Methane Dynamics And Related Microbe In Sediment And Water Column Of Land-based Shrimp Ponds Of The Min River Estuary

With the increasing trend of the transformation of natural wetlands into shrimp ponds in coastal areas,great changes have taken place in sediment and water environment.There is a lack of related research on the effects of these changes on methane metabolism in sediments and water columns during shrimp culture period.In this paper,three adjacent aquaculture shrimp ponds in Minjiang Estuary Wetland were selected as the research objects.Monthly in-situ sediment and culture water samples were collected from May 2018 to October 2018,and indoor microcosmic culture experiments and 16S techniques were used.The monthly variation characteristics of methane production and oxidation rate and sediment production rate,depth change characteristics,influencing factors and the changes of methane-related microbial community structure in shrimp ponds were studied.The main results are as follows:（1）The contents of carbon,nitrogen and phosphorus in sediments not only have time dynamic characteristics,but also fluctuate and decrease with the passage of culture time,and show obvious depth dynamic characteristics（surface layer>middle layer>bottom layer）.The physical and chemical properties of aquaculture water column and the concentration of nutrients such as DOC,POC and TDN fluctuated and increased with the passage of culture time,but the difference in depth was not significant.（2）The time characteristics of CH₄production rate in sediment in Minjiang Estuary were the late culture stage>middle stage>early stage（P<0.01）,and the vertical change was 0～5 cm(26.95±3.90 ng·g^-1·d^-1)>5～15 cm(14.15±1.80 ng·g^-1·d^-1)>15～25 cm(13.23±1.58 ng·g^-1·d^-1)（P<0.01）.The CH₄production rate of shrimp pond sediment was positively correlated with sediment temperature,SOC,TN,moisture content and organic carbon,negatively correlated with sediment C/N and p H.（3）The time characteristics of CH₄production and oxidation rate in the late culture stage was higher than that in the early and middle stages（P<0.01）,and the vertical change of CH₄production was the middle layer(10.32±1.49 nmol·L^-1·d^-1)>surface layer(9.73±1.12nmol·L^-1·d^-1)>bottom layer(9.31±1.19 nmol·L^-1·d^-1)（P>0.05）,and the vertical change of CH₄oxidation rate also was the middle layer(16.02±3.37nmol·L^-1·d^-1)>surface layer(15.74±3.01 nmol·L^-1·d^-1)>bottom layer(13.52±3.68nmol·L^-1·d^-1)（P>0.05）.Correlation analysis showed that the production rate of CH₄in water column was correlated with TDN and EC.The oxidation rate of CH₄was positively correlated with p H,Chl-a,DOC,TDN,SO₄^2-and so on,but negatively correlated with water temperature,EC and PO₄^3-.（4）The dominant genera in 0～5 cm and 5～15 cm sediments of the shrimp ponds were Methanosarcinales,and the dominant genera in 15～25 cm sediments were Methanomirobiales.With the change of culture environment,the dominant genera of methanogens in three depths were transformed into Methanosarcinales.According to the type of substrate used by this species of methanogenic bacteria,it can be preliminarily determined that the main pathway of methane production in the 0～25 cm sediments of shrimp ponds in Minjiang Estuary is hydrogen nutrition.The number of methanogenic bacteria in the sediment of the three depths showed that the middle stage>the early stage>the end stage（P<0.05）,and the vertical change of sediment showed 0～5 cm>5～15 cm>15～25 cm（P>0.05）,and positively correlated with CH₄production in sediments（P<0.05）.The results of canonical correspondence analysis（CCA）and correlation analysis showed that temperature,moisture content and nutrient concentration were the main factors affecting the composition and quantity of sediment community.（5）The dominant genus of methanogens in different depths of water column was Methanobacteriales,and the characteristic of quantitative depth change was surface layer>bottom layer>middle layer（P>0.05）.16S detection showed that the dominant species of methane oxidizing bacteria in water column developed from Type II to Type I with the culture time,while the dominant species of sulfate reducing bacteria developed from Desulfobacterales to Desulfovibrionales vibrio.Generally speaking,DO,ORP,salinity,Cl^-,TDP and Chl-a are the environmental factors affecting the composition and quantity of methane-related microorganisms,and there was no significant correlation between the number of methanogenic bacteria and CH₄metabolic rate in water column.