Device and method for identifying relationship between sediment bubble state methane and water body soluble methane

Abstract

The invention discloses a device and a method for identifying a relationship between sediment bubble state methane and water body soluble methane. The device comprises a culture box, an acrylic column fixed in the culture box, a flux box hoisted at the top in the acrylic column, a gas analyzer communicated with the flux box through a circulating pipeline and a bubble blocking structure fixedly arranged in the middle of the acrylic column, and the side wall of the acrylic column is provided with an overflow port and is connected with a peristaltic pump through the overflow port and a pipeline; the input end of the water-gas balancing device is further connected with an inert gas supply tank, and the output end of the water-gas balancing device is connected with a gas analyzer. The method realizes simple and efficient control of a methane release path in the sediment, is helpful to identify the influence of the sediment on the methane release flux of a water-gas interface, and is expected to demonstrate that the water soluble methane mainly comes from sediment bubble release and to demonstrate that the water soluble methane is mainly from the bubble release of the sediment under the condition of considering the bubble state methane release. The methane release flux of the shallow water body is far greater than the diffusion release flux.

Description

Technical Field

[0001] The invention relates to the technical field of environmental monitoring, and in particular to a device and method for identifying the relationship between bubbling methane in sediment and dissolved methane in water. Background Art

[0002] Methane (CH4) is an important greenhouse gas with a greenhouse effect potential more than twenty times that of carbon dioxide. Therefore, the research and control of methane emissions are particularly important. Freshwater bodies such as lakes and reservoirs are important sources of methane emissions. Their methane is mainly discharged into the atmosphere through bubbling emissions and diffusion emissions. The production and release of methane in freshwater bodies such as lakes and reservoirs mainly comes from bottom sediments, especially in areas rich in organic matter. The organic matter in these sediments will produce a large amount of methane gas through the decomposition of microorganisms in anoxic environments.

[0003] In shallow water areas, methane gas produced in sediments is usually released directly into the atmosphere in the form of bubbles, further exacerbating the greenhouse effect. Methane bubbling emissions are equivalent to directly transmitting methane produced and stored in anaerobic sediments to the atmosphere. When transmitted in the water column, there is almost no physical or chemical consumption or interaction with organisms due to the barrier of bubbles. It has a higher methane transmission efficiency and is the most important way of methane emission in shallow water bodies. In deep water areas, due to the extremely high hydrostatic pressure, this pressure will inhibit the formation and rise of methane bubbles. Under high pressure, methane gas is more likely to dissolve in the water to form soluble methane, rather than being released into the atmosphere in the form of bubbles.

[0004] It is well known that gas exchange at the water-air interface is an important way for aquatic ecosystems to exchange carbon, nitrogen and other biogenic elements with the atmosphere. At present, the monitoring methods for gas exchange flux at the water-air interface include micrometeorological method, model estimation method, flux box method, remote sensing inversion method, etc. Among them, model estimation method and flux box method are the most commonly used in field monitoring due to their simplicity, flexibility and easy operation. However, the traditional flux box method and model estimation method are difficult to identify the impact of sediments on the methane release flux at the water-air interface. However, sediments are the main source of methane gas production and release. Therefore, it is particularly important to identify the impact of sediments on the methane release flux at the water-air interface. Summary of the invention

[0005] The technical problem to be solved by the present invention is that it is difficult to identify the influence of sediments on the methane release flux at the water-air interface by the current traditional flux box method and model estimation method.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a device for identifying the relationship between bubbling methane in sediments and dissolved methane in water, including an incubator, an acrylic column fixed in the incubator, a flux box hoisted at the top of the acrylic column, a gas analyzer connected to the flux box through a circulation pipe, and a bubble barrier structure fixedly arranged in the middle of the acrylic column. The bottom of the filter structure is filled with sediment and a covering water layer is arranged above it. The side wall of the acrylic column is provided with an overflow port and is connected to a peristaltic pump through the overflow port and a pipeline. The output end of the peristaltic pump is connected to a water-gas balance device. The input end of the water-gas balance device is also connected to a gas supply tank of inert gas. The output end of the water-gas balance device is connected to the gas analyzer.

