Recent cyanobacteria abundance in a large sub-tropical reservoir inferred from analysis of sediment cores

Abstract

Salto Grande is a large South American reservoir on the border between Uruguay and Argentina that was impounded in 1979 and experiences recurrent, massive cyanobacteria blooms. A water-monitoring program was initiated 20 years after the dam was built, hence the causes and onset of cyanobacteria blooms remain poorly known. We collected two sediment cores from the old river channel in the reservoir (z = 17 m) and used physical, chemical and biological variables in the sediments, along with existing limnological data, to explore the history of cyanobacteria in the sub-tropical water body. Cyanobacteria fossil pigments were present at low concentrations during the first 24 years after impoundment, but more than doubled thereafter. Phytoplankton abundance tracked shifts in cyanobacteria pigment concentration, indicating an overall increase in all primary producers. Several sediment variables indicate a decline in water quality after 2003, such as increases in the number of photosynthetic sulfur bacteria and a reduction in sediment magnetic susceptibility. Akinetes (dormant cyanobacteria cells, Daniela Gangi and Marı ´a Sofı ´a Plastani share first authorship.

Spatial and temporal assessment of the risk associated to bacteria in recreational waters of a large South American Reservoir

“…Source: INDEC 2010) significantly increase during summer due to the tourism (7 and 400%, for Concordia and Federación, respectively). This reservoir is eutrophic (Bordet et al 2017) and has been suffering massive and recurrent cyanobacteria blooms during the last 20 years (Bordet 2009, O’Farrell et al 2012, CARU 2016, Bordet et al 2017, Izaguirre et al 2018; Rougier et al 2018, Gangi et al, 2020). Cyanobacteria blooms occur mostly in summer-coinciding with the peak tourism season- and in autumn.…”

“…In South America, the Salto Grande Reservoir (Uruguay River), suffers recurrent and massive cyanobacteria blooms (Bordet 2009; Chalar 2009; O’Farrell et al 2012; Bordet et al 2017; Gangi et al 2020), has high concentration of coliform bacteria (CARU 2016, Rougier et al 2018), and is heavily used for recreation during the warm season. This area has been monitored by two water agencies - Comisión Administradora del Río Uruguay (CARU) and the Comisión Técnica Mixta (CTM)-for about two decades.…”

“…Moreover, up to date reports are presented in isolated formats and have not yet been synthesized for assessing annual or interannual trends, albeit for short periods (Rougier et al 2018). Finally, in the Salto Grande Reservoir, despite a wealth of environmental information available for cyanobacteria, and to a lesser extent for coliform bacteria (Bordet 2009; Chalar 2009; O’Farrell et al 2012; CARU 2016; Bordet et al 2017; Rougier et al 2018; Gangi et al 2020), there is a remarkable absence of documentation of human illness that could be related to recreational exposure, except for one case of a young boy who was exposed to a dense bloom of cyanobacteria while using his jet ski and who developed serious health effects (Giannuzzi et al 2011).…”

First Evidence of Potential Toxic Cyanobacteria in the Water-Sediment Interface of a Tropical Drinking Water Reservoir

“…Cyanobacteria of the order Nostocales (Anabaena, Aphanizomenon, Dolichospermum, Cylindrospermopsis, Sphaerospermopsis) develop resistance structures called akinetes, which morphologically and physiologically correspond to differentiated cells originating from vegetative cells (Head et al 1999, Karlsson-Elfgren and Brunberg 2004, Gangi et al 2020, giving them the ability to survive under unfavorable conditions for long periods, like the sediment environment (Everson et al 2011).…”

Paleolimnological reconstruction of the centennial eutrophication processes in a sub-tropical South American reservoir

“…Consequently, a main difficulty in assessing the current state is the lack of knowledge of their pre-disturbance environmental conditions during periods of low anthropic impact and the identification of early evidence of change. Despite the importance of reservoirs as sources of water supply, few paleolimnological studies tackling trophic state changes related to anthropic and natural forces have been conducted in South America (Costa-Böddeker et al, 2012;Fontana et al, 2014;Gangi et al, 2020). Our reconstruction aims to infer paleolimnological conditions of SRr, especially prior to the beginning of water quality monitoring in AD 1999.…”