Required reading for river managers

There’s a widespread movement to fence livestock out of rivers – it seems to make intuitive sense where there are a lot (and I mean a lot) of cows and sheep in fields next to rivers, and they’re kicking up a lot of sediment into the water.

But there are two sides to this story and this article – British Wildlife: fencing of rivers is not ‘good for biodiversity’ by three of Britain’s most respected wildlife biologists – should be required reading for everyone in watery nature conservation.

What’s this got to do with ponds? Well, pond, streams, rivers and lakes are part of a continuum of habitats that shelter our freshwater biodiversity. But more directly, light trampling is a natural part of the ecology of all freshwaters – something we noted a long time ago in an article called ‘New approaches to pond management‘, which you can read here (page 284 has the discussion about trampling).

Of course, the intensity of trampling that goes with modern livestock densities is probably not a good thing. But equally, fencing all rivers is not the ideal solution either.

At this rate, maybe one day we’ll have to write a ‘New approaches to river management’ article too!

Backswimmers don’t just eat mosquitos – they scare them off too

Although backswimmers (our four species of Notonecta) have a bit of a popularity problem because they can bite, they will probably redeem themselves in many people’s eyes for eating mosquito larvae.

Now, new research suggests that, as well as eating the pesky larvae, they may also simply scare mosquitos away with great smell of backswimmer – because the mosquitos can sense chemicals released into the water by backswimmers, and avoid laying their eggs in these places.

I’m intrigued by these results as, just now, I have no backswimmers in any of my ponds – as a result of the summer drawdown and, I suspect, a dense cover of duckweed on the old pond – but I do have quite a lot of mosquito larvae. And up until water levels dropped this summer (and in the case of the New Pond, disappeared completely), backswimmers have been a regular feature of the ponds, and mosquito larvae have been a rarity.

It’s just possible this new research explains why.

So for the mosquito-ly challenged, how do you go about attracting backswimmers? One might assume it wouldn’t be too difficult, but in the Abingdon garden pond survey they were only found in about a quarter of the ponds, so there’s no guarantee you’ll get them.

They don’t seem to need all that large ponds – we found them in one Abingdon pond that was only 0.7 square metres, and they were abundant in one that was three square metres. Some open water looks important, and they probably avoid ponds completely covered in Lemna. They don’t need terribly deep water – until recently there was no shortage of them in my old pond which has a maximum depth of only 25 cm.

So that shouldn’t be too difficult, though many ponds will struggle with the amount of Lemna, if this turns to be an real requirement.

To read the mosquito work in detail, the paper is here although only the abstract is free to view; if you e-mail the authors they will usually send a free pdf of the full report.

Just in case you’re wondering (as the Telegraph is not quite sure), backswimmers are sometimes also called Greater Waterboatmen.

Enviropig™

This to be sung to the tune of ‘Spiderpig’ (just about my favourite part of the Simpsons movie). In case you haven’t seen the movie, you can hear the song here.

Enviropig, Enviropig

Does whatever an Enviropig does

Is there any….evidence

He can save

The environment

Not yet…..he is juuuuuust a pig

Pigs produce a lot of phosphorus in their dung – which is a major problem when the nutrients in this dung wash into ponds, lakes and rivers.

Reports show that the genetically modified Enviropig produces between 30 and 75% less phosphorus in its faeces, with the promoters then going on to put 2 and 2 together to make the suggestions that this:

“greatly reduces [this pig's] impact on the environment“.

Although this animal is clearly a triumph of genetic engineering, there’s a problem. The pigs seem to be just another in a long line of technologies (like buffer strips along fields and wetlands that intercept dairy farm waste) which, while apparently capable of reducing the amount of polluting nutrients entering ponds, streams and rivers, haven’t yet shown a great deal of success in allowing the damaged plant and animal communities in those waterbodies to actually recover.

Like buffer strips there’s no evidence yet that using these pigs in the real world actually reduces environmental impact. They might do, but there again they might not.

I don’t want to be too much of a killjoy but this has a familiar feel of people (in this case GM pig breeders) trying hard to do good but, like many agricultural scientists before them, allowing their hopes to get ahead of the reality because they haven’t had the ecology explained to them well-enough.

Over to you, freshwater people, to make it clearer.

