Welsh Journals

Some Factors ControDÌng VarÌatíons in Chenüstry of an Upland Stream in Mid-Wales. B.REYNOLDS, M.HORNUNG AND S.HUGHES Institute of Terrestrial Ecology, Bangor Research Station, Penrhos Road, Bangor, Gwynedd. (Received November 1983; in revised form December 1983) Abstract The chemistry of a first order tributary stream of the Upper Wye in Mid-Wales and underlain by hard Palaeozoic mudstones has been studied over a two year period. The stream water is characterised by a low solute content and a mean pH of 5.27 while sodium and chloride are the principal ions present. Several patterns have been observed in the temporal variation in concentration of solutes and these include cyclic patterns, patterns demonstrating a response to specific climatic events and patterns reflecting the balance in the stream of water from different sources within the catchment. The processes controlling these variations in concentration are discussed and the relationship between solute concentrations and streamflow investigated using a mixing model. Introductíon In recent years considerable attention has been focussed on the possible impact of land use changes in the uplands, such as affore- station and land improvement, on water quality and stream biota. To assess the impact of such changes, data are required on the chemistry of streams draining unmanaged catchments, the natural variations in chemistry that occur and the factors controlling these variations. This paper presents such data for a small tributary stream in the uplands of Mid-Wales. StudyArea The study reported here concerns a small, first order tributary of the Afon Cyff, one of the headwater streams of the River Wye which rises on the eastern slopes of Plynlimon, Fig. 1. The tributary catch- ment rises from 410m to 509m above sea level and is underlain by hard mudstones of the Silurian Frongoch formation. The soils are dominated by stagnopodzols formed in slope deposits derived from the mudstone and associated with an acid grassland vegetation dom- inated by Nardus stricta. Significant areas of acid Eriophorum peat