The effect of phosphorus binding clay (Phoslock®) in mitigating cyanobacterial nuisance: a laboratory study on the effects on water quality variables and plankton

This laboratory study examined the lanthanum modified clay PhoslockA (R) for its effectiveness to bind soluble reactive phosphorus (SRP), release of nutrients from this modified clay, its influence on water quality variables (pH, oxygen saturation %, conductivity and turbidity), effects on phytoplankton growth (green alga Scenedesmus obliquus, cyanobacteria Microcystis aeruginosa and Anabaena sp.), and, lastly, its effect on the population growth of the rotifer Brachionus calyciflorus. A clear dose-response for SRP binding by the modified clay was observed. A small amount of ammonium is released from PhoslockA (R). We found no effect of PhoslockA (R) on pH or oxygen saturation. Conductivity increased with the increasing concentration of PhoslockA (R). An application of PhoslockA (R) caused a transient increase of turbidity up to 211 NTU. However, due to rapid settlement, turbidity fell below 13 NTU (similar to 1 m Secchi depth), after 6 h. Phoslock(A (R)) addition caused a reduction in growth of all phytoplankton species tested that we attribute to the combined effects of light limitation, flocculation with the bentonite and binding of SRP to Phoslock(A (R)). We estimated the EC50 of Phoslock(A (R)) on the population growth of rotifer B. calyciflorus to be 0.15 g Phoslock(A (R)) l(-1). Overall, the results of our study indicate Phoslock(A (R)) seems to be suitable for field applications.