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

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.

The phytoplankton community as a descriptor of environmental variability: a case study in five reservoirs of the Paraná River basin

“…The construction of reservoirs disrupts the longitudinal gradient of rivers and causes conspicuous upstream physical and chemical modifications, including the attenuation of downstream flood pulses (Stanford & Ward, 2001;Jati et al, 2017a). In addition, they are prone to nutrient enrichment, which often causes the proliferation of potentially harmful algal blooms, such as those of Cyanobacteria, compromising ecosystem services such as multiple water uses (Akhurst et al, 2017;Marques et al, 2019).…”

Phytoplankton species richness as an ecological indicator in a subtropical, human‐regulated, fragmented river

“…Rychteck and Znachor (2011) also observed that the spatial heterogeneity of phytoplankton in the Římov Reservoir of the Czech Republic was most clear in the wet season, reflecting obvious gradients of environmental parameters extending from the river to the dam, consistent with our results. Finally, Jati et al (2017) observed the disappearance of rapids caused by damming in the Paraná River led to decreased seasonal differences in phytoplankton species richness.…”

“…also observed that the spatial heterogeneity of phytoplankton in the Římov Reservoir of the Czech Republic was most clear in the wet season, reflecting obvious gradients of environmental parameters extending from the river to the dam, consistent with our results. Finally,Jati et al (2017) observed the disappearance of rapids caused by damming in the Paraná River led to decreased seasonal differences in phytoplankton species richness.5 | CONCLUSIONSThis study was conducted in subtropical rivers with 13 ladder dams in the main river channel, investigated the correlation between seasonal and spatial distribution characteristics of environmental factors and species richness, and tested the prediction of SDC. The results showed that the construction of cascade dams enhanced the spatial differences in phytoplankton species richness, especially during wet periods.…”