[0007] Preferably, the bubble barrier structure is a silk mesh, the middle part of the acrylic column is a splicing structure, including two butt-jointed flanges, two rubber gaskets are arranged between the two flanges, and the bubble barrier structure is located between the two rubber gaskets.

[0008] Preferably, a stainless steel screen is provided at the bottom of the silk mesh.

[0009] Preferably, reinforcing ribs are provided at the connection between the acrylic column and the flange, and the reinforcing ribs are evenly arranged around the acrylic column.

[0010] Preferably, the flux box is cylindrical, the top of the flux box is a closed end, a hanging hook is provided on the top of the flux box, a rope that passes through the acrylic cover plate at the top of the acrylic column is connected to the hanging hook, and the top of the rope is wrapped around a wooden stick placed on the acrylic cover plate.

[0011] Preferably, a fan is installed on the top of the flux box, and the fan is powered by an external mobile power supply. An air inlet and an air outlet are opened on the top of the flux box, and a PU air pipe connected to the flux box is fixedly installed in the air inlet and the air outlet, and a three-way valve is arranged on the top of the PU air pipe. The input end of the gas analyzer is connected to the PU air pipe in the air outlet through a pipe, and the output end is connected to the PU air pipe in the air inlet pipe through a pipe, and a vacuum filter is installed on the pipe at the input end of the gas analyzer.

[0012] Preferably, the water-gas balance device includes a support column and a gas exchange tube, the support column is arranged vertically, the gas exchange tube is wrapped around the periphery of the support column, both ends of the gas exchange tube are connected to syringes, the output pipe of the gas supply tank is connected to an aeration head, the aeration head is located in the syringe at the input end of the gas exchange tube, the output end of the peristaltic pump is connected to the syringe at the input end of the gas exchange tube, the input end of the gas analyzer is located in the syringe at the output end of the gas exchange tube, and a water collecting bucket is provided below the drain outlet at the bottom end of the syringe at the output end of the gas exchange tube.

[0013] Preferably, a gas flow meter is provided on the output pipeline of the gas supply tank.

[0014] A method for using a device for identifying the relationship between sediment bubble-state methane and water-soluble methane comprises the following steps: Step 1: Preliminary research; S1.1. To explore the variation law of headspace methane release flux, spread sediments at the bottom of the incubator, set a water layer above the sediments, and after bubbles accumulate under the gas barrier structure, hang the flux box on the top of the acrylic column and ensure that the lower edge is completely immersed in the water layer in the acrylic column; S1.2. Turn on the fan to allow the gas in the flux box to flow into the gas analyzer through the circulation pipe. Use the gas analyzer to measure the change in the methane gas concentration in the headspace of the water layer in the flux box for ten minutes. Step 2: Accurately measure. When the headspace methane gas concentration produces an obvious and stable gradient, use a peristaltic pump to extract the water in the overlying water layer cultured in the acrylic column into the water-gas balance device, use a gas supply tank to input nitrogen into the water-gas balance device, purge the extracted water, and purge the methane gas dissolved therein. Use another gas analyzer to measure the concentration of the purged gas, thereby completing the measurement of the dissolved methane concentration in the overlying water layer.

