The Garden Pond Blog

It’s easy to assume that as the weather gets colder life shuts down under water. The bulrushes are dying back now, and it won’t be long before we have our first frosts.

But dipping the pond today shows just how much is going on over winter.

I can see swarms of tiny, recently hatched Smooth Ram’s-horn snails (Gyraulus laevis – pictures here: dead shells show best the distinctive glossy appearance) – there seem to be hundreds amongst the grasses at the pond edge. With them are full grown Whirlpool Ram’s-horns.  The Smooth Ram’s-horn is the most unusual animal in the pond at present: it’s a specialist of new ponds and only patchily distributed across the country.

Lurking in the dense cover of trailing ivy, fallen leaves and submerged mosses at the back of the pond are mating Spotted Backswimmers (Notonecta maculate), Broad-bodied Chaser dragonfly larvae (Libellula depressa) and quite a number of full grown Large Red Damselfly larvae.

Numbers of Pond Olive mayflies are rising now too – there are many hundreds in the pond, including tiny specimens that hatched in the autumn and will grow over the winter to emerge in the spring.

Water beetles are usually harder to find in autumn and winter when many species migrate away from smaller ponds but I did find a Common Black Scavenger Beetle (Hydrobius fuscipes – there’s a rather beautiful picture of it here on this Russian website showing the distinctive rows of fine dots on the wing cases), a Helochares lividus – another edge loving scavenger beetle found amongst the trailing grasses – and the larvae of the Common Black Water Beetle (Agabus bipustulatus) and of small diving beetles in the genus Hydroporus (these are not really identifiable in the field).

There are still pond skaters but no sign of any lesser water boatmen at present.

And in some ways most surprising of all: a couple of frog tadpoles quietly sheltering amongst the marginal grasses. It’ll be interesting to see whether they make it through the winter.

Having crowed about seeing a Grey Wagtail visiting the pond, I’m quickly taken down a couple of notches when two correspondents point out they’ve both had them too.

So I look up the Big Garden Bird Watch results for 2009 and find that Grey Wagtails were the 45th most abundant bird recorded, seen in 1.6% of all gardens – in other words every 62nd person watching saw a Grey Wagtail in their gardens.

You might ask what took me so long!

But they’re still one of my absoulte favourite birds.

Anthony commented a day or two ago:

“Another good thing about bulrushes is that female Aeshnea cyanea (Southern Hawker) dragonflies lay their eggs in the emerging stems of bulrushes. They have a sickle shaped ovipositor that they insert just above the water level….I’m waiting ’til next spring to watch them emerge and drop into the water where they spend up to 4 years before metamorphosing into adults when they will use the bulrushes to climb out and dry their wings before taking off and starting the process all over again.

And the picture above is the evidence from his garden pond in La Montagne in Brittany.

Anthony also comments:

“Our wildlife pond is just over two years old and is coming on strong… we already have frogs breeding and this summer we found some Palmate Newts in the garden and one newt tadpole in the pond!! Lots of dragonflies and damselflies using the facilities.”

Finally, for those of you more interested in your stomachs than your wildlife you might like to check out just how much of the bulrush plant you can eat.

http://www.northernbushcraft.com/plants/cattail/notes.htm

Now you know it makes sense to dig up the veg. patch and replace it with a nice pond full of bulrushes.

Exiting news from correspondent John Woolliams of Fairy Shrimps in Oxfordshire.

These inch long animals are rare inhabitants of temporary ponds that dry out in summer – usually in the least polluted, semi-natural landscapes – well-known spots for these animals are the heathland ponds of the New Forest and pools made by tanks on the extensive chalk grasslands of Salisbury Plain. Both places are notable for having escaped the 20th centuries intensification of farming and its associated water polluting chemicals.

Over the country as a whole Fairy Shrimps have probably been seen in less than 50 ponds over the last 50 years – and they are so distinctive its hard to mistake them for anything else so we can be pretty sure they really are this rare.

What’s exiting about the new find is this is the only place in Oxfordshire where they are currently known – it’s on the edge of ancient woodland in the north-west of the county.

Fairy shrimps – the species is almost certainly Chirocephalus diaphanus [ky-ro-ke-fa-luss di-a-fa-nus], the only species known from the UK at present – are dependent completely on ponds: they never occur in permanent lakes or rivers where they would quickly be snapped up by fish or washed away.

They glide gracefully through the water on their backs, filtering tiny particles from the water. As their preferred ponds dry out in summer the eggs produced by the adults drop to the bottom to lie in the mud, waiting to hatch when the water returns.

The slightly misnamed Grey Wagtail - it's most striking feature is the blaze of yellow on its bottom and back (I can't claim the pic - this is simply culled from the web)

I mentioned before that Grey Wagtails – a bird that really needs streams and rivers – often fly over the garden, and from time to time make brief stopovers on the roofs around us.

The reason we see them is the stream at the end of the road, about 250 m from the garden.

So I’ve been hoping for some time to twitch one in the garden – and today, I got my wish as one tripped its way around the new pond for a minute or two before chink-chinking its way back to the rooftops (check out the characteristic call here – the sound captured on this Italian website is the closest I could find to the real thing amongst the free sites, although the calls recorded by Andreas Schulze on the 17 CDs of Die Vogelstimmen Europas are better, but more expensive to access).

