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We revisit the serial discontinuity concept (SDC), which predicts river ecosystem responses to stream regulation in the context of recovery with distance downstream from the dam (discontinuity distance). Many studies have described pervasive interruptions of natural biophysical gradients of dams by comparing conditions in tailwaters to reference or pre-impoundment conditions. But only a few studies provide data or interpretations that explicitly test the SDC within entire stream corridors or along specifically defined reaches where recovery was expected in view of the predictions of the SDC. We present discontinuity distance measures for nine rivers around the world where the predictions of the SDC were substantiated....
Samples were taken year-round at eleven sites along the altitudinal profile (2900-1400 m a.s.l.) of the Gunnison River, a 329 km tributary of the Colorado River, to document the distribution of the Plecoptera and to evaluate responses to hypolimnial-release dams in the headwaters and middle reaches. Twenty-two species were present, with the greatest species richness occurring in an unregulated segment upstream of the middle reach dams; average nymphal biomass over the study period (175 organisms, 395 mg dry mass m?2) was also greatest in this segment. Only four species (58 organisms, 48 mg m?2) were present in the tailwaters of the headwater dam and values were greatly reduced (nine species; 35 organisms, 180 mg...
Preservation of biodiversity depends on restoring the full range of historic environmental variation to which organisms have evolved, including natural disturbances. Lotic ecosystems have been fragmented by dams causing a reduction in natural levels of environmental variation (flow and temperature) and consequently a reduction of biodiversity in downstream communities. We conducted a long-term study of the macroinvertebrate communities before and after natural flood disturbances in an unregulated reference site (natural flows and temperatures), a regulated site (regulated flows and temperatures), and a partially regulated reference site (regulated flows and natural temperatures) on the upper Colorado River downstream...