Acidification and otter (Lutra lutra) distribution on a British river

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Abstract
On a river catchment in upland Wales, U.K., otters were not resident on streams draining conifer plantations where pH fell periodically below pH 5.5, whereas a tributary draining open moorland held resident otters. An absence of fish in forested streams appeared to be the reason. Elevated Cd, Cu, Pb and Zn measured in mosses, occurred in streams receiving water from disused mines, rather than with high acidity and were not associated with absence of otters. High levels of Al in mosses were associated with afforestation, but the maximum concentrations occurred below the forest where the minimum recorded pH was 6.3. The possible consequences of increased afforestation, with attendant stream acidification, on the internationally important upland populations of British otters is discussed.