| Water pollution is one of the major environmental problems through the world, and water eutrophication resulting from nitrogen and phosphorus enrichments not only is universal phenomenon in water pollution, but also is the most difficulty problem for water remediation. Ecological floating bed technology is a surface soilless planting technology of modern agronomic and ecological engineering measures integrated comprehensively, and is a cost-effective and feasible method of the green for eutrophic water remediation in situ. Purification capacity to eutrophic water bodies by the different economic plant, impact of environmental factors (including pH and aeration, temperature and floating bed epiphytic algae) on eutrophication water quality improvement by economic aquatic plants, the absorption kinetics of NH4+ and NO3- by aquatic plants and the relation between nitrogen metabolism enzyme characteristics in plants and different forms nitrogen removal in eutropihc water were carried out using ecological floating bed system in this paper. With the current trend of the latest research on phytoremediation, this paper was to reveal the difference between different aquatic plants in eutrophic water body remediation, from the nitrogen cycle bacteria population and their action in rhizosphere. The results enriched the knowledge of plant nutritional ecology, pollution ecology and microbial ecology, and provided a necessary foundation of knowledge and theoretical guidance for the development and utilization of plant and microbial resources in the restoration of eutrophic water bodies. Research and the main findings are as follows:①Comparative studies on the purification ability to eutrophic water bodies by different economic plantsFor building the ecological engineering to purify the eutrophic water, six economic plants, which are water dropwort, water convolvulus, leek, shallot, watercress, and celery, respectively, were selected, and their purification ability in different N level eutrophic water were studied. The results showed that each species had great ability to remove total nitrogen (TN) and total phosphorous (TP), especially watercress, water dropwort, and water convolvulus, their removal rate to TN and TP in high N level eutrophic water afer 20 days'treatment is 92.5%, 95.6%, and 98.2%, respectively. The change trend of CODcr concentration decreased firstly and increased later and decreased finally in the different N level eutrophic water bodies with different economic plants, but the acrid smell in the water aggravated during leek and shallot treatment. The changes of Chla and BOD5 decreased with time continuing in the different N level eutrophic water with other economic plants treatment, except for leek and shallot. The integrated analysis of all indices indicated that in the different N level eutrophic water, the purification effect of water convolvulus was the best, water dropwort and watercress take second place, celery place in the center, leek was worst.②Effect of pH and aeration on eutrophication water quality improvement by economic aquatic plantEffect of pH and aeration on eutrophication water quality improvement by aquatic plants on floating bed was investigated in the greenhouse in this paper. The results showed that at different pH treatments for 6d, removal efficiencies for TN, CODMn, and BOD5 were highest at pH8.9, TP removal was highest at pH6.7, Chla removal was highest at pH5.0 in the plant system. However, removal efficiencies of TN and TP were highest at pH8.9, BOD5 removal was better at pH6.7, removal for Chla and CODMn was highest at pH5.0 in the no plant system. TN removal with aeration treatment was much smaller than that with no-aeration (P <0.001) in the planted and unplanted system. CODMn removal was affected, but removal of TP and Chla was not impacted by aeration, except for in the watercress system. In addition, removal efficiencies of NH4-N, NO3-N, and NO2-N were highest at pH8.9 and pH8.9+aeration.③Eutrophication water quality improvement by the synergistic effects of economic aquatic plant and periphyte on floating bedsEffect of the synergistic effects of economic aquatic plant and periphyte on floating bed on the improvement of eutrophication water quality was investigated under light and non-light control using floating culture system in the greenhouse. The results showed that the amount of green algae in the water body decreased, but the periphytes on floating bed increased with treatment of growing plants (water dropwort and watercress) under light or without light conditions for 20 days. The dominant periphyte species were Chlorella.vulgaris and Chamydomonas, Microsphaera, at the end of the experiments. The removal rate of TN,TP,CODMn,BOD5 in the P-PFB and NP-PFB treatment systems were higher than that of P and NP treatments, and higher removal rates for TN and TP were noted in planted treatment than in unplanted treatment. After 20 days's treatment, removal rates of TN and TP were above 76.8%, 89.9%, respectively, in the P-PFB treatment systems, while were only 61.1%, 85.4%, respectively, for the P treatment systems. Removal rates of CODMn and BOD5 were above 94.0% in the P-PFB treatment systems, whereas was only 89.5% in the P treatment systems. The concentrations of NH4-N, NO2-N, DP and Chla in the eutrophic water bodies decreased with increasing treatment time in all treatments in the plant floating bed, whereas the reduction of their concentrations in the P-PFB treatment system were markedly greater than that of P treatment system. However, the change of DO concentration increased with increasing treatment time, and DO concentration in the P-PFB and NP-PFB treatment systems was higher than in the P and NP treatment systems. The concentrations of NH4-N, NO3-N, NO2-N, and DP in the eutrophic water bodies in the NP-PFB and NP system were higher than in the P-PFB and P treatment systems. The results also indicated that the nitrogen accumulation in the shoots of WD and W were 0.5908 and 0.3675mg·plant-1·d-1, and phosphorus accumulation were 0.1530 and 0.0665mg·plant-1·d-1, respectively. While the nitrogen accumulation were 0.2566 and 0.1162mg·plant-1·d-1, and phosphorus accumulation were 0.0548 and 0.0181mg·plant-1·d-1, respectively, in the shoots of WD-PFB and W-PFB treatment.