| The vigorous development of phosphate rock in the upper reaches of the Yangtze River Economic Belt,the rapid development of industrial enterprises,the substandard discharge of urban domestic sewage and the discharge of non-point source pollution in rural areas have made total phosphorus one of the main pollution factors in the Yangtze River Basin.Under the influence of multiple factors such as changes in hydro-chemical indicators,changes in hydrodynamic conditions,changes in aquatic plants,and disturbances in aquatic organisms,river and lake water sediments have the potential to be re-released as endogenous pollutants,and there is a risk of pollution to water bodies.In this study,68 water sampling points and 57 sediment sampling points were set up in the Dongting Lake Basin to analyze the spatial distribution characteristics of total phosphorus.The sediments in the Xiangjiang River Basin with serious total phosphorus pollution were selected as the research object,and a water tank device was designed and fabricated,and indoor controlled experiments were carried out.Sediments under the action of three ecological measures under three different hydrodynamic conditions(static water-sediment static,v=0.05 m/s dynamic water-sediment static,v=0.13 m/s dynamic water-sediment resuspension)release pattern of phosphorus.At the same time,the variation characteristics of phosphorus species,bacterial community structure and diversity during sediment release were compared,and the relationship between the microbial community structure diversity characteristics and phosphorus species was analyzed.The following conclusions are drawn:(1)Characteristics of total phosphorus in water and sediments in the Dongting Lake Basin.According to the water quality results of 68 water sampling points,the evaluation results of water quality single-factor pollution index show that the PTP values of East,South and West Dongting Lake are 4.22,0.85 and 0.97,respectively,and the values of Xiangjiang,Zishui,Yuanjiang and Lishui are 0.06,0.08,0.09 and 0.12.Except for the east Dongting Lake,the TP content in the water body exceeded the standard by 3.22 times,and other areas did not exceed the standard.According to the results of 57 sediment sampling points,the evaluation results of the single-item pollution index of sediments show that the STP values of East Dongting Lake,Xiangjiang River,Yuanjiang River and Lishui River are 1.80,1.72,1.89 and 1.89,respectively,all of which are greater than 1.5,which are heavily polluted.The STP of water and water resources were 1.15,1.47 and 1.40,which were between 1.0 and 1.5,which belonged to moderate pollution.The degree of pollution in the lake area is ranked from largest to smallest as East Dongting Lake>West Dongting Lake>South Dongting Lake,and the river entering the lake is Lishui=Yuanjiang>Xiangjiang>Zishui.Based on the analysis results of total phosphorus pollution in the sediments,the heavily polluted Xiangjiang River sediments were selected as the test object to study the phosphorus release law.(2)Indoor controlled experimental study on the release of phosphorus from sediments by different ecological measures.Through the analysis of 14 sampling results of sediments in the Meishu River Basin,a secondary tributary of the Xiangjiang River,it is concluded that the level of phosphorus pollution in this Basin is severely polluted.The collected sediment was mixed uniformly as the test material,and a water tank test device for simulating the release of sediment pollutants was designed and fabricated.First,according to the sediment particle gradation and pre-experiment,it was determined that the flow rate of sediment static or a small amount of starting is 0.05 m/s,the flow rate to resuspend the sediment was 0.13 m/s.Secondly,the release of total phosphorus in sediments under different hydrodynamic conditions and still water conditions under three ecological measures,submerged plants(Vallisneria natans),phosphorus accumulating bacteria,and submerged plants+phosphorus accumulating bacteria,was designed.Simulation studies of sediment phosphorus release under different hydrodynamic conditions show that,the higher the flow rate,the more obvious the regularity of the total phosphorus concentration in the overlying water,and the shorter the time to reach the equilibrium concentration.When the sediment is static and unsuspended,the concentration of phosphorus released is small,which basically does not affect the water quality.When the flow rate is large and the sediment is suspended,the phosphorus is released quickly in the early stage and the release concentration is large.When the static water-sediment is static,the concentrations of submerged plants,phosphorus accumulating bacteria,and submerged plants+phosphorus accumulating bacteria are expressed as bitter grass+phosphorus accumulating bacteria<phosphorus accumulating bacteria<bitter grass<blank.When the flow of water is small and the sediment is static,the planting of submerged plants or phosphorus accumulating bacteria can significantly reduce the total phosphorus release of the sediment,which is reduced by more than 80%.When the flow rate is high to resuspend the sediment,planting submerged plants(bitter grass),spraying phosphorus accumulating bacteria,and submerged plants+phosphorus accumulating bacteria can reduce the proportion of total phosphorus released to the overlying water from 56%.To 16%,19%,and 48%,bitter grass has the strongest reduction effect on phosphorus release.(3)Bacterial community structure and diversity in sediments and their relationship to phosphorus species.In the sediments under the action of submerged plants,the contents of TP,Fe-P and IP decreased significantly with the growth of the bitter grass and its roots.Phosphorus accumulating bacteria will convert Ca2-P into polyphosphate and store it in the body,resulting in a significant decrease in Ca-P.Fe-P was reduced the most under the combined action of submerged plants and phosphorus accumulating bacteria.It can be seen that Fe-P is released more than Ca-P,and it is phosphorus with greater release potential.form.The microbial community structure of the sediments in Meishu River basin,a secondary tributary of Xiangjiang River,consists of 27 phyla and 106 genera.At the phyla level,the dominant species include Proteobacteria,Nitrobacteria,Sva0485,Desulfobacteria,Acidobacteria,MBNT15,Chloroflexi,Bacteroidetes.The relative abundance was 25.65%,20.42%,11.67%,11.21%,11.08%,6.52%,6.35%and 1.38%,respectively.Proteobacteria were still the most abundant phyla.The abundance of Proteobacteria in sediments treated by submerged plants,phospho-accumulating bacteria and phospho-accumulating bacteria+submerged plants increased by 17%,27%and 27%compared with the original sediments,respectively.Spearman correlation analysis of sediment bacterial community structure and phosphorus species showed that,the bacterial community diversity in sediments was negatively correlated with phosphorus species,but the correlation was not significant,indicating that phosphorus was an important element in the process of microbial growth and metabolism.Redundancy analysis RDA showed that Latescibacterota and Myxomycota had the strongest correlation with TP;Acidobacteria,Patellomycota,Nitrobacteria,Desantisbacteria were significantly positively correlated with Fe-P,Chlorobacteria and Spirochetes were significantly and positively correlated with Fe-P.Fe-P and OP were strongly correlated;Cyanobacteria、MBNTI15、Marine_Benthic_Group_D_and_DHVEG-1 and Subgroup were significantly positively correlated with OP;Proteobacteria,Broadarchaea,Actinobacteria were associated with IP,Ca-P or no correlation.Among the eight dominant bacterial phyla,Acidobacteria and Chloroflexi were more closely related to phosphorus forms. |
