Based on comparative tests of removal effect between Ecological Floating-Beds (EFBs) planted with Canna indica and Acorus calamus and the unplanted bed, the mechanism of EFBs was investigated through the tracer study and mass balance calculation. Results of the study showed that, the average removal efficiencies of TN,TP and CODCr of EFBs planted with Canna indica and Acorus calamus were 29.5%,28.7%,23.7% and 31.8%,27.9%,24.4%, the average removal loadings were 1.141,0.111,0.684 g·m-2·d-1 and 1.244,0.108,0.689 g·m-2·d-1, respectively, apparently higher than those of the unplanted bed.The removal effect exhibited positive relationships with the plants growth with the correlation coefficient higher than 0.786(p＜0.05) in both units.The sedimentation of nitrogen and phosphorus was the dominating pathway for pollutants removal in EFBs, while plants uptake contributed to only about 10% of total pollutants removed. The study indicated that plants help to keep the flow pattern of EFBs more close to plug flow pattern, good DO concentration gradient distribution and decontamination by filtration of roots, testifying that plants played a critical role in pollutants removal in EFBs.
