Variaciones espaciales y temporales del fitoplancton en un lago subtropical de Argentina

Abstract

Temporal and spatial variations of the phytoplankton in a subtropical lake of ArgentinaSpecies composition, biomass and diversity of the phytoplankton in a subtropical lake (27°29'S; 58°45'W) were studied from February 1995 to March 1996. One or two samples were taken monthly in the limnetic and the littoral area. Cell counts were done by the Utermöhl method (1958 Cyanophyta was the dominant group all the year contributing among 25% and 83% of the total biomass. Cylindrospermopsis raciborskii, Aphanizomenon sp. and Microcystis aeruginosa were the dominant species. The Chlorophyta, second group in importance, contributed among 8% and 50% being Botryococcus braunii the dominant species. Bacillariophyceae, Xanthophyceae, Euglenophyceae and Cryptophyceae they did not surpass 20% of total biomass. Chrysophyceae and Dinophyceae they did not surpass 5% of total biomass. Chlorophyll a content ranged between 0.7 and 8 µg.L -1 reflecting the annual variation of phytoplankton biomass. Phytoplankton density diversity varied among 0.34 and 3.69 bits.ind -1 . Biomass diversity varied among 1.04 and 2.92 bits.µm 3 , with a similar variation in the depths of the lake.The lowest biomass and the highest diversity were always found in the littoral zone. C-Strategists, with a high SA/V ratios prevailed in density (Monoraphidium contortum, M. tortile, Chlorella vulgaris and other small flagellates of Chlorophyta) while S-Strategists (with a low SA/V ratios) such as Microcystis aeruginosa and Botryococcus braunii prevailed during the greater part of the year. Cylindrospermopsis raciborskii and Aphanizomenon sp. were dominant in density and biomass when the temperatures were superior to 20°C and the solar radiation surpassed 20 MJ.m -2 . The R-Strategists (Aulacoseira italica and Gymnodinium sp.) prevailed during great unstability of water column.Phytoplankton biomass was positively correlated with rain falls 10 days before each sampling (r = 0.772; p < 0.01; g.1. = 30). During the period that prevailed the filamentous Cyanophyceae an increase in the heterocysts frequency was observed in coincidence with a period of notorous drought.

Chlorococcalean algae as palaeoenvironmental indicators: new data from the Los Rastros Formation, Triassic of central-western Argentina

“…La lista de autores correspondiente a cada una de las especies citadas puede chequearse en Zavattieri & Batten (1996) Distintos autores enfatizaron el valor paleoecológico que presentan las Chlorococcales, y en especial, Botryococcus Kützing 1849, en la evaluación de algunos parámetros tales como el nivel de nutrientes presentes en un cuerpo de agua (estado trófico), y en menor medida, la profundidad. Botryococcus es una forma dulceacuícola y eurihalina, que prospera inclusive en albúferas (Medeanic, 2006); para algunos autores sería un elemento de valor ecológico discutido (Hutchinson, 1957), en tanto que otros señalan que puede p v estar presente y aún ser relativamente abundante en medios eutróficos (Zalocar de Domitrovic et al, 1998;Jankovská & Komárek, 2000;van Geel, 2001); sin embargo, Botryococcus parecería darse preferentemente en cuerpos de agua oligotróficos (Ottone et al, 2005), y de hecho, su disminución y eventual desaparición es usada como índice de eutrofización (Blomqvist et al, 2001;Smittenberg et al, 2003), en tanto que su incremento, como signo de oligotrofización (Wake & Hillem, 1980;UNEP, 2000;Huszar et al, 2003;Khursevich et al, 2003;Chmura et al, 2006;Riera et al, 2006), llegando a ser dominante en ambientes extremos, oligotróficos o hasta eventualmente distróficos, donde otras algas Chlorococcales no pueden prosperar (Jankovská & Komárek, 2000). Plaesiodictyon Wille 1970, en cambio, por comparación con Pediastrum Meyen 1829, podría darse tanto en medios eutróficos como oligotróficos (Komárek & Jankovská, 2001;Ottone et al, 2005).…”

Factors Triggering Cyanobacteria Dominance and Succession During Blooms in a Hypereutrophic Drinking Water Supply Reservoir

“…The lake has two tributaries: El Divisorio Stream and Sauce Grande River, which run through an important agricultural area. The reservoir has a surface area of 36 km 2 , with a mean depth of 8.2 m. It is a nonstratifying system; the continuous mixing is due to morphometric features along with the wind effect (Intartaglia and Sala 1989). Paso de las Piedras reservoir is a highly eutrophic system which has experienced recurrent cyanobacterial blooms since 1982 (Gayoso 1993;Pizzolon et al 1999;Echenique et al 2001;Fernández et al 2009).…”

Seasonal fluctuation of some limnological variables on a floodplain lake (Patos lagoon) of the Upper Paraná River, Mato Grosso do Sul State, Brazil

“…Floodplain lakes are fundamental for the maintenance of floodplain biodiversity. These small lakes favour the development of aquatic macrophytes in the littoral zone during low water periods, contributing a great variety of niches for aquatic organisms (Zalocar de Domitrovic et al, 1998; and breeding grounds for Brazilian Archives of Biology and Technology many species of fish (Agostinho and Zalewski, 1996;Agostinho et al, 2000). Several studies on floodplains have been undertaken; nevertheless, due to the diversity of these environments these researches are still scarce.…”