Wetland types

Submitted by olipescott on Mon, 09/26/2016 - 09:29

This is a reply to a question posted under a blog post. The original comment thread is here. The questions were:

What is it that you are calling a 'flush'? There is no mention of such a noun relating to water features on the web.

You clearly don't mean a stream or spring because you use those words separately in The Guidance Notes.

So please give us a full definition of a 'flush'.

(already answered here)

followed by:

Thanks for that definition. So since the water is oozing out from below, its source will not be visible. That water could create a STREAM [habitat5] or 'saturated ground' which could be a MARSH, MIRE, MOOR, SWAMP or FEN [habitat8] or a BOG or MOOR [habitat2]. However a MARSH, MIRE, MOOR, BOG or FEN can also be formed by water accumulating or flowing onto/into flat ground, so is the difference between them the source of the water?

Is a legitimate simplification of a 'flush' for survey purposes: where water from underground on a slope creates a bog rather than a spring ?

This would mean that the ditches in our calcareous square [some of which dry out in the summer and some not], would have their sources as either SPRINGS or FLUSHES [habitat8] near the bottom of the slope and the ditches would count as STREAMS [habitat5]

which I answer below:

Hi Nic

Sorry for the slight delay in replying. Your conclusion sounds fine to me. We no doubt should have dealt more explicitly with ditches in the guidance; we will update this in due course. As you say, a more ‘natural’ ditch in a lowland landscape (perhaps a stream that has been straightened or deepened to improve drainage) would be quite likely to begin as a flush at its source (although in a lowland setting where the soil is not peaty these might also give rise to fens, given that they might have tall-herb vegetation rather than being on open, gravelly substrates). In general though, flushes are almost always on gently sloping ground close to the source of the water, and therefore mineral soils/peats don't form to the same extent as on level ground where they go on to form mires, fens etc. Flushes are also more or less seasonally inundated, and this helps to maintain open conditions.

This distinction between peaty and non-peaty (i.e. mineral) soils is the other key distinction between some of the habitats you mention. Marshes, swamps, fens refer to habitats formed through the waterlogging and build-up of mineral soil; moors and bogs result from the water-logging and build-up of peaty soils; mire is often used as more of a 'catch-all' term that can refer to the water-logging/build-up of either soil type. The source of the water is also an important part of defining types of wetlands, but it is not the main distinction between the habitat types that you mention.

We recommend this recent book if you would like any more information on any of these topics (see also this gloss relating NPMS habitats to sections of that book). I believe that NPMS volunteers are still entitled to a discount on this book through Summerfield (email support@npms.org.uk to confirm this).

We realise that sometimes these habitat definitions can be challenging, and it is also the case that some of these habitats blend into one another (and that some authors give subtly different definitions), but we hope that you are finding the process of learning about them interesting. Many thanks for your efforts on behalf of the NPMS.

All the best