[0015] Preferably, the methane concentration in the overlying water layer on the sediment is The calculation formula is: According to Fick's law, the model estimation method is calculated as follows: F=K( )(1); Where: F is the diffusion flux of water-air interface, ; is the original concentration of greenhouse gases at the surface of the water body; The concentration of greenhouse gases on the surface of the water body at a specific temperature when they are in equilibrium with greenhouse gases in the atmosphere, using the average concentration of greenhouse gases in the atmosphere and the measured temperature of the water body; K is the gas exchange coefficient, cm / h, and its calculation formula is: = ; Where: is the gas exchange coefficient of sulfur hexafluoride, cm / h; is the Schmidt number, The Schmidt number is 600 at 20°C; n is the wind speed coefficient, which is 0.67 when the wind speed is less than 3.7 m / s and 0.5 when the wind speed is greater than 3.7 m / s; The Schmidt number calculation formula for methane gas in freshwater ecosystems is: =1897.8 114.258t 3.2902 0.039061 ; Where t is the water temperature; =2.07+0.215× ; In the formula is the wind speed 10m above the water surface (m / s). Just take 0; When the flux box method is used to measure the greenhouse gas emission flux at the water-air interface, it is calculated according to the following formula: F= (2); Where: F is the greenhouse gas flux to be measured at the water-air interface, mmol / ( ); k is the slope of the greenhouse gas concentration in the flux box over time, ; , are conversion coefficients, representing volume fractions ( )-mass concentration (mg / ), and the conversion factor between minutes and days (1440); V is the volume of air in the box when it is placed on the water surface. ; A is the water surface area covered by the box, ; M is the molar mass of the measured greenhouse gas, g / mol; Combining the above two equations (1) and (2), the methane concentration in the water body above the sediment can be calculated: .

[0016] The present invention proposes a device and method for identifying the relationship between bubbly methane in sediments and dissolved methane in water bodies. The release of bubbly methane at the sediment-water interface is controlled by silk screens of different mesh sizes, and the contribution of bubbly methane in sediments to dissolved methane in overlying water is identified by combining the traditional flux box method and model estimation method. The realization of simple and efficient control of the methane release pathway in sediments helps to identify the impact of sediments on the methane release flux at the water-air interface, in order to demonstrate important conclusions such as "soluble methane in water bodies mainly comes from the release of bubbles in sediments" and that the methane release flux of shallow water bodies is much greater than the diffusion release flux when considering the release of bubbly methane. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention will be further described below in conjunction with the accompanying drawings and embodiments: Attached Figure 1 A schematic diagram of the structure of an embodiment of the present invention when exploring the variation law of headspace methane release flux.

[0018] Attached Figure 2 A schematic diagram of the structure of an embodiment of the present invention for accurately measuring the concentration of dissolved methane in an overlying water body.

[0019] Attached Figure 3 A schematic diagram of the front view of the acrylic column in the present invention.

[0020] Attached Figure 4 Schematic diagram of the acrylic column cover in the present invention.

[0021] Attached Figure 5 Front view of the homemade flux box in the present invention.

[0022] Attached Figure 6 A schematic cross-sectional view of the middle joint of the acrylic column in the present invention.

[0023] Attached Figure 7 It is a schematic diagram of the structure of the water-gas balance device in the present invention.

[0024] Attached Figure 8 A flow chart of a method according to an embodiment of the present invention.

[0025] Attached Fig. 9 This is a graph showing the methane release flux in the headspace of different silk mesh groups in an embodiment of the present invention.

[0026] In the figure: 1. incubator; 2. acrylic column; 3. peristaltic pump; 4. water-gas balance device; 5. gas analyzer; 6. flux box; 7. three-way valve; 8. PU air pipe; 9. vacuum filter; 10. air pipe joint; 11. gas supply tank; 12. gas flow meter; 13. overlying water layer; 14. sediment; 15. overflow port; 16. fan; 17. air inlet; 18. air outlet; 19. rope; 20. hanging hook; 21. wooden stick; 22. flange; 23. acrylic cover; 24. rubber gasket; 25. silk mesh; 26. stainless steel screen. DETAILED DESCRIPTION

