Biotic Responses along the Recovery Gradient of a Regulated Stream

Abstract

Voeln, N. J., and I. V. Ward. 1991. Biotic responses along the recovery gradient of a regulated stream. Can. J. Fish. Aquat. Sci. 48: 2477-2490 Samples were collected year-round over a I-yr period at six sites located downstream from a reservoir with a hyplirnnetic release on the upper Colorado River to examine the longitudinal patterns of macroinvertebrates along an environmental gradient induced by river regulation. The impoundment had only minimal effects on river chemistry, and chemical variables did not exhibit a distinct downstream gradient. Macroinvertebrate density was highest at sites near the Granby Reservoir dam, but diversity increased with distance from the impoundment. A percentage similarity matrix identified two areas sf rapid transition in macroinvertebrate assemblages along the regulated river gradient. Detrended correspondence analyses (DCAB showed a sequential faunal gradient with the most rapid change occurring within the first 3.0 km below the impoundment. Detrended canonical correspondence analysis (DCCA) suggested that downstream decreases in periphyton standing crop and minimum temperatures and downstream increases in most food resources and maximum temperatures were major variables structuring faunal assemblages. The results of this study, when compared with research conducted in free-flowing and other impounded rivers, indicated the predictability of some longitudinal patterns and the recovery potential of regulated iotic systems.Des echantiilons ont ete prklev6s pendant toute une ann6e en six endroits situes en aval d'un reservoir 2 dkcharge hypolimnetique sur le cours superieur du Colorado, dans le but d'exarniner Jes tendances longitudinales des macroinvertebres le long d'un gradient envirionnemental dir 3 la regularisation du cours d'eau. Le reservoir n'a eu que des effets minirnes sur la chirnie du cours d'eau, et les variables chimiques n'ont present6 aucun gradient distinct en aval. La densit6 de macrovertebr6s etait la plus forte aux endroits proches du barrage de Granby Reservoir, mais la diversite augmente en s'eioignant du reservoir. Une matrice de pourcentages de similarit4 a permis de reperer deux zones de transition rapide dans les assemblages de macroinvept6br$s le long du gradient du cours regularis& Des analyses de correspondances d6compos6es ont r$vel& la pr6sence d'e~n gradient faunistique s6quentiel avec la variation la plus forte se produisant dans les 3'0 premiers km en aval du reservoir.Une analyse de correspondances canoniques d6composees a indiqu6 que les principales variables de structure des asserrkblages faunistiques etaient les diminutions en aval de la biomasse de periphyton et des temperatures minimaies, ainsi que les augmentations en aval de la pluparts des ressources de nourriture et des temperatures maximales. les rksarltats de cette etude, une fois comparkes 3 celles de la recherche menee des eaux vives et d'autres r6servoirs, ont montre que certaines tendances longitudinales ktaient previsibles et que les syst&r=i es lotiques regularises pouvaient &re...

Evaluating macroinvertebrate biological metrics for ecological assessment of streams in northern Portugal

“…According to Chirhart (2003), the presence of moderate numbers of intolerant taxa is an indicator of good aquatic health. Trophic and functional benthic structure measures (e.g., gShr, sFil, and fGath) are also useful since they are influenced by nutrient enrichment (Fitzpatrick et al 2001;Quinn and Hickey 1990), disturbance of riparian corridors (Cummins 1973;Cummins et al 1989), and impoundment and regularization (Cortes et al 2002a;Voelz and Ward 1991). Concerning dominance measures and despite the difficulty of providing guidelines for interpreting a community structure because of the existence of a myriad of natural communities (Lillie et al 2003), results have shown that the percentage of a dominant organism increases with increasing perturbation (Barbour et al 1996;Chirhart 2003) notwithstanding they are not particularly sensitive to moderate amounts of organic or toxic loadings (Plafkin et al 1989).…”

Fish Assemblage Recovery Along a Riverine Disturbance Gradient

“…They concluded that the biota of regulated streams only partially resemble that of comparable freeflowing streams, and that sequential changes in faunas can indicate recovery potential. Voelz and Ward (1991) reported that their most downstream sampling site (12 km from a dam) had many similarities with an unmodified reference stream, and they reviewed other invertebrate studies of stream disturbance gradients. Although shoreline fish assemblages in the Tallapoosa change over a much greater length (at least 66 km) of river than invertebrates in Colorado, the form of flow regulation differed completely and other environmental modifications were important in the Voelz and Ward studies.…”

Bioaccumulation of aluminium and iron in the food chain of Lake Loskop, South Africa

“…Samples were taken from macrophytes and boulder/sand substrates at each sampling site with a pond net (25 cm diameter; 500 μm mesh), by pushing the net through the loose upper part (1-2 cm) of the substrate over a distance of 1 metre. A random sampling procedure was used to reduce hydrobiological variability between sites (Voelz and Ward, 1991). Samples were immediately preserved in 70 % ethanol and later washed through a 75 μm mesh 9 sieve to remove fine particles.…”