Nitrogen and phosphorus remediation of aquatic garden plants in laboratory-scale constructed wetlands.

摘要

This research investigated the potential of growing marketable aquatic garden plants that also remediate nursery and greenhouse runoff in a subsurface-flow constructed wetland. The cost of wastewater treatment is offset by the production of revenue-generating horticultural crops. Aquatic garden plants that offer the dual benefits of nutrient remediation and aesthetic value may also be used in bioretention basins, rain gardens, buffer zones, and filter strips.;Fifteen commercially available aquatic garden plants were grown for 8 weeks in a laboratory scale subsurface wetland in a greenhouse and received nitrogen (N) and phosphorus (P) from Hoagland's nutrient solution every two days for eight weeks. The N and P rates (0.39 to 36.81 mg·L -1 of N and 0.07 to 6.77 mg·L-1 P, respectively), encompassed low to high rates of nutrients found at various points between the discharge and inflow points of other constructed wetland systems currently in use at commercial nurseries. Plant biomass, nutrient recovery, and tissue nutrient concentration and content were measured. Among rhizomatous plants, highest N recovery rate were found in Louisiana Iris hybrid 'Full Eclipse', Canna 'Bengal Tiger', Canna 'Yellow King Humbert', Colocasia esculenta (L.) Schott 'Illustris', Peltandra virginica (L.) Schott, and Pontederia cordata L. 'Singapore Pink.' The P recovery rates were similar for the cannas, Louisiana Iris 'Full Eclipse,' Peltandra virginica , and Pontederia cordata 'Singapore Pink.' Among the fibrous-rooted aquatic garden plants, highest N and P recovery rates were exhibited by Thalia geniculata f. rheumoides Shuey and Oenenathe javanica (Blume) DC. 'Flamingo.' Floating plants with the highest N recovery rates were exhibited by water hyacinth (Eichhornia crassipes [Mart.] Solms.) and water lettuce (Pistia stratiotes L.). Phosphorus recovery rates were similar for water hyacinth, water lettuce, and dwarf redstemmed parrotfeather (Myriophyllum aquaticum [Vell.] Verdc.).;To determine the effect of N:P ratio on P recovery, Typha latifolia and Canna 'Bengal Tiger' were grown in a greenhouse-based laboratory-scale subsurface constructed wetland system with a 4-day hydraulic retention time for 8 weeks. Plants were supplied with the following N:P ratios: 6:1, 3:1, 1:1, 1:3 and 1:6. Mean total P concentrations ranged from 6.9 mg·L-1 (6:1) to 252.2 mg·L -1 P (1:6); nitrate-nitrogen (NO3-N) was maintained at a constant mean level of 42.4 mg·L-1. Measured endpoints at 20, 40, and 60 d included height, biomass, nutrient recovery/allocation, and nutrient use efficiency. Canna and Typha whole plant N:P concentration was linearly correlated with N:P ratio of treatments. For the 1:3 and 1:6 treatments, Canna assimilated 40.7 and 30.6% of supplied P compared to 9.7 and 6.2% for Typha. Although both species exhibited luxury consumption of P, Typha latifolia was nitrogen-limited at the 1:1, 1:3, and 1:6 N:P ratios. The high P shoot and root concentrations of Canna in the 42N:252P treatment--19.8 and 11.6 mg·g-1, respectively, were significantly higher than the 3.0 and 4.4 mg·g-1 cattail shoot and root P, respectively. These high shoot and root P concentrations for Canna 'Bengal Tiger' have not been previously reported.;In summary, results of this research showed the differential uptake of N and P by commercially available aquatic garden plants and the ability of some species to recover N and P at levels comparable to traditional constructed wetland plants. Also, the N:P ratio of wastewater influent affects P assimilation and appears to be species-specific in nature.