Coring and assessment of the lagg fen at Cors Caron NNR, Ceredigion, Wales

Hughes, P.D.M. (2002) Coring and assessment of the lagg fen at Cors Caron NNR, Ceredigion, Wales (Reports from PLUS, 2002/01) Southampton, UK. PLUS

Record type: Monograph (Project Report)

Abstract

Five sample cores were taken from two areas of lagg fen surrounding Cors Caron West Bog and described using the Tröels-Smith system of sediment classification. Two cores were selected for further laboratory analyses; one (Lagg2) was located near to the western hill slope margin and the other (Lagg5) on the banks of the Teifi river channel. Plant macrofossil analyses of core Lagg2 showed that peat development began in a marginal woodland, which was overtaken by a relatively dry raised bog community. The bog developed for several thousand years and was eventually invaded by low hummock and lawn Sphagna typical of wet oceanic raised bogs. At the same point the Sphagnum-rich peat shows signs of disturbance in the form of charcoal layers and an increase in soil fungi. These features may represent secondary decomposition after peat cutting. The bog assemblage is abruptly replaced by a wet fen assemblage that may represent in-filling of an abandoned peat cutting. Lagg2 is almost certainly not an intact sequence and the modern lagg vegetation most probably represents the latest stage in a secondary succession towards raised bog. The succession from wet fen to the modern vegetation appears to be an undisturbed record. This part of the sequence may represent a valuable analogue for the development of marginal pools and blocked former-cuttings on the present day peat surface. The depth of the hiatus in the Lagg2 record (110cm) suggests that the presumed peat cutting occurred several hundred years ago. This conclusion is supported by some preliminary observations of SCP concentrations in the upper peat. Most if not all of the industrial period appears to be represented within the upper three zones of Lagg2.

Core Lagg5 provides a contrasting history of lagg development. On the banks of the Teifi fen conditions have prevailed throughout the time period represented by the core. Various Carex species, including Carex rostrata and Curta are present throughout the peat sequence. Other constant species include potentilla palsutris, Galium palustre and Eriophorum vaginatum. More detailed pollen and SCP analyses will be required to verify these findings prior to using the site for a high resolution reconstruction of vegetation development.

In summary, the lagg fen on the banks of the Teifi may provide a valuable record of continuous lagg fen development, whereas the superficially similar lagg communities on the western margin of the West Bog have been significantly disturbed albeit several hundred years ago. The western lagg does provide a detailed and well preserved record of secondary lagg development after the abandonment of cuttings.

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