| River sediment is the circulation center of pollutant accumulation and diffusion.Sediment sedimentation and re-suspension is one of the important causes of water pollution.For gating rivers,such not only change the hydrology and water quality and easy to cause the settlement of sediment and release,cause secondary pollution to water,due to such formed the velocity field of complex operation and lead to mud interface migration mechanism of pollutants is complex,therefore,to effectively improve the prevention and control of the sites for river must focus on the process of such cause endogenous pollution mechanism.In this thesis,the hydrology and water environment characteristics of mojiapu sluice and dam reach of Hunhe River were investigated,and then the temporal and spatial distribution of river water indexes and nitrogen forms in sediment before and after sluice and dam were analyzed.Then,through laboratory experiment of ammonia nitrogen adsorption and release from sediment,experiment of nitrogen release from sediment by different environmental factors and PCR amplification sequencing,the phenomenon of nitrogen pollutant release from sediment of river under the influence of sluice dam is comprehensively analyzed from physical,chemical and biological perspectives,and the migration and transformation mechanism of nitrogen in sediment of sluice dam section was obtained.Finally,the river pollution prevention and control scheme is put forward by using sediment dredging and sluice dam combine source control,so as to effectively control nitrogen release from sediment and improve water quality,and also provide scientific basis for comprehensive pollution control of sluice dam section.The main research contents and results are as follows:（1）Analysis of hydrological and water environment characteristics in the study area.Collect the hydrological data of the Hunhe Shenyang Station,analyze the hydrological characteristics of the water storage area of the Hunhe Gate,and reflect the change of the flow,water level and water quality of the Hunhe Gate to control the Hunhe Shenyang Station.Determine the water function type and water environment capacity of the study area,and use the fuzzy comprehensive evaluation method to evaluate the water in the dry and wet periods of the study area.The results show that the study area belongs to the transition area,and the surface water quality is mainly grade IV,and some sections have grade V.The trend of water quality in the wet season is slightly better than that in the dry season.Spatially,the water quality in the upstream is slightly better than that in the downstream.The changes in the water quality of the river are affected by the operation of the gates and dams.（2）Analysis of temporal and spatial distribution characteristics of river water and sediment pollutants in the study area.The temporal and spatial distribution and content of p H,DO,BOD5,COD,ammonia nitrogen and nitrate nitrogen in the overlying river water and nitrogen in the sediment are analyze in dry,wet and flat water periods.The results show that the sluice and dam reaches are generally neutral and alkaline,with higher concentrations of COD and ammonia nitrogen,and the upstream pollution is higher than the downstream pollution,which is affected by tail water discharge and sluice and dam operation.Nitrogen in the bottom sediment mainly exists as ammonia nitrogen and nitrate nitrogen,and the nitrate nitrogen content in the surface sediment is relatively high.（3）Study on the adsorption and release of nitrogen in the sediment in the study area.The adsorption and release kinetics and thermodynamic tests of ammonia nitrogen are carry out on the sediment collect at each sampling point,the optimal adsorption and release equation is determine,and the adsorption and release characteristics of different points were compared and analyzed.Microbial conditions explore the influence of different environmental factors on sediment release.The results show that the adsorption and release kinetics of ammonia nitrogen conformed to the pseudo-second-order kinetic model,and the Henry model is well fitted for the thermodynamic process of ammonia nitrogen adsorption.The increase of temperature will promote the release of nitrogen in the sediment,the increase of p H will inhibit the release of nitrogen in the sediment,the ammonia nitrogen will decrease with the increase of dissolved oxygen,and the nitrate nitrogen will increase with the increase of dissolved oxygen.Nitrogen release in sediments increased with the increase of disturbance intensity.Microorganisms can inhibit the release of ammonia nitrogen and promote the release of nitrate nitrogen.This study starts with the release of sediment pollutants,filling in and enriching the theory of sediment pollution release in the sluice and dam reaches,and has certain innovations.（4）Research on the interaction between the microbial community structure and nitrogen in the study area.The diversity of sediment microbial community in dry season was studied by DNA extraction and PCR amplification and sequencing.The results show that the study area is rich in microbial species,of which point C have the highest relative abundance.The dominant bacterial species at each taxonomic level were analyzed,and the dominant bacterial species at the phylum level were Proteobacteria,Firmicutes and Bacteroidetes.The dominant bacteria at the class level areγ-Proteobacteria,Bacteroidetes,andα-Proteobacteria.The dominant bacteria at the order level are Burkholderia,Pseudomonas and Xanthomonas.The dominant bacteria at the family level are Pseudomonas,Hydrogenobacteriaceae and Xanthomonas.The dominant bacteria at the genus level are Pseudomonas,Thiobacillus and Shigella.The dominant bacteria at the species level are Escherichia coli,Thiobacillus spp,and Marseille Timone.According to the predict functional bacteria,it is determine that nitrogen fixation reaction,nitrification and denitrification reaction and nitrate dissimilatory reduction reaction mainly occur in the nitrogen cycle process.The Spearman correlation heat map reflect the bacterial species that are significantly correlate with each form of nitrogen.（5）Research on the prevention and control of nitrogen pollution in sediments in the study area.Based on the above research,combine with the pollution and the actual situation in the study area,the governance method of sediment dredging and joint source control of gates and dams is proposed.According to the flow rate ratio and the vertical nitrogen content of the sediment,the optimal dredging depth is determined to be between 0.4m and 0.5m,which provides effective data and practical significance for the pollution control of the sluice and dam reaches,which is also the innovation of this research.place.Using MIKE11 software to establish a water quality and quantity model,simulate different regulation methods and source control methods of gates and dams,and put forward a scientific and effective plan to improve the water,which provides practical significance for the comprehensive management of gates and dams. |
PDF Full Text Request