[0027] like Figure 1-7As shown, the present invention provides a device for identifying the relationship between bubbling methane in sediments and dissolved methane in water, comprising an incubator 1, an acrylic column 2 fixed at the top of the incubator 1, a flux box 6 hoisted at the top of the acrylic column 2, a gas analyzer 5 connected to the flux box 6 through a circulation pipeline, and a bubble barrier structure fixedly arranged in the middle of the acrylic column 2, the bottom of the filter structure is filled with sediment 14, and a water layer 13 is arranged on the top, the side wall of the acrylic column 2 is provided with an overflow port 15 and a peristaltic pump 3 is connected to the overflow port 15 and a pipeline, the output end of the peristaltic pump 3 is connected to a water-gas balance device 4, the input end of the water-gas balance device 4 is also connected to a gas supply tank 11 of inert gas, and the output end of the water-gas balance device 4 is connected to the gas analyzer 5.

[0028] The incubator 1 is made of PVC, with a size of 770 mm in length×515 mm in width×430 mm in height, and a capacity of 170 L. The height of the culture sediment 14 is 15 cm, and the depth of the overlying water layer 13 is 15 cm.

[0029] The acrylic column 2 is a custom-made acrylic device with an inner diameter of 20 cm, a height of 40 cm, a wall thickness of 5 mm, and a volume of 12.56 L. The entire device is made up of two acrylic columns spliced ​​together, with the bottom opening being convenient for direct insertion into the sediment 14; the middle joint is made up of two upper and lower flanges 22, and the middle of the flange 22 is sandwiched with a rubber gasket 24, a silk mesh 25, a stainless steel screen 26, and a rubber gasket 24 from top to bottom, each with twelve holes corresponding to each other and fixed by twelve bolts and nuts, and the lower flange 22 is supported by twelve reinforcing ribs; an overflow port 15 of the overlying water layer 13 is opened 10 cm from the upper end of the middle, with a hole size of 1.2 cm, and is assembled by a PU tube 8, a waterproof joint, and a three-way valve 7. The acrylic cover plate 23 at the top of the acrylic column 2 is provided with two air inlets 17 and air outlets 18 with an aperture of 1.2 cm each, and is assembled with a PU tube 8, a waterproof joint, and a three-way valve 7; when measuring the concentration of methane gas in the headspace, the top acrylic cover plate 23 is spliced ​​with the flange plate at the upper end of the acrylic column 2, with a layer of rubber gasket 24 sandwiched in the middle, and twelve holes are opened one by one and fixed by twelve bolts and nuts to ensure the air tightness of the upper end of the device; twelve reinforcing ribs are added to the upper end of the acrylic column 2 to play a load-bearing support role when the overall height of the device is raised by splicing in the later stage.

[0030] The peristaltic pump 3 model is LHZW002-10, the inner tube is 4.8×8BPT, the outer tube is 5×7 silicone, and the flow rate is 0.1-510ml / min.

[0031] Gas analyzer 5 is DLT-100, model number is 908-0010-0001.

[0032] The flux box 6 is made of PVC, with a closed upper end and an open lower end, a diameter of 16 cm, and a height of 16 cm. The box cover has three holes, and the middle hole is convenient for connecting the power supply to the fan 16 in the flux box. The openings at both ends are equipped with air pipe joints and three-way valves to provide air inlet and outlet ports.

[0033] The three-way valve 7 is a medical three-way stopcock.

[0034] The PU air tube 8 is a transparent tube, and its maximum pressure resistance value is 1.6 MPa.

[0035] The vacuum filter 9 is ZFC-100, and the pressure range is -100-0 kpa.

[0036] The air pipe connector 10 is straight-through type, and both sides can be connected to air pipes with an outer diameter of 6 mm.

[0037] The gas supply tank 11 is a standard nitrogen tank, the cylinder specification is 8L, and the filling pressure is 10±0.5Mpa.

[0038] The gas flow meter 12 model is AST10-DLCMX, and the flow range is 500SCCM.

[0039] like Figure 6 The bubble barrier structure is a silk mesh 25 , the middle part of the acrylic column 2 is a splicing structure, including two butted flanges 22 , two rubber washers 24 are arranged between the two flanges 22 , and the bubble barrier structure is located between the two rubber washers 24 .

