Phytoplankton chlorophytes in a saline lowland river

GABELLONE, N. A.; NESCHUK, NANCY CAROLINA; SOLARI, LÍA CRISTINA

Joao Pessoa

Congreso; Plankton Symposium IV; 2007

A for PLANKTON RESEARCH

The  plankton  of  the  Salado  River  was  characterised  by  the  abundance  and  richness  of green algae (Chlorophyta), but not by diatoms as is usual in lowland rivers of temperate regions. Spatio-temporal changes of the green algae were analysed seasonally during the period May 1998- May 1999 at 13 locations, from the headwaters to the river mouth, in the main channel of the river and its tributaries. One  hundred  and  four  species  were  founded  (2  Volvocales,  93  Chlorococcales,  2 Ulotrichales and 7 Desmidiaceae). The mean maximum of species richness was recorded in  summer  with  35  species  in  the  lower  basin  and  30  species  in  the  middle  basin; meanwhile, the mean minimum was recorded in autumn in the tributaries (8 species). The number of species increased downstream due to the contributions from shallow lakes and  tributaries  connected  to  the  main  channel  of  the  Salado  River  basin.  Changes  in density and richness were related to temperature, nutrient concentrations, water velocity and  hydrological  conditions,  as  well  as  the  presence  of  dead  zones,  backwaters  and shallow  lakes  associated  with  the  river.  The  mean  maximum  density  for  the  basin  was recorded in spring 1998 and summer 1999 during low and normal water periods, whereas the        minimum        occurred    in        autumn      1998,        coinciding    with        a        high        water        period. Monoraphidium minutum and Chlamydomonas spp. were the most conspicuous species in spring in the middle basin. The Salado River basin is a nutrient enriched environment and this, in conjunction with the high temperature, promotes the development of Chlorophyta, especially Chlorococcales.