Study On Purification Effects And Growth Characteristics Of Wetland Plants Under Varying Hydraulic Conditions

As an important component of wetland ecosystem,wetland plants play a significant role in water environment remediation.Faced with the increasingly serious problem of water shortage,reclaimed water becomes more suitable for wetland water supply as its lower cost and abundant reserve.In the process of reclaimed water reusing,varying hydraulic conditions have significant effects on reclaimed water purification.Based on the constructed wetland system with reclaimed water,the experiments on removal efficiency of TN,NH₄⁺-N and TP under varying hydraulic retention time?1d?2d?3d?,water depth?10cm?20cm?40cm?,surface flow velocity?0.01m/s?0.03m/s?0.05m/s?and percolation flow velocity?0.05m/d?0.1m/d?0.2m/d?in Acorus calamus L.,Canna glauca L.,Pontederia cordata L.,Thalia dealbata L.and Myriophyllum verticillatum L.were done.Furthermore,the dynamic changes of plant height,leaf number or stem number,biomass and dry weight of five plants were statistically analyzed.The main results as follows:?1?The suitable hydraulic conditions of wetland plantsThe treatment of hydraulic retention time in three groups?1d,2d,3d?glaucated that the five species' removal tendency of TN,NH₄⁺-N and TP first gradually rising and then fall,the suitable hydraulic retention time suggested at 2 d.Under varying water depth?10cm,20 cm,40cm?,the removal efficiency of TN,NH₄⁺-N and TP vary greatly between species,but the purification rate in 40 cm depth is not as good as 20 cm or 10 cm.The varying treatments of surface velocity?0.01m/s,0.03m/s,0.05m/s?would have significant effect?P<0.05?on the removal efficiency of TN,NH₄⁺-N and TP in reclaimed water,the average surface removal rate of TN,NH₄⁺-N and TP would be 21.08%,22.14% and 17.63%,while the percolation water velocity treatments?0.05m/d,0.1m/d,0.2m/d?wouldn't have significant effect?P>0.05?on the pollutants' removal,the mean values of TN,NH₄⁺-N and TP in system treated effluent were57.72%,67.84% and 64.84% respectively.?2?Interspecific differences in nitrogen and phosphorus removal of wetland plantsThe experimental results verified that five plants' TN removal rate in the range of18.72% to 96.22%,and the purification capability followed by Acorus calamus L.,Canna glauca L.,Thalia dealbata L.,Pontederia cordata L.and Myriophyllum verticillatum L.,with the mean removal rate were 95.97%,89.42%,59.62%,40.66%,25.72%.NH₄⁺-N removal rate in the range of 22.92% to 94.5%,followed by Pontederia cordata L.,Acorus calamus L.,Canna glauca L.,Thalia dealbata L.,Myriophyllum verticillatum L.with 93.1%,92.54%,2.34%,89.01%,28.05%.TP removal rate in the range of 17.41% to 95.49%,followed by Canna glauca L.,Acorus calamus L.,Thalia dealbata L.,Pontederia cordata L.and Myriophyllum verticillatum L.,the mean removal rate were 95.06%,89.14%,57.49%,53.16%,29.59%.Generally,the removal rate of TN,NH₄⁺-N and TP became lower in submerged plant than in other four emergent aquatic plants.?3?Purification effects of wetland plants in reclaimed waterThe surface water purification rate is not high because the samples from surface water,but other experiments all glaucated that Acorus calamus L.,Canna glauca L.,Pontederia cordata L.,Thalia dealbata L.and Myriophyllum verticillatum L.have certain effects on the removal efficiency of TN,NH₄⁺-N and TP.According to the requirements of the Environmental Quality Standards For Surface Water?GB3838-2002?,the TN concentrations of Acorus calamus L.and Canna glauca L.could achieve Class ? Standard,and which of TP could achieve Class ? Standard.The TP concentrations of Pontederia cordata L.and Thalia dealbata L.could achieve Class?Standard,and the five plants' NH₄⁺-N concentrations could achieve Class ? Standard except Myriophyllum verticillatum L..?4?Different growth characteristics of wetland plantsIn three groups of water depth treatment?0cm-10 cm,10cm-20 cm,20cm-40cm?,the responses of the five wetland plants in varying water depth were significantly different.Wetland plants through changing their appearance to adapt the water environment.In a certain range,the plants' height and biomass amplification positively correlated with the increase of water depth,while the number of leaf and leaf area were negatively correlated with the increase of water depth.?5?The dynamic growth characteristics of wetland plantsAcorus calamus L.and Canna glauca L.in 10cm-20 cm water depth changed rapidly in growth traits,while Pontederia cordata L.and Thalia dealbata L.got the biggest changes in water depth of 20cm-40 cm,but Myriophyllum verticillatum L.in varying water depth didn't show significant effect.