| As a huge biofilm in water, periphyton is more complex than other microorganisms. They are sensitive to changes in water quality and, in particular, respond rapidly and predictably to nutrient enrichment in water. Also, they have a great potential of application in waste water treatment. In recent years, due to the rapid urbanization and demographic changes in most cities, the deterioration of water quality and decrease in the number of aquatic organisms are the most serious environmental problems that rapidly urbanizing areas face. Periphyton assemblage structure, as well as the changes of spatial and temporal distribution in rivers, has been demonstrated as important available indices in freshwater biology and environmental biomonitoring. Periphyton-based water treatment has become a potential development of new environmental remediation technology.This study focus periphyton as a research object, on which a whole year of biotic and abiotic variables investigation was performed at a typical urbanizing tidal river and its major tributary in Shanghai. Based on the principles of ecology, aquatic ecology, water environmental science and ecological restoration engineering, this study applied a set of research methods that can be used to analyze the relationships between environment variables and species distribution to reveal the differences in algae responses to both natural and anthropogenic environmental changes. On this basis, periphyton based treatment systems were set up to remove contaminants from polluted urban river water under laboratory conditions. The results would contribute to provide a theoretical basis for the application of periphyton in water quality bio-monitoring in urbanized tidal rivers and demonstration projects of aquatic ecosystem restoration.The main conclusions were summarized as follows:(1) A remarkable temporal variation pattern was observed for both communities of phytoplankton and periphyton in Huangpu River and Suzhou Creek. Chlorophytes (>50%) were the most important taxonomic group in phytoplankton, while Bacillariophytes (>60%) exhibited numerical dominates in periphyton found in study area. The peak density of phytoplankton (1.91×104 Ind·L-1) occurred in summer, and the lowest density (0.08×104 Ind·L-1) appeared during winter, while periphyton ranged from over 8,000 Ind·cm-2 in dry season (autumn) to less than 4,000 Ind·cm-2 in the moist spring season.(2) Periphyton assemblage showed a considerable spatial variation in two rivers. Taxa numbers and density were abundant at upstream, while diversity decreased significantly at downstream (p<0.05). The findings further suggested that 12 dominant periphyton species, including Navicula cincta, Chroococcus minutus, Fragilaria capucina, possessed high sensitivity to changes in nitrogen and phosporus levels, thus these species could serve as a good bio-indicator of urban watersheds.(3) Canonical correspondence analysis (CCA) suggested that both environmental factors (water temperature) and anthropogenic disturbances (such as N and P substances) displayed similar effects on algae on the distribution of species; in which water quality, watershed function zone types and nutrients (TN, TP) were the important anthropogenic influence factors on assemblage and spatial distribution variables. Phytoplankton responded more quickly to seasonal changes than periphyton and appeared to be more sensitive indicators of water quality variation among seasons, while periphyton spatial distribution were more influenced by water quality, watershed function zone and nutrients.(4) Filamentous green algae dominated water treatment system showed a remarkable P removal efficiency: TP was decreased up to 50%, associated with 72% removal of TSS. The removal efficiencies of soluble species, PO43- and NH4+ -N, were up to 90% and 85% respectively. Under heavily polluted conditions (TP>3.0 mg·L-1, TN>22.0 mg·L-1), the average removal efficiencies of TP and TN were 89% and 45% respectively, while under lightly polluted conditions (TP<0.50 mg·L-1, TN<10 mg·L-1), the average effluent concentration of PO43- and NH4+ -N were well below 0.1 mg·L-1 and 2.0 mg·L-1 respectively. During the experiments, the biomass of filamentous green algae was increased significantly (38.78%), simultaneous to the occurrence of a large number of unicellular Chlorophytes and Cyanophytes species on the interior wall surface of experimental fertility. The maximum biomass occurred at the highest concentration of DO.(5) Relative to the P removal effects of filamentous green algae, the unicellular periphyton based water treatment system showed a significant removal of N that compared with about 20.0% removal of TN and NH4+ -N in standard medium, more than 30.0% of TN was removed from urban contaminated river water associate with 50.0% removal of NH4+ -N, while the removal rate of TP was relatively low (<10.0%). The maximum removal rates of TN (65.0%) and NH4+ -N (80.0 %) were accrued at influent concentration of TN being about 11.0mg·L-1. The removal rate of TP was decreased with the increase of influent concentration. During the experiments, the biomass and Chl-a concentration of periphyton were increased significantly (54.0% and 58.2% respectively). It was also observed that the original unicellular species of Bacillariophytes and Chlorophytes was succeeded to filamentous Cyanobacteria dominate.
|
PDF Full Text Request