Application of trophic state indices in the dam of Salto Grande

Eutrophication is the process by which nutrients, mainly phosphorus, are contributed. Currently, this has increased due to human activity and population growth which has caused the deterioration of water quality and limited its potential uses. In this study, the trophic state of the Salto Grande Reservoir was determined in the stretch between Monte Caseros/Bella Union and the dam, during the summer period of 2010 through the application of different indices. Moreover, the representative blue green algae from the area corresponding to the genera Microcystis and Dolichospermum and their relation to the nutrients were studied. Nutrient concentrations, mainly phosphorus, were relatively high, determining an eutrophic state from the area of study. Due to the flooding which began in November 2009, the relative abundance of cyanobacteria was not high, with a maximum of approximately 40,000 cells/ml. Furthermore, no linear correlation was established between cyanobacteria and the nutrients studied. We conclude that, as suggested by the records, nutrients would not be a limiting factor for the proliferation of cyanobacteria in the reservoir area of Salto Grande.La eutrofización es un proceso de aporte de nutrientes principalmente de fósforo. Actualmente, se encuentra acrecentado por las actividades antrópicas y crecimiento poblacional que provoca un deterioro de la calidad del agua limitando sus usos potenciales. En este trabajo se determinó el estado trófico en el río Uruguay, en el tramo comprendido entre Monte Caseros/Bella Unión y la represa, durante el período estival 2010 a través de la aplicación de diferentes índices. Además, se estudiaron las cianobacterias representativas del área correspondientes a los géneros Microcystis y Dolichospermum y su relación con los nutrientes. Las concentraciones de nutrientes fueron relativamente elevadas, principalmente el fósforo, determinando un estado eutrófico para el área de estudio. Debido a las crecientes iniciadas en noviembre de 2009, la abundancia relativa de cianobacterias no fue alta, tuvo un máximo de aproximadamente 40.000 cél/ml. Por otro lado, no se estableció una correlación lineal entre las cianobacterias estudiadas y los nutrientes. Se concluye que, como indican los antecedentes, los nutrientes no serían un factor limitante para la proliferación de cianobacterias en el área del embalse de Salto Grande.Fil: Crettaz Minaglia, Melina Celeste. Universidad Autónoma de Entre Ríos. Facultad de Ciencia y Tecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Bordet, Hugo Facundo. Universidad Nacional de Entre Ríos. Facultad de Ciencias de la Alimentación; Argentina. Complejo Hidroelectrico de Salto Grande. Área de Gestión Ambiental; Argentin

Multiannual trends (2004–2019) in the abundance of larvae of the invasive mussel Limnoperna fortunei and crustacean zooplankton in a large South American reservoir

The behavior of non-indigenous species with time since introduction varies widely and is a major issue in the understanding of their long-term effects on the habitats colonised. We analysed the long-term trends in the densities of larvae of the invasive mussel Limnoperna fortunei and planktonic Copepoda and Cladocera in Salto Grande, a large South American reservoir in the Uruguay River (Argentina-Uruguay), on the basis of weekly samples collected between June 2004 and November 2019. All three groups depicted variable interannual abundances. While mussel veligers showed no significant interannual trends (overall mean: 2552 larvae L−1), crustaceans decreased significantly in the time elapsed (Copepoda: from ˜1000 to 100 ind. L−1; Cladocera: from ˜500 to 100 ind. L−1). We conclude that increasing discharge rates by the Uruguay River and the concomitant decreases in reservoir water residence times are the most likely cause for these drops in their populations. As opposed to many other invasive species elsewhere, and to the same mussel in other South American waterbodies, L. fortunei larvae did not change in abundance with time since introduction. Our results underscore the assumption that each biological introduction is a particular and highly context-dependent event and the dynamics of biological invasions in general elude broad generalizations.Fil: Boltovskoy, Demetrio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; ArgentinaFil: Bordet, Hugo Facundo. Ministerio de Relaciones Exteriores, Comercio Internacional y Culto. Comisión Técnica Mixta de Salto Grande; ArgentinaFil: Leites, Valentín. Ministerio de Relaciones Exteriores, Comercio Internacional y Culto. Comisión Técnica Mixta de Salto Grande; ArgentinaFil: Cataldo, Daniel Hugo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentin

Bloom forming cyanobacterial complexes co-occurring in a subtropical large reservoir: Validation of dominant eco-strategies

