An apparatus and method for identifying the relationship between bubble methane in sediments and dissolved methane in water

Abstract

The present invention discloses a device and method for identifying the relationship between bubble methane in sediment and dissolved methane in water. The device includes an incubator, an acrylic column fixed inside the incubator, a flux chamber suspended at the inner top of the acrylic column, a gas analyzer connected to the flux chamber through a circulation pipeline, and a bubble barrier structure fixedly arranged in the middle of the acrylic column. An overflow port is provided on the side wall of the acrylic column and is connected to a peristaltic pump through the overflow port and a pipeline. The input end of the water-gas balance device is also connected to a gas supply tank of inert gas, and the output end of the water-gas balance device is connected to the gas analyzer. It realizes simple and efficient control of the methane release pathway in sediment, helps to identify the influence of sediment on the methane release flux at the water-gas interface, in order to demonstrate important conclusions such as "dissolved methane in water mainly comes from the release of bubbles in sediment" and that the methane release flux in shallow water bodies is much greater than the diffusion release flux when considering the release of bubble methane.

Description

Technical Field

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

[0002] Methane (CH4), as an important greenhouse gas, has 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. Methane in these water bodies is mainly discharged into the atmosphere through bubbling emissions, diffusion emissions, etc. The generation and release of methane in freshwater bodies such as lakes and reservoirs mainly come 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 an anoxic environment.

[0003] In shallow water areas, the methane gas generated in sediments is usually directly released into the atmosphere in the form of bubbles, further exacerbating the greenhouse effect. Methane bubbling emissions are equivalent to directly transporting the methane generated and stored in anaerobic sediments to the atmosphere. When transporting in the water column, there is almost no physical or chemical consumption or interaction with organisms due to the barrier of bubbles, and it has a higher methane transport efficiency. It is the most important way of methane emissions 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. In a high-pressure environment, methane gas is more likely to dissolve in the water body to form dissolved methane, rather than being released into the atmosphere in the form of bubbles.

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

[0006] To solve the above technical problems, the technical solution adopted by the present invention is as follows: An apparatus for identifying the relationship between bubble methane in sediment and dissolved methane in water body, comprising an incubator, an acrylic column fixed in the incubator, a flux chamber suspended at the inner top of the acrylic column, a gas analyzer connected to the flux chamber through a circulation pipeline, and a bubble barrier structure fixedly arranged in the middle of the acrylic column. Sediment is filled below the filtering structure, and a water covering layer is arranged above. An overflow port is arranged on the side wall of the acrylic column 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-air balance device. An inert gas supply tank is also connected to the input end of the water-air balance device. The output end of the water-air balance device is connected to the gas analyzer.

[0007] Preferably, the bubble barrier structure is a silk net. The middle part of the acrylic column is a splicing structure, including two butted flange plates. Two rubber gaskets are arranged between the two flange plates. The bubble barrier structure is located between the two rubber gaskets.

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

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

[0010] Preferably, the flux chamber is cylindrical. The top of the flux chamber is a closed end. A hanging hook is arranged at the top of the flux chamber. A cord connected to the hanging hook penetrates through an acrylic cover plate at the top end of the acrylic column, and the top end of the cord is wound around a wooden stick placed on the acrylic cover plate.

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

[0012] Preferably, the water-air balance device includes a support column and a gas exchange pipe. The support column is arranged vertically, and the gas exchange pipe is wound around the periphery of the support column. Syringes are connected to both ends of the gas exchange pipe. The output pipeline of the supply tank is connected to an aeration head, and the aeration head is located in the syringe at the input end of the gas exchange pipe. The output end of the peristaltic pump is connected to the syringe at the input end of the gas exchange pipe. The input end of the gas analyzer is located in the syringe at the output end of the gas exchange pipe. A water collecting hopper is arranged below the drain port at the bottom end of the syringe at the output end of the gas exchange pipe.

[0013] Preferably, a gas flowmeter is arranged on the output pipeline of the supply tank.

[0014] A method for using a device for identifying the relationship between bubble methane in sediment and dissolved methane in water body, comprising the following steps:

[0015] Step 1. Preliminary exploration;

[0016] S1.1. Explore the change law of headspace methane release flux. Spread sediment evenly on the bottom of the incubator, set a water layer above the sediment. After obvious bubbles accumulate below the gas barrier structure, hang the flux chamber at the top of the acrylic column and ensure that the lower edge is completely immersed in the water layer inside the acrylic column.

[0017] S1.2. Turn on the fan so that the gas in the flux chamber flows into the gas analyzer through the circulation pipeline. Use the gas analyzer to measure the change of the headspace methane gas concentration in the water layer of the flux chamber for ten minutes continuously.

