‘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.