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Edaphic Factors in the Distribution of Aquatic Plants in the English Lakes

R. D. Misra
Journal of Ecology
Vol. 26, No. 2 (Aug., 1938), pp. 411-451
DOI: 10.2307/2256257
Stable URL: http://www.jstor.org/stable/2256257
Page Count: 41
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Edaphic Factors in the Distribution of Aquatic Plants in the English Lakes
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Abstract

1. The distribution of aquatic plants in the English lakes has been studied with particular regard to the nature of the substratum. 2. Physical and chemical characters of the lake muds have been found to be closely correlated with the vegetation on them. This view is supported by suitable culture experiments done in Lake Windermere. 3. The source, its distribution on the lake floor and nature of the organic matter have been given in some detail. A relationship with the quantity of organic matter in the substratum and plant successions has been shown. 4. An analysis of carbon and nitrogen ratio of the substratum shows that in general this ratio is high (12-20) although the ratio for submerged plants is low. 5. Decomposition of organic matter in submerged muds has been shown to be chiefly anaerobic. During this process a large amount of marsh gas and some carbon dioxide are produced. Oxygen if available is rapidly absorbed. 6. Sulphides have been shown to be present in appreciable amounts in practically all the submerged muds containing more than 5-10% of organic matter. 7. Nitrates are absent from the substratum and nitrogen is available for the aquatic plants in the form of ammonia. 8. A modification of Comber's thiocyanate test has been devised to measure the amount of easily replaceable ferrous iron and the reductivity of the muds. 9. By measurements of oxidation-reduction potential the highest reduction intensities are found to exist in soils of moderate organic content. These are most fertile, contain most available ammonia and the least replaceable hydrogen. 10. The exchangeable bases (with N ammonium chloride) in the muds are related to the organic content of the mud. In general, a better relation with plant distribution is shown by the bases leaching into water under anaerobic conditions. There is evidence, as the substratum becomes more organic, of increased availability of calcium and nitrogen. The sterility of the most organic soils is attributed to absorption of ferrous iron and to lower available nitrogen. These conclusions are based also on analyses of plant material.

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