The water quality of rivers belonging to an arid sub‐basin in northern Argentina was evaluated in a longitudinal gradient, during the period of maximum dryness in 2017. The composition and structure of the phytobenthos were studied using biotic indices. A total of 126 spp. were determined, with a predominance of diatoms and Cyanobacteria. Most of the diatom species found were meso to polyhalobus and tolerant to organic contamination. Despite the rivers of the basin cross areas with very different land uses, no differences were recorded in phytobenthos abundances between sites. The Pantle & Buck Saprobity index classified the sub‐basin in the α‐mesosaprobability range, and the diatomaceous eutrophication/pollution index assigns poor quality to most of the sites. Salinity should induce phycoflora homogenization that limits the sensibility of biotic indices to anthropogenic impacts.
ResumenSe evaluó la calidad del agua de los ríos de una subcuenca árida del norte de Argentina en un gradiente longitudinal, durante el período de sequía máxima de 2017. Se estudió la composición y estructura del fitobentos mediante índices bióticos. Se determinaron 126 spp. en total, con predominio de diatomeas y cianobacterias. La mayoría de las especies de diatomeas encontradas eran de meso a polihalobas y tolerantes a la contaminación orgánica. A pesar de que los ríos de la cuenca atraviesan zonas con usos de la tierra muy diferentes, no se registraron diferencias en las abundancias de fitobentos entre los sitios. Según el Índice de Saprobiedad de Pantle & Buck, la subcuenca se clasificó en el rango de α‐mesosaprobiedad, y el Índice de Eutrofización/Contaminación por Diatomeas asigna una calidad baja a la mayoría de los sitios. La salinidad debe inducir una homogeneización de la ficoflora que limita la sensibilidad de los índices bióticos a los impactos antropogénicos.
Cyanobacterial blooms represent a major problem in reservoirs that are used for potable water supplies. The El Limón reservoir is one of the main reserves of water for consumption in northern Argentina (22°6′12.29″ S). This study analyzed the role of abiotic factors in the promotion of blooms in El Limón during warm seasons and explored the physical and chemical parameters affecting the morphological development of the most abundant cyanobacteria species. The results showed that short-term meteorological variations correlated with cyanobacterial abundances in this shallow reservoir. Average daily temperatures for 6 and 8 months before the sampling date were positively correlated with cyanobacterial abundances as well as filament length, while accumulated precipitation limited the abundances of cyanobacteria. Considering the highly probably effects of short-term meteorological factors on cyanobacterial blooms, the results support the need for continuous and periodic monitoring of tropical reservoirs.
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