Keywords: SRP, turbidity, constructed wetlands, mesocosm, free floating grasses, pH change, Phragmites karka, Vetiveria zizanioides, surface water quality, quality improvement, pond water, phosphorus
Comparison of the ability of two grasses viz., Phragmites karka (Retz.) Trin. ex. Steud and Vetiveria zizanioides (L.) Nash to improve surface water quality in a constructed wetland
The aim of the study was to investigate the ability of two grasses viz., Phragmites karka (Retz.) Trin. ex. Steud (Common reed) and Vetiveria zizanioides (L.) Nash (vetiver), to improve the quality of turbid pond water with a high content of Soluble Reactive Phosphates (SRP) in a constructed wetland. Pot experiments with the individual plants showed the removal of SRP from the pond water at a faster rate in P. karka. The phosphorus accumulation rate was also found more in P. karka with a value of 0.46 ? 0.05, slightly higher than that of V. zizanioides at 0.41 ? 0.09. The pH range at which higher removal of SRP by the two grasses occurred was observed to be under neutral to a slightly alkaline medium, respectively. The removal of turbidity was found to be greater in P. karka from an initial value of 70.0 ? 12.5 to 3.0 ? 0.8 NTU followed by V. zizanioides, with a final turbidity of 8.3 ? 0.06 NTU. Microbial count reduction was observed to be significant in V. zizanioides but little impact on microbial diversity was observed in P. karka. The growth patterns of both the grasses in water under floating conditions were investigated. Mesocosm studies showed a clear relation between the pH of the water and phosphorus uptake by these two grasses.