Studies On Plant Diversity And The Evaluation Of The Constructed Wetland In Subtropical China

The Constructed wetland is a new-style ecological technology of wastewater treatment, and its characteristic neither resembles to the natural wetland, nor to the general terraneous environment, the species diversity in which has become a newly issue. In this paper, we mainly studied the biodiversity and the value of its ecosystem services in an integral vertical flow constructed wetland in HangZhou Botany Gardon, which locates in humid subtropical area of China. The primary contents include several parts as follows: the biological characteristics of the plants growing in this wetland and their landscape function , the relationship between plant diversity and ecosystem function, the value of its ecosystem services, and the assembled mode in natural wetland also be analyzed.The results of research on plant diversity in constructed wetland of subtropical area shows that there were 46 species in early spring of which 13 species are natural immigrated;and 61 species in summer including 43 species are immigrated naturally;and 72 species in autumn of which 54 species are natural immigrated. The assembled species in constructed wetland are the main components of community structure, while the immigrated are accompanied. In order to maintain the high diversity, it is strongly recommended to reserve some valuable immigrated species to effectively absorb the redundant nutrition as well as glorify the natural environment.The niche in constructed wetland can be divided into four groups according to the different water levels and light intensity, which result in the species' different distribution. During spring and summer, the main factor contributes to the species distribution and its diversity is light intensity, while in autumn water gradually exerting its impact. The rule of diversity in whole constructed wetland as follows: there is no significant difference between seasons for species richness index, and the diversity rank sequence is autumn>summer>spring;other three indexes are in consistent, that is spring> autumn>summer, and significant difference is discovered between spring and summer;The community structure of constructed wetland can be divided into 15 typical blocks, and 5 height group are compartmentalized according to the average height. The average total biomass of 20 species ranged from 32.8 to 1316.7 g m^<sup>-2 of which Iris pseudacorus is the highest while Alternanthera philoxeroides is lowest, of which exist significant differences (P<0.05), and three functional groups are engendered subsequently as high nutrition accumulation, middle nutrition accumulation and low nutrition accumulation groups respectively. Meanwhile, the correlation between biomass and its height is strongly significant at 0.05 level.Integrated vertical flow constructed wetland had a good purification performance and benefits for low eutrophic sightseeing water. Most indexes of its effluent reach or near the first class standard of Chinese surface water (GB3838-2002), such as NH₄-N, NO₃-N, TP, COD, BOD₅, etc. Meanwhile, the seasonal changes of removal rate of NH₄-N, NO₃-N and TN are similar to that of species richness index, while the removal rate of TP is resemble to the changes of simpson index. However, according to the Pearson correlations analysis, there is no significant relationship between biodiversity and itsecosystem function such as the purification of sightseeing water (P>0.05).With the notable economic benefits, ecological benefits and social benefits, the value of this constructed wetland is remarkable within its lifecycle. According to evaluation of the Contingent Valuation Method, its total economical benefits reach to 1.2224 million$, and no significance correlation can be calculated between personal factors and willingness to pay(P>0.05), while the economic value reaches to 10 millionY evaluated by another method as the Shadow Engineering Method, the actual ecosystem services value between the two above.The whole study analyzed the plant diversity and ecosystem service value in constructed wetland, confirmed the plant functional group, selected the plant species which adapted to different constructed wetlands, and provided reference for plant collocating model. This study established the theoretical basis of botany for new constructed wetland, and also quantified the ecosystem service value, provided scientific instruction for management and became one part of the entire national economy calculation system.