The response of zoobenthos to “natural channelization” of a small river

In October 2003, the small-sized river Gałęzówka (Lublin Upland) was channelized on its prevailing length, according to the assumptions of so-called “natural channelization”, i.e. among others, without straightening the river channel and leaving some river sections untouched. The surveys were carried out in 2003–2004, before and after the channel works, at two 100 m long sections: the disturbed site, and one placed upstream untouched reference site.Physical and chemical analysis suggested slightly better water quality at the reference site. Both density and biomass of the zoobenthos at the two sites were predominated by chironomid larvae and Tubificidae. The channel works did influence strongly taxa richness, dominance structure, density and biomass of the fauna. This was evident especially one month after the channel works. Values of Shannon-Wiener diversity index were higher at the disturbed site, however. The seasonal changes in density and biomass at the disturbed site exhibited a different pattern than at reference one. After one month after the channel works, the fauna of the two sections studied exhibited rather high level of faunistic similarity, suggesting high rate of animal communities reviving.