In this study, we analyse the spatial distribution of cyanobacterial summer blooms in a large subtropical reservoir located in the Uruguay River, from 2007 to 2011; these extraordinary algal growth events are mainly represented by scum-forming and nitrogen-fixing eco-strategists of the Dolichospermum and Microcystis genera. The use of the eco-strategists approach, based on ecophysiological work and field observations, allowed us to explain the differences in the distribution pattern and temporal dynamics of both cyanobacterial complexes. Spatial differences were produced due to much higher and fluctuating cyanobacterial abundances at the right margin of the reservoir and at the littoral areas closer to the dam. Satellite imagery (LANDSAT 5 TM) clearly depicted the stronger algal development in the reservoir arms and in the section closer to the dam. The Microcystis spp. complex achieved higher density than the Dolichospermum spp. complex. We hypothesise that the hydrological cycle explains the inter-annual fluctuations of the intensity and frequency of cyanobacterial blooms, and that spatial differences in cyanobacterial presence between the reservoir arms, its margins and the main channel is mainly a response to morphometrical and hydrological characteristics.Fil: O'farrell, Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; ArgentinaFil: Bordet, Hugo Facundo. Ministerio de Relaciones Exteriores, Comercio Internacional y Culto. Comisión Técnica Mixta de Salto Grande; Argentina. Universidad Nacional de Entre Ríos; ArgentinaFil: Chaparro, Griselda Noemí. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentin

Effects of El Niño-Southern Oscillation (ENSO) on the reproduction of migratory fishes in a large South American reservoir

The ENSO (El Niño-Southern Oscillation) phenomenon affects, through climate teleconnections, hydrometric variables of water bodies worldwide, influencing biota communities. The aim of this work is to analyze ENSO effects on water discharge, water level, cyanobacterial blooms and, consequently, on the reproduction of migratory fishes with high-frequency monitoring of ichthyoplankton data from Salto Grande, a large South American reservoir. Two highest peaks of ichthyoplankton density were observed; the first one (2015–2016) occurred during a very strong El Niño event, while the second one (2019–2020) was preceded by weak El Niño events that lasted 18 months. These results suggest that ichthyoplankton abundance may be affected by the intensity and temporal extent of the episodes. In contrast, mean fish larval and egg densities were reduced by 65% and 85%, respectively during La Niña periods. Cross-correlation function (CCF) analysis indicates that water discharge, water level, and ichthyoplankton abundance were positively related to the Oceanic Niño Index, while cyanobacteria showed an inverse relationship. Cyanobacterial density increased by 574% during La Niña compared with El Niño events. Based on an uninterrupted monitoring of ichthyoplankton over 11 years, it seems reasonable to consider ENSO as a predictive tool for the intensity of reproductive activity of migratory fishes.Fil: Cataldo, Daniel Hugo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; ArgentinaFil: Leites, Valentín. Comisión Técnica Mixta de Salto Grande; ArgentinaFil: Bordet, Facundo. Comisión Técnica Mixta de Salto Grande; ArgentinaFil: Paolucci, Esteban Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; Argentin

Impact of a hydroelectric power plant on migratory fishes in the Uruguay River

Dams alter river functioning and hinders the free movement of migratory fishes. We analysed the effects of a subtropical dam on the reproduction of migratory fishes using data from ichthyoplankton monitoring surveys. These were conducted at six sampling stations upstream, downstream and within the reservoir on a weekly basis during 6 years. The dam had a direct impact on fish movement, leading to the fragmentation of fish populations. Two different and independent reproductive areas became evident: one located in the reservoir headwater area and the other downstream of the dam. The long temporal scale of our study facilitated the detection of the impact of Salto Grande on the species of ichthyoplankton. Freshwater secondary fish species (mainly Lycengraulis grossidens) increased in abundance in the stations located inside the reservoir and closer to the dam, whereas most fishes found in the headwater of the reservoir corresponded to river migratory species (potamodromous fish). These differences are most likely due to changes in the physicochemical characteristics of the water induced by the transformation of a river into a reservoir. During rainy summers, Microcystis spp. densities were lower than 1,000 cells ml−1 and fish densities were higher than 4 ind. m−3, whereas in dry summers, there were important Microcystis spp. blooms (401,573 ± 112,559 cells ml−1) and fish larvae decreased sharply (<1 ind. m−3) in the reservoir headwater area. This could indicate that the discharge of water in the reservoir may also indirectly affect the regulation of fish reproduction. The alternating periods between dry and rainy summers associated with El Niño-Southern Oscillation poses a challenge to ichthyofauna management in the reservoir.Fil: Cataldo, Daniel Hugo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; ArgentinaFil: Gattás, Florencia María. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; ArgentinaFil: Leites, Valentín. Comisión Técnica Mixta de Salto Grande ; ArgentinaFil: Bordet, Hugo Facundo. Comisión Técnica Mixta de Salto Grande ; ArgentinaFil: Paolucci, Esteban Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; Argentin

