g. brooklime), with foliage both in the water and above it, be adding oxygen under the ice or is it all released into the air above the water?

Jeremy: I think there would be two ways oxygen produced by the Brooklime might get under the water.

First: many marginal water plants pump oxygen to their roots, and this oxygen can get out into the sediment that the roots are growing in. What I don’t know is whether the oxygen produced like this is enough to get from the mud into the water. I suspect not if the sediment is very muddy and has lots of oxygen-using decay going on. But it’s not a area I have first hand experience of.

I don’t know whether Brooklime specifically takes oxygen to its roots, but I wouldn’t be surprised if it did.

The second way the Brooklime could get oxygen into the water is by ordinary photosynthesis going on in the submerged leaves which I think could probably go on producing oxygen too.

Helen: The decrease in oxygen when the pond is covered by snow or mats is presumably accompanied by an increase in carbon dioxide. Is this also the case when the ponds are covered only with ice because although plants continue producing oxygen, the CO2 they produce at night gets trapped??

Jeremy: I haven’t measured carbon dioxide in my ponds (or any other for that matter!) so don’t have direct experience to go on here.

But like you I would have assumed that carbon dioxide would go up as oxygen went down. However, just looking at some old American information from shallow lakes with winter fish kills due to icing over, it seems that carbon dioxide was pretty much unchanged as oxygen went down. So maybe it won’t be as straighforward as we might intially assume.

Helen: High CO2 levels can kill fish. Can they also harm other pond life?

I don’t know whether increasing carbon dioxide concentration would affect the other animals. I suspect they’d succumb to lack of oxygen first – though again I’ve no first hand experience of this and I haven’t found any information about it specifically.

I did see one study that showed Daphnia, at the end of the winter, to be less abundant in lakes with fish winterkill, but then the Daphnia went on to be more abundant later, presumably because there were fewer fish to eat them. Whether the Daphnia were knocked back overwinter by CO2 or lack of oxygen I don’t know.

The snow story: a surprising development

The day the snow fell: 6 January 2010

A thick blanket of snow covered our ponds nine days ago.

I assumed that, by cutting out the light, the snow would effectively stop photosythesis in the pond, causing oxygen levels in the ponds to go down.

But it didn’t.

As you can see on the graph below, for the first three days after the snow fell, oxygen levels in both ponds were little changed. The old pond dropped a bit from the 6th to the 7th January, but the new pond oxygen went up a bit.

Pond oxygen levels: 19 December 2009 to 14 January 2010

So I began to wonder: could the small area I’d cleared of snow around the ice holes where I was making my oxygen measurements, could these small holes be lettting enough light in to allow photosynthesis and oxygen production to continue?

The answer was a pretty resounding yes.

I covered the snow holes with a couple of black door mats to cut out the light, the old pond on the 9th January and the new pond on the 10th. To make oxygen measurements I could simply lift the mats off for a few minutes.

The result was dramatic: on both ponds the oxygen dropped, most markedly in the old pond which has abundant underwater mosses. The fall in oxygen levels on the new pond was slower, perhaps because there is much less underwater plant growth in that pond. But the effect was clear in both ponds. With all light excluded, oxygen production appeared to have ceased. I should perhaps add that the mats were not creating an airtight seal over the ice holes!

So clearing the snow around the ice holes – which I’d done without thinking about the consequences – was allowing enough light in for plants and algae to go on making oxygen. When I blocked out that light, oxygen levels in both ponds fell to their lowest values so far measured.

This is a pretty conclusive demonstration of the effect of snow cover: not too surprising really. Perhaps more interesting is the fact that even quite small amounts of light entering the ponds seemed to maintain their oxygen levels.

And there is further, perhaps final, twist to this story. I will report that over the next few days.

Snow Watch

Thanks to the Snow Watch team for highlighting the icy pond story.

You can see it here (for a few days) on the iPlayer.

Go to minute 44.

Have fun: spot the Fen Raft Spider

Fen Raft Spider

The Fen Raft Spider is one of Britain’s most endangered freshwater animals.

