The main factors inducing chemical spatial heterogeneity in the Salto Grande, a reservoir on the Uruguay River

Abstract

Saito Grande (mean flow 4640 m'/s; surface 757 km') is a subtropical polymictic reservoir built in 1979 for power generation by damming the Uruguay River. Relevant Iirnnological differences be tween the main channel and lateral arms of the reservoir were registered due to different circulation patterns. The main force driving the system was assumed to be the sharp seasonality of the hydrolog ical cycle. Due to the dendritic shape and complex morphometry. a lacustri ne-type reservoir devel ops during the summer. whilst a ri ver-like system occurs in winter. Runoff from the northern area of the basin is the main source of phosphorus entering the reservoir. whereas nitrogen and silicate enter the lacustrine area of the reservoir through lateral arms receiving local runoff.

Water flow and temperature as main factors that regulate phytoplankton and cyanobacterial blooms in a large subtropical river

“…A new species of Dolichospermum was also described: Dolichospermum uruguayense, referring to the Uruguay River (Kozlíková-Zapomèlová, et al, 2016). Cyanobacterial blooms commonly occur during summer in the lower Uruguay River and they have been reported since 1974 (Quirós and Luchini, 1982;Di Persia, et al, 1986;Berón, 1990;Conde, et al, 1996;Chalar, et al, 2017). M. aeruginosa had already been reported in this study area, reaching high concentrations from September 2006to November 2008(O'Farrell and Izaguirre, 2014 and its toxin, microcystin, was detected in the Uruguay River on several occasions (Vidal y Britos, 2012;UNESCO, 2009;Bonilla, et al, 2015;Kruk, et al, 2015).…”

“…Consequently, nutrients would not be a limiting factor for phytoplankton development. According to previous studies upstream, in the Salto Grande reservoir, the main access route of nutrients into the system is also the flow of the Uruguay River (Berón, 1990;Conde, et al, 1996;Chalar, et al, 2017;EcoMetrix, 2006). The lower stretches of the river are a natural receptor for nutrient discharge.…”

The use of phytoplankton patterns of diversity for algal bloom management

“…In addition, they pointed out the turbidity of the system is a limiting factor for algal development during the summer low water periods. Conde et al (1996) emphasized the importance of spatial heterogeneity determined by physical and chemical parameters, differentiating the main channel from the lateral arms where frequent summer algal blooms take place. De Leo´n and Chalar (2003) described the annual succession of phytoplankton functional groups and the annual diversity pattern.…”

Planktic Cyanobacteria in the Lower Uruguay River, South America.

“…N:P relationship is never limiting for P, as it happens in other aquatic systems. Cyanobacterias blooms in Lower Uruguay River were reported since 1974(ono 1978ose 1978;Quirós & Lucchini 1982;Di Persia & neiFF 1986;berón 1990;conDe et al 1996;chaLar et al 2002). In the summer 2005, a bloom of Microcystis aeruginosa was reported in the study area, reaching 20000-30000 cells.…”

“…According to previous studies in the Salto Grande reservoir and upstream, the main access route of nutrients to the system was also the channel flow of the Uruguay River (beron 1990;conDe et al 1996;chaLar et al 2002). When flow increases, not only do levels of phosphorous increase, but also the basin bottom is removed by increasing turbulence and suspended solids, which in turn, decreases transparency and increases the light extinction coefficient, resulting in decreasing values of phytoplankton density.…”