Planktonic and physico–chemical dynamics of a markedly fluctuating backwater pond associated with a lowland river (Salado River, Buenos Aires, Argentina)

Abstract

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 physical–chemical 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 physical–chemical 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 different degrees of hydrological connection with the Salado River produce changes in dissolved phosphorus 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 phosphorus– particle 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.

Phytoplankton and primary production in clear-vegetated, inorganic-turbid, and algal-turbid shallow lakes from the pampa plain (Argentina)

“…Other studies on phytoplankton structure from shallow lakes of the Salado River Basin also revealed that this algal group was favored in water bodies with anthropogenic impact (Izaguirre & Vinocur, 1994a;Gabellone et al, 2001). Eutrophic and hypertrophic lakes are susceptible to bloom formation.…”

“…Due to their shallowness, these water bodies show a great variability in their residence time. For example, Gabellone et al (2001) found that the degree of hydrological connection with the Salado River has a great effect on the limnological features and planktonic communities of an associated shallow lake. In a more recent study, have also demonstrated the role of hydrology, as one of the major factors that can regulate the plankton biomass of the lakes in this region.…”

Nutrients, Conductivity and Plankton in a Landscape Approach to a Pampean Saline Lowland River (Salado River, Argentina)

“…In previous investigations carried out on the lower reaches of the Salado River, physical and chemical changes were identified as factors controlling the plankton community within the main channel and in a backwater pond (Gabellone et al 2001). During low water periods, suspended solids increased, causing a decline in plankton density.…”

Zooplankton biomass in an eutrophic shallow lake (Buenos Aires, Argentina): spatio-temporal variations

“…In the last decade, there have been some contributions for particular shallow lakes as Lobos (Boltovskoy et al 1990), San Miguel (Gabellone et al 2001, Solari et al 2002a) and San Miguel del Monte (Benítez & Claps 2000, Claps et al 2002. All of these studies emphasised the importance of rotifers and the larval stages of copepods in determining the zooplankton density.…”