Frogs spawn in spring and tadpoles emerge in summer…but not always

Tadpole from the Old Pond today on the point of metamorphosing

I hear reports of people worrying about having tadpoles not yet metamorphosing.

But this is not so unusual: for example, in a survey a few years ago of Glasgow parkland and garden ponds, 4 sites in a sample of 21 ponds had overwintering tadpoles.

Common Frog tadpoles usually take about 3 months to get through to metamorphosis – but they can take quite a lot longer where food is short or they are crowded (as they were in my pond). As my spawn was all laid by about the 21st March this means that the tadpoles,  still in the pond like the one above, have now been in the pond for about 5 months.

One recent investigation suggests that some tadpoles may quite early in the summer ‘decide’ that they are going to overwinter, delaying their metamorphosis. What triggers this  early decision is not yet entirely clear, though it seems more to do with the immediate environment rather than inbuilt frog genetics.

Early emerging tadpoles are usually bigger than the late emergers; and emerging from the water at a small size is a bad survival strategy. Being bigger gives you a better chance of surviving your first winter but how tadpoles know in July that they should sit out the winter is not yet known.

The animal above, having got its hind legs, might leave the pond this year or it may hang on until next year. But in August, this animal is still inside the ‘normal’ period for emergence for the Common Frog, which continues until the early autumn.

I love the rain

A typical quandry I often find myself in on rainy days like today.

My neighbour, as we meet briefly: “What a terrible day”

Me, non-commitally: “Mmmm” (as I can’t bring myself to say what I’m really thinking which is “What brilliant weather – just tipping down”).

Oh dear. I suppose one day I’ll have the courage to contradict the standard British distaste for rain.

‘Questions, Questions’: What is a pond?

I’m always pleased to hear people talk about ponds, but the answers on  ’Questions, Questions‘ on Radio 4 today to the question ‘What is a pond’ were….how shall I put it …..idiosyncratic?

In fact, it’s been a while since I heard quite so many old-fashioned misunderstandings of what makes a pond packed into such a short space of time!

Here’s a few of them:

‘A pond is a body of water largely fed by groundwater‘: Err, no. Ponds can be fed by rainwater falling directly into them, surface water running off the land, inflowing ditches, inflowing streams and, of course, groundwater: that is, water flowing through the ground, as in sandy, gravelly or peaty areas. My guess is that the greatest proportion are fed by surface water running off of the land around them.

‘….so there is no stream or river flowing in or out‘.  About one-third of all of Britain’s half million or so ponds have a stream or ditch inflow. Mostly they don’t have rivers running into them because rivers quickly bring in enough water to make a lake!

‘The whole point about a pond is that they are largely man-made‘. Err, no. Of course many ponds are man made  in the modern landscape, but ponds existed long before people, and there are plenty still around made by natural processes. A few examples: tree-fall pools, oxbow ponds and other depressions left on river floodplains, dune slacks, natural depressions in wet ground, the many kinds of small water body made by glaciers , beaver ponds etc etc.

‘Given time any pond will become marshland and eventually dry land‘. Err, no. Many ponds do become marshy as they age. That’s true.  However, there’s remarkably little evidence that ponds naturally become dry land – even though its a widely repeated idea. Usually, most examples of dried up ponds are places where the water has been taken away as a result of land drainage or a dam breaking. Wet places, like ponds, naturally stay wet.

‘Ponds tend to be limited in age‘ Not necessarily. In the British landscape there are no lakes more than about 10,000 years old (because that’s roughly when we emerged from under the ice). There are quite a few ponds that also date from this time.

Lakes are by and large much older so there’s much more opportunity for things to get into them. This is one of the most widely believed misunderstandings about freshwater habitats perpetuated by professional freshwater biologists who mostly still know surprisingly little about ponds. The time when a hole was made has very little influence on the range of species living in it compared to the influence of water chemistry, the degree of pollution and the presence of other freshwater habitats nearby. A 10,000 year old lake polluted by sewage effluent and farm fertilisers over the last 50 years will have fewer plants and animals than a 50 year old gravel pit which is unpolluted and in pristine condition and therefore able to support the full range of species to be expected in a clean waterbody. In fact, freshwater plants and animals exists in networks of habitats – ponds, lakes, rivers, streams and wetlands, and it’s the longevity of these networks of habitats that really determines how rich individual waterbodies will be. It doesn’t matter too much how old the hole in the ground is – it will take on the character of that ancient environment within a few years of being created.