[0040] The whole set of acrylic columns 1 is made of two sections of acrylic columns. First, the water overflow port on the upper acrylic column is modified, and a three-way valve 7, PU air pipe 8 and waterproof joint are installed on it, and hot melt glue is welded on the inner and outer walls to ensure its sealing; then the two sections of acrylic columns are spliced, and the middle splicing order is as follows: Figure 5 As shown, rubber gaskets 24 are installed at the top and bottom to ensure the air tightness of the connecting section and prevent gas and liquid from escaping.

[0041] A stainless steel screen 26 is fixed below the silk mesh 25 to prevent the silk mesh from breaking, and the silk mesh 25 is tightly clamped in the middle to block the release of bubbles in the sediment.

[0042] like Figure 1 and Figure 2 The flux box 6 is cylindrical, the top of the flux box 6 is a closed end, a hanging hook 20 is provided on the top of the flux box 6, and a string 19 penetrating the acrylic cover plate 23 at the top of the acrylic column 2 is connected to the hanging hook 20, and the top of the string 19 is wound around a wooden stick 21 placed on the acrylic cover plate 23.

[0043] like Figure 1 and Figure 2A fan 16 is installed at the top of the flux box 6, and the fan 16 is powered by an external mobile power supply. An air inlet 17 and an air outlet 18 are opened at the top of the acrylic cover plate 23. A PU air pipe 8 connected to the flux box 6 is fixedly installed in the air inlet 17 and the air outlet 18, and a three-way valve 7 is installed at the top of the PU air pipe 8. The input end of the gas analyzer 5 is connected to the PU air pipe 8 in the air outlet 18 through a pipeline, and the output end is connected to the PU air pipe 8 in the air inlet pipe 17 through a pipeline, and a vacuum filter 9 is installed on the pipeline at the input end of the gas analyzer 5.

[0044] like Figure 7 As shown. The water-gas balance device includes a support column and a gas exchange tube, the support column is arranged vertically, the gas exchange tube is wrapped around the periphery of the support column, both ends of the gas exchange tube are connected to syringes, the output pipe of the gas supply tank 11 is connected to an aeration head, the aeration head is located in the syringe at the input end of the gas exchange tube, the output end of the peristaltic pump 3 is connected to the syringe at the input end of the gas exchange tube, the input end of the gas analyzer 5 is located in the syringe at the output end of the gas exchange tube, and a water collecting bucket is provided below the drainage port at the bottom end of the syringe at the output end of the gas exchange tube.

[0045] The water-gas balance device 4 consists of a support column and a gas exchange tube. The support column is made of a PE hard barrel with an inner diameter of 10.5 cm, a height of 30 cm, and a thickness of 0.5 cm. The gas exchange tube is tightly wrapped around the periphery of the support column with a PC transparent hose. The length of the air tube is controlled to be 6 m. A 100 ml syringe is connected to each end to connect the air pipe and the water pipe, which are tightly fixed with a rubber cock. The air inlet end is connected with an aeration head to ensure that the gas and liquid are fully mixed. The drainage outlet uses a collection basin to collect the overlying water.

[0046] A gas flow meter 12 is provided on the output pipeline of the gas supply tank 11 .

[0047] like Figure 8 As shown, a method for using a device for identifying the relationship between sediment bubble-state methane and water-soluble methane comprises the following steps: Step 1: Preliminary research; Silk screens 25 with different mesh sizes were used for isolation, and a total of 5 gradients were designed, namely, silk screens without silk screen, 50 mesh, 100 mesh, 500 mesh, and 900 mesh. Three parallel samples were set in each group, and a blank control sample was added to each group with silk screen, totaling 19 sets of devices. Before cultivation, the modified stainless steel screen 26 was covered on the surface of the sediment and white stones were evenly laid on it to ensure the uniform release of bubbles in the sediment. Then, the assembled 19 sets of devices were respectively inserted into the corresponding 5 groups of culture boxes 1 filled with sediment, and water was connected to the culture box 1 for cultivation. After the water level of the overlying water layer 13 was stable, the three-way stopcock at the overflow port 15 was closed; the top opening of the acrylic device in the parallel group was double-covered with plastic wrap and a shower cap and then sealed with an acrylic cover plate 23, and the top opening of the blank control group was double-covered with plastic wrap and a shower cap and then tied with a string to ensure the air tightness of the device, thereby completing the device assembly and cultivation work.

