Water Purification Function Of Three Waterscape Plants

Wetland is one of the important components of the urban landscape.It has the function of filtering pollutants and purifying water quality.In recent years,due to human development,the pollutants discharged into wetlands are far more than the self-purification capacity of wetlands,causing the environment to deteriorate.Aquatic phytoremediation technology is one of the most economical and ecological wetland restoration technologies.Different plants have different purification effects on wetland,and different regions have different reaction to aquatic plants.This paper used Orthogonal experimental design[L₁₂?3¹×4²?]to explore the Aquatic phytoremediation technology which could be used suitably for Guangzhou.Three species of submerged landscaping plants such as Echinodorus amazonicus,Myriophyllum verticillatum,and Vallisneria natans were selected as the research object,and four levels of water quality and planting depth were selected to perform the experimental study.Four kinds of experimental water sources were selected,including ultrapure water,park lake water,urban river water and river branch water.Four planting water depth gradients were 20 cm,40 cm,60 cm,and 80 cm,respectively.In order to analyze the factors that affect plant growth and water purification capacity,the ability of plant growth indexes,wetland landscape improvement index and adsorption capacity indexes of seven kinds of heavy metals such as Cu,Zn,Pb,Cd,Cr,As,and Hg were measured.And the water purification capacity of the three aquatics were compared.This article also discusses the principle of landscape configuration of aquatic plants and puts forward suggestions for the governance of wetlands in Guangzhou.The main conclusions are as follows.?1?The influence of plant species and planting depth on the increase of plant length and biomass were significant.The effect of experimental water source on plant growth and biomass was not significant.The growth length of three plants during the experiment were ranked as follows:Myriophyllum verticillatum?81.13cm?>Echinodorus amazonicus?18.88cm?>Vallisneria natans?7.13cm?.At the planting depth of 20 to 80cm,the plant growth length increased with the planting depth.The order of increase in biomass of these three plants was:Myriophyllum verticillatum?1.55g?>Echinodorus amazonicus?0.49g?>Vallisneria natans?0.04g?.At the planting depth of 60 cm,plant biomass reached the highest value.?2?The growth feature of aquatic was greatly affected by the experimental water source and planting water depth,and the river branch water inhibited the growth feature of Echinodorus amazonicus and Vallisneria natans and promoted the growth feature of Myriophyllum verticillatum.?3?The effects of plant species,experimental water source and planting depth on the ability of plants to improve wetland landscapes were significantly different.Myriophyllum verticillatum and Vallisneria natans had a significant effect on improving the water transmittance of the wetlands.Compared between different experimental water sources,the order of effects of water transmittance change rate was:ultrapure water?0.33?>river branch water?0.10?>urban river water?0.04?>park lake water?-0.05?.When the planting water depth was 80cm,the increase rate of water transmittance was the fastest,reaching0.17.?4?Three species of plants had different enrichment and transport capacities for the seven heavy metals.The order of their heavy metal enrichment ability was:Vallisneria natans>Echinodorus amazonicus>Myriophyllum verticillatum.Echinodorus amazonicus had the highest transport capacity for Cu,Pb,Cd,As,and Hg.Myriophyllum verticillatum had the highest transport capacity for Zn,Vallisneria natans had the highest transport capacity for Cr,and Vallisneria natans corresponded to the hyperaccumulator feature of Cr.?5?Among 12 treatment groups,the total amount of heavy metals adsorbed by per plant was the highest?132.953?g/plant?when Echinodorus amazonicus was planted in ultrapure water with a depth of 20cm,and the total amount of heavy metals adsorbed by per plant was the lowest?11.620?g/plant?when Vallisneria natans was planted in river branch water with a depth of 40cm.The amount of plants adsorbed heavy metals Cu ranged from1.178 to 24.044?g/plant,the amount of adsorbed Zn ranged from 2.703 to 87.067?g/plant,the amount of adsorbed Pb ranged from 0.117 to 9.205?g/plant,the amount of adsorbed Cd ranged from 0.001 to 24.044?g/plant,the amount of adsorbed Cr ranged from 6.751 to38.823?g/plant,the amount of adsorbed As ranged from 0.610 to 9.523?g/plant,the amount of adsorbed Hg ranged from 0.002 to 0.067?g/plant.?6?The adsorption capacities of heavy metals by the three plants were different.The total amount??g/plant?of Cu,Zn,Pb,Cd,Cr,As,and Hg adsorbed by the three plants were ranked as follows:Echinodorus amazonicus?102.287?>Myriophyllum verticillatum?99.101?>Vallisneria natans?18.592?,but the adsorption of each heavy metal ranked differently.In each treatment group,the total amount of adsorption of seven heavy metals by Echinodorus amazonicus was 68.713-132.953?g/plant,and the adsorption of heavy metals Pb,Cr,and As was the most.The total among adsorption of Myriophyllum verticillatum on seven heavy metals reached 51.314-156.853?g/plant,while the adsorption of Cu,Zn,Cd and Hg was the highest.Although the enrichment and transport capacities of Vallisneria natans was high,but its biomass was small,the total amount of adsorption of seven heavy metals was 11.620-24.473?g/plant,so its adsorption capacity of heavy metals was significantly lower than that of Echinodorus amazonicus and Myriophyllum verticillatum.And under some environmental conditions,it even released heavy metals into the water environment.?7?AHP method is used to establish a comprehensive evaluation system for aquatic purification capacity.The result shows that the comprehensive aquatic purification capacity of the Myriophyllum verticillatum is the highest,followed by Echinodorus amazonicus and Vallisneria natans.