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The Faunistic Recovery of a Lead-Polluted River in North Cardiganshire, Wales

R. Douglas Laurie and J. R. Erichsen Jones
Journal of Animal Ecology
Vol. 7, No. 2 (Nov., 1938), pp. 272-289
DOI: 10.2307/1161
Stable URL: http://www.jstor.org/stable/1161
Page Count: 18
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The Faunistic Recovery of a Lead-Polluted River in North Cardiganshire, Wales
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Abstract

1. From 1919 to 1921, the Lower Rheidol River only yielded 14 species of animals, all of them Arthropoda, in a careful survey made by Carpenter. During this period estimations of dissolved lead in the water revealed the presence of 2-5 parts of lead per 10 million of water. 2. From 1922 to the present time it would appear that lead has been indeterminable, or in the order of 2 parts per 100 million, except during flood periods. In one such period in 1924 Carpenter recorded 4 parts per 10 million, but no estimation exceeded 1 part per 10 million during the 2 years following. From June 1931 to the present time no greater flood concentration than 1 part in 10 million has been observed by Prof. James. 3. With the reduction in the amount of dissolved lead has been associated a steady improvement in the fauna. During the year following May 1922 the number of species recorded by Carpenter increased to 29, while the survey of July 1931 to May 1932 yielded 103 species, a fauna which appears to have remained stable since. 4. The Appendix gives the survival times of a number of species in a 3/1,000,000 solution of lead (as lead nitrate). The figures have some value as suggesting indices of pollution. 5. The stickleback (Gasterosteus aculeatus), which is one of the most sensitive to lead of the animals found in the Rheidol, was found, in laboratory experiments, to be killed after 14 days exposure to 1 part lead per 10 million of water. This is the maximum concentration which has been observed in the Lower Rheidol for some years, even during flood, and the normal content is of the order of only 2 parts per 100 million, a concentration that the fish seems able to withstand indefinitely. It would appear therefore, that, provided no abnormal flood periods occur, there should be little direct danger to fish (at any rate, stickleback) life. And from the 1936-7 survey, made after a summer of exceptionally heavy rainfall, it appears that even when the river continues well above its normal level over long periods, there is now no appreciable effect upon the fauna. This has recovered very materially, we think fully, from the effects of the metallic pollution. Since 1932, trout have been sufficiently abundant to lead to some fishing.

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