Experimental Study Of River Sediment Purification Based On Submerged Plants Coupled With Benthic Fauna

Sediments is an important part of the ecosystem of river and lake water bodies.Nitrogen,phosphorus,heavy metals and organic pollutants are repeatedly transported between the sediment and the overlying water bodies,which makes sediment management the crux of urban water environment management.To address the problems of sediment pollutant reduction and sediment diffusion to overlying water bodies,this project proposes an innovative ecological approach to purify sediment by coupling submerged plants with benthic animals.The microbial diversity and community structure were also analyzed by 16S r DNA high-throughput sequencing.The main findings of the study are as follows.（1）Analysis of the effect of submerged plants coupled with benthic fauna on the purification of sedimentss and their dispersion to the overlying water column.Compared with the control group,the submerged plant-coupled benthic animals all had good effects on the removal of sediment pollutants,and the combination of submerged plant-coupled benthic animals showed better removal effects than the bittercress,mussel,snail and eelgrass alone,while each combination also had better inhibitory effects on the diffusion of sediment pollutants to the overlying water.The bitter herb mussel combination（50%bitter herb sediments coverage,mussel dosage 2 kg/m²）showed significantly better results in the removal of organic matter,NH₄⁺-N,NO₃^--N,NO₂^--N and TP from the sediments,with removal rates of 13.14%,27.4%,9.82%,54.38%and 12.2%,respectively,and the best inhibition of the diffusion of pollutants from the sediments to the overlying water column.The inhibition effect was the best,and the inhibition rates of COD,NH₄⁺-N,NO₃^--N,NO₂^--N and TP in the overlying water column were 48.68%,91.4%,24.1%,94.64%and 88.2%,respectively.（2）Analysis of the enhanced effect of biochar and aeration on the reduction of contaminants in the sediments and their dispersion to the overlying water column.At winter temperature（5-15°C）,the addition of biochar at 3%of the dry weight of the sediments had the best effect in promoting the development of benthic biological systems and microbial community diversity,and the removal rates of organic matter,TN,NH₄⁺-N,NO₃^--N,NO₂^--N and TP from the sediments were 30.1%,11.2%,45%,11%,40.1%and 6.9%,respectively.The best inhibition of diffusion of pollutants from the sediments to the overlying water column was also achieved,with inhibition rates of75%,64.7%,65%,76%and 68.3%for COD,NH₄⁺-N,NO₃^--N,NO₂^--N and TP in the overlying water column,respectively.At summer temperatures（15-25°C）,the 5%content of biochar was the most effective in removing organic matter,TN,NH₄⁺-N,NO₃^--N,NO₂^--N and TP from the contaminated sediments,with removal rates of 29.4%,29.8%,70.2%,84.5%,28.2%and 28.2%,respectively,and inhibition of diffusion of sediments pollutants to the overlying water column for COD,53.9%,65.7%,65.9%,36.2%,75%and 61.2%for NH₄⁺-N,NO₃^--N,NO₂^--N and TP,respectively.It was also found that the addition of biochar at 10%of the dry weight of the sediments at both winter and summer temperatures not only inhibited the growth of submerged plants,but also reduced the abundance and diversity of the sediments microbial community,which was detrimental to the removal of sediments pollutants as well as exacerbated the diffusion of sediments pollutants to the overlying water column.When the aeration rate was 6L/min,the ecosystem of the Bittercress River mussel system purified the polluted sediment with the best pollutant removal effect.The removal rates of organic matter,TN,NH₄⁺-N,NO₃^--N,NO₂^--Nand TP in the sediment were 25.2%,39%,89.3%,99.4%and 20%,respectively;the best inhibition of the diffusion of sediment pollutants to the overlying water bodies was achieved.The inhibition rates of COD,TP,NH₄⁺-N,NO₃^--N and NO₂^--N were 50.1%,89%,43%,77.7%and 31.5%,respectively.（3）High-throughput sequencing analysis of 16s rDNA.The Chao indices of the control group,the Ileagrass group,the bittergrass snail group,the snail group,the mussel group,the bittergrass mussel group and the Ileagrass snail group were 1958.11,2379.3,2363,2126.68,2378.37,2152.48,2340.19,2394.37 and 2316.45,respectively,with the abundance of microbial communities in the sediments of the bittergrass mussel group The abundance and diversity of microbial communities in the sediments of the bitter grass mussel group were the highest.The relative abundance of Proteobacteria,Chloroflexi and Bacteroidetes as dominant genera in the submerged plant-coupled benthic ecosystem sediments was significantly higher than that of the control group,with these genera playing a key role in organic matter biodegradation and material nitrogen and phosphorus cycling.The dominant dominant genera unclassified＿Anaerolineaceae,Thiobacillus,Sulfurovum were all higher in relative abundance than the submerged plant-coupled benthic group.The highest abundance and diversity of microbial communities were found in the group with 5%dry weight of sediments at winter temperatures（5-15°C）,with a Chao index of 1892.0,and in the group with 7%dry weight of sediments at summer temperatures（15-25°C）,with a Chao index of 2262.2.The dominant genera in the biochar-added bittercress mussel system were unclassfied＿Anaerolineaceae,unclassfied＿bacteria,Thiobacillus,and Sulfuricurvum spp.The abundance and diversity of the microbial community increased slightly with increasing aeration,and aerobic genera such as Nitrospirae and Planctomycetes increased with increasing aeration.Experimental results show that submerged plants coupled with benthic ecosystems have a significant effect on the reduction of sediment pollutants.This study will provide core data on the nature and principle of the role of submerged plants coupled with benthic animals in the purification of river sediment,and provide a reliable technical support and scientific basis for the ecological purification of river sediment.This study will help improve the waterfront habitat environment,increase people’s sense of well-being and access,and promote sustainable urban environmental development.