There are very few, if any, truly natural water courses in Wales: most rivers, for example, have undergone one or more of channel straightening, bank modifications, water extractions, the insertion of weirs and dams or the construction of marinas and barrages where they enter the sea. They have also, along with most smaller streams, suffered varying degrees of pollution as a consequence of acid rain, nitrogen deposition, sheep dips, sewage treatment plants, eutrophication from land run-off etc. For the purposes of nature conservation, watercourses in the UK have been assessed for changes in their expected or known trophic status, with a view to detecting signs of acidification or eutrophication, while invertebrate sampling has been used as an indicator of water quality.
Watercourses
Streams
Rocky, acidic upland streams are potentially the most ‘natural’ of the watercourses in Wales. The banks have rarely been modified and carbon dioxide is freely available in the water, allowing mosses and liverworts, for example, to thrive. They are also less prone to pollution from industry and sewage plants, though they will still be impacted…
Rivers
The flora and fauna of a river is determined by the availability of sufficient oxygen and the variety of essential chemicals for river life. The flora is influenced by the trophic status of the water, i.e. soft acidic water, hard calcareous, or something in between, and these conditions will typically be influenced by the nature…