Dragonflies

A Four Spotted Chaser dragonfly

About half the ponds in the Big Pond Dip are reporting finding dragonflies or damselflies.

So the common species are certainly making use of ponds in gardens.

If you want to find out more about the biology of the UKs dragonflies and damselflies a good place to look is here on the website of the British Dragonfly Society.

To find out more about the larval stages living in garden ponds, look here on the Pond Conservation website.

I’m a BDS life member, so once you’ve joined Pond Conservation to protect the habitat, why not join the BDS too!

Will ponds help save the native crayfish?

The crayfish native to the UK is the White-clawed or Atlantic Stream Crayfish

Our native crayfish, the White-clawed Crayfish, mainly lives in rivers – but it can also be found in limy ponds.

In rivers it has largely disappeared from southern England because of crayfish plague – replaced by the American Signal Crayfish.

So now a plan to help save the English populations is beginning to come to fruition as crayfish lovers rescue remnant crayfish populations and move them to isolated ponds and pools (see the Guardian).

And this project emphasises one of the great virtues of ponds: they can be isolated from the nastiness going on in the world around.

This is the essence of our Million Ponds Project where we’re creating ponds isolated from the all-pervasive pollution which affects so many ponds, lakes and rivers. By putting new ponds in places where they are filled by clean water – from woodland, old meadows, heathland, unfertilised grassland, and by making sure that the ponds are not connected to streams or ditches which are usually polluted, we can quickly create something now rare in much of the landscape: clean unpolluted freshwater.

In the case of the crayfish, the ponds and pools are being used to create another kind of isolation: from the disease carried by the Signal Crayfish population – so that maybe one day, if native crayfish become immune or the Signal’s die out,  the native species can recolonise the places they have now been eliminated from.

To make a wildlife garden pond, first find your water

My new pond needed about two and a half of these to get it half filled

Most guides to pond making start with the location and design of the pond.

In fact the most important thing to think about is where the water will come from.

This is because we are so used to getting unlimited quantities of water from the tap that we are often stumped when it comes to finding the several hundred, or maybe even several thousand, litres of water needed to fill a pond with clean water.

So in planning a new wildlife pond – given the importance of getting clean water if we want to maximise the wildlife value of the pond – the key design feature is not what shape or depth or size the pond should be but – how will I get the water that I need to start the pond off.

And that first fill of clean water is critical. Once you got the pond started its easy to find enough rainwater to keep it topped up – mostly the stuff will simply fall straight into the pond from the sky.

But most people don’t have 500-1000 litres of stored rainwater just lying about to get everything started – that’s why this is the most cricital planning step.

You don’t have to store water in rainwater butts of course – any reasonably large clean container will do. Or dozens of buckets!

Can leeches fly?

A quick snap of one of our Horse Leeches - not the best picture, but you get the idea

I’ve been meaning to write about this for a few days – another case of the surprising power of freshwater animals to get from place to place.

Amazingly, a week or so ago, two Horse Leeches (known to biologists as Haemopis sanguisuga – hee-mo-pis sang-gwi-soo-ga) turned up in the new pond.

We found them a few days before the recent change of water.

I have now idea how they got to the pond – they are partly amphibious, so do come out of the water. Chatting with Professor Malcolm Elliott – who has the teeshirt when it comes to leeches – Horse Leeches are partial to earthworms and leave the water to hunt for them.

But whether they do longer distance migrations overland, no-one really knows.

And for ours it’s quite a long way to the nearest water – at least 300 m to the nearest stream. As streams are not really the preferred habitat of Horse Leeches, they may have come from even further away.

So how did these leeches arrive? The birds foot seems unlikely as these are quite big animals, so presumably they did indeed travel overland. It also looks like they prefer to go about in pairs (I made that bit up!).

The bad, the good and the errr…..

Introduced American Signal Crayfish (left) and native Atlantic Stream Crayfish

I saw this unusual artwork earlier in the week, visiting the Eden Rivers Trust at Penrith.

On the right is the plucky little Brit – the Atlantic Stream Crayfish.

On the left is the Champ – the American Signal Crayfish.

When the two meet, the Champ nearly always wins.

This is the frontline of the extinction crisis – where the alien invader brings death and destruction to the native population (the Champ carries the crayfish ‘plague’ so it’s not really a fair fight).

The River Eden is still a stronghold for the native crayfish – so far, signals have had little effect here, though for how much longer is uncertain.

And what’s this got to do with ponds?

It’s possible that clean, unpolluted and isolated ponds, with plenty of calcium, could be a refuge for the native crayfish – places the signals can’t get too.

The pond seasons: July

The old pond after adding a bit more clean sand to the middle shallows that divide the three basins: left is the 'deep' pool, currently about 15 cm; right is the 'middling' pool; front is the shallow pool

July in the pond

Water levels are dropping; this is the time of year when ponds which are going to dry out will do so. Maybe one of my three separate basins will eventually dry out (it’s what the pond was designed to do, to maximise habitat diversity in the space).

The water is still crystal clear.

The early dragonflies and damselflies have mostly emerged now. I’ve seen the first of the summer dragonflies, a Common Darter, emerging.

My bulrushes are putting up new shoots – I’ve got 7 now!

Tadpoles are still in the pond, growing slowly and providing occasional meals for backswimmers.

