Nutrient Uptake Efficiency and Growth of Two Aquatic Macrophyte Species under Constructed Wetlands, Ethiopia

Abstract

This study was carried out to investigate the growth and nutrient uptake of two wetland plants from Lake Tana. Rhizomes of Cyperus papyrus and Phragmites karaka were grown outdoors in four parallel-aligned horizontal sub-surface flow constructed wetland (hssfcw) treatment beds. The treatment beds were irrigated with wastewater sourced from students’ residence from January 21 to March 20, 2011. The results of the study showed that Cyperus papyrus had higher rate of biomass accumulation as evidenced by increase in shoot and root weights (83.93 gm) compared to Phragmites karka. It had also significantly (p < 0.05) higher root total phosphorus and leaf total nitrogen content than that of Phragmites karka. The mean removal efficiency of the papyrus-planted treatment bed was 56.37% (NO₃-N), 84.04% (PO₄^3-); the phragmites- planted treatment bed was 58.37% (NO₃-N), 65.18% (PO₄ ^3- ) and the unplanted (control) treatment bed was 36.13% (NO₃-N) and 50.21% (PO₄ ^3-).  Pollutant removal efficiency differences were statistically significant (p < 0.05) between planted and unplanted treatment beds for PO4^3- but  not  for NO₃-N. The study also showed that the progressive increase in the plant density, shoot length and stem diameter was positively correlated with the nutrient removal efficiency of the treatment beds. The average removal efficiency of the two planted treatment beds was higher than unplanted bed. The study proved that these macrophytes had the ability to accumulate high biomass and remove nutrients and therefore have high potential in biological nutrient removal processes.