[0048] S1.1. To explore the change law of headspace methane release flux, first, dig the bottom mud of black and smelly water body into the incubator 1 for incubation; control the depth of sediment 14 in 6 groups of incubators to be maintained at about 15 cm, set the water layer 13 above the sediment 14, and cover the surface of the sediment 14 with the modified stainless steel screen 26 before incubation, and evenly lay white stones on it to ensure the uniform release of sediment bubbles. After obvious bubble accumulation under the gas barrier structure, hang the flux box 6 on the top of the acrylic column 2 and ensure that the lower edge is completely immersed in the water layer 13 in the acrylic column 2; S1.2, turn on the fan 16, so that the gas in the flux box 6 flows into the gas analyzer 5 through the circulation pipe, and the gas analyzer 5 is used to measure the change of the methane gas concentration in the headspace of the water layer 13 in the flux box 6 for ten minutes; the device is used to measure the methane gas release flux in the headspace of the water layer 13 of 900, 500, 100, 50 mesh silk screens and the silk screen-free group. Fig. 9 It can be seen that there is a relatively obvious gradient change in the headspace methane gas release flux values ​​between different silk mesh groups, which can be used to determine that the feasibility of the device is good.

[0049] Step 2: Accurately measure. When the headspace methane gas concentration produces an obvious and stable gradient, use the peristaltic pump 3 to extract the water in the overlying layer 13 cultured in the acrylic column 2 into the water-gas balance device 4, use the gas supply tank 10 to input nitrogen into the water-gas balance device 4, purge the extracted water, and purge the methane gas dissolved therein, and use another gas analyzer 5 to measure the concentration of the purged gas, thereby completing the measurement of the dissolved methane concentration in the overlying layer 13.

[0050] The methane concentration value in the overlying water layer 13 on the sediment 14 is The calculation formula is: According to Fick's law, the model estimation method is calculated as follows: F=K( )(1); Where: F is the diffusion flux of water-air interface, ; is the original concentration of greenhouse gases at the surface of the water body; The concentration of greenhouse gases on the surface of the water body at a specific temperature when they are in equilibrium with greenhouse gases in the atmosphere, using the average concentration of greenhouse gases in the atmosphere and the measured temperature of the water body; K is the gas exchange coefficient, cm / h, and its calculation formula is: = ; Where: is the gas exchange coefficient of sulfur hexafluoride, cm / h; is the Schmidt number, The Schmidt number is 600 at 20°C; n is the wind speed coefficient, which is 0.67 when the wind speed is less than 3.7 m / s and 0.5 when the wind speed is greater than 3.7 m / s; The Schmidt number calculation formula for methane gas in freshwater ecosystems is: =1897.8 114.258t 3.2902 0.039061 ; Where t is the water temperature; =2.07+0.215× ; In the formula is the wind speed 10m above the water surface (m / s). Just take 0; When the flux box method is used to measure the greenhouse gas emission flux at the water-air interface, it is calculated according to the following formula: F= (2); Where: F is the greenhouse gas flux to be measured at the water-air interface, mmol / ( ); k is the slope of the greenhouse gas concentration in the flux box over time, ; , are conversion coefficients, representing volume fractions ( )-mass concentration (mg / ) and the conversion factors between minutes and days; V is the volume of air in the box when it is placed on the water surface. ; A is the water surface area covered by the box, ; M is the molar mass of the measured greenhouse gas, g / mol; Combining the above two equations (1) and (2), the methane concentration in the water body above the sediment can be calculated: .

