Llanelli Naturalists Newsletter - September 1999 - No 64
Richard Pryce

The recent discovery of Petalwort (Petalophyllum ralfsii) (illustrated on back cover) at the former ash lagoon west of the recreation ground at Pwll, further endorses the unprecedented importance of this site in nature conservation terms, not only in a Welsh context but also in the UK. The wildlife interest of the lagoon has been known for some years with records of Royal Fern (Osmunda regalis), several pairs of Lapwings breeding in some seasons and large numbers of Snipe feeding in winter. It is only in the last two years, however, that sustained and regular botanical monitoring has been carried out.

Prior to these more intensive studies, the lagoon was flooded to a depth of up to 2m. The physical nature of the fly-ash that was pumped as a slurry from the now demolished Carmarthen Bay Power Station was that it separated into two fractions: particles that sank and particles that floated. The ‘floaters’ tended to coalesce to form floating islands which drifted with the wind and ultimately became vegetated with a distinctive and diverse floral community whilst still drifting from end to end of the lagoon. Due to an unfortunate incident in which a visiting child was stranded on one of the floating islands, the lagoon was drained about four years ago. Floating islands are not an uncommon feature of fly-ash lagoons elsewhere in the country but the Pwll system was destroyed during the draining process and the islands became beached and are now fixed in position. Water from old colliery workings ensures that the lagoon remains flooded to a depth of up to 300mm to 400mm at the western end whilst it is always ‘soggy’ at the eastern end, even in dry summer weather.

The chemistry of the ash is such that after leaching for a few years it is able to support plant species which in natural habitats are often confined to highly acid or highly alkaline conditions. Thus, normally acidophile species such as Royal Fern (illustrated on front cover), Lemon-scented Fern (Oreopteris limbosperma) and species of bog-moss including Sphagnum fimbriatum and S. subnitens, grow in juxtaposition with acidophobes such as Blunt-flowered Rush (Juncus subnodulosus), Slender Clubrush (Isolepis cernua) and Southern Marsh-orchid (Dactylorhiza praetermissa). One of the most notable features of the plant community is the great abundance of Common Sundew (Drosera rotundifolia). This is a fly-catching plant with leaves bearing sticky tentacles growing up to about 150mm tall. It is usually found sparsely in upland, acid bogs and flushes, often growing on mosstussocks but here it carpets some areas of the floor of the drained lagoon in such great profusion that it is impossible to walk without treading on the delicate plants.

The visit to the lagoon by members of the Botanical Society of the British Isles on 21 August this year enabled it to be scrutinised by over forty of the country’s most eminent botanists all of whom expressed their delight and sense of privilege at being introduced to such a unique site . Not surprisingly several new and outstanding findings were made. Several hundred tiny plants of the acidophobic Lesser Centaury (Centaurium pulchellum) were discovered in one spot. This species is known from the dune systems of Tywyn and Laugharne Burrows where characteristically it grows in rabbit-grazed dune slacks and formerly in a few rides in Pembrey Forest. It has not, however, been seen in the county since 1991, even at its previously known sites.

But the discovery by Arthur Chater during the meeting of Petalwort was extremely important. This species is a liverwort which is rarely more than about 10mm across but when examined under the lens resembles a tiny lettuce! It is included on Schedule 8 of The Wildlife and Countryside Act and therefore enjoys total protection from uprooting or other intentional disturbance. It has been previously recorded from single sites at both Tywyn and Pendine Burrows but is known nationally only from pristine dune grassland. This new finding therefore extends the known type of habitat on which the species is able to grow and demonstrates its ability to effectively colonise new habitat.

It is vital that this Pwll Lagoon is conserved as part of Llanelli’s Millennium Coastal Park. It has already been proposed by Carmarthenshire County Council as a Local Nature Reserve but the discovery of Petalwort affords it a whole new status which qualifies the site for designation as a Site of Special Scientific Interest. Future management will present its own problems, with the arrest of scrub colonisation being foremost amongst the urgent measures required.