Changes Of Microorganisms Under Disturbance And Their Influence On Phosphorus Control

Sediment disturbance is an important influencing factor of endogenous phosphorus regeneration and morphological transformation in sediments in natural waters.However,from the current research,the mechanism of endogenous phosphorus disturbance on endogenous phosphorus regeneration and morphological transformation has not been fully clarified.At the same time,previous studies have mostly focused on disturbing the migration and transformation process of source phosphorus at the mud-water interface and its distribution in different forms of phosphorus under the condition that the source phosphorus is cut off.Although the input of exogenous phosphorus in the actual water body is gradually controlled,the two coexist,and it is difficult to capture this part of the phosphorus between the two phases of the mud and water,especially the transformation process of different forms of phosphorus in the mud.In addition,previous studies of this kind mostly used traditional chemical analysis methods to determine the phosphorus forms of overlying water and sediments.The conversion path of endogenous phosphorus forms is only a reasonable theoretical guess based on the relationship between quantity increase and decrease.It does not provide direct evidence for the phosphorus conversion pathway in the two phases of mud and water.Therefore,the following questions need to be further studied about the laws of phosphorus migration and transformation caused by physical disturbance of the sediment under continuous input of external phosphorus.On this basis,this study takes the Beijing-Hangzhou Grand Canal（Suzhou Section）as the research object,and conducts a comprehensive investigation and analysis of its phosphorus pollution status by sampling from different sections.In addition,using laboratory simulation experiments,³²P isotope tracing and high-throughput sequencing molecular biological methods were used to explore the changes of microorganisms during long-term disturbances and the effects of endogenous phosphorus forms after they entered the water body.The analysis results of the phosphorus pollution survey of the Beijing-Hangzhou Grand Canal（Suzhou Section）show that compared with the sampling points near residential areas and scenic spots,the internal load of the sediments near the tailwater discharge outlet of the sewage treatment plant is greater,and the sampling points of the New District Wastewater Treatment Plant reached 1130 mg·kg^-1,the sampling point of Fuxing Wastewater Treatment Plant reached 870 mg·kg^-1.When the ship is sailing,on the section where the water quality is often affected by the sewage treatment plant’s tailwater discharge,a combined disturbance pattern of physical and waterworms is actually formed,which significantly changes the quantity distribution of different forms of phosphorus in the covered water on the section.In the disturbance state,Fe/Al-P and Ca-P in the sediments increased,while NH₄Cl-P was released,and Res-P did not change significantly,and the change decreased with increasing depth.In addition,the physical disturbance caused by the ship’s navigation at the sampling point at the sewage discharge outlet has a more significant effect on promoting the transformation of endogenous phosphorus forms in the sediments of the Beijing-Hangzhou Grand Canal（Suzhou Section）.The results of³²P isotopic tracer simulation experiments show that different disturbances can promote exogenous phosphorus migration from overlying water to sediment,but the promotion effect of physical disturbance is more obvious.On the6th day,the content of³²P in the four different conditions decreased to 28%（control）,11%（physical disturbance）,36%（biological disturbance）,and 17%（combined disturbance）.The formation of different forms of phosphorus has an obvious chronological order.Exogenous phosphorus is more likely to form weakly adsorbed phosphorus（NH4Cl-P）,but as the physical disturbance time is extended,the conversion of weakly adsorbed phosphorus to refractory phosphorus（Ca-P）is strengthened.Under the condition of physical disturbance,on the 8th day,NH₄Cl-P accounted for 41%of the total phosphorus,and on the 16th day it dropped to 31%.Correspondingly,Fe/Al-P increased by 4%,and Ca-P Increased by 6%.By using high-throughput sequencing technology to analyze the sediment microbial community under different disturbance conditions,it can be seen that the sediment disturbance has a significant effect on the sediment microbial colony structure.That is,physical disturbance,biological disturbance,and combined disturbance will increase the microbial abundance of the sediment to a certain extent,and also reduce the diversity of microorganisms,which is mainly manifested by increasing the proportion of dominant bacteria in the total microbial biomass.In addition,Anaerolineaceae in the physical disturbance group was significantly lower than that in the blank group,the biological disturbance group and the combined disturbance group,which indicates that under the physical disturbance conditions,the anaerobic environment of the sediment has been greatly improved,thus making the abundance of anaerobic mycobacteria was reduced.Compared with the blank group,the Simpson index in the physical disturbance group,the biological disturbance group and the combined disturbance group increased by 8.47%,16.65%,and 15.21%,respectively.In addition,the proportion of Anaerolineaceae in the physical disturbance group was 9.47%,which was significantly lower than that in the blank group（10.39%）,the biological disturbance group（14.57%）,and the combined disturbance group（12.72%）.Under the conditions of physical disturbance,the anaerobic environment of the sediment has been greatly improved,thereby reducing the abundance of microorganisms in the family Anaerolineaceae.Sediment disturbance will increase the abundance of two types of phosphorus accumulating bacteria,Acinetobacter and Pseudomonas to a certain extent,which will be beneficial to the fixation of phosphorus in the sediment.The results of RDA analysis showed that Fe/Al-P and Ca-P were positively correlated with the abundance of nitrifying bacteria and acid bacteria,while NH₄Cl-P had less correlation with nitrifying bacteria.Nitrobacteria,as bacteria that have obvious requirements for the oxygen environment,increase their abundance under the conditions of sediment disturbance,combined with their correlation with the three phosphorus forms of NH4Cl-P,Fe/Al-P and Ca-P It can be seen that this bacterium is beneficial to the conversion of NH4Cl-P into more stable endogenous phosphorus forms of Fe/Al-P and Ca-P in the sediment.Acinetobacter is a typical phosphate-dissolving bacteria,which can lead to the potential risk of phosphorus release and utilization in the sediment.The reduction of Acinetobacter abundance caused by sediment disturbance and the correlation between NH₄Cl-P,Fe/Al-P and Ca-P indicate that Acinetobacter decrease under the condition of sediment disturbance,which can effectively reduce Source phosphorus is released to the water body,in other words,it is beneficial for endogenous phosphorus fixation.