| The ratio of green space to water in Shanghai’s green belt is about 9:1,and it forms a “water around Green Belt” pattern.On the one hand,the green space has the functions of controlling surface pollution,storing rainwater and regulating urban microclimate,but on the other hand,apoplastic matter may enter the water and cause new ecological and environmental problems.In this study,the effects of four plant species of apoplastic matter on the water quality and substrate of nine "forest-inclusive" water bodies in Shanghai’s green belt were initially investigated through ecological monitoring of the water environment,and on this basis,a study was conducted to investigate the effects of apoplastic matter on the water quality and substrate of "forest-inclusive" water bodies."The main findings of the study are as follows:(1)Through ecological monitoring of the”water around Green Belt”type water bodies in the Shanghai Green Belt,it was found that dissolved oxygen was higher in spring and summer,while turbidity was higher in autumn.Inorganic nutrient indicators show a pattern of high in spring and winter and low in summer and autumn,while organic pollution indicators show a pattern of slightly higher in summer and autumn than in spring and winter,and chlorophyll a concentration is highest in summer.The water quality of these three water bodies fluctuates seasonally at the Wuwei Road section,Jianxin Road section and Hengxin Road section,while the water quality at other sections is relatively stable.The evaluation results of the integrated nutrient status index and the integrated water quality marker index respectively show that the water bodies at the nine monitoring points are dominated by mesotrophic levels,with more than half of the surface water category III water.The evaluation results of the individual pollution indices for the substrate of the water bodies show that the total nitrogen and total phosphorus contents of the substrate at the monitoring sites are all at heavy pollution levels.The results of the combined pollution index showed that the substrate at all monitoring sites was heavily polluted,while the results of the organic pollution index showed that 61% of the sites had moderate and heavy organic pollution levels.The phytoplankton density in the water column is generally higher in summer and lower in winter,and the phytoplankton diversity index H’ shows that the water column is generally moderately and lightly polluted at nine monitoring sites;the zooplankton density is generally higher in summer than in spring,autumn and winter,and the zooplankton diversity index H’ shows that the water column is generally moderately polluted at all monitoring sites;the benthic density is highest in autumn and the benthic diversity index H’ shows that the benthic diversity index H’ shows that the benthic diversity index H’ shows that the benthic density is highest in autumn.The results of the benthic diversity index H’ showed that the percentage of heavily polluted water bodies was 33% among all monitoring sites.Although the results of the indices at the Wuwei Road section are moderately polluted,the snails in the sediment are dying and their shells and flesh are semi-separated due to heavy organic pollution,which needs attention.(2)The effects of apoplastic material from four common plants(balsam fir,willow tree,two-bulb pendula and saposhnikovia)on the overlying water and the substrate were analysed,and the results showed that the pH of the overlying water tended to decrease and then increase,and the turbidity,colour,pH,nutrient concentration and CODCr concentration of the overlying water increased after the four species of apoplastic material entered the water body.The four plant species had similar effects on the pH of the overlying water,and the other indicators of the overlying water were(from the highest to the lowest)Sapotaceae leaves > willow leaves > balsam fir leaves≈ dicotyledon leaves,with balsam fir leaves and dicotyledon leaves having less effect on the total phosphorus(TP)and total nitrogen(TN)concentrations of the overlying water.The fading of Sapindus leaves into the water column increased both nitrogen and phosphorus in the substrate by the greatest amount,while Balsam fir leaves increased the nitrogen content of the substrate by the least amount,while the entry of Dictyostelium leaves into the water column reduced the phosphorus content of the substrate,and willow and Balsam fir leaves reduced the carbon content of the substrate.The results of the molecular biology of microorganisms in the substrate of each experimental group showed that the Chao1 index was the largest in the Sapotaceae leaf group,the Simpson index was the largest in the Balsam fir leaf group and the Shannon index was the largest in the poplar and willow leaf group.The relative abundance of microbial phyla in the substrate under the effect of plant apomixis varied considerably,with balsam fir and saprophytic leaves promoting the growth of the green curvilinear phylum,dictyostelium leaves promoting the growth of the green curvilinear phylum and the acidic anhydride phylum,and willow leaves promoting the growth of the green curvilinear phylum and the thick-walled phylum.At the genus level,the genus with the greatest relative abundance in the willow and dicotyledon leaf groups was Anaerolineaceae,the greatest relative abundance in the saprophytic leaf group was Moraxellaceae,and the greatest relative abundance in the balsam fir leaf group was Sideroxydans.(3)Four experimental groups were set up,namely the aeration group,the calcium peroxide group,the artificial water plants group and the calcium peroxide-membrane artificial water plants group,to simulate the restoration of the water bodies in the green belt around Shanghai.The results showed that the nitrogen removal rate of the artificial water grass group was the highest(82.4%),followed by the aeration group(70.5%),followed by the calcium peroxide + artificial water grass group(61.6%),and the lowest was the calcium peroxide group(39.7%);the calcium peroxide group and the calcium peroxide + artificial water grass group had the highest removal rate of phosphorus from the overlying water(92.8% and 92.7%).The calcium peroxide + artificial hydrophytes group had the best removal of nitrogen from the substrate with 27.3%,and the aeration group had the best removal of phosphorus from the substrate with 6.1%.The results of high-throughput sequencing of the substrate showed that the combination of calcium peroxide and artificial hydrophytes could effectively improve the richness and uniformity of the microbial community in the substrate,which in turn improved the degradation efficiency of pollutants.For lightly polluted water bodies,either film-mounted artificial water plants or artificial aeration can be used for remediation,both of which are effective in removing nitrogen and phosphorus from the water body.For water bodies with more serious substrate pollution,calcium peroxide + membrane hanging artificial water plants can be selected for remediation.This method has a better effect on the removal of nitrogen and phosphorus in the overlying water,and can also stimulate the growth of microorganisms in the substrate and improve their activity,which is conducive to the degradation of endogenous pollutants in the substrate.The above investigations reveal the water quality characteristics of”water around Green Belt”type water bodies and the potential impact of forested areas on the environment of water bodies in Shanghai’s green belt around the city.Through simulation experiments,the effects of different apoplastic decomposition on the overlying water and sediment under near-natural conditions are investigated,providing a theoretical basis for the subsequent investigation of the impact of forested areas on water bodies and their treatment and restoration.Based on the above research,we will also carry out experiments to improve the water bodies in the”water around Green Belt”type of water pollution in the green belt,so as to screen out the suitable treatment methods for these water bodies and provide a basis for engineering applications. |
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