The Ecosystem Overviews provide a summary introduction to the main habitat types covered in APIS and the main air pollutant pressures to those habitats in the UK. In specific locations, e.g.. close to a major source, other pollutants may be a concern for a habitat and the user should use the searches by location or by habitat/pollutant in these cases.
Freshwater habitats include both flowing and standing waters. The UK has a great variety of running waters, from fast-flowing upland rivers, to chalk streams in the south-east and slow-flowing rivers of eastern England. Standing waters are similarly diverse, ranging from small mountain corrie lochs to lowland ponds, large lakes and reservoirs (JNCC, 2010).
BAP Habitats: Mesotrophic lakes (priority); Eutrophic standing waters (priority); Aquifer fed naturally fluctuating water bodies (priority); Chalk rivers (priority); Rivers and streams
Main Pollutant Impacts
Nutrients, specifically phosphorus and nitrogen, are responsible for the eutrophication of rivers and lakes. Many lakes in the UK are now affected in this way, particularly in low lying areas (Gibson et al. 1995, Bailey-Watts 1990). More recently, there are signs of eutrophication in rivers (Environment Heritage Service 1998), mainly of lower oxygen concentrations and increased macrophyte growth.
For oligotrophic lochs and lakes N deposition plays an important role as the dominant source of nitrogen is through atmospheric inputs. Higher dissolved inorganic nitrogen DIN and total nitrogen is experienced in high deposition areas. N deposition also increases primary productivity (phytoplankton) of oligotrophic lakes. N deposition can drive lakes from N limitation to P limitation (Elser et al 2009). On a species level shifts in algal communities have been observed and also losses in rare macrophyte species, with an increase of other (nuisance) species. See Noordwijkerhout workshop reports.
Bergström & Jansson (2006) showed that N limitation is widespread in upland lakes and that even P-limited sites may once have been N-limited but are now so modified by anthropogenic N deposition their nutrient status has changed (RoTAP, 2012)
Acid deposition onto freshwaters (and catchments) can lead to acidification. The areas affected by freshwater acidification in the UK are parts of Wales, The Lake District, the Pennines, parts of southern England, the Cairgorms, the Trossachs and Galloway, and in Northern Ireland, the Mourne Mountains (Critical Loads Advisory Group 1995; Review Group on Acid Rain 1997). Over 20% of freshwaters in the UK exceed their critical loads for acidity (2006-2008 deposition data). The biological groups affected by freshwater acidification include fish (mainly brown trout), invertebrates (mayfly and caddis larvae), macrophytes and the dipper (Critical Loads Advisory Group 1995), (Kernan et al 2010).
In 1988 the UK Government established the Acid Waters Monitoring Network to monitor the response of acidified surface waters to emission reductions. Twenty years of monitoring shows that acidified lakes and streams are now showing clear signs of both chemical and biological recovery from acidification in all affected regions but that the recovery so far is limited and that other stresses in future, especially from atmospheric nitrogen deposition and from climate change, may prevent a full recovery (Kernan et al, 2010). http://awmn.defra.gov.uk/resources/interpreports/20yearInterpRpt.pdf
Heavy metals and POPs
Deposition of heavy metals and POPs onto lakes occurs, even in rural and remote areas (Battarbee et al. 1988; Duarte-Davidson et al. 1996; Gevao et al. 1997), but the ecological effects of this are not known. If any biological groups are affected, they are likely to be fish (and fish-eating birds) and sediment-dwelling organisms. Endocrine disrupters are not normally considered as POPs, but they can be mentioned in this section as an emerging issue.