Seasonal variation in the phytoplankton during an intensive sampling period in a saline lowland River (Bs. As. Argentina)

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

Joao Pessoa

Congreso; Plankton Symposium IV; 2007

A for Plankton Research

The  main  aim  of  this  survey  was  to  analyze  seasonal  variations  in  phytoplankton composition, relating its behaviour to temperature and conductivity, at two sampling sites in  the  Salado  river  lower-basin:  El  Destino  (ED)  and  Guerrero  (G).  At  each  site,  28 samples were taken twice a week from 9/3 to 20/7/2004. A total of 145 and 143 species were identified for ED and G respectively, although rare species were discarded to avoid statistical misinterpretation. Correlation coefficients and autocorrelation  analyses  (Q-Ljung-Box  statistic)  were  performed  in  order  to  establish seasonal patterns of species abundance. Significant autocorrelations (p <0.05) were observed between phytoplankton species and temperature-conductivity  patterns,  illustrating  their  seasonal  behaviour.  Moreover,  the species  were  grouped  according  to  their  occurrence  during  different  water  temperature periods:  ‘summer’  group:  included  34  species  that  were  well  represented  during  warm- waters (>22ºC): Planctonema lauterbornii, Gloeocapsa dermochroa, Geminella interrupta, among others; ‘winter’ group: included 10 species whose highest densities were reached during  cold-waters  period  (<12ºC):  e.g.  Binuclearia  sp.,  Nitzschia  fruticosa,  Schroederia indica,  Microcystis  firma;  ‘transitional’  group:  of  only  4  species  with  abundance  peaks during   ‘intermediate’   conditions   (15.5   ºC  average),   Closteriopsis   sp.   and   Nodularia spumigena  being the most remarkable; and ‘indifferent’ group: with 22 species of random behaviour  whose  autocorrelations  remain  within  confidence  limits:  Oscillatoria  limnetica, Monoraphidium griffithi, Scenedesmus linearis, etc. Aforementioned  results  correspond  to  species  with  similar  behaviour  in  both  sampling sites; remaining ones presented slightly different patterns. An evident seasonal succession was detected, having species substitution from summer warm-stagnant adapted species to cold-waters favoured ones, hence indicating different successional stages.