Impact of filamentous cyanobacteria on the water quality of two tropical reservoirs

Abstract

Artificial lakes play an important role in water availability in tropical semi-arid Northeastern Brazil. However, in addition to the negative effects that dams have on the water quality of rivers, other practices such as discharge of untreated wastewater, intensive crop fertilization and fish farming have been contributing to water quality deterioration. Climate change may be another driver of water quality decrease. Increases in precipitation and drought intensities as well as temperature increase may redefine the dynamics of planktonic communities and favour species more adapted to the new environment. Water samples were collected in two reservoirs selected based on the recurrence of positive results for saxitoxins, Acarape do Meio (AM) and Sitios Novos (SN). In general, diversity in SN (1.08) was higher than in the AM (0.60). Phytoplankton dynamics in these reservoirs differ from other reservoirs in the same region of Brazil, in the sense that filamentous cyanobacteria are dominant. Furthermore, lower diversity, concentration and richness of chlorophyceae and bacillariophyceae were found in both reservoirs. Increase in diversity was observed during the intense rainy season of 2011, suggesting a slight improvement of water quality. A close inverse correlation between Cylindrospermopsis sp and other cyanobacteria was found in SN (R 2 = -0.862) and in AM (R 2 = -0.997) and the data collected demonstrates that a season with intensive rainfall may lead to lower cyanobacteria concentrations probably due to water dilution and higher flushing rates.Keywords: Artificial reservoirs; Freshwater cyanobacteria; Semi-arid regions; Temporal phytoplankton dynamics; Eutrophication. RESUMOOs lagos artificiais tem um papel primordial na disponibilidade hídrica no semi-árido Brasileiro. Entretanto, além dos efeitos negativos que os barramentos dos rios causam sobre a qualidade da água, a descarga de esgotos, a irrigação e a piscicultura intensivas vêm acentuando a deterioração da qualidade da água em um ritmo sem precedentes nesta região. A mudança climática é outro fator de impacto negativo na qualidade da água. O aumento da intensidade das precipitações pode redefinir a dinâmica das comunidades de plâncton e espécies mais adaptadas a ambientes extremamente variáveis. Os reservatórios estudados, Acarape do Meio (AM) e Sítios Novos (SN), foram selecionados com base na recorrência de resultados positivos para saxitoxinas. A dinâmicas do fitoplâncton encontrada, difere de outras áreas da mesma região, no sentido em que as cianobactérias filamentosas são dominantes. Baixas diversidade, concentração média e riqueza de Chlorophyceae e Bacillariophyceae foram encontrados em ambos os reservatórios, embora tenha sido observado um aumento durante o intenso período chuvoso de 2011, sugerindo uma ligeira melhoria da qualidade da água. Em geral, a diversidade no reservatório SN (1,08) foi maior que no AM (0,60). Uma correlação inversa entre a concentração de Cylindrospermopsis sp e outras cianobactérias foi encontrada nos reservatór...

Rapid Changes in the Phytoplankton Community of a Subtropical, Shallow, Hypereutrophic Lake During the Rainy Season

“…The genera Planktothrix and Cylindrospermopsis were the dominant groups of cyanobacteria (Figure 6). This finding is similar to the results found in other freshwater studies, which report the dominance of any of these two genera (Lira et al, 2011;Bonilla et al, 2012;Barros et al, 2017;Guellati et al, 2017).…”

“…Shallow lakes regularly display a polymictic character with complete mixing events during summer, mainly due to precipitation and wind, which results in destratification and complete mixing of the water column (do Nascimento-Moura et al, 2012;Kerimoglu and Rinke, 2013;Cavicchioli et al, 2019;Gradilla-Hernández et al, 2020a). According to relative read abundance, Planktothrix and Cylindropermopsis were consistently the most abundant cyanobacterial genera across all sampling sites (58.01% and 24.43, respectively), and months (47.37 and 37.80%, respectively), of this study, which have been dominant in other tropical or subtropical lakes studies (Figures 6A,B and Supplementary Tables S7, S8; Jöhnk et al, 2008;Gallina et al, 2011;Michalak, 2016;Barros et al, 2017;Guellati et al, 2017). Other groups that were not able to be classified at the genus level were Un.…”

“…According to relative read abundance, Planktothrix and Cylindropermopsis were consistently the most abundant cyanobacterial genera across all sampling sites (58.01% and 24.43, respectively), and months (47.37 and 37.80%, respectively), of this study, which have been dominant in other tropical or subtropical lakes studies ( Figures 6A,B and Supplementary Tables S7 , S8 ; Jöhnk et al, 2008 ; Gallina et al, 2011 ; Michalak, 2016 ; Barros et al, 2017 ; Guellati et al, 2017 ). Other groups that were not able to be classified at the genus level were Un.…”

“…Planktothrix is one of the most important microcystin-producing genera in temperate lakes (Fastner et al, 1999;Vasas et al, 2013). However, very few articles have reported Planktothrix as a predominant genus for tropical and subtropical areas (Reynolds et al, 2002;Jöhnk et al, 2008;Gallina et al, 2011;Michalak, 2016;Barros et al, 2017;Guellati et al, 2017). Within the Planktothrix genus, it is frequently the P. agardhii and P. rubescens species that dominate the phytoplankton community in the water column (Kurmayer et al, 2016).…”

Hazardous cyanobacteria integrity response to velocity gradient and powdered activated carbon in water treatment plants

“…In tropical regions, for example, toxin-producing filamentous cyanobacteria, among them R. raciborskii, have been dominating the phytoplankton community of artificial reservoirs, with average cell concentrations of around 10 6 cells mL -1 . D. circinale and M. aeruginosa have also been of major concern to water companies in these regions (Barros et al, 2017).…”