i) Acid deposition has declined across Europe and North America but chemical and biological recovery in streams is slow. Mitigation techniques such as liming are still being considered, but they have seldom been evaluated across whole catchments. ii) At 42 stream sites in the upper catchment of the River Wye, macroinvertebrates and diatoms were evaluated as bio-indicators of water quality. Both groups indicated continued acidification in headwaters. iii) Chemical and biological responses to catchment liming in the upper Wye were assessed through a Before-Afler-Control-Impact (BACI) experiment across multiple limed, acid control and circumneutral reference sites. Liming did not change pH, alkalinity, calcium or aluminium at limed sites relative to acid controls because effects were small or masked by marked inter-annual variations in discharge. iv) There was no significant change in the abundance or richness of macroinvertebrate assemblages at treated sites in the first two post-liming years. Acid-sensitive species (e.g. Baetis rhodani) colonised some limed sites, but not at a significantly increased frequency. v) In-situ survival experiments revealed increased mortality in Baetis rhodani in limed and acid streams relative to circumneutral reference streams even following brief exposures. vi) These data illustrate that recent liming of streams in the Wye catchment has not yet changed stream chemistry sufficiently to support acid-sensitive macroinvertebrate assemblages similar to those found at circumneutral sites. Further lime applications and continued evaluation is recommended.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:583940 |
| Date | January 2006 |
| Creators | Lewis, Bethan Rhiannon |
| Publisher | Cardiff University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://orca.cf.ac.uk/56101/ |
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