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The degree of purity of surface waters can be seen from investigations on the communities of life of plant and animal organisms. A great number of organisms characteristic of certain degrees of pollution were classified in the "saprobic system", which is still valid. As a supplement to the chemical water analysis, the bio-ecological test is an optional method for characterizing the quality of waters--as, for instance, in the case of the river Lippe. 相似文献
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