A Bit of a Bubble

Dear Readers, I’m still trying to get out for a walk every day, although with the dark mornings, the Year End (which I fear will be a theme for the next few weeks) and the habit some companies have of scheduling meetings for the Crack of Doom, it’s been a bit trickier than it was in spring. Plus, hauling oneself out of bed on a freezing cold morning takes more willpower than being woken by the sound of the dawn chorus. Nonetheless, I found myself in Coldfall Wood on Friday, and I was very pleased that I did. Although it is still muddy, it is now alive with the sound of Great Spotted Woodpeckers drumming on the trees. I listened to one as it drummed, flew to another tree, drummed on a thinner branch which resulted in a higher pitched sound, and then whizzed back to its original tree. A few weeks ago I reported on a study in San Francisco that found out that white-crowned sparrow femalesĀ  preferred a deeper- pitched call so maybe female woodpeckers feel the same? At any rate, it’s a joyful sound and, along with the yaffle of green woodpeckers and the male song thrushes testing out their spring songs it gives me some hope that the world is still turning. Plus, the rose-ringed parakeets are getting very over-excited, as well they might – they start selecting nesting sites long before anyone else gets round to it, and some of them are now actively courting.

If you haven’t heard any of these sounds before, here they are. Firstly, a great spotted woodpecker drumming in the Highlands of Scotland.

Secondly, a green woodpecker ‘yaffle-ing’

And here’s a song thrush.

And finally, the sound of rose-ringed parakeets in flight. It’s becoming as much a sound of English woodland as any of the three above, although the sight of those elegant bright-green birds munching on horse chestnuts is still strangely exotic.

Anyway, on we go. You might remember that last year the seasonal pond in the woods overtopped all of the bridges and boardwalks. This year, there has been some work done on the drainage, and the water is flowing freely. Hopefully we’ve found a happy medium, so that there is water enough for the plants and animals that rely on the dampness, while also not turning the whole site into a lake. Let’s see how we get on.

But what is this?

There is foam on some of the rivulets and streams. It doesn’t have the tell-tale soapy odour of pollution, but I’m intrigued nevertheless. So I have a look at the Environmental Agency website, which tells me that the foam (which is made up of millions of tiny bubbles) occurs when molecules such as fatty acids (known as surfactants) interact with the surface tension of the water, and allow air and water to mix more easily. Sometimes these surfactants are natural – they can occur when there is a high volume of organic material, such as dead leaves, in the water. Fatty acids are also released in small amounts by living organisms. When these organic compounds are dissolved in water, they’re known as Dissolved Organic Carbon (DOC). The majority of foam in rivers and streams is natural, and has the following characteristics:

  • It might start off white but quickly becomes cream-coloured or brown as it picks up matter and sediment
  • It has a natural, earthy, fishy or grassy smell
  • It occurs in many locations and accumulates in eddies and sheltered areas

  • The foam can persist for some time, but will gradually diminish in size
  • It’s often found where the water is turbulent or agitated (the majority of the foam in Coldfall was along the streams running into the main pond)
  • It’s often seen on windy days or following heavy rain that washes down leaves etc.

So, this seems very like natural foam to me, though I will keep an eye on it – the streams are often contaminated with run-off from the roads round about, and many of the nearby houses have been wrongly connected to the water system.

Just so that we know the difference, man-made foam

  • Appears white in colour, but often has a perfumed or soapy odour
  • Usually appears over a small area, near the site of discharge
  • Doesn’t usually occur over long distances
  • Foam disappears quickly, as modern detergents are biodegradable and will dissipate once the source of the surfactant is removed
  • Generally not related to natural events.

However, when foam-pollution events do occur they can be devastating – the River Ouse was contaminated by a soapy substance that killed thousands of fish in 2018. In 2019 a long stretch of the river Irwell in Salford turned into a ‘bubble-bath’ after someone disposed of something down a surface drain. Rivers have long been thought of as being a way to get rid of something liquid that we don’t want, with little thought for the other creatures and people who rely on it. And I haven’t forgotten the day back in 2011 when the stream in Coldfall turned bright green following someone deciding to get rid of something noxious. Some recent water testing in the Wood showed that the quality was actually surprisingly good, so let’s hope that we can keep it that way.

Sound Credits

Great Spotted Woodpecker by Simon Elliott from XC593993 Great Spotted Woodpecker (Dendrocopos major) :: xeno-canto (xeno-canto.org)

Green Woodpecker by Ramya from XC610865 European Green Woodpecker (Picus viridis) :: xeno-canto (xeno-canto.org)

Song Thrush by Rombout de Wijs from XC611036 Song Thrush (Turdus philomelos) :: xeno-canto (xeno-canto.org)

Rose-ringed Parakeet by Stanislas Wroza from XC606442 Rose-ringed Parakeet (Psittacula krameri) :: xeno-canto (xeno-canto.org)

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