[0051] The above calculation method was used to estimate the dissolved methane concentration in the water overlying different silk net groups and obtain Table 1; Table 1 Estimated dissolved methane concentration in the water above different silk net groups

[0052] From Table 1, we can observe that there is an obvious gradient change between the groups. With the increase of silk screen mesh number, the concentration of dissolved methane in the water body gradually decreases, which lays a foundation for proving that "the dissolved methane in the water body mainly comes from the release of bubbles in the sediment" and that when considering the release of bubble-state methane, the methane release flux of shallow water bodies is much greater than the diffusion release flux.

Claims

1. A device for identifying the relationship between bubbling methane in sediments and dissolved methane in water, characterized in that: The invention comprises an incubator (1), an acrylic column (2) fixed in the incubator (1), a flux box (6) suspended at the top of the acrylic column (2), a gas analyzer (5) connected to the flux box (6) via a circulation pipeline, and a bubble barrier structure fixedly arranged in the middle of the acrylic column (2); a sediment (14) is filled below the filter structure, and a water layer (13) is arranged above the structure; an overflow port (15) is arranged on the side wall of the acrylic column (2) and is connected to a peristaltic pump (3) via the overflow port (15) and a pipeline; the output end of the peristaltic pump (3) is connected to a water-gas balance device (4); the input end of the water-gas balance device (4) is also connected to a gas supply tank (11) of an inert gas; and the output end of the water-gas balance device (4) is connected to the gas analyzer (5).

2. A device for identifying the relationship between bubbling methane in sediments and dissolved methane in water as claimed in claim 1, characterized in that: The bubble barrier structure is a silk mesh (25), the middle part of the acrylic column (2) is a splicing structure, including two butted flanges (22), two rubber gaskets (24) are arranged between the two flanges (22), and the bubble barrier structure is located between the two rubber gaskets (24).

3. A device for identifying the relationship between bubbling methane in sediments and dissolved methane in water as claimed in claim 2, characterized in that: A stainless steel screen (26) is provided at the bottom of the silk mesh (25).

4. A device for identifying the relationship between sediment bubble-like methane and water-soluble methane as claimed in claim 2, characterized in that: A reinforcing rib is provided at the connection between the acrylic column (2) and the flange (22), and the reinforcing rib is evenly arranged around the acrylic column (2).

5. A device for identifying the relationship between sediment bubble-like methane and water-soluble methane as claimed in claim 1, characterized in that: The flux box (6) is cylindrical, the top of the flux box (6) is a closed end, the top of the flux box (6) is provided with a hanging hook (20), the hanging hook (20) is connected with a string (19) that passes through the acrylic cover plate (23) at the top of the acrylic column (2), and the top of the string (19) is wound around a wooden stick (21) placed on the acrylic cover plate (23).

6. A device for identifying the relationship between bubbling methane in sediments and dissolved methane in water as claimed in claim 5, characterized in that: A fan (16) is installed at the top of the flux box (6), and the fan (16) is powered by an external mobile power supply. An air inlet (17) and an air outlet (18) are opened at the top of the flux box (6). A PU air pipe (8) connected to the flux box (6) is fixedly installed in the air inlet (17) and the air outlet (18), and a three-way valve (7) is installed at the top of the PU air pipe (8). The input end of the gas analyzer (5) is connected to the PU air pipe (8) in the air outlet (18) through a pipeline, and the output end is connected to the PU air pipe (8) in the air inlet pipe (17) through a pipeline, and a vacuum filter (9) is installed on the pipeline at the input end of the gas analyzer (5).

