Preliminary Study On The Effect Of Pond Sediments On Nitrogen Transformation Of Overlying Water

In recent years,the aquaculture industry has developed rapidly,and pond aquaculture pollution has become increasingly serious.In order to achieve large-scale,high-yield and environmentally-friendly farming models,it has become a new development direction.The sediment is used as a gathering place for nutrient elements in aquaculture ponds.Improper treatment will cause damage to the aquaculture ecological environment.At present,how to control the sediment to improve and maintain the pond environment has become a current research hotspot.In order to further understand the denitrification effect of pond sediments and the microbial community,this article mainly explores from the following three parts:1. Preliminary study on the effect of nitrogen removal on sedimentThis article takes pond sediments as the research object to study its effect on nitrogen removal and microbial community in overlying water.The experiment used baking soda（Na HCO₃）to regulate the alkalinity of the water body.The initial alkalinity of the overlying water（calculated as Ca CO₃）was 143.3±7.10 mg/L in group A、275.2±22.01mg/L in group Band 385.1±28.01 mg/L in group C.And D group 466.5±61.50 mg/L.The results showed that the denitrification rate of sediment to the overlying water was 93.31%in group A,93.54%in group B,94.88%in group C,and 93.53%in group D,and there was no significant difference between groups（P>0.05）.The NH4+-N and NO₂^--N of each experimental group were reduced to the lowest point on the 17th and 20th days,and the final concentrations of NH₄⁺-N and NO₃^--N were lower than 0.2mg/L.The N content in the sediment was slowly released with the increase of the experimental time.The alkalinity promoted the release of N in the sediment and had no effect on the DOC concentration in the overlying water.Studies have shown that the addition of alkalinity has no significant effect on the nitrogen removal effect of sediments,and the nitrogen removal effect on sediments is significant.2. Analysis of microbial diversity in pond sedimentsIn order to study the structure of sediment microbial community and the evolution of microbial community under the control of alkalinity,initial sediment samples and experimental samples were set up.High-throughput results showed that the initial sediments at the level of the phylum and the experimental group system were mainly Proteobacteria、Bacteroidetes、Chloroflexi、Acidobacteria、Nitrospirae and Epsilonbacteraeota.The dominant genus are all denitrifying bacteria mainly based on sulfur autotrophic denitrification,Thiobacillus,、Thioalkalispira.After cultivation during the experiment,the microbial diversity in the sediment decreased and the population structure changed.The relative abundance of Chloroflexi and Acidobacteria decreased,while the relative abundance of Nitrospirae and Epsilonbacteraeota increased.It was also found that Nitrospirae is the main nitrite oxidizing bacteria（NOB）in the sediment.Studies have shown that pond sediments have a significant nitrogen removal effect on overlying water,and alkalinity regulation has no significant effect on them.3. Study on the rate of nitrogen removal in sedimentsBased on the sediments of Group C in Chapter 3,the experiment set four TN（NH₄⁺-N:NO₂^--N 1:1）concentration gradients of 10mg/L、20mg/L、30mg/L and 40mg/L respectively.Nitrogen removal rate of the sediment at substrate concentration.After 8days,the results showed that the nitrogen removal rate was 86.32%in group A 87.02%、group B 79.29%、group C and 81.24%in group D.The TN concentrations in groups A and B were lower than 2.5 mg/L,and the TN concentrations in groups C and D were6.40±4.76 mg/L and 7.39±1.66 mg/L,respectively.The removal efficiency of TN in group C and D was significantly lower than that in the other two groups（P<0.05）.At the 4th day of the experiment,NH₄⁺-N dropped to the lowest point,and the concentration of NO₂^--N in each group fell to the lowest value at 6、7、and 8 days.The final concentrations of NH₄⁺-N and NO₂^--N were less than 0.2mg/L.The concentration of NO₃^--N in group C and D increased on the 6th day and finally higher than that in the other two groups.With the increase of the concentration gradient,the nitrogen removal rate of the sediments accelerated,and the nitrogen removal rate in group D was significantly higher than that in the other experimental groups（P<0.05）.Studies have shown that pond sediments can effectively remove ammonia nitrogen and nitrite nitrogen from water bodies at lower concentrations,and the removal rate decreases at higher concentrations.