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

Abstract

Cultural eutrophication has promoted theapplication of several mitigation strategies in the last50 years. In this study we tested the combined effectsof two techniques: calcium hydroxide [(Ca(OH)2),lime] and a free-floating macrophyte (Salvinia rotundifoliaWilld) to examine the soluble reactive phosphorusremoval capability and the effects on plankton(phytoplankton and zooplankton) structure in a in situlake mesocosms experiment. The experiment lasted10 days (n = 12, 500 l each) with a control and threetreatments (lime (CH), plants (FM), and thecombination of both (CH ? FM)). Samples of severalphysical and chemical variables (including nutrients)and phytoplankton were taken at the beginning, 2 daysafter, 4 days, and 10 days (end of the experiment).Zooplankton was sampled at the beginning and at theend. The highest depletion effect of soluble reactivephosphorus (SRP) was observed in presence of lime.Phytoplankton biovolume was highly and negativelyaffected in lime treatments (CH and CH ? FM).Zooplankton changed from Rotifera to Cladocera andCopepoda in presence of macrophytes. We concludethat lime ? plants reduces more effectively SRP,phytoplankton biovolume and promotes herbivorouszooplankton development; becoming by this way, in asuitable mitigation strategy to be explored in futurefield manipulation studies.