[0018] Step 2. Accurate measurement. When an obvious and stable gradient of the headspace methane gas concentration occurs, use a peristaltic pump to pump the water in the water layer cultured in the acrylic column into the water-gas equilibrium device. Input nitrogen into the water-gas equilibrium device using a gas supply tank to purge the pumped water and blow out the dissolved methane gas in it. Use another gas analyzer to measure the concentration of the blown-out gas, thus completing the measurement of the dissolved methane concentration in the water layer.

[0019] Preferably, the methane concentration value in the water layer above the sediment The calculation formula is:

[0020] According to Fick's law, the model estimation method is calculated as follows:

[0021] F = K ( )(1);

[0022] In the formula: F is the water-air interface diffusion flux, ;

[0023] is the original concentration of the greenhouse gas on the water surface;

[0024] The concentration when the greenhouse gas on the water surface reaches equilibrium with the greenhouse gas in the atmosphere at a specific temperature, using the average concentration of the greenhouse gas in the atmosphere and the measured water temperature;

[0025] K is the gas exchange coefficient, cm / h, and its calculation formula is:

[0026] = ;

[0027] In the formula: is the gas exchange coefficient of sulfur hexafluoride, cm / h;

[0028] is the Schmidt number, is the Schmidt number of 600 at 20 °C;

[0029] n is the wind speed coefficient, taking 0.67 when the wind speed is less than 3.7 m / s and 0.5 when it is greater than 3.7 m / s;

[0030] Calculation formula for the Schmidt number of methane gas in freshwater aquatic ecosystems:

[0031] = 1897.8 114.258t 3.2902 0.039061 ;

[0032] where t is the water temperature;

[0033] = 2.07 + 0.215 × ;

[0034] where is the wind speed (m / s) 10 m above the water surface. For this experiment, taking 0 is fine;

[0035] When using the flux chamber method to measure the greenhouse gas emission flux at the water-air interface, calculate according to the following formula:

[0036] F = (2);

[0037] where: F is the greenhouse gas flux to be measured at the water-air interface, mmol / ( );

[0038] k is the slope of the greenhouse gas concentration change with time in the flux chamber, ;

[0039] and are conversion coefficients, representing the conversion coefficient from volume fraction ( ) to mass concentration (mg / ), and the conversion coefficient between minutes and days (1440);

[0040] V is the volume of the air inside the chamber when the chamber is placed on the water surface, ;

[0041] A is the water surface area covered by the chamber, ;

[0042] M is the molar mass of the measured greenhouse gas, g / mol;

[0043] By simultaneously solving the above two equations (1) and (2), the methane concentration value in the overlying water of the sediment can be calculated. .

[0044] The present invention provides a device and method for identifying the relationship between bubble methane in sediment and dissolved methane in water. By using silk meshes with different mesh numbers to control the release of bubble methane at the sediment-water interface, and then combining the traditional flux chamber method and the model estimation method to identify the contribution of bubble methane in sediment to dissolved methane in the overlying water. It realizes simple and efficient control of the methane release pathway in sediment, helps to identify the influence of sediment on the methane release flux at the water-air interface, in order to demonstrate important conclusions such as "dissolved methane in water mainly comes from the release of sediment bubbles" and that the methane release flux in shallow water bodies is much larger than the diffusion release flux when considering the release of bubble methane. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The present invention will be further described below in conjunction with the drawings and embodiments:

[0046] Attached Figure 1 Schematic structural diagram when exploring the variation law of the headspace methane release flux in the embodiment of the present invention.

[0047] Attached Figure 2 Schematic structural diagram when accurately measuring the dissolved methane concentration in the overlying water in the embodiment of the present invention.

[0048] Attached Figure 3 Front view of the acrylic column in the present invention.

[0049] Attached Figure 4 Schematic diagram of the cover of the acrylic column in the present invention.

[0050] Attached Figure 5 Front view of the self-made flux chamber in the present invention.

[0051] Attached Figure 6 Schematic cross-sectional view of the middle splicing part of the acrylic column in the present invention.

[0052] Attached Figure 7 Schematic structural diagram of the water-air balance device in the present invention.

[0053] Attached Figure 8 Flowchart of the method in the embodiment of the present invention.

[0054] Attached Figure 9 Diagram for measuring the headspace methane release flux of different silk mesh groups in the embodiment of the present invention.

