GABELLONE Nestor Adrian
Planktonic and physical-chemical dynamics of a markedly fluctuate backwater pond in a plaine basin (Salado river, Buenos Aires, Argentina)
GABELLONE, N. A.; SOLARI, LÍA CRISTINA; CLAPS, MARÍA CRISTINA
Lakes & Reservoirs Research and Management
Año: 2001 vol. 6 p. 133 - 142
An investigation was performed in a pond (San Miguel) directly associated with the Salado River (Pampean grasslands). The aim of the study was to analyze river interactions. Physical and chemical conditions and the plankton community were studied in order to determine the effects of changes in hydrological conditions. The main factors that influenced the physicalchemical characteristics of the pond have been identified by means of cluster analysis. Conductivity was the main factor that determined groups in sampling periods. Changes in conductivity were clearly associated with the water-level of the pond and depended on the flow of the Salado River and fluctuations of its conductivity, which is itself a function of evaporation and the inflow of underground water of high conductivity. Other factors that affected the physicalchemical conditions included concentrations of phosphorus and polyphenols, the main allocthonous sources. The concentration of these compounds was decreased in low water conditions. Principal Components Analysis suggested that there were four major regulatory factors in the pond, as follows. First, a dry season, with a prolonged isolation phase and a considerable increase in conductivity, turbidity and suspended solids, during which the abundance of plankton was greatly reduced, as were incorporated benthic species. A high and sudden increase of river flow determines the second regulatory factor, the flood season, when dissolved allocthonous material enters, conductivity decreases and there is a conspicuous dominance of cyanophytes, protozoans and crustaceans. The ifferent degrees of hydrological connection with the Salado River produce changes in dissolved hosphorus forms and the composition of the plankton. The third regulatory factor is an increase in particulate material. This is associated with the highest total phosphorus values as a consequence of the phosphorusparticle relationship. The opposite situation, the fourth regulatory factor (a decrease in particulate material), produces clear water conditions with a dominance of chlorophytes, planktonic diatoms and rotifers.