Effects of plant diversity and hydraulic retention time on pollutant removals in vertical flow constructed wetland mesocosms

Plant species richness and hydraulic retention time (HRT) are two important variables in mediating pollutant removals of constructed wetlands, but their collective effects have not been clear. Pollutant removals in vertical flow mesocosms were investigated using both plant species richness and HRT as fixed factors. Both BOD5 and COD removals were enhanced by the longer HRT and the significant species richness × HRT interaction, as shown by two-way ANOVA. Differently, the removals of the NH4–N, NO3–N and phosphate were improved by the species richness, HRT, and the species richness × HRT interaction. The present findings highlight the importance of the interaction between the plant species richness and the HRT in improving the pollutant removals in vertical flow constructed wetlands.

► Plant and microbial biomass parameters were enhanced by the plant species richness.
► Removals of BOD5 and COD were enhanced by the hydraulic retention time (HRT).
► Removals of nitrogen or phosphate were enhanced by the species richness, HRT and their interaction.