CONICET | Buscador de Institutos y Recursos Humanos

> A transect was performed along the Chubut River (Patagonia) from the Atlantic towards the Andes measuring major water parameters of this drainage area. Samples were taken at different locations of the Chubut River, and also brooks several Andes lakes in the Chubut and Río Negro Provinces as well as from several Andes rivers and mountain creeks. For comparison, the Laguna Cacique Chiquichano in Trelew (Chubut) was investigated. Several physico-chemical parameters were determined (pH, oxygen, nitrogen compounds, conductivity, redox potential, water hardness and spectral transmission), as well as photosynthesis by means of PAM fluorimetry. Water toxicity was assessed with a bioassay based on toxicity-induced changes of the movement behavior of a flagellate. Water quality was very good in the upper part of the river, deteriorating towards its mouth. Transmission spectra of the water indicate the presence of Gelbstoff. The photosynthetic efficiency and chlorophyll fluorescence were considerably high in the FlorentinoAmeghino reservoir and remained high downstream. Toxicity measurements did not indicate significant pollution. The Laguna Cacique Chiquichano differed considerably from all other water samples. The water was high in nitrogen compounds and the conductivity was much higher than in the river samples. Phytoplankton composition varied along the transect as well as in the lakes: diatoms dominated in the Chubut River, whereas Chlorophytes and/or Cyanophytes also contributed an important share in the lakes and brooks samples. Since phytoplankton populations were most abundant in the lower part of the Chubut River, the species composition was intensively evaluated in this part. Here, a total of 38 species was identified belonging to the Bacillariophyceae, Chlorophyceae, Cyanobacteria, Dinophyceae and Euglenophyceae in the order of species diversity.

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