The combined effect of clethodim (herbicide) and nitrogen variation on allelopathic interactions between Microcystis aeruginosa and Raphidiopsis raciborskii.

The large-scale use of herbicides deteriorates water quality and threatens aquatic biodiversity. Unfortunately, there are few studies on the ecological effects of herbicides on toxin-producing strains of cyanobacteria under changing nutrient conditions. The objective of the present study was to investigate the effects of the herbicide clethodim and nitrogen variation on the allelopathic interactions and toxin production of Microcystis aeruginosa BCCUSP232 and Raphidiopsis raciborskii (formerly known as Cylindrospermopsis raciborskii) ITEPA1. M. aeruginosa had increased cell density when exposed to the clethodim (H +) (23.55 mg/L), whereas the highest cell density of R. raciborskii was observed in the treatment with clethodim plus limited nitrogen. Also, the cell-free exudate of R. raciborskii significantly stimulated the growth of M. aeruginosa on day 3 of the experiment. The concentration of chlorophyll-a in M. aeruginosa cultures generally increased in all the treatments, while in R. raciborskii cultures, the opposite occurred. Total microcystins (MCs) content of M. aeruginosa in the mixed cultures was 68% higher in nitrogen-enriched conditions than the control. A similar increase in MC content occurred in M. aeruginosa unialgal culture treated with R. raciborskii exudate. Total saxitoxin concentration was 81% higher in mixed cultures of R. raciborskii simultaneously exposed to high nitrogen and clethodim. Similarly, unialgal cultures of R. raciborskii exposed to either high nitrogen or clethodim had higher saxitoxins concentrations than the control. The intracellular H2O2 content of M. aeruginosa cultures decreased, whereas, in R. raciborskii cultures, it increased during exposure to high nitrogen and clethodim. Only R. raciborskii had a significant variation in peroxidase activity. The activities of glutathione S-transferase of both strains were higher in the presence of clethodim. These results revealed that nitrogen enrichment and the presence of clethodim might lead to the excessive proliferation of M. aeruginosa and R. raciborskii and increased production of cyanotoxins in aquatic environments.

Clethodim (herbicide) alters the growth and toxins content of Microcystis aeruginosa and Raphidiopsis raciborskii.

Increased agricultural intensification goes with the widespread use of herbicides that adversely affect aquatic biodiversity. The effects of herbicides on toxin-producing cyanobacteria have been poorly studied. The present study aimed to investigate the toxicological and physiological effects of the herbicide clethodim on Raphidiopsis raciborskii (a.k.a. Cylindrospermopsis raciborskii) ITEPA1 and Microcystis aeruginosa BCCUSP232. On day four of the experiment, the exposure to 25 mg/L clethodim resulted in the highest cell density of R. raciborskii. Similarly, exposure to the 1, 5, 20, and 50 mg/L clethodim treatments resulted in the highest cell densities of M. aeruginosa on day 4 of the experiment. Medium effect concentrations (EC50) after 96 h of exposure of both strains to clethodim were 192.98 mg/L and 168.73 mg/L for R. raciborskii and M. aeruginosa, respectively. The presence of clethodim significantly increased the total microcystin content of M. aeruginosa compared to the control cultures. At 400 mg/L, total saxitoxins content of R. raciborskii was 27% higher than that of the control cultures on day 4. In contrast, cultures exposed to 100 mg/L clethodim had the lowest saxitoxins levels per cell quota. There was an increase in the levels of intracellular hydrogen peroxide in both species during exposure to clethodim, which was followed by significant changes (p < 0.05) in the activity of antioxidant enzymes such as peroxidase and superoxide dismutase. These results revealed that the presence of low levels of clethodim in the aquatic environment might lead to the excessive proliferation of cyanobacteria and alteration of their cyanotoxins content.

Water quality of a coastal lagoon (ES, Brazil): abiotic aspects, cytogenetic damage, and phytoplankton dynamics.

