Seasonal variation in the phytoplankton of a saline lowland river (Buenos Aires, Argentina) throughout an intensive sampling period

BAZZURI, MARÍA E; GABELLONE, N. A.; SOLARI, LÍA CRISTINA

RIVER RESEARCH AND APPLICATIONS

JOHN WILEY & SONS LTD

Año: 2010 vol. 26 p. 766 - 778

1535-1459

The main aim of this survey was to analyze seasonal variations in phytoplankton composition, with respect to its behavior to temperature and conductivity values at two sampling sites in the Salado river lower basin: El Destino and Guerrero. Samples were taken twice a week from 9/3/2004 to 20/7/2004 and analyzed according to Utermöhl method. A total of 145 and 143 species were identified for these two respective sites. Infrequent species were discarded to avoid statistical misinterpretations. Autocorrelation analyses (Ljung-Box Q-statistic) were performed in order to establish seasonal patterns for species abundance. Similar significant (p <0.05) autocorrelations patterns were observed for phytoplankton species composition, temperature and conductivity, thus illustrating correspondence and seasonal behavior. On the basis of these data, species were grouped as: (1) late-summer group: with 34 species well represented in warm-waters (>22ºC) such as Planctonema lauterbornii, Chrooccocus spp. and Merismopedia spp.; (2) winter: with 10 species that reached their highest densities in cold waters (<12ºC) (e.g., Binuclearia sp., Microcystis firma); (3) transitional: of only 4 species with abundance peaks during intermediate conditions (average 15.5ºC) such as Closteriopsis acicularis and Nodularia spumigena; and (4) independant: with 22 species of random behavior whose autocorrelations remain within confidence limits. These four classifications pertain to species with similar presence at both sampling sites; the rest of the species evinced slightly different patterns. An apparent seasonal-associated succession of species was detected; with those adapted to the warm, stagnant water of the late-summer being replaced by others acclimated to the cold water of the winter.Planctonema lauterbornii, Chrooccocus spp. and Merismopedia spp.; (2) winter: with 10 species that reached their highest densities in cold waters (<12ºC) (e.g., Binuclearia sp., Microcystis firma); (3) transitional: of only 4 species with abundance peaks during intermediate conditions (average 15.5ºC) such as Closteriopsis acicularis and Nodularia spumigena; and (4) independant: with 22 species of random behavior whose autocorrelations remain within confidence limits. These four classifications pertain to species with similar presence at both sampling sites; the rest of the species evinced slightly different patterns. An apparent seasonal-associated succession of species was detected; with those adapted to the warm, stagnant water of the late-summer being replaced by others acclimated to the cold water of the winter.