It lives on small ponds in peat at Redgrave and Lopham Fen on the Norfolk / Suffolk border, in ditches on lowland marshes at Pevensey in Sussex and on a disused canal near Swansea.

Have some fun spotting it on the Fen Raft Spider project web site.

Click here to go to the game.

More snow today

There's a pond there somewhere

Snowfall last night in Oxfordshire – a dramatic 4 cm (the amount formerly known as  ‘Not Quite Two Inches’) – was enough to bring transport chaos and school closures to the snowy wastes of, er, Abingdon again today.

Unplanned holidays aside, a definite benefit was the return, with no effort, of a nice tidy look to the garden,  something that would be handy at other times of the year if it could be arranged.

The ponds carried on as if nothing had happened.

Pond temperatures 13 Jan 2010

Temperatures in the water were completely stable night and day – with both ponds (blue for the old pond, green for the new pond) practically identical.

The thick red line is the air temperature. The thin red line is the ground temperature.

Pond temperatures over the last few days

Here’s the first combined plot showing temperatures both in the air and in the ponds. [Click the graph to see it properly].

Over the last five days, the ponds have stayed at virtually the same temperature: the new pond around 1.o C and the old pond a little higher at 1.3 C.

The air temperatures have fluctuated between +1 and -1 C.

It again emphasises how stable the temperature regime is in the ponds – even under these extreme conditions.

Soup, car wash firms, winter sun destinations, corner shops…..and ponds

I hadn’t expected to put a picture of a bowl of soup on this blog.

But soup, along with car wash firms, winter sun destinations, corner shops and ponds have all, according to the BBC, benefitted from the freeze (or at least in the case of ponds, not suffered as much as we might have expected).

You can read about it here on the BBC Website New Magazine.

From The Times today

The Times also picked up the frozen ponds story.

Dog stories

Two nice doggy stories I’ve just noticed in the papers.

http://www.telegraph.co.uk/news/uknews/6912509/Dog-rescued-from-duck-pond-by-17-firemen.html

http://www.telegraph.co.uk/news/worldnews/northamerica/usa/4959216/St-Bernard-rescued-in-Montana-after-tail-freezes-to-pond.html

Now remember Fido: ponds are dangerous!

Gear for geeks

Nige at frogpondweatherblog asks what I’m using for measuring the dissolved oxygen, conductivity and temperature in the pond.

So here, for the technically minded, is a list of the equipment I’m using.

The oxygen meter is a Hanna Instruments HI 9142 portable waterproof dissolved oxygen meter. To get reliable measurement water needs to be moving past the probe at 0.3 m a second. No problem in rivers and stream but for ponds I remove a cupful and stir gently to get the essential water movement.

I have a Hanna ‘Combo’ pH, temperature and conductivity meter. Conductivity is one of the most important measurements as it gives a rough idea of the degree of pollution.

For some time I’ve had continuous temperature monitoring on the old pond (though only just reinstated after chopping the cable with garden shears last autumn).

This uses a Novus myPCLab datalogger, which is plugged into the PC with a USB lead, to which is connected a PT100 thermistor probe on a 30 m long wire which trails untidily from the 1st floor workroom window to the pond, which is on the ground floor.

The Novus logger is pretty basic and can only be connected to two probes.

So, just in the last few days, I’ve added a wireless temperature recording system made by Arexx Engineering which, for virtually the same price as the myPCLab two probe system, can receive signals from up to 50 temperature sensors.

I use the Arexx TL-3BS - this is the slightly higher spec BS-500

The Arexx system has a base station – I use the basic TL-3BS – which plugs into the USB port, which in turn communicates with the wireless temperature sensors. These are scattered up to 20 m away, around the garden and in the ponds. You can also get longer distance sensors which work up to 90 m away.

Wireless temperature sensor

Sensors can be placed underwater or in the air. You need to get them in the right position and they can be a little temperamental in getting a signal through to the base station. But still pretty impressive for all that.

Waterproof wireless temperature sensor

Altogether, hours of endless fun to satisfy the inner geek in everyone.