Effect of the reduction of the outflow restriction discharge from the Xingó dam in water salinity in the lower stretch of the São Francisco River

Abstract

Among the water quality parameters subjected to changes in river flow variations, salinity stands out for being intrinsically associated to ecosystem quality. Nonetheless, salinization can cause irreversible damage to the structure and functions of aquatic communities. This work evaluated the effect of successive reductions of outflow discharges from Xingó dam in water salinity in the lower stretch of the São Francisco River, Brazil. Salinity was analysed downstream of the dam, in addition to the relation between discharge reductions and salinity levels, as well as the spatial evolution of salinity in function of the distance of the sampling points from the river mouth. Secondary water quality data from 17 monitoring points were analysed, moreover, field samples and laboratory analyses were performed. With the reductions of outflow discharges, that started in 2013, there was a considerable increase in salinity in the sampling point located 9 km far from the river mouth, and with the continuation of discharge reductions, points that are farther away from the river mouth also presented high salinity values, both in the bottom and on the surface. This study indicates salinity values above the limits of fresh water (0.5 ‰), established by the CONAMA Resolution 357, for human consumption.

Interspecific variation in fish spatial synchrony relates to reproductive traits in a highly fragmented river

“…In other words, the data describing the population dynamics in a specific reservoir cannot be safely extrapolated to other reservoirs (Rhodes & Jonzén, 2011) and this is true for many species in our study area because of the low levels of spatial synchrony. Finally, the São Francisco River basin is heavily impacted by anthropogenic impacts that occur on a regional scale, such as water transposition, increased salinization at the lower stretches of the cascade and increased drought frequency due to climate change (Fonseca et al, 2020; Jong et al, 2018). Therefore, despite the conspicuous fragmentation of this river, if these extreme impacts continue to occur, we speculate that the spatial synchrony of fish populations in the cascade could increase, as these impacts would affect all the reservoirs simultaneously, acting as a Moran effect (Hansen et al, 2020).…”

Effects of an outflow regime adoption of the São Francisco River reservoir system to meet water demands for multiple uses

“…However, the consequences of outflows practiced resulted in the reduction of water depths downstream of the reservoirs. This subsequently created several inconveniences to water users, in the lower stretch of the river, especially the degradation of water quality for the supply of riparian communities (Fonseca et al, 2020).…”

“…The reduction in the magnitude of the flow not only causes an increase in the concentration of pollutants, but also allows the intrusion of the saline wedge into the river, which produces an increase in salinity levels. Some aquatic species are more sensitive to changes in quality standards, resulting in loss in biodiversity and ecosystem services (Wang et al, 2015;Mosley, 2015;Huang et al, 2015;He et al, 2018;Fonseca et al, 2020).…”

Ocorrência do mexilhão-dourado (Limnoperna fortunei, Dunker 1857) no Canal do Sertão, Delmiro Gouveia-AL, Brasil

“…Grandes obras de engenharia foram e estão sendo realizadas em seu curso, sendo as mais importantes, as usinas hidroelétricas e as obras de transposição. Tais empreendimentos modificaram a paisagem e alteraram as condições naturais provocando impactos ambientais, sociais e econômico (Santos et al, 2022;Holanda et al, 2007;Fonseca et al, 2020). Importantes obras de transposição vêm sendo realizadas, Eixo Norte e Eixo Leste e o Canal do Sertão.…”