Abstract
The terrestrial plant Luffa cylindrica was applied to a surface-flow-constructed wetland (SFCW) to treat effluent from rice fields. To control the excessive growth of weeds that interfere with the maintenance of SFCWs, SFCWs with and without shading were constructed and the effect of shading was investigated. The average removal efficiencies of T-N and T-P for 135 day operation of the SFCW with shading were 57 and 53%, respectively, while in the case of those without shading were 44 and 41%, respectively. This result indicates that the nutrient removal efficiency was stimulated by shading. Although L. cylindrica completely dominated the SFCW with shading, the total plant biomass production including weeds was higher without shading. The total length of the roots in the SFCW with shading was, however, 2.2-fold that without shading. Consequently, it was suggested that the longer root length observed in SFCW with shading promoted the sedimentation of nutrients, resulting in a nutrient removal efficiency higher than that in the case without shading. These results demonstrate that shading is effective not only to control the growth of weeds but also to enhance the growth of roots in SFCWs, resulting in easier maintenance and a higher nutrient removal efficiency.