Assessment of water resources requires interdisciplinary studies that include multiple ecosystem aspects. This study evaluated the water quality of Juara Lagoon (ES, Brazil) based on physical and chemical variables, cytogenetic responses in Allium cepa and phytoplankton dynamics. Three sampling sites were defined and water samples were collected during two sampling periods. Analyses such as determination of photic zone, conductivity, and concentrations of nutrients and metals were conducted as well as cytotoxic, mutagenic, and genotoxic potentials using A. cepa test. The main attributes of phytoplankton community, such as total richness, total density, density by class, dominance, and diversity, were also evaluated. Results have revealed that Juara Lagoon has signs of artificial eutrophication at two sampling sites due to high levels of total phosphorus and ammonia nitrogen. Cytotoxic, genotoxic, and mutagenic potentials were detected as well as high concentrations of Fe and Mn. Furthermore, 165 phytoplankton taxa were recorded, with highest richness in Chlorophyceae and Cyanophyceae classes. In addition, Cyanophyceae presented as the highest density class. A. cepa test and phytoplankton community evaluation indicated that the ecological quality of Juara Lagoon is compromised.

Periphytic algae in two environments of the lower Doce river (Juparanã lagoon and Pequeno river Linhares, Espírito Santo State, Brazil): spatial and temporal variation - DOI: 10.4025/actascibiolsci.v30i4.535 / Algas perifíticas em dois ambientes do baixo rio Doce (lagoa Juparanã e rio Pequeno Linhares, Estado do Espírito Santo, Brasil): variação espacial e temporal - DOI: 10.4025/actascibiolsci.v30i4.535

This research aimed to evaluate the spatial and temporal variation of the periphytic algae community within two environments of the lower Doce River: Juparanã Lagoon and Pequeno River. Samplings were carried out every three months from August 2004 to May 2005 at both sites. Natural substrata of Eichhornia azurea (Sw.) Kunth petioles were collected from the sites. The community was analyzed according to species richness, frequency of occurrence, density of organisms, abundance and dominancy. Eighty-six taxa were recorded in the lagoon, and the density of organisms varied from 20,595 ind cm-2 (May/05) to 88,712 ind cm-2 (Nov/04). Eighty-three taxa were recorded in the river, and the density of organisms varied from 16,049 ind cm-2 (Feb/05) to 71,663 ind cm-2 (Aug/04). At both sites, the classes that predominated qualitatively were Cyanophyceae, Bacillariophyceae and Zygnemaphyceae, in which filamentous and unicellular forms dominated, followed by colonial forms. Quantitatively, the most representative classes were Cyanophyceae and Bacillariophyceae. A spatial variation was not observed. Precipitation, water temperature, electric conductivity and transparency were the variables that most oscillated according to seasonal variation (dry or rainy season). They also presented a greater number of significant correlations with the biological variables, showing evidence of temporal heter

A pesquisa objetivou avaliar a variação espacial e temporal da comunidade de algas perifíticas em dois ambientes do baixo rio Doce: lagoa Juparanã e rio Pequeno. Foram realizadas coletas trimestrais (agosto/04 a maio/05) em duas estações amostrais, uma na lagoa e outra no rio. Foram coletados pecíolos de Eichhornia azurea (Sw.) Kunth. Os atributos da comunidade analisados foram: riqueza de táxons, freqüência de ocorrência, densidade, abundância e dominância. Na lagoa Juparanã, foram registrados 86 táxons e a densidade variou de 20.592 ind cm-2 (mai/05) a 88.712 ind cm-2 (nov/04). No rio Pequeno, foram registrados 83 táxons e a densidade variou de 16.049 ind cm-2 (fev/05) a 71.663 ind cm-2 (ago/04). Em ambos os ambientes, as classes predominantes qualitativamente foram Cyanophyceae, Bacillariophyceae e Zygnemaphyceae, havendo domínio das formas filamentosas e unicelulares seguidas das coloniais. As classes Cyanophyceae e Bacillariophyceae foram mais representativas quantitativamente. Não houve variação espacial. Pluviosidade, temperatura da água, condutividade elétrica e transparência foram as variáveis que mais oscilaram conforme a estação (seca ou chuvosa) e as que apresentaram maior número de correlações significativas com as variáveis biológicas, evidenciando heterogeneidade temporal.