The Plynlimon catchments are located in the headwaters of the rivers Wye and Severn in mid-Wales UK about 24 km from the Irish Sea coast. The catchments have an upland character at 300-700 m above sea level, are located on base-poor Lower Palaeozoic shales overlain by a mosaic of acid soils with some locally derived drift. The experiment was orginally conceived in 1968 to compare water yields from plantation forestry (Upper Severn)and grassland (Upper Wye)catchments. Three instrumented subcatchments are nested within each of the main instrumented catchments, each with its own flow gauging structure supported by automatic weather stations and a raingauge network. The site now has nearly 40 years of high temporal resolution river flow and meterological data, supplemented by hydrological process studies on flow pathways, forest intereception and evaporation. Hydrochemical measurements commenced in the Upper Wye sub- catchments at Plynlimon in 1979 and in the Upper Severn sub-catchments in 1983. Subsequently, the measurements have generated a 30 year uninterupted record of weekly to monthly measurements of wet deposition and stream water chemistry for a wide range of determinands including pH, alkalinity, nutrients, major cations, anions, trace metals, dissolved organic carbon and dissolved organic nitrogen. At various times throughout the last 30 years, "routine" monitoring has been supplemented by more detailed plot and small catchment-scale studies of flow generation, weathering and element cycling in grassland and forest systems, biogeochemical responses to forest harvesting, acid rain and atmospheric nitrogen deposition. The data from the site have been used to report on the hydrochemical responses of upland catchments to declining acid deposition, forest harvesting, agricultural management and climate change. More recently, high temporal resolution sampling has been used to develop new mathematical and statistical methods for the interpretation of short and long-term chemical trends. Data from the site have been used extensively to inform the development and calibration of biogeochemical models of acidifcation, weathering and carbon and nitrogen dynamics.
Plynlimon data, which include spatial data, time series hydrology and time series stream water chemistry, are publicly available for download at the CEH Information Gateway. From the Gateway homepage, click on "Start searching" to bring up a simple search engine, enter Plynlimon in the box and hit start search.
PI: Brian Reynolds
PI: Mark Robinson