UN ECE Convention on Long-Range Transboundary Air Pollution - International Cooperative Programme on Integrated Monitoring of Air Pollution Effects on Ecosystems. Report of the UK Focal Point to DoE

Data collected at 22 lake and stream sites under the UK Acid Waters Monitoring Network, 'established in 1988. arc assessed. Non-marine sulphate concentrations in surfacewaten largely reflect the sulphur deposition gradient across the country. Time seria analysis indicates an increase in non.rnazine sulphate concentrations at sites in SW Scotland, the Lake District and in Wales. No similar trends have beendetected in deposition data for the samc pcnod. Predictions of water chemistry response at each site to the new UNECE sulphur protocol have been made using a long-term, dynamic acidification model (MAGIC). The results indicate that the agreed emissions reductions will lead to recovery at many sites over a 15-20 year timescale but will have little effect at thc most impacted sites, within the next 15 years. Hydrological Processes, 10: 183-203 (1996) WATER QUALITY TRENDS AT AN UPLAND SITE IN WALES, UK, 1983-1993 A. J. ROBSON AND C. NEAL Institute of Hydrology. Growlnarsh Gifford. Wallingford. OXIO 888. UK ABSTRACT Ten years of detailed upland stream and bulk deposition water quality data from Plynlimon, mid-Wales. are etamined for trend. A robust statistical test (the seasonal Kendall test) is applied and data are presented graphically. Smoothing techniques are used to highlight the patterns of change which underlie high data scatter. The graphs show longterm cycles within the data which violate the assumptions of common statistical tests for trend. These cycles relate to fluctuations in the weather patterns at Plynlimon. Even though the seasonal Kendall test is significant for some determetands. the evidence from the graphs suggests that many of these 'trends' are unlikely to continue. For solutes in rainfall, there is no convincing long-term trend. There is • possible increase in ammonium concentrations. which may indicate an increasing •tmospheric source generated by farming activities, but this will require a longer data series for confirmation. Several trace metal concentrations increased significantly part way through the study period, but later returned to the original levels. The bulk precipitation sea salt input has been uneven over the 10-year sampling period. with the highest inputs occurring during the wetter winten. For solutes in streamwaters, there are clear trends in dissolved organic carbon (DCC). iodine and bronude. which increase over time •nd may be aunbuted to an increase in organic decomposition in the catchment. Previous studies in Wales have shown similar behaviour for colour, which is related to DCC. but thecorresponding changes for bromide and iodine are new. For most other streamwater determinands, anyciunges are masked by the effects of year to yearvariations in the quality and quantity of rainfall. For example, zinc and chromium variations parallel the corresponding rainfall quantity variations. The effect of rainfall quality variation is marked for marine-derived elements such as chlonde. For sulphate, streamwa ter variations •re inverted relative to chloride. This suggests that dry deposition may flry Intl%washer conditions: high when the wind direction is from the land and low when weather systems art predominantly frontal and laden with sea salts. Alternatively, high sea salt rainfall may be affecting absorption/solubility reactions in de soils. There are four main conclusions. Firstly, there is no indication of changing acid deposition inputs Of changing acidity within the runoff, despite a decline in UK sulphur dioxide emissions. Secondly, st reamwa ter DOC has showan increase over time, but there is no clear corresponding decrease in pH as might he ex peeredfrom acidification theory. Thirdly. there are cyclical variations in bulk precipitation inputs and in ssreamwater quality, which mean that trends cannot be established even with 10 years of data. Long-term cycles are likely to exist in other environmental data •nd extreme care is required for the interpretation of trend, especially if data seu are short. This aspixt strongly supports thecontinuation of long-tenn monitoring programmes over several decades. Finally, the graphical application strongly enlunces data analysis and should be considered an essential component of trend investigation.Ten years of detailed upland stream and bulk deposition water quality data from Plynlimon, mid-Wales. are etamined for trend. A robust statistical test (the seasonal Kendall test) is applied and data are presented graphically. Smoothing techniques are used to highlight the patterns of change which underlie high data scatter. The graphs show longterm cycles within the data which violate the assumptions of common statistical tests for trend. These cycles relate to fluctuations in the weather patterns at Plynlimon. Even though the seasonal Kendall test is significant for some determetands. the evidence from the graphs suggests that many of these 'trends' are unlikely to continue. For solutes in rainfall, there is no convincing long-term trend. There is • possible increase in ammonium concentrations. which may indicate an increasing •tmospheric source generated by farming activities, but this will require a longer data series for confirmation. Several trace metal concentrations increased significantly part way through the study period, but later returned to the original levels. The bulk precipitation sea salt input has been uneven over the 10-year sampling period. with the highest inputs occurring during the wetter winten. For solutes in streamwaters, there are clear trends in dissolved organic carbon (DCC). iodine and bronude. which increase over time •nd may be aunbuted to an increase in organic decomposition in the catchment. Previous studies in Wales have shown similar behaviour for colour, which is related to DCC. but thecorresponding changes for bromide and iodine are new. For most other streamwater determinands, anyciunges are masked by the effects of year to yearvariations in the quality and quantity of rainfall. For example, zinc and chromium variations parallel the corresponding rainfall quantity variations. The effect of rainfall quality variation is marked for marine-derived elements such as chlonde. For sulphate, streamwa ter variations •re inverted relative to chloride. This suggests that dry deposition may flry Intl%washer conditions: high when the wind direction is from the land and low when weather systems art predominantly frontal and laden with sea salts. Alternatively, high sea salt rainfall may be affecting absorption/solubility reactions in de soils. There are four main conclusions. Firstly, there is no indication of changing acid deposition inputs Of changing acidity within the runoff, despite a decline in UK sulphur dioxide emissions. Secondly, st reamwa ter DOC has showan increase over time, but there is no clear corresponding decrease in pH as might he ex peeredfrom acidification theory. Thirdly. there are cyclical variations in bulk precipitation inputs and in ssreamwater quality, which mean that trends cannot be established even with 10 years of data. Long-term cycles are likely to exist in other environmental data •nd extreme care is required for the interpretation of trend, especially if data seu are short. This aspixt strongly supports thecontinuation of long-tenn monitoring programmes over several decades. Finally, the graphical application strongly enlunces data analysis and should be considered an essential component of trend investigation. KEY aromas trends. water quality. Plynlimon. Wales; seasonal Kendall, robust rtgrasion Science of the Total Environment, In Press. Dissolved chromium pollution in rainfall and surface waters in mid-Wales during the mid 1980s Colin Neal, Christopher J. Smith, Hazel A. Jeffery, Martin Harrow and Margaret Neal. Institute of Hydrology, Maclean Building, Crowmarsh Gifford, Wallingford, OXON, OXIO8BB, UK