Enhancement of benthic macroinvertebrates by minimum flow from a hydroelectric dam

Abstract

The biological consequences of instituting a summer minimum flow from the Conowingo Hydroelectric Dam were investigated by comparing invertebrate abundance in the Susquehanna River during 1980, when flow shutdowns were frequent, to that in 1982, when the minimum flow (142 m3 s-') was maintained. The minimum flow was only maintained from April 15 to September 15, and additional investigations compared invertebrate abundance before and after the minimum flow was terminated in the fall of 1982 and 1983. There was a large difference in summer invertebrate density in the between-year comparison, with almost a 100-fold increase in the year when the minimum flow was maintained. Most of this difference was exhibited by two taxa, chironomids and net-spinning trichopterans. These results were consistent with findings from the fall of 1982 and 1983, when cessation of the minimum flow in September led to declines of more than three orders of magnitude in both of these taxa. The rate of decline was faster in the shoal habitat (areas dewatered at low flow, but submerged when the minimum flow is released), suggesting that dewatering was the predominant mechanism of effect. Declines were also evident in the channel habitat (always submerged), suggesting that maintenance of current velocity is also an important beneficial component of the minimum flow.

Regional‐scale effects of flow regulation on lowland riverine fish communities in New South Wales, Australia

“…These results are consistent with the findings of Weisberg and Burton (1993), who found that growth rates of white perch (Morone americana) were greater after introducing a minimum environmental flow in the Susquehanna River, because of an increase in prey abundance (Weisberg et al, 1990). Length distributions of New South Wales species do not suggest enhanced growth in unregulated rivers by attainment of greater maximum size than in regulated rivers.…”

The effects of water abstractions on invertebrate communities in U.K. streams

“…The faunal aspects of these results will be developed and elaborated in another paper, but it can be stressed that the taxa which appeared in this study to be exhibiting the largest changes, such as the Baetidae, Chironomidae, Hydropsychidae, Gammaridae and Simuliidae are also those most frequently mentioned as being significantly affected by reduced or intermittent flow conditions and drought (Ladle & Bass, 1981;Extence, 1981;Wright et al, 1984;Wright & Berrie, 1987;Weisberg et al, 1990). Furthermore, the extensive character of this study and the large variability of faunal responses it highlights, help to place the above single-case studies within the overall picture of a multiplicity of possible trends in faunal responses to reduced flow conditions.…”

The future of habitat modeling and instream flow assessment techniques

“…Other pertinent research within the broader arena of instream flows has focused on the delineation of key life history characteristics in terms of ontogenetic shifts in habitat use under natural and induced flow variability (Bardonnet and Gaudin, 1990;Crisp and Hurley, 1991;Bardonnet et al, 1993;Heland et al, 1995), the relationship between flow and macroinvertebrate community dynamics (Statzner, 1988;Gore, 1989;Weisberg et al, 1990;Jowett et al, 1991;Lancaster and Hildrew, 1993) and the importance of trophic level dependencies between macroinvertebrates and fish (Easton and Orth, 1992;Weisberg and Burton, 1993;Roell and Orth, 1994;Filbert and Hawkins, 1995;Bevelhimer, 1996). Efforts employing mechanistic individual based bioenergetics, physical habitat based approaches utilizing population models and multivariate statistical approaches have also produced encouraging results (Jowett, 1992;Addley, 1993;Hill and Grossman, 1993;Jager et al, 1993;Bovee et al, 1994).…”