Plankton community changes due to the addition of treated effluents to a freshwater reservoir used for drip irrigation

Abstract

The present paper defines the structure and dynamics of the planktonic populations before and after the addition of reclaimed effluents to an operational irrigation reservoir. The analysis of the effects of the inflow of the effluents on the parameters that characterize the planktonic populations may serve to determine the means that have to be taken to improve the quality of the water used for drip irrigation. The planktonic communities in the reservoir were defined by factor analysis. The input of effluents led to a change from phyto- and zooplankton communities dominated by small species, to communities dominated by large species (greater than 200 μm). This change was characterized by an increase in biomass without an increase in the total number of algae. The dominating algae were species of Cyanophyta which responded to the input of N compounds rather than to the increase in phosphate concentration. Laboratory enrichment experiments support the idea that the limiting factor was the N compounds.