The Recovery of the Biotic Community in a Lotic Freshwater Habitat after Extensive Destruction by Chlorine

The recovery of a temperate zone biotic community in a lotic freshwater habitat after acute chlorine poisoning was nearly completed in four months (May to September). This was facilitated by the water flow, which rapidly removed the toxic residues of the chlorine and transported organisms from the intact community upstream into the impoverished habitat. The first aggregation in the ditch after the chlorine was eliminated consisted of survivors, including members of species that failed to produce new generations. These were joined by pioneer species of the families Simuliidae and Chironomidae, the larvae of which appeared in massive numbers. This aggregation was displaced by a more diverse fauna as the macroflora and microbiota re‐established themselves, providing food and anchorage for the invertebrates. The populations of large fishes are slowest to return because a considerable amount of time is required for the migration and growth of the recruits. While the chronic intoxication of a habitat produces changes in community structure, an acute poisoning is followed by a nearly complete restoration of the original biota, the recovery time being determined by the proximity of recruits for resettlement.