Approaches for phosphorus removal with calcium hydroxide and floating macrophytes in a mesocosm experiment: impacts on plankton structure

Abstract

Cultural eutrophication has promoted the application of several mitigation strategies in the last 50 years. In this study we tested the combined effects of two techniques: calcium hydroxide [(Ca(OH)2), lime] and a free-floating macrophyte (Salvinia rotundifolia Willd) to examine the soluble reactive phosphorus removal capability and the effects on plankton (phytoplankton and zooplankton) structure in a in situ lake mesocosms experiment. The experiment lasted 10 days (n = 12, 500 l each) with a control and three treatments (lime (CH), plants (FM), and the combination of both (CH + FM)). Samples of several physical and chemical variables (including nutrients) and phytoplankton were taken at the beginning, 2 days after, 4 days, and 10 days (end of the experiment). Zooplankton was sampled at the beginning and at the end. The highest depletion effect of soluble reactive phosphorus (SRP) was observed in presence of lime. Phytoplankton biovolume was highly and negatively affected in lime treatments (CH and CH + FM). Zooplankton changed from Rotifera to Cladocera and Copepoda in presence of macrophytes. We conclude that lime + plants reduces more effectively SRP, phytoplankton biovolume and promotes herbivorous zooplankton development; becoming by this way, in a suitable mitigation strategy to be explored in future field manipulation studies.