What’s a bit more interesting about this than just an unusual garden tick is that here we have a way to get seeds, spores, eggs, bits of plant and live animals from the margins of the nearby stream straight to our pond – and back – on the feet of a Grey Wagtail.

So next time I need to get it to wipe its feet on the welcome mat to see what its bringing along.

And then there was one: after rain I have one pond again

A couple of blogs back I wrote about how pleased I was the pond was at last drying down a bit.

And as it went down, and became three ponds rather than one, we saw how the water chemistry of the three basins started to change, with conductivity values of 72 in the big basin (at the back), 94 in the medium basin (right) and an intermediate 84 in the small basin at the front. It’s not a huge difference between the three – but I think this can only but help to contribute to the habitat diversity in the pond.

This was what I hoped would happen when I made the pond – by having three basins there would be more variety in pond habitat, in this case greater variation in water chemistry.

Now after a bit of rain I’ve got one pond again – and the process has been reversed. Conductivity measured in the same places is 71, 68 and 67 – practically the same again in all parts of the pond.

The new pond showing that looks aren't everything - it already has an unusually good crop of animals

We surveyed the new pond last week.

The pond looks pretty awful but we found a surprisingly wide variety of animals: most exiting was a full grown Emperor Dragonfly larva (there are excellent pictures of this species on the Biopix website).

It’s actually one of the easier larvae to recognise – and, with practise, do-able in the hand. The shape of the head is the distinctive feature – it’s more rounded in outline compared to other hawkers.

Actually it’s not such a big surprise to find this dragonfly in the garden: emperors are well known for being able to breed in garden ponds, although we’ve no idea at present what proportion of garden ponds they actually occur in.

There’s no way of knowing whether ours was brought in with the plants we added or was the result of natural colonisation.

This emperor is the fifth species we’ve found breeding in the ponds in the garden: the others are Common Darter, Brown Hawker, Broad-bodied Chaser and Large Red Damselfly.

The three basins have separated out now as water levels have gone down

For the first time in two and a half years the pond is just starting to look the way it was designed to:  as water levels fell during the dry September weather, it separated into three basins of different depths.

So rather than keeping it constantly topped up, a very unnatural state of affairs as water levels naturally go up and down during the year with many advantages for wildlife, I made it with three basins which would separate out into three different ponds as water levels fell.

In this way I hoped to maximise diversity of habitat in the pond – the three ponds will have slightly different water chemistry, different habitats, and should dry out at different times.

The conductivity today was 72 in the big basin (at the back), 94 in the medium basin and an intermediate 84 in the small basin at the front. When the pond is full conductivity does not change by more than 5 or 10 points from one part of the pond to another, so even a short period of separation looks like it may be causing greater than normal variation in water chemistry – it is this kind of variation from one pond to another which helps to make ponds collectively such rich wildlife habitats.

With Win Fairchild of West Chester University (Philadelphia) – who’s visiting Pond Conservation – I’ve started some detailed surveys of garden ponds in Abingdon.

These surveys will give us the first indication of exactly what’s living in garden ponds, what affects the variety of wildlife they contain, and how they compare to ponds in the rest of the landscape.

I’ll keep you posted as to how the results are going.

This is the first survey we did: Sally’s pond, just across the road from us.

It’s just about the cushiest survey work I’ve ever done! And complete with generous supplies of tea and biscuits!

All's not well with Ruth's new pond

Ruth has asked whether I could diagnose the source of a sour milk smell in her new pond. She wrote a little while ago:

“Help please!
My new pond smells of sour milk!
It was made for me about 2 months ago.
It’s filled with rain water. It is 2′ deep at the centre and about 2×1.5m surface – it has a logpile next to it. It has lots of wiggly things – some kind of larvae I guess – water now looks quite black. I added some snails and weed from a local pond 2 wks ago.”

So……what’s the answer?

First – I don’t know why its smelling of sour milk, but I would guess that somewhere along the line water quality is a problem.

The rain water is a good start but there’s no reason I can think of why that should go black or smell unless something else had been added to make that happen. A black colour is often a sign of overloading with organic matter.

I wonder whether the emergent plants have been planted in a compost that might be adding either organic matter or nutrients to the pond. It’s also possible that the plants you added (nothing wrong with that) could have died and now be rotting down.

My advice would be to start again: its very difficult to get pollutants out of the water once they’re in – and on the small scale of a pond its perfectly feasible to take the water out, take out anything thats been added to the pond that might be adding pollutants and start again with water that you know for sure is clean.

This is what I did with my second pond when I found it had a conductivity of 300 – nearly 3x what it should have been. I just knew this was a bad start so I chucked the water and refilled it with rainwater.

It may seem like a lot of trouble but clean water, free from added pollutants is so fundamental that it’s worth the effort.

The larvae are probably mosquitos, which are usually amongst the first colonists of new ponds. As other animals colonise they’ll be eaten – mosquitos are usually a very small part of the life in a garden pond, if they occur at all (we have none).