The Acid Waters Monitoring Network was set up by the predecessor to Defra in 1988 to monitor the response of acidified lakes and streams in the UK to planned reductions in the emissions of S and N gases from UK power stations under various UNECE Protocols and EU Directives. It has since become one of the highest quality upland water monitoring and research networks in Europe, providing nationally unique information on long-term environmental and ecological change in source water areas of importance for key ecosystem services, including biodiversity, water supply, salmonid fishery and recreation.

In 2013, following a change in funding arrangements and the widening of the Network’s remit, the Network was modified and re-launched as the Upland Waters Monitoring Network (UWMN) ( external link) with the additional objectives of tracking trends in water quality and freshwater biodiversity across the Uplands in response not only to S and N deposition but also to climate and land-use change. Sites with higher alkalinity are being added and new protocols are being introduced as resources become available.

Key areas

  • 24 acid sensitive headwater streams and lakes across the UK draining moorland and forested catchments and spanning a depositional gradient from low to high S and N for which there is now a 26 year time series of measurements;
  • chemical measurements (monthly at stream sites, quarterly at lake sites) include pH, alkalinity, ANC, Ca, Mg, Na, K, SO4, xSO4, Cl, NO3, Total P, Sol Al, Labile Al, Non-lab Al, DOC, Cond.) using methods, limits of detection, accuracy and quality control appropriate to low alkalinity upland waters;
  • annual biological sampling including diatoms, aquatic macrophytes, macroinvertebrates and quantitative fish surveys, with identification to species;
  • recent addition of four new sites to extend the environmental range to cover higher alkalinity waters not sensitive to acid deposition;
  • lake temperature data-loggers from 1999, and addition of stream thermistors and water level monitoring at three lake sites from 2010;
  • rigorous quality control data analysis, interpretation and presentation in annual reports with interpretative reports prepared and published every five years;
  • submission of data from four sites to the UK ECN, LTER Europe and ILTER, six sites to UNECE ICP Waters and two sites to UNECE ICP Integrated Monitoring;
  • publication of highly cited research papers in peer-reviewed literature;
  • support for a wide range of national (e.g. NERC or national government funded) and international (e.g. EU Framework) research projects and water quality tool development projects.

Principal findings over the first 20 years (1988-2008)

  • major decline in the concentration of sulphate in acidified waters throughout the UK illustrating the success of UK’s policy on sulphur emissions under UNECE and EU Protocols and Directives;
  • water quality (pH and alkalinity) is improving at previously acidified sites (forested and non-afforested, lake and stream) in the UK;
  • the quality and biodiversity of previously acidified upland waters, despite the improvement, remain a long way from achieving good ecological status;
  • Dissolved Organic Carbon (DOC) concentrations have more than doubled in upland waters across the UK over the last two decades as a result of de-acidification;
  • Nitrogen deposition has caused a long-term increase in nitrate concentration in many upland waters, nitrate is continuing to increase in some sites, despite the significant reduction in emissions that has occurred over the last two decades, and atmospherically deposited nitrogen threatens upland ecosystems both through acidification and eutrophication;
  • the acidity of upland surface waters is influenced by variability in regional-scale variation in climate, as represented for example by the North Atlantic Oscillation (NAO), and anticipated future climate change especially increased winter precipitation could reduce or even negate improvements achieved by reductions in acid deposition;
  • lead and mercury levels in animals, plants and sediments at some sites remain at high levels despite reductions in emissions, probably as a result of remobilisation from previously contaminated catchment soils, a concern for the future, should higher rainfall promote accelerated soil erosion.

Legislative Drivers for which UWMN data provides evidence

  • UNECE Convention on Long-Range Transboundary Air Pollution (LRTAP);
  • EU National Emissions Ceilings Directive;
  • EU Water Framework Directive 2000/60/EC;
  • EU Environmental Quality Standards Directive (Priority Hazardous Substances) 2008/105/EC;
  • EU Habitats Directive 92/43/EEC;
  • Convention on Biological Diversity

Operational arrangements

The UWMN is a consortium of funders and scientists coordinated by ENSIS Ltd. at University College London (UCL). In addition to ENSIS, it includes the Department for Environment, Food and Rural Affairs (the principal funder), The NERC Centre for Ecology and Hydrology, Marine Scotland Science, the Department of the Environment Northern Ireland, the Environment Agency, Natural Resources Wales, Forestry Commission, Scottish Natural Heritage, Scottish Environment Protection Agency, the Welsh Government, Queen Mary University of London and University College London.