Phosphorous and nitrogen effect on metal tolerance in Salvinia herzogii.

HADAD, H. R.; MAINE, M. A.; BONETTO, C.

Lisboa, Portugal

Conferencia; 10th International Conference on Wetlands Systems for Water Pollution Control.; 2006

IWA

Two successively constructed wetlands for wastewater treatment from a tool factory containing Zn, Ni and Cr showed floating macrophyte disappearance followed by T. domingensis colonisation. Experimental work was developed to test the hypothesis that nutrient enrichment might enhance metal tolerance of floating macrophytes. Relative growth rates and chlorophyll concentrations in Salvinia herzogii (water fern) were measured in laboratory incubations exposed to different Zn, Ni and Cr concentrations, and compared with simultaneous treatments enriched with nutrients. Treatments exposed to Zn and Ni showed significantly lower relative growth rates than the controls at the metal concentrations assayed, while the treatments enriched with nutrients showed no significant differences compared with the controls. The treatment exposed to the highest Cr concentration showed a significant biomass reduction; nutrient enrichment significantly decreased the magnitude of biomass reduction. Root growth inhibition caused by Cr exposures was reverted by nutrient enrichment. Zn concentration in leaves decreased by nutrient addition while P concentration in leaves decreased by Zn exposure through P and Zn immobilisation in roots. Metal concentrations in water decreased with time, being Cr removal faster than the others. Zn and Ni were mainly stored in S. herzogii biomass, while Cr was mainly retained in the detrital fraction. Nutrient enrichment increased Zn removal by enhancing the detrital fixation and increased the amount of Cr retained in S. herzogii biomass. Ammonium and soluble reactive P were also removed from the solution. Zn and Ni exposures decreased nutrient removal and P content in leaves, while Cr did not produce any observable effect.