Abstract
ABSTRACT The construction of hydroelectric power plants has many social and environmental impacts. Among them, the impacts on fish communities, which habitats are drastically modified by dams, with consequences across the ecosystem. This study aimed to assess the influence of water level (WL) variations in the reservoirs of the Itá and Machadinho hydroelectric plants on the recruitment of fish species from the upper Uruguay River in southern Brazil. The data analyzed resulted from the WL variation produced exclusively by the hydroelectric plants generation and were collected between the years 2001 and 2012. The results showed significant correlations between the abundance of juvenile fish and the hydrological parameters only for some reproductive guilds. The species that spawn in nests showed, in general, a clear preference for the stability in the WL of the reservoirs, while the species that spawn in macrophytes or that release demersal eggs showed no significant correlation between the abundance of juvenile fish and hydrological parameters. A divergence of results between the two reservoirs was observed between the species that release semi-dense eggs; a positive correlation with a more stable WL was only observed in the Machadinho reservoir. This result can be driven by a wider range of WL variation in Machadinho reservoir.
Highlights
The damming of rivers is an intense and dramatic process that results in the creation of a new ecosystem with other structures, biota and functioning; the occurrence of environmental impacts is inherent in any impoundment, a process fundamentally connected to the river flow control (Agostinho et al, 2004a)
To obtain the hydrological parameters related to the variations in the water levels and the storage volume of the reservoirs (VRWL e Variation of the Storage Volume (VSV), respectively), standard deviation calculations were performed, while the hydrological parameters related to the WL average and the storage volume (AVRWL and Average Value of the Storage Volume (AVSV), respectively) were obtained by calculating the average of the data
The WL of the Machadinho reservoir showed an annual variation from 0.79 m to 3.88 m and the average values of the water levels ranged from 473 m to 479 m (Tab. 1)
Summary
The damming of rivers is an intense and dramatic process that results in the creation of a new ecosystem with other structures, biota and functioning; the occurrence of environmental impacts is inherent in any impoundment, a process fundamentally connected to the river flow control (Agostinho et al, 2004a). Despite describing a single hydrological attribute, water flow is the key driving force in freshwater ecosystems and it is responsible for their geological/hydrological structure, dynamics of production (material and energy), nutrient cycling and distribution and evolution of biota (Agostinho et al, 2004b). Biogeochemical cycles are strongly influenced by periodic increases in water levels, because in addition to the direct exchange of nutrients resulting from this dynamics, floods promote nutrient pulses from the decomposition of flooded vegetation. The primary productivity and the biophysical responses of the aquatic vegetation, and of several taxa of invertebrates, are dependent on the flood pulse (Agostinho et al, 2004a). Fluctuations may be daily, seasonally or annually, largely depending on the purpose of the reservoir, and present many problems related to the management of fish habitat (Miranda, 2001)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