‘Many mountain tarns will be no more than one, one and half yards deep.’ Err, no. Most are quite deep, and you’d need a diving suit to walk across the bottom. In fact, they are characteristically rather deep compared to their area!

Oh dear, I think we must draw a veil over all  all this.

For the record, the widely accepted definition of a pond in the UK is a body of water between 1 m square and two hectares in area.

Marsh Dock progress

The Marsh Dock this morning

Although the Marsh Dock that hatched – sorry germinated – in my New Pond earlier in the year didn’t survive, the seedling we potted-up is looking pretty healthy and growing well.

With luck we’ll be able to add it to the New Pond sooner or later.

Our real aim, though, is to grow the plant on and return seeds or young plants to Pinkhill Meadow where the original seeds came from.

As far as we know, this is the only site in Oxfordshire where this plant grows.

Thank you to the Indy

Another nice piece in the Independent yesterday on the Million Pond Project.

Click here, and thanks to Gillian Orr, who wrote the article.

A remarkable degree of chemical variation in the Old Pond

The Old Pond yesterday showing water conductivity values (and rather more Lemna than I'd expected this pond to have!)

One of the special things about ponds is how much they differ from place to place.

And the Old Pond is providing an excellent example of this phenomenon at the moment in its water quality.

Because the three basins of the pond – which have now been separate for about two months as a result of the dry weather – are showing big difference in water conductivity, considering how close they are to each other and that they have been supplied with exactly the same water throughout.

Yesterday the front small pool had a conductivity of 232 – that’s quite high, at the top end of what I’d expect to be unpolluted’; the middle right shaded pool was at 162 – a good low value; and the back Typha pool was a very low 53.

I was very surprised by the differences in the three ponds.

Conductivity is a very useful measure (and cheap) but it can’t tell you which dissolved chemicals are contributing to the overall score. To find that out you need a much more time consuming / expensive laboratory analysis.

So I don’t know what’s causing these differences.

But two things are interesting:

- the back Typha pool, which still has rich growths of moss – is cleaner than rainwater.

- designing the pond to have basins that separated when the water levels went down in summer was intended to create diversity in physical and chemical conditions.

At the moment it certainly seems to be working.

Wee-vil get to zee truth

A typical scary picture of water fern

I notice silly season coverage of British Waterways kill-the-water-fern-using-weevils story:

The BBC and Independent both covered it. And it has propagated around the world too.

This is a case where the writers involved would do well to follow up the press release from the productive British Waterways PR team and dig a bit more deeply about the cause of plagues of water fern (Azolla filiculoides).

In fact, dense growths of water ferns usually occur only where there are exceptional levels of phosphorus pollution.

This is because water fern has a symbiotic relationship with an alga that can fix nitrogen from the air. So when there is a plentiful supply of the plant’s other main nutrient – phosphrous – it’s growth is effectively unlimited, and it can go wild. So in fact, this is another story about water pollution. Dense growths of Azolla are caused by pollution.

The problem is: it’s much easier to control the symptoms (the growth of water fern), than the cause (the pollution).

So is Azolla, and I quote from the BW press release, ‘a serious threat to waterway wildlife in the UK‘, or indeed any other, freshwater habitat? Not much. A far bigger impact on the canals is their generally poor water quality, and the constant churning up and down of boats which, together, virtually eliminates all underwater plants. But boaters can justifiably argue that this is what the canals are for.

In fact, water fern is petty rare and phosphorus pollution, although all pervasive and damaging, is still usually below the exceptional levels that allow water fern to grow explosively.

In ponds, where you might expect water fern to be most prevalent, we estimate it’s in about 1% of ponds nationally. Or put it another way, its absent from 99% of ponds – which is most of them! Although there are no equivalent statistics from canals, I would guess it’s equally infrequent there too.

But Azolla makes a a dramatic and deeply disturbing looking picture so it’s easy to get people exited about it.

(And for the headline, apologies to my German friends. I was unable to escape from my own cultural stereotype of constantly resorting to ancient World War II jokes – but I couldn’t resist the temptation).