A new pollution index based on macroinvertebrates has been devised which can be used as a surveillance system in Danish streams. The index is inspired by the Trent Index although it was necessary to incorporate two new principles. First, the pollution indicators Asellus aquaticus and Chironomus sp. are used as negative taxa, with a negative influence on the index value, thereby strongly enhancing the utility of the keygroups. Secondly, the taxonomic groups used in the Trent Index have been replaced by establishing positive and negative index groups, where the number of negative index groups is subtracted from the number of positive. Thus, the utility of the basic principle, increasing pollution effecting decreasing numbers of taxonomic groups, is enhanced. © 1984.
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