两栖榕在人工湿地的生长特性及其对污水的净化效果

Growth characteristics and sewage purifying effect of amphibious banyan in const ructed wetland

研究了两栖榕在潜流型人工湿地的生长特性及其对污水的净化效果。一年多的实验表明 ,生长在人工湿地的两栖榕具有发达的侧根和不定根 ,保持正常的净光合速率、蒸腾速率、根系活力和生长速率。两栖榕人工湿地对 TN,TP,CODCr和 BOD5的去除率分别为 54.2 %、40 .9%、72 .4%和 74.3% ,与无植物系统相比较 ,去除率分别提高了 1 7%、1 2 %、1 0 %和 1 1 %。此外 ,两栖榕人工湿地系统中 ,水力停留时间对去除效果有一定影响。

The amphibious banyan (Ficus spp.), an evergreen tree mainly in Guangdo ng Province, is conspicuously distinct from a commonly cultivated and widely dis tributed banyan in subtropical China, Ficus microcarpa, in morphology, anatomy a nd flooding tolerance. In the study presented in this report, two main approache s were made to: (1) the morphological, growth-related and photosynthetic charac t eristics, and (2) the purifying efficiency for sewage of amphibious banyan culti vated in the constructed wetland. The experiment was performed in South China Normal University, Guangdong Provinc e of China. Seedlings of one-year old of amphibious banyans were planted in row s with a density of 6 plants per square meter in the subsurface flow constructed wetland (SFW) (length×width×depth: 1.3m×0.84m×0.6m), and another SFW wit h th e same dimension but without amphibious banyans and other plants was taken as th e control. The photosynthesis/transpiration rate and stomatal conductance, the v igor of the root system and the relative growth rate of the plant were measured when the plants grew to a height of about 1.5m. From April through July, 2000, the wetlands had been continuously receiving sewage with a flow rate of 50Ld -1 a nd a hydraulic retention time (HRT) of approximately 4 days. After the wetlands were running for two months, water samples from the influx and efflux were colle cted respectively once a week for seven weeks, and analyzed for COD Cr, BOD 5, total nitrogen (TN) and total phosphorus (TP) . The following results were obtained: (1) The plants in the constructed wetland p ossessed a large amount of lateral roots and aerial roots emerged from the basal and upper parts of trunks and most branches, some aerial roots were able to rea ch the soil and developed proper roots. (2) The amphibious banyan in the constru cted wetland maintained a normal rate of net photosynthesis（18.4±2.0μmolCO 2·m -2s -1），with a transpiration rate of 21.7±1.8 mmol H 2O· m -2s -1， a stomatal conductance of 638.1±61 mmol H 2O·m -2s -1, a vigor of 22.5±4.2μg·C 10H 7NH 2·g -1DW min -1 in the root system and a relative growth rate of 7.1±0.4 mg·g -1day -1 DW, respectively. These measured parameters in plants growing in wetland were not sign ificantly different from those in plants of the same species growing in natural conditions. (3) The removing rates of TN, TP, COD Cr and BOD 5 from the se wage in the constructed wetland with amphibious banyan were 54.2%, 40.9%, 72.4% and 7 4.3 % respectively，corresponding to increases of 17%, 12%, 10% and 11% over those i n the control wetland, respectively. (4) The removing efficiencies of TN, TP, CO D Cr and BOD 5 were influenced by the hydraulic retention time (HRT) in th e amphib ious banyan wetland. For example, the removal efficiencies in HRT2d and HRT3d ac counted only for 65% and 90% of that in HRT4d, respectively. Generally, the amphibious banyan in the constructed wetland possessed a complex and well developed root system to keep normal physiological metabolism and high capability of pollutant removal. The plant appeared to be a desirable and constr uctive species in the constructed wetland because of its long growth period，lit tle secondary pollution, simple management and pleasing landscape.al a