Paul A. Stevens

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Dissolved organic nitrogen (DON) has been hypothesized to play a major role in N cycling in a variety of ecosystems. Our aim was to assess the seasonal and concentration relationships between dissolved organic carbon (DOC), DON, and NO3- within 102 streams and 16 lakes within catchments of differing complexity situated in Wales. Further, we aimed to assess(More)
Ombrotrophic peats in northern England and Scotland, close to industrial areas, have substantial contents of potentially toxic metals (Al, Ni, Cu, Zn, Cd and Pb) and of pollutant sulphur, all derived from atmospheric deposition. The peat sulphur, ordinarily in reduced form, may be converted to sulphuric acid under drought conditions, due to the entry of(More)
Data are presented demonstrating how clearfelling has changed soil and stream water aluminium chemistry. For soil waters, a strong empirical relationship was observed between inorganic aluminium (Al(inorg)) and total inorganic anion (TIA) concentrations. Before felling, chloride and sulphate accounted for the largest proportion of the TIA concentration.(More)
We assessed the effects of different simulated sampling regimes (weekly, fortnightly, monthly and bimonthly) on parameters describing the water chemistry of 72 streams in acid-sensitive areas of Wales. For pH, sulphate, total hardness and aluminium, reduced sampling frequency had no discernible or systematic effect on the apparent annual mean chemistry(More)
Changes in the chemistry of bulk precipitation and stream water between 1982 and 2000 are described for small moorland and forest catchments located within Beddgelert Forest in north Wales. Two forest catchments were partially clearfelled in 1984 (D2; 68% and D4; 28%) whilst a third (D3) remained as an unfelled control until autumn / winter 1998/99 when(More)
Water was sampled from an acid forest soil 1 year after a Sitka spruce crop had been clear-felled. In samples extracted using porous ceramic cups, total dissolved nitrogen varied according to depth from 2.6 to 3.6 mg.l−1. In the organic horizons, dissolved nitrogen was mainly in organic form. As it passed down the profile, it was progressively transformed(More)
An input-output budget for dissolved inorganic-N in a small forested catchment in North Wales is presented. From 1982 to 1990, bulk precipitation inputs averaged 10.3 kg ha(-1) year(-1), whereas throughfall inputs in 1983-1984 were 20.3 kg ha(-1) year(-1). Streamwater outputs were consistently larger than bulk precipitation inputs, averaging 14.6 kg ha(-1)(More)
Zeolite-based catalyst bodies are employed on a global scale in important chemical processes, such as the synthesis of many bulk chemicals as well as crude-oil refining. 4] Particular examples include xylene isomerisation, 6] benzene alkylation 8] and methanol conversion to hydrocarbons. 10] Catalyst bodies, such as extrudates, have millimetre-sized(More)
A catchment approach was used to estimate mean dissolved inorganic-N concentrations and fluxes through three mature Sitka spruce plantations at Beddgelert (north Wales), Plynlimon (mid-Wales) and Kershope (Cumbria). Dissolved inorganic-N in bulk precipitation, throughfall, stemflow, soil water at 4 or 5 depths, and streamwater was measured every two weeks(More)
The need and ability of an organisation to manage and control its impact on the environment has been hotly debated in recent times. However, the uptake of certificated environmental management systems (EMS), specifically BS EN ISO 14001 (ISO 14001) (British Standards Institution, 2004), is becoming more prevalent, even though evidence of the individual(More)