Growth characteristics and nutrient removal capability of plants in subsurface vertical flow constructed wetlands

Three species of plants, Phragmites australis, Sparganium stoloniferum and Typha orientalis Presl., were selected to assess their growth characteristics and their capability to remove and accumulate nutrients such as nitrogen and phosphorous in pilot-scale-size subsurface vertical flow constructed wetland systems. During the experimental period, the growth situation of each plant was comprehensively evaluated. The rank order of the total influence value was as follows: P. australis (62.5)>T. orientalis Presl. (52)>S. stoloniferum (46). Both the maximum root length and root volume of the three species of plants had significant differences. S. stoloniferum reached maximum individual plant height (1.32m) at the end of July, while P. australis and T. orientalis Presl. did not reach a maximum individual plant height (2.08m and 1.58m, respectively) until the middle of September. Before cultivation, the total biomass of P. australis, S. stoloniferum and T. orientalis Presl. were 0.33, 0.69 and 0.71kgm^-2, respectively. After 5 months' growth, total biomass of the three species had become 3.81, 2.86 and 4.22kgm^-2, respectively; about 11.5, 4.1 and 5.9 times that the amount before cultivation. The total nitrogen (TN) ranked distributions in all three plants' tissues could be summarized as leaf>root>stem before cultivation and root>leaf> stem at the end of the experiment. P. australis, S. stoloniferum and T. orientalis Presl. mainly accumulated TN and total phosphorus (TP) in their roots, the ratio of belowground and aboveground TN and TP accumulation were 1.58 and 1.59, 2.47 and 3.61, and 2.74 and 5.18, respectively. The chemical oxygen demand (COD), TN, ammonia-nitrogen (NH₄-N) and TP removal rates of planted units were significantly higher than those of the unplanted control unit (p<0.05); but no significant differences were found between the different planted units (p>0.05).