Macroinvertebrate community structure in a regulated river segment with different flow conditions

Two types of modification of the hydrological system are present in the same regulated segment of the Lima River (NW Portugal): (a) a reduced and constant flow from hypolinmetic release; (b) an intense irregular flow (daily and seasonal). Using multivariate techniques it was possible to compare the effects of these two kinds of disturbance on the macroinvertebrate communities. The communities colonizing both sites exhibited a higher variation in composition and diversity when compared to undisturbed sites. However, such variability was even more evident in the first case, in spite of the stability of the environmental conditions. Such temporal replacement of species is linked to the dominance of tolerant taxa with short life cycles. In the regulated segment the poor water quality and the lack of litter input impacted mainly on the shredders group. This work shows the failure of the practice of releasing constant flows as an attempt to mitigate regulation impacts. Copyright (C) 2002 John Wiley Sons, Ltd.