Aldo A. Mariazzi

Bacterioplankton and phytoplankton production in a large patagonian reservoir (República Argentina)

Relationships between the secondary production of bacterioplankton and the primary production of phytoplankton in the Ezequiel Ramos Mexia Reservoir were examined. Monthly surveys, parallel measurements on consecutive days, and measurements at different times during the same day were undertaken to determine factors that might influence the relationships between the two sets of productivity measurements.The vertical and seasonal distribution of bacterial production appeared to be strongly related to primary production, with temperature as an important component of this trend. The bacterial production in the water column was equivalent to between 2 and 45% of the phytoplankton production over a period of one year.In a diel study, bacterial secondary production rates fluctuated, with maximum values during the night and early morning. There was no temporal coincidence between algal primary production and bacterial secondary production in daily surveys. It was therefore concluded that isolated measurements of productivity reflect events only at the particular time at which they are obtained. The relationship between algae and bacteria is extremely complex and must be carefully evaluated. The nature of the relationship could be underevaluated if the only measurements taken into consideration were made during the daylight period.

Impact of a nuclear power plant on water quality of Embalse del Río Tercero Reservoir, (Córdoba, Argentina)

We studied the water quality of Embalse del Río Tercero Reservoir after the building of a nuclear power plant, completed in 1983, and compare the results with available information for the period before the plant started operating. At present, the reservoir is eutrophic. It has a period of stratification in spring and summer and it is fully mixed in fall and winter. Seasonal variations are large. Diatoms are dominant during homothermous periods, while primary production seems to be light-limited. Aphanocapsa sp. is dominant during periods of stratification, at the end of which nutrient exhaustion (specially inorganic nitrogen) limits production. At present, mean inorganic nitrogen, total phosphorus and chlorophyll concentrations are lower than before the power plant started operating. It is suggested that this improvement in water quality is due to a change in water management. Extensive drawdown of the reservoir was allowed before 1983. Since large volumes of water are required for cooling purposes in the nuclear power plant, water level fluctuations have strongly diminished. Changes of colonization in Elodea sp. and fish composition have also been observed.

Physical and chemical characters, phytoplankton and primary production of Ezequiel Ramos Mexía Reservoir (Argentina)

We describe the distribution in space and time of a series of physical and chemical variables, phyto-plankton, and primary production in Ezequiel Ramos Mexía Reservoir (Argentina). Its waters are soft, poor in nutrients and with a low transparency that greatly depresses primary production. Phytoplankton data indicate the presence of 79 taxa with Bacillariophyceae, Cyanophyta and Chlorophyta alternatively dominant. Chlorophyll a was always low and never exceeded 3 mg m−3. Based on these results, the trophic status of this ecosystem is discussed.

Bacterial secondary production and it relation with primary production in the Embalse del Río III Reservoir, Argentina

During an annual period the bacterial biomass (epifluorescence) and secondary production (methyl-3H-thymidine incorporation), as well as biomass (Chlorophyll) and algal primary production (incorporation of NaH14CO3) were studied in the Embalse del Río III Reservoir, Argentina. The relations between these variables and their responses to seasonal changes in water temperature were analyzed. A close relationship in seasonal patterns of algal primary production and bacterial secondary production was observed, with the estimated rates of bacterial production similar to that obtained by other authors in eutrophic lakes. Bacterial production was 17 to 46% of the primary production, thus, at 60% assimilation efficiency, the bacterioplankton would consume 28 to 77 % of the total fixed carbon. Seasonal trends in algal primary production and bacterial secondary production were mainly affected by temperature.