Trends and seasonality in stream water chemistry in two moorland catchments of the Upper River Wye, Plynlimon
- 1Institute of Terrestrial Ecology, Bangor Research Unit, UWB, Deiniol Road, Bangor, Gwynedd, LL57 2UP.
- 2Institute of Hydrology, Maclean Building, Crowmarsh Gifford, Wallingford, Oxon OX10 8BB.
- 3Institute of Terrestrial Ecology, Monks Wood, Abbots Ripton, Huntingdon PE17 2LS.
- 4Institute of Hydrology, Staylittle, Llanbrynmair, Powys, SY19 7DB.
- 5Institute of Terrestrial Ecology, Merlewood Research Station, Windermere Road, Grange-over- Sands, Cumbria LA 11 6JU.
Abstract. Stream water chemistry in the Cyff and Gwy subcatchments within the headwaters of the River Wye has been monitored regularly since 1980. In the Gwy, which is a predominantly semi-natural grassland catchment, land use has remained relatively static over the monitoring period, whilst the Cyff catchment is more buffered because of base cation inputs from agricultural improvement and ground water sources. Using a variety of statistical techniques, the long-term data are examined for evidence of trends after eliminating seasonal effects. The results highlight some of the difficulties associated with the analysis of longterm water quality data which show considerable variability over a variety of timescales. Some of this variability can be explained in terms of hydrochemical responses to climatic extremes and episodic events such as large atmospheric inputs of seasalts. The long-term fluctuations in solute concentration underline the continuing need for maintaining consistent long-term monitoring at sensitive upland sites if underlying trends related to gradual changes in pollutant deposition or climate are to be detected with any certainty.