Friday, 11 December 2015

New turlough ??

Reading Georges blog on his trip to the Alun Valley I remembered I had also come across a large area of Marchesinia mackaii (MacKays Pouncewort) on a wooded Carboniferous Limestone outcrop on the western margin of the Nedern Brook Wetland, nr Caldicot (ST 48259 89508).
Marchesinia mackaii...I think !
That in itself is perhaps not that interesting, however the site in question certainly is !

I’ll keep it short: The Nedern Brook Wetland, is quite unusual, it is for all intents and purposes a ‘turlough’, however I don’t really like using that name in Wales.  It is dry in the summer and in the winter groundwater flooding creates a lake 1.5km long and up to 2m deep (report being finalised for NRW as we speak).  As you will know this is a very rare habitat in the UK, only one site in Wales, Pant-y-llyn nr Crosshands, currently fits the description, and there are only three very small ones in Northern Ireland completing the UK habitat.

Nedern Brook Dry (with Egret in shot too!)

Nedern Brook full of water 
Why have I never heard of this site?’ I hear you cry….well good question, I really don’t know, and I am convinced it deserves a higher profile, if only for its hydrology.

Hydrologically the site fits the turlough description however I would love to find some of the bryos that are associated with this habitat, namely: Fontinalis antipyretica and Drepanocladus aduncus and others, across the margins where seasonal flooding occurs.  I had a trip to the site with Julian Woodman looking for water peppers but we didn’t really attack the bryos on the seasonally flooded margin.

If anyone finds themselves near Caldicot and fancies a look let me know!


  1. That certainly increases my appreciation of what turloughs are all about. I'm guessing this is the site you can see along the south side of the old M4, and should I ever find myself in the area I'll certainly take a look at the bryos

  2. Thanks. I have water level and flood duration for the site so any bryos could be assigned flood depth and duration data which would be fun.

  3. It's a much appreciated birding site: I saw my first Gwent Ring-necked Duck there (I think it might even have been the first county record), and it was also a regular site for Bewick's Swan in the past.

    More pertinent to this Blog is that I did a bit of recording there in December 2002, when I found 52 species. Gareth was quite right about Marchesinia, which has one of its few VC35 sites outside the Wye Valley there. Other species of note include Reboulia hemisphaerica on thin soil, and abundant Plagiomnium cuspidatum on limestone. I noted a few species on molehills, but water levels were high so I couldn't look for flood ephemerals. It would be nice if Ephemerum hibernicum (E crassinervium var rutheanum) was there... it is present nearby at Wentwood Reservoir and also grows at Pant-y-llyn and in Pembrey Forest (its only known British sites).

  4. PS I would anticipate Drepanocladus aduncus on the fluctuating wetland margin, but it might not have enough trees (or rocks) in the wetland for Fontinalis to be present. I must look, if my colleagues can sort out access: it's only 40 minutes from home.

  5. Hi Sam, I can sort access for you if you need as Ive been working on the site recently so on good terms with landowners (I hope!). On the west (ST 48277 89515) there are lots of rocks and trees at the wetland margin covered in bryos. This part can be accessed via a footpath from the main road (ST 47895 89428). Its very wet at the moment but if we get prolonged dry period levels should fall, it would certainly be dry by March/April and the flooded margins perhaps earlier?? Pack your wellingtons !

  6. My experience at Pant-y-llyn suggests that it's best to check in mid to late summer, so that Ephemerum have time to fruit. In contrast, relatively short draw-down periods on reservoirs in the Beacons can produce vast numbers of Riccia huebeneriana etc, even in winter. I suspect the best option will be for me to visit some time in June or July 2016.