Phytoplankton community in the last undammed stretch of the Paraná River: considerations on the distance from the dam

Susicley Jati,Yasmin Rodrigues Souza,Geovani Arnhold Moresco,Patricia Iatskiu,Matheus Vieira Da Silva,Aline Caroline Magro De Paula,Luzia Cleide Rodrigues,Alfonso Pineda,Jascieli Carla Bortolini,Bárbara Furigo Zanco

doi:10.1590/s2179-975x4017

Abstract

Abstract Aim: To evaluate the influence of upstream reservoirs on the temporal and spatial variation of the phytoplankton community in the Paraná River channel and the importance of its main tributaries in reducing the oligotrophication process along this stretch of the river. Materials and Methods Sampling of phytoplankton and physical and chemical variables was performed quarterly between August 2013 and May 2015, in the Paraná River main channel and in the mouth of the main tributaries, at the stretch located between downstream Porto Primavera reservoir and the backwaters of Itaipu reservoir. To summarize the variation of phytoplankton density in relation to the main physical and chemical variables, we performed a Redundancy Analysis (RDA). Results A total of 214 taxa were identified throughout the study. We registered low values of phytoplankton species richness and abundance, which showed no patterns of temporal and spatial distribution, both for the Paraná River and the tributaries. However, RDA results showed spatial segregation among samples from the Paraná River main channel, such that the stretch located closer to the dam was associated with higher values of water transparency and Cyanobacteria density, exported by upstream reservoirs, whereas the middle and lower stretches were associated with higher phytoplankton complexity and higher nutrient concentration and turbidity. Conclusion Through the analysis of the phytoplankton community we could verify a reduction in the effects of oligotrophication along the longitudinal axis of the Paraná River and the important role of the tributaries in diminishing this effect.

Highlights

The Paraná River is among the largest Brazilian rivers and is fragmented by reservoir constructions
The last undammed stretch of this entire basin is located at the Upper Paraná River region, between downstream Porto Primavera reservoir and the backwaters of Itaipu reservoir
This stretch is approximately 230km long and has an extensive flood area located at the right margin, creating a mosaic of habitats which harbours great phytoplankton diversity (Train & Rodrigues, 2004), constituting an important species pool at both local and regional scales. Considering that this area is located downstream a series of cascading reservoirs, it is possible to test the theory proposed by Ward & Stanford (1983), which suggests that upstream reservoirs disrupt the longitudinal continuum of the river and, in the areas situated immediately downstream, the attributes of the aquatic communities return to less complex stages of development in response to alterations in the physical and chemical water characteristics. In this stretch of the Paraná River, at the region situated immediately downstream Porto Primavera reservoir, there was a drastic reduction in the values of suspended solids (Souza-Filho, 2016), with a consequent increase in water transparency and a decrease in nutrient concentration, causing an oligotrophication process resulting in profound alterations in all aquatic biota (Agostinho et al, 2008; Roberto et al, 2009; Thomaz et al, 2004; Bovo-Scomparin et al, 2013; Rodrigues et al, 2009, 2015)

Summary

Introduction

The Paraná River is among the largest Brazilian rivers and is fragmented by reservoir constructions. This stretch is approximately 230km long and has an extensive flood area located at the right margin, creating a mosaic of habitats which harbours great phytoplankton diversity (Train & Rodrigues, 2004), constituting an important species pool at both local and regional scales Considering that this area is located downstream a series of cascading reservoirs, it is possible to test the theory proposed by Ward & Stanford (1983), which suggests that upstream reservoirs disrupt the longitudinal continuum of the river and, in the areas situated immediately downstream, the attributes of the aquatic communities return to less complex stages of development in response to alterations in the physical and chemical water characteristics. Reservoir construction is among the main causes of biodiversity loss in continental aquatic environments (Agostinho et al, 2004; Winemiller et al, 2016)

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Conclusion