The summer generation of pond olive mayfly larvae are growing – the eggs were laid in the spring, the adults will emerge later in the summer, lay eggs and then the next generation of larvae will grow over winter.

This seasons baby water snails are also beginning to grow: I have three species now: dwarf pond snail, whirlpool ram’s-horn and white ram’s-horn. I’ve no idea how they got to the pond. They have not come in on plants (I’ve not brought any plants in), and I haven’t brought in mud or water. Birds? Frogs?

The new pond plus new water

Here is the new pond with its shiny new water. Not quite full to the brim: this was 2 and 1/2 water butts full.

Next, clean sand plus clean gravel to be added.

Start again….

At the end of April I posted this picture of the recently nearly completed new pond.

The new pond on 26 April 2009

I didn’t make much progress after that. A hectic spring and early summer – busy with Big Pond Dip, the Blue Peter pond makeover, setting up a new research programme on Water Friendly Farming and a myriad other things meant the pond simply had to be on the back burner.

And in the meantime all was definitely not well with the water quality: the conductivity was much higher than I wanted. By the end of last week, when it reached 320, I decided enough was enough.

So out with both baby and pondwater to start again with new clean water.

So here is the pond reset, just before I added the water (I’m writing this on a train and have realised I didn’t download the last of today’s photos). Anyway, the pond is now re-filled with rain water, from the water butts, and the conductivity is back down to around 85.

The pond before refilling today 12 July 2009

I don’t really know why the conductivity got so high over the last two months. I have a feeling that when we emptied a tap-water filled paddling pool earlier in the summer onto the lawn some of that water drained into the pond.

So now its time to get on with putting down clean washed sand and gravel to provide a substrate, and to add some locally sourced plants.

How clear is my pond?

Clear water in the pond today: the edge of the net is resting on the bottom of the pond

I’m pleased to say that the pond is now crystal clear again.

It’s probably due to a combination of very low nutrient levels (conductivity is around 80), and a host of water fleas filtering any algae that remain.

There are a lot of water fleas in the pond: I just dipped the tray in the water to catch these

Also taddie numbers are down now so they’re probably not having such a big effect on the pond.

A new variation on the ‘leaves are bad’ myth

My little animals (and bacteria and fungi) gradually skeletonise fallen leaves: this is one from the pond tonight

Most guides to ponds say that leaves are ‘a bad thing’ and you should do your best to keep them out.

Here’s a few typical quotes:

‘During autumn, falling leaves should be skimmed off the pond surface before they sink and overload the nutrient balance of the pond.’

‘Net floating leaves before they sink in autumn’

‘Falling leaves in large numbers could clog up ponds and cause a nutrient overload in autumn.’

But is this right?

As I have written before, leaves are a natural part of the pond ecosystem providing food, shelter and case building materials for animals like the larvae of caddis flies. Leaves falling in the water is entirely natural, so you might expect plants and animals to have adpated to exploit this process over the millenia.

In fact it makes no more sense to keep out all leaves than it would do to keep all plants out. In streams and rivers, it is a commonplace amongst biologists that leaves are a good thing – in fact a vital part of the food supply for invertebrates and, therefore, also for fish. Something similar is probably true of ponds.

One of the things that people say about leaves is that they add nutrients to ponds. So, given that you want to keep nutrient levels low in ponds, doesn’t it make sense to keep leaves out?

There have never been any proper surveys which tell us the real answer to this question: no-one has carefully measured nutrient concentrations in garden ponds with and without added leaves. So in the absence of definitive information I thought I’d have a quick look around at what research is available about the nutrient content of leaves to get a rough handle on the problem.

American research shows a dead leaf falling into a pond contains about 125 micrograms (that is, 125 millionths of a gram) of phosphorus, the most important plant nutrient. Phosphorus is an essential element for plant growth – the problem is in many freshwaters it is now in huge excess because of things people do: spread fertilisers like there was no tomorrow, discharge sewage effluent into rivers, keep cows – all these things release huge quantities of phosphorus into the environment.

Assuming that all the phosphorus in the leaf that falls in a pond is available to the plants and animals (this is quite a big assumption), I estimate that if you added 100 leaves to a 750 litre pond, roughly the size of mine, this would be equivalent to a phosphorus concentration of 17 micrograms of phosphorus in each litre of water. This is at the low end of the range you see naturally in ponds and lakes – so a perfectly acceptable value.

If you added 1000 leaves, then you would theoretically have added 10 times as much phosphorus to the pond – 170 micrograms of phosphorus in each litre of water. This is getting to the level where you might start to see some unwanted effects.

In my own pond, where there’s a constant moderate leaf fall, I think there’s little sign of detrimental effects so far. But the problem is this is just one pond, and the calculations above are entirely theoretical. There have never been any careful experiments on the effects of leaves in ponds.

And at the extreme end of leaf fall – like the pond below – the effect of the leaves is obviosuly overwelming (though even this pond had one or two smooth newts in this spring, and yellow irises – but it doesn’t look very appealing!).

This school pond is directly under several trees: the branches are no more than a couple of metres above the pond

Yellow Irises (you can just see them at the back of the pond in the picture above) are one of the plants that can grow in dense shade with accumulated leaves; they naturally inhabitat swampy fen woodland

So should you remove the leaves from your pond? Almost certainly not if the leaf fall is modest; but if you’re destined to get a blizzard of leaves every autumn – well, maybe then’s the time to take some action.