Role of Eichhornia crassipes uptake in the removal of nitrogen and phosphorus from eutrophic waters

Stimulation experiments were carried out to study nitrogen and phosphorus uptake and removal ability of Eichhornia crassipes from varying degrees of eutrophic waters for the period from Nov. 2007 to Oct. 2008. The results show that E. crassipes grows normally in different degrees of eutrophic waters with initial concentrations of 2.06~20.08 mg·L^-1 TN and 0.14~1.43 mg·L^-1 TP. Accumulated E. crassipes biomass in eutrophic waters increases by 41.03~47.12 kg·m^-2, at a mean growth rate of 0.096~0.262 kg·m^-2·d^-1 for the period of study. Nitrogen and phosphorus concentrations in E. crassipes aboverground part are 24.16~34.15 mg·g^-1 and 3.46~6.90 mg·g^-1 respectively. Those in the belowground part are 11.76~18.45 mg·g^-1 and 6.02~8.50 mg·g^-1 respectively. Total nitrogen and phosphorus uptaken by E. crassipes are 43.06~71.16 g·m^-2 and 8.68~16.63 g·m^-2 respectively. Meanwhile, accumulated assimilation of nitrogen and phosphorus increases with increasing initial nitrogen and phosphorus concentration in eutrophic waters. There is a significant positive correlation between accumulated nitrogen and phosphorus assimilation with E. crassipes biomass. In eutrophic waters Ⅰ and Ⅱ with lower nitrogen and phosphorus load, contribution of E. crassipes uptake to nitrogen and phosphorus removal is above 100% indicating some uptake of nitrogen and phosphorus from the sediment by E. crassipes. In eutrophic waters Ⅲ and Ⅳ with higher nitrogen and phosphorus load, contribution of E. crassipes uptake to nitrogen and phosphorus removal is above 42.32% and 83.79% respectively. E. crassipes uptake is therefore a major pathway of nitrogen and phosphorus removal in eutrophic waters.