7. A device for identifying the relationship between sediment bubble-like methane and water-soluble methane as claimed in claim 1, characterized in that: The water-gas balance device comprises a support column and a gas exchange tube, the support column is arranged vertically, the gas exchange tube is wound around the periphery of the support column, both ends of the gas exchange tube are connected to a syringe, the output pipe of the gas supply tank (11) is connected to an aeration head, the aeration head is located in the syringe at the input end of the gas exchange tube, the output end of the peristaltic pump (3) is connected to the syringe at the input end of the gas exchange tube, the input end of the gas analyzer (5) is located in the syringe at the output end of the gas exchange tube, and a water collecting bucket is provided below the drainage port at the bottom end of the syringe at the output end of the gas exchange tube.

8. A device for identifying the relationship between bubbling methane in sediments and dissolved methane in water as claimed in claim 1, characterized in that: A gas flow meter (12) is provided on the output pipe of the gas supply tank (11).

9. A method for using the device for identifying the relationship between bubbling methane in sediment and dissolved methane in water as claimed in claim 1, characterized in that: The steps include: Step 1: Preliminary research; S1.

1. To investigate the variation law of the headspace methane release flux, a sediment (14) is laid flat on the bottom of the incubator (1), and a water layer (13) is set above the sediment (14). After bubbles are obviously accumulated under the gas barrier structure, the flux box is hung on the top of the acrylic column and the lower edge is ensured to be completely immersed in the water layer in the acrylic column. S1.2, turning on the fan (16) to allow the gas in the flux box 6 to flow into the gas analyzer (5) through the circulation pipe, and using the gas analyzer (5) to measure the change in the methane gas concentration in the headspace of the water layer (13) in the flux box (6) for ten minutes; Step 2: Accurately measure. When the headspace methane gas concentration produces an obvious and stable gradient, use a peristaltic pump (3) to extract water in the overlying water layer (13) cultured in the acrylic column (2) into the water-gas balance device (4). Use a gas supply tank (10) to input nitrogen into the water-gas balance device (4) to purge the extracted water and purge the methane gas dissolved therein. Use a gas analyzer (5) to measure the concentration of the purged gas, thereby completing the measurement of the dissolved methane concentration in the overlying water layer (13).

10. A method for using the device for identifying the relationship between bubbling methane in sediment and dissolved methane in water as claimed in claim 9, characterized in that: The methane concentration value in the water layer (13) overlying the sediment (14) The calculation formula is: According to Fick's law, the model estimation method is calculated as follows: F=K( )(1); Where: F is the diffusion flux of water-air interface, ; is the original concentration of greenhouse gases at the surface of the water body; The concentration of greenhouse gases on the surface of the water body at a specific temperature when they are in equilibrium with greenhouse gases in the atmosphere, using the average concentration of greenhouse gases in the atmosphere and the measured temperature of the water body; K is the gas exchange coefficient, cm / h, and its calculation formula is: = ； Where: is the gas exchange coefficient of sulfur hexafluoride, cm / h; is the Schmidt number, The Schmidt number is 600 at 20°C; n is the wind speed coefficient, which is 0.67 when the wind speed is less than 3.7 m / s and 0.5 when the wind speed is greater than 3.7 m / s; The Schmidt number calculation formula for methane gas in freshwater ecosystems is: =1897.8 114.258t 3.2902 0.039061 ； Where t is the water temperature; =2.07+0.215× ； In the formula is the wind speed 10m above the water surface (m / s). Just take 0; When the flux box method is used to measure the greenhouse gas emission flux at the water-air interface, it is calculated according to the following formula: F= （2）； Where: F is the greenhouse gas flux to be measured at the water-air interface, mmol / ( ); k is the slope of the greenhouse gas concentration in the flux box over time, ; , are conversion coefficients, representing volume fractions ( )-mass concentration (mg / ) and the conversion factors between minutes and days; V is the volume of air in the box when it is placed on the water surface. ; A is the water surface area covered by the box, ; M is the molar mass of the measured greenhouse gas, g / mol; Combining the above two equations (1) and (2), the methane concentration in the water body above the sediment can be calculated: .

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