④Relationship between nitrogen metabolism enzyme characters in economic aquatic plants and different forms nitrogen removals in eutrophic water bodiesAbsorption kinetics of different forms nitrogen by water dropwort and watercress was studied firstly, and then the relationship between nitrogen metabolism enzyme characteristics in two aquatic plants and different forms nitrogen removal in eutrophic water was carried out by floating bed plant system. NH4-N and NO3-N uptake of two aquatic plants was fitting Michaelis-Menten kinetics model. Among them, the Vmax and Km of NH4+ absorption were significantly greater than the Vmax and Km of NO3- absorption for water dropwort, and the Vmax of NH4+ absorption was greater than the Vmax of NO3- absorption, but the Km is obviously less than the Km of absorption of NO3- for watercress. In addition, the uptakes of NH4-N and NO3-N for water dropwort were stronger than that of watercress at low concentrations. GS activity of water dropwort and watercress was significant correlation with TN and NH4-N removal in water bodies (r> 0.91). GOGAT and NR activity in two aquatic plants were exponential decay with TN, NH4-N, NO3-N, NO2-N removal, but had no significant correlation.⑤Effects of different temperature on the purification ability to eutrophic water by aquatic plantsThe effects of different temperature on the purification ability to eutrophic water by two aquatic plants in the ecological floating bed system were studied. The results showed the lower leaves of floating bed plants grew yellow, and the stems grew small and slow at 10℃treatment, and the leaves grew yellow seriously and the stems became smaller at 35℃, and aphids had occurred on the leaf of watercress. At 22℃treatment, the plant grew normally and the height of plants was between 10℃and 35℃. Moreover, the TN and TP net accumulations in plants at 22℃treatment were significantly higher than 10℃and 35℃treatments, and at 35℃treatment also was higher than at 10℃treatment. The TN and TP net accumulation in the watercress were significantly higher than that of the water dropwort at different temperature treatments (P <0.05).At different temperature treatments, no plants floating bed system (NPFBS) for the removal of TN: 10℃<22℃<35℃, and plants floating bed system (PFBS) was: 10℃<35℃<22℃, however, CODMn and BOD5 removal efficiency in floating bed system (FBS): 10℃<22℃<35℃, and TN removal in the watercress floating bed system (WFBS) was higher at 10℃and 22℃treatments, and is obviously lower at 35℃than in the water dropwort floating bed system (WDFBS). At 22℃and 35℃treatments, TN removal was no obvious difference in the WDFBS, but BOD5 removal was obviously lower than in the WFBS. NH4-N concentration decreased level in the FBS: 22℃>35℃>10℃; NO3-N, NO2-N concentration level for the decline: 35℃>22℃>10℃, and NH4-N, NO3-N, NO2-N concentrations decreased significantly in the PFBS more than in NPFBS. At 10℃and 22℃treatments for 5d, NH4-N concentration in the WFBS was significantly lower than in the WDFBS, but the decrease of NH4-N concentration was no significant difference for the two plants at 35℃. NO3-N concentrations in the WFBS at 22℃and 35℃were higher than in the WDFBS, but the decrease of NO2-N concentration was no significant difference between two plants floating bed systems (TPFBS). pH level in the FBS was 35℃>22℃>10℃, pH in the WFBS was significantly higher than that in the WDFBS, but pH in the TPFBS was significantly lower than that of NPFBS. However, for 3 d treatment, DO concentration in the FBS was higher at 10℃than that of 22℃and 35℃, and it was higher in the WFBS at 10℃and 35℃than that of NPFBS and WDFBS. DO concentration in the NPFBS at 22℃was higher than that of PFBS.⑥Nitrogen cycle bacteria and their action in the rhizosphere of economic aquatic plants in the floating bed systemThe nitrogen removal effect in water and the changes of the nitrification and denitrification bacteria population and their action in the rhizosphere with plant monoculture and mixture were studies in the ecological floating bed system. The result indicated that nitrogen removal in the plant mixture was better than in plant monoculture and non plant systems, and plant system was better than no plant systems, nitrogen removal in the order were no plant system (NPS)< watercress system (WS) < water dropwort system (WDS)< mixture system (MS), except for 8 d treatment. There were significant difference in the nitrifying bacteria population and nitrification rates, and denitrifying bacteria population and denitrification rates of the rhizosphere between monoculture and mixture. Furthermore, the number of nitrifying bacteria population and its rate: WDS |
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