Impact of interaction between Limnoperna fortunei and Roundup Max® on freshwater phytoplankton: An in situ approach in Salto Grande reservoir (Argentina)

The joint impact of the glyphosate-based commercial formulation Roundup Max® and the invasive mussel Limnoperna fortunei on phytoplankton and water quality was assessed in Salto Grande reservoir, a scenario were both stressors coexist. We performed an in situ mesocosm approach, through a 7-day experiment using 400-L enclosures. The following treatments were applied by triplicate: addition of 250 mussels (M); addition of 5 mg L−1 of active ingredient (a.i.) in Roundup Max® (R); addition of 250 mussels and 5 mg L−1 of a.i. in Roundup Max® (MR), and controls, without any addition (C). R showed higher total phosphorus (TP) and ammonium nitrogen (N–NH4 +) concentrations due to the herbicide input, and a significant increase in algal abundance, biovolume and chlorophyll a levels (Chl-a). In M mussels grazed on phytoplankton, which resulted in subsequent phosphates (SRP) release. A decrease in species diversity was observed in R and M with respect to C. In MR, there were higher TP and N–NH4 + concentrations, a decrease in biovolume, an antagonistic effect on Chl-a and a synergistic effect on phytoplankton abundance. Species diversity and evenness showed a significant decrease due to the explosive growth of a small and opportunistic Chlorophyta, Spermatozopsis exsultans. The dominance of this species may be due to negative selectivity for S. exsultans and/or release of potential competitors by L. fortunei, and to the input of nutrients by Roundup Max® and/or removal of competitors by its toxicity.Fil: Gattás, Florencia María. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; ArgentinaFil: de Stefano, Lucia Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; ArgentinaFil: Vinocur, Alicia Liliana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y Biología Experimental; ArgentinaFil: Bordet, Hugo Facundo. Ministerio de Relaciones Exteriores, Comercio Internacional y Culto. Comisión Técnica Mixta de Salto Grande; ArgentinaFil: Espinosa, Mariela Soledad. Comisión Nacional de Energía Atómica; ArgentinaFil: Pizarro, Haydee Norma. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; ArgentinaFil: Cataldo, Daniel Hugo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentin

Hyperspectral remote sensing monitoring of cyanobacteria blooms in a large South American reservoir: High-and medium-spatial resolution satellite algorithm simulation

We used hyperspectral remote sensing with the aim of establishing a monitoring program for cyanobacteria in South American reservoir. We sampled at a wide temporal (2012-2016, 10 seasons) and spatial (30km) gradient, and retrieved 111 field hyperspectral signatures, chlorophyll-a, cyanobacteria densities, and total suspended solids. The hyperspectral signatures at cyanobacteria dominated situations (n=75) were used for selecting the most suitable spectral bands in 7 high and medium spatial resolution satellites (Sentinel-2, Landsat 5, 7 and8, Spot 4/5 and6/7, WorldView 2), and for the development of chlorophyll and cyanobacteria cell abundance algorithms. The best performing chlorophyll algorithm was Sentinel 2 ((λ_560- λ_660+ λ_703)/(λ_560+ λ_660+ λ_703)) (R2 0.80), followed by WorldView 2 ((λ_550- λ_660+ λ_720)/(λ_550+ λ_660+ λ_720)) (R20.78), Landsat and SPOT series(λ_550- λ_650+ λ_800)/(λ_550+ λ_650+ λ_800) (R2 0.67-0.74). When these models were run for cyanobacteria abundance, the coefficient of determination remained rather similar, but the root mean square increased. This could affect the cyanobacteria cell abundance estimation in about 20%, yet it still allowed assessing the alert level categories for risk assessment. Our results highlight the importance of the red and near infrared region in identifying cyanobacteria in hypereutrophic waters, showed coherence with field cyanobacteria abundance, and allowed assessing bloom distribution in this ecosystem.Fil: Drozd, Andrea Alejandra. Comision Administradora del Rio Uruguay; ArgentinaFil: de Tezanos Pinto, Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Botánica Darwinion. Academia Nacional de Ciencias Exactas, Físicas y Naturales. Instituto de Botánica Darwinion; ArgentinaFil: Fernandez, Virginia. Comision Administradora del Rio Uruguay; ArgentinaFil: Bazzalo, Mariel. Comision Administradora del Rio Uruguay; ArgentinaFil: Bordet, Hugo Facundo. Ministerio de Relaciones Exteriores, Comercio Internacional y Culto. Comisión Técnica Mixta de Salto Grande; ArgentinaFil: Gómez Santibáñez, Guillermo del Carmen. Comision Nacional de Actividades Espaciales; Argentin