Improving Urban Stormwater Runoff Quality by Nutrient Removal through Floating Treatment Wetlands and Vegetation Harvest.

Two floating treatment wetlands (FTWs) in experimental tanks were compared in terms of their effectiveness on removing nutrients. The results showed that the FTWs were dominated by emergent wetland plants and were constructed to remove nutrients from simulated urban stormwater. Iris pseudacorus and Thalia dealbata wetland systems were effective in reducing the nutrient. T. dealbata FTWs showed higher nutrient removal performance than I. pseudacorus FTWs. Nitrogen (N) and phosphorous (P) removal rates in water by T. dealbata FTWs were 3.95 ± 0.19 and 0.15 ± 0.01 g/m2/day, respectively. For I. pseudacorus FTWs, the TN and TP removal rates were 3.07 ± 0.15 and 0.14 ± 0.01 g/m2/day, respectively. The maximum absolute growth rate for T. dealbata corresponded directly with the maximum mean nutrient removal efficiency during the 5th stage. At harvest, N and P uptak of T. dealbata was 23.354 ± 1.366 g and 1.489 ± 0.077 g per plant, respectively, approximate twice as high as by I. pseudacorus.

[Study on the nitrogen and phosphorus uptake ability of four plants cultivated on floating-bed].

Plant floating-bed tested engineering was constructed for eutrophication control in Dian-shan Lake, the characteristics and nutrient uptake abilities of Canna indica, Iris pseudacorus, Thalia dealbata and Lythrum salicaria were compared. It shows that using upper and lower nylon nets to fix the plants on the floating-bed is beneficial for them to grow and reproduce rapidly. Survival rates of Canna indica, lris pseudacorus, Thalia dealbata and Lythrum salicaria are 83.33%, 83.33%, 76.67% and 53.33% respectively. Ramets of Canna indica and Thalia dealbata are 64 and 78 respectively in November, and the biomass (fresh weight) of these two plants are 32.0 and 38.6 kg per individual plant. Nitrogen (N) and phosphorus (P) content in stems/leaves of Canna indica and Thalia dealbata are greater than those in roots. The ratio between stems/leaves and roots of N, P content in Canna indica are 1.40 and 1.21 respectively, while 1.59 and 1.08 in Thalia dealbata. The difference of cumulative N, P content in plants is mostly on account of different plant biomass. N uptake ability of Thalia dealbata is the highest, which is 457.11 g per square; Canna indica has the highest P uptake ability, which is 41.29 g per square. N, P uptake ability of stems/leaves in Canna indica are 2.17 and 1.86 times higher than that of roots, while 1.73 and 1.17 times higher respectively in Thalia dealbata. Thus, Canna indica and Thalia dealbata are recommended as the floating-bed plants to control the eutrophication in Dian-shan Lake.