CONICET | Buscador de Institutos y Recursos Humanos

Physico-chemical and biological, temporo - spatial variations in a northwestern argentine reservoir: Monthly samplings from October 1997 to March 1999 were conducted in the limnetic zone and at the intersection of the Salí and Tapia tributary rivers for the purpose of evaluating the phytoplankton dynamics in two vertical profiles of Dr. C. Gelsi reservoir (Tucumán, Argentina). This reservoir was characterized as warm monomictic, with bicarbonate, chloride, sodium, calcium and/or magnesium waters. In both sites, the rate of total nitrogen was higher than 1 mg/l, whereas that of orthophosphate reached 0.2 mg/l. Out of the eleven organochlorine pesticides analyzed, the presence of lindane and methoxychlor with higher concentrations in warm months was particularly confirmed. Bacterial load values were compatible with water quality standards, and variations in the number of colonies of actinomycetes in the sediments were correlated, among other parameters, with dissolved oxygen. In the two zones studied a total of 57 phytoplankton taxa: 49% green algae, 37% diatoms, 9% Cyanobacteria and 5% dinoflagelates were identified. Central diatoms (Aulacoseira granulata and Cyclotella meneghiniana) prevailed in the phytoplankton and in a lesser degree in the other groups, low values of specific diversity being obtained. Principal components analysis based on the absolute abundance of species and on some physico-chemical parameters arranged the samples of the various levels, this abundance is being more evident in the limnetic zone. There was also a tendency to the separation of stratifications from the two consecutive years and homogeneity in the samples from the mixing period was noticed. On the basis of the saprobic index, water quality was from â-á-mesosaprobic to á-mesosaprobic. degree in the other groups, low values of specific diversity being obtained. Principal components analysis based on the absolute abundance of species and on some physico-chemical parameters arranged the samples of the various levels, this abundance is being more evident in the limnetic zone. There was also a tendency to the separation of stratifications from the two consecutive years and homogeneity in the samples from the mixing period was noticed. On the basis of the saprobic index, water quality was from â-á-mesosaprobic to á-mesosaprobic. Aulacoseira granulata and Cyclotella meneghiniana) prevailed in the phytoplankton and in a lesser degree in the other groups, low values of specific diversity being obtained. Principal components analysis based on the absolute abundance of species and on some physico-chemical parameters arranged the samples of the various levels, this abundance is being more evident in the limnetic zone. There was also a tendency to the separation of stratifications from the two consecutive years and homogeneity in the samples from the mixing period was noticed. On the basis of the saprobic index, water quality was from â-á-mesosaprobic to á-mesosaprobic.â-á-mesosaprobic to á-mesosaprobic.