Phytoplankton of the Paraná River Basin

Abstract

We summarize the information on the phytoplankton of the Paraná River in the Argentine stretch, comparing the density, biomass, functional groups and diversity studies of the mainstem and fl oodplain since the 70's. We described the Yacyretá Reservoir and its impact downriver since it started operating in 1994. The spatio-temporal changes of the phytoplankton are associated to the hydrosedimentological regime. Regular variations in the hydrological phases and shorter permanent fl uctuations are essential for phytoplankton maintenance, since they allow the lateral exchange with zones of higher algal accumulation in the main channel and with the fl oodplain. During ordinary hydrological cycles, the mainstem shows a typical potamoplankton, dominated by Aulacoseira granulata and, alternatively, with sub-dominance of Chlorococcales, Cryptophyceae at the Middle and Lower Stretch, Cyanobacteria abound at Yacyretá Reservoir and downriver at the High and the beginning of the Middle Stretch. The disruption of Yacyretá Reservoir produces profound changes in the High Paraná phytoplankton evidenced in increased density and replacement of dominant species; Cryptophyceae replaced the Bacillariophyceae. Since 2001, water transparency increased and phosphorus concentration decreased, as well as the density and diversity of phytoplankton. Since 2004, an increase in Cyanobacteria was observed with bloom of Microcystis aeruginosa that extended 220 km downstream of the dam. Anomalous hydrological cycles, related to the ENSO phenomenon produced changes in phytoplankton density and structure. During El Niño, the system maintains a relative homogeneous phytoplankton assemblage, although mean density values are signifi cantly lower than those registered in ordinary hydrological periods. La Niña provokes a more drastic change in the community, due to the disruption in the exchange with the alluvial valley. The river-fl oodplain connectivity is essential for the maintenance of phytoplankton diversity.

Plankton metacommunities in floodplain wetlands under contrasting hydrological conditions

“…Depending on the hydrological connectivity with the river, floodplain habitats range from lotic, turbid, nutrient rich and frequently disturbed to lentic, clear vegetated conditions. Previous studies found that along such gradient, phytoplankton changed from taxa adapted to turbulent waters to those adapted to more stable conditions (Devercelli, ; Gallardo, Gascón, González‐Sanchís, Cabezas, & Comín, ; Schagerl, Drozdowski, Angeler, Hein, & Preiner, ); likewise, a shift from small fast growing to large (Baranyi et al., ) and from pelagic filter feeding to scraping zooplankton taxa associated with macrophytes was reported (Van den Brink, Van Katwijk, & Van der Velde, ). Our results regarding the great relevance of β2 ( between sections ) as component of regional diversity agree with these expectations, as this spatial scale comprises the main environmental gradient in dynamic floodplains.…”

Phytoplankton dynamics in the Congo River

“…Studies conducted in tropical rivers have shown that a substantial part of the phytoplankton production can take place in slow‐flowing areas of the main channel, as in the Orinoco River (Lewis, ) or in the Daly River, tropical Australia (Townsend, Przybylska & Miloshis, ). Moreover, the success of Aulacoseira species, which are abundant in the turbulent and turbid waters of the Paraná river, while being absent from the floodplain lakes (O'Farrell, Izaguirre & Vinocur, ; Devercelli et al ., ), suggests that they originate from the river environment rather than being imported from lakes.…”

“…This is quite different from most reports on phytoplankton composition in large tropical rivers, particularly of South America (e.g. Garcia de Emiliani, ; Lewis et al ., ; Davies et al ., ; Devercelli et al ., ; O'Farrell & Izaguirre, ) but also from Africa (Prowse & Talling, ; Talling & Rzόska, ): one would have expected dominance of diatoms during both discharge conditions, owing to light limitation resulting from the TSM concentration in the mainstem and large tributaries, and from high DOC in the blackwater tributaries (Mayora, Devercelli & Frau, ). Indeed, considering a mean daily surface irradiance of 750 μE m −2 s −1 , calculated from continuous recordings during the cruises, the mean light exposure of phytoplankton would have been on average 35 μE m −2 s −1 in FW versus 71 μE m −2 s −1 in HW (Table ).…”

“…While it has been stated that ‘tropical rivers are poorly understood compared with their temperate counterparts’ (Davies, Bunn & Hamilton, ), the studies conducted in the tropical and subtropical regions suggest that phytoplankton dynamics in tropical rivers obey the same rules as in temperate rivers given above, even though specific features of tropical rivers further constrain development of algal populations within the river channel. The best studied tropical rivers are South American rivers such as the Amazon (Fisher & Parsley, ; Wissmar et al ., ; Forsberg et al ., ), but also the Uruguay (O'Farrell & Izaguirre, ), Paraná (Bonetto, ; Garcia de Emiliani, ) and Paraguay (Zalocar De Domitrovic, ; Zalocar de Domitrovic, Devercelli & Garcia de Emiliani, ; Devercelli et al ., ). The emerging general view is that, in lowland high‐order rivers, phytoplankton production in river channels is ‘exceedingly low’ (Lewis, Hamilton & Saunders, ) due to extreme light limitation, combined in black water rivers with low nutrient concentrations (Wissmar et al ., ).…”

Spatial variability of chromophoric dissolved organic matter in a large floodplain river: control factors and relations with phytoplankton during a low water period

“…In subtropical floodplain fluvial systems, physical variables (especially light availability and hydrological conditions) are important factors regulating the structure of phytoplankton, whereas nutrients play a secondary role (Zalocar de Domitrovic et al, 2007;Devercelli et al, 2014). The relative importance of CDOM as another controlling variable of phytoplankton structure has not been explored in these systems.…”