The quality of water draining the UK uplands has been profoundly affected by atmospheric pollution since the onset of the industrial revolution. Of primary concern has been the widespread acidification of lakes and streams by acid deposition, in the form of sulphur (S) and nitrogen (N) compounds, and hydrochloric acid, derived primarily from fossil fuel combustion.
Controls on acidic emissions were initiated in the 1980s through the United Nations Economic Commission for Europe (UNECE) Convention on Long Range Transboundary Air Pollution (LRTAP) with the specific aim of reducing the impact of acid deposition on soils, vegetation and surface waters. As a result, over the last three decades there have been dramatic reductions in the emissions of S and N gases to the atmosphere in the UK and in Europe as a whole.
UK Acid Waters Monitoring Network
To assess the chemical and biological response of acidified lakes and streams in the UK to the planned reduction in emissions, the UK Acid Waters Monitoring Network (AWMN) was established by the UK Department of Environment (now Defra) in 1988, following the recommendations of the UK Acid Waters Review Group (AWRG, 1987).
The AWMN was set up explicitly to monitor responses to reduction of acidifying emissions of S and N, and compare responses along a gradient of deposition (essentially north to south), using acid-sensitive sites in the low-deposition region in the north-west as controls. The Network was also designed to assess the differences between lakes and streams, especially with respect to differences in their respective hydrological regimes, and the differences between sites with afforested and moorland catchments. Site selection attempted to include sites in all the principal acidified regions across the UK.
The 22 original AWMN sites were all located in relatively acid-sensitive regions, in upland areas with catchments underlain by base-poor soils and geology. Although monitoring has been underway at most sites since 1988, sampling at certain sites began later and there have also been a small number of interruptions in the record when sampling was not possible (eg. Foot and Mouth). The Network originally comprised 10 stream and 10 lakes sites. In 1990 two sites in Northern Ireland were added (Blue Lough and Coneyglen Burn), supported by funding from the Department of Environment (Northern Ireland). At the start of 1991 the Nant y Gronwen (site 18) was removed from the Network following a request from the landowner and was replaced by a nearby moorland stream, Afon Gwy. In 2001, as a result of water abstraction and damming by a local fish farm at Coire nan Arr a new control site was added to the Network, Loch Coire Fionnaraich. In 2011 a site in the chronically acidified and previously unrepresented North York Moors was incorporated, Danby Beck.
Between 1988-2004 the network was funded primarily by the Air Quality Division at Defra (previously Department of the Environment), with two sites in Northern Ireland being funded by the Department of Environment (Northern Ireland) (DoE(NI)). The Scottish Executive (SE) and subsequently Scottish Government (SG) contributed 50% of the funding for AWMN work by The Scottish Government's Marine Scotland Freshwater Laboratory (FRS). In 2001 DoE(NI) withdrew from the Programme and Defra took up funding of the Network in Northern Ireland.
UK Upland Waters Monitoring Network
In 2013 the UK Upland Waters Monitoring Network (UK UWMN) replaced the UK Acid Waters Monitoring Network. Designed to augment the already broad suite of monitoring, the new Network has added thermistors to all stream sites, thermistor chains to all lake sites and is rolling out lake level and outflow monitoring as funding allows. To increase the alkalinity gradient of the Network, two new less acidic sites were added, both already possessing long time-series of chemical and biological data; ECN Trout Beck and Baddoch Burn.
Following a funding hiatus at Defra in mid-2007, chemical sampling and analyses at several sites were halted and, more widely, fish surveys and lake macrophyte surveys were cancelled for that year. The reduction in funding was formalised later in 2007 with the annual budget from Defra reduced in 2007-2010 by 78% over 2006-2007 levels. Support was withdrawn completely in 2016.
The Network of sites and analyses that remained after reductions in central funding has been sustained only as a result of significant contributions in kind from UKCEH and ENSIS-ECRC at UCL; financial assistance from the Environment Agency (EA), the Forestry Commission (FC), Natural Resources Wales (NRW), the Scottish Environmental Protection Agency (SEPA), Scottish Natural Heritage (SNH) and the Welsh Government; and assistance from Marine Scotland, the School of Biological Sciences, Queen Mary University of London (QMUL) and several private individuals. This support enabled most sampling protocols to be maintained, but considerable backlogs of un-analysed biological samples started to accumulate from around 2016.
In 2019, the UWMN was recognised as a key contributor of data on the impacts of air quality on freshwater ecosystems to the UK’s developing UK Air Pollution Impacts on Ecosystem Networks (UK APIENs). The purpose of UK APIENs is to monitor and report the negative impacts of air pollution (e.g. acidification, eutrophication, ozone damage or changes in biodiversity) on ecosystems that are representative of freshwater, natural and semi-natural habitats and forests in the UK. It was established initially as the UK contribution to the EU National Emissions Ceilings Directive reporting requirements, now referred to as UK National Emissions Ceilings Reporting. As a result of UK UWMN's importance, Defra funded the analysis of the large biological sample backlog. In 2021 it underpinned an interpretive assessment of chemical and biological (epilithic diatom and macroinvertebrates only) trends and will be supporting summer fieldwork activities across the network.