[0055] In the figure: 1. Incubator; 2. Acrylic column; 3. Peristaltic pump; 4. Water-air balance device; 5. Gas analyzer; 6. Flux chamber; 7. Three-way valve; 8. PU air pipe; 9. Vacuum filter; 10. Air pipe joint; 11. Gas supply tank; 12. Gas flow meter; 13. Water covering layer; 14. Sediment; 15. Overflow port; 16. Fan; 17. Air inlet; 18. Air outlet; 19. String; 20. Hanging hook; 21. Wooden stick; 22. Flange; 23. Acrylic cover plate; 24. Rubber gasket; 25. Silk mesh; 26. Stainless steel screen. Detailed implementation manner

[0056] As Figures 1-7 shown, the present invention provides a device for identifying the relationship between bubble methane in sediment and dissolved methane in water body, including an incubator 1, an acrylic column 2 fixed at the top inside the incubator 1, a flux chamber 6 hoisted at the top inside the acrylic column 2, a gas analyzer 5 communicated with the flux chamber 6 through a circulation pipeline, and a bubble barrier structure fixedly arranged in the middle of the acrylic column 2. Sediment 14 is filled below the filtering structure, and a water covering layer 13 is arranged above. An overflow port 15 is arranged on the side wall of the acrylic column 2 and is connected to a peristaltic pump 3 through the overflow port 15 and a pipeline. The output end of the peristaltic pump 3 is connected to a water-air balance device 4. The input end of the water-air balance device 4 is also connected to a gas supply tank 11 of inert gas, and the output end of the water-air balance device 4 is connected to the gas analyzer 5.

[0057] The material of the incubator 1 is PVC, with a length of 770 mm × a width of 515 mm × a height of 430 mm and a volume of 170 L. The height of the cultured sediment 14 is 15 cm, and the depth of the water covering layer 13 is 15 cm.

[0058] The acrylic column 2 is a customized 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 whole device is composed of two acrylic columns spliced together, with an open bottom for direct insertion into the sediment 14; the middle splicing part is composed of two upper and lower flange plates 22. Between the flange plates 22, there are rubber gaskets 24, silk screens 25, stainless steel screens 26, and rubber gaskets 24 from top to bottom in the middle, all of which are provided with twelve holes corresponding to each other and are spliced and fixed by twelve sets of bolts and nuts. The lower flange plate 22 is supported by twelve reinforcing ribs; at a position 10 cm above the middle part, an overflow port 15 for the overlying water layer 13 is opened, with a pore size of 1.2 cm, which is filled and assembled by a PU tube 8, a waterproof joint, and a three-way valve 7; at the top of the acrylic column 2, the acrylic cover plate 23 is provided with two air inlets 17 and air outlets 18 with pore sizes of 1.2 cm each, which are also filled and assembled by 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 upper flange plate of the acrylic column 2, with a rubber gasket 24 in the middle, all of which are provided with twelve holes corresponding to each other and are spliced and fixed by twelve sets of bolts and nuts to ensure the airtightness of the upper end of the device; twelve reinforcing ribs are added to the upper end of the acrylic column 2 to play a role in bearing and supporting when the overall height of the device is increased by splicing in the later stage.

[0059] The peristaltic pump 3 is of model LHZW002 - 10, with an inner tube of 4.8×8 BPT and an outer tube of 5×7 silicone, and a flow rate of 0.1 - 510 ml / min.

[0060] The gas analyzer 5 is a DLT - 100, with a model of 908 - 0010 - 0001.

[0061] The flux chamber 6 is made of PVC material, with a closed upper end and an open lower end, a diameter of 16 cm, and a height of 16 cm. The lid of the chamber is provided with three holes, and the middle hole is for leading wires to connect the power supply for the fan 16 inside the flux chamber. The two open ends are equipped with gas pipe joints and three-way valves to provide inlet and outlet ports.

[0062] The three-way valve 7 is a medical three-way stopcock.

[0063] The PU gas pipe 8 is a transparent pipe, and its maximum pressure resistance is 1.6 MPa.

[0064] The vacuum filter 9 is a ZFC - 100, with a pressure range of - 100 - 0 kPa.

[0065] The gas pipe joint 10 is of a straight-through type, and both sides can be connected to gas pipes with an outer diameter of 6 mm.

[0066] The gas supply tank 11 is a standard nitrogen gas tank, with a steel cylinder specification of 8 L and a filling pressure of 10 ± 0.5 Mpa.

[0067] The gas flowmeter 12 is of model AST10 - DLCMX, with a flow range of 500 SCCM.

[0068] As shown in Figure 6 Figure [ID]. The bubble barrier structure is a silk screen 25. The middle part of the acrylic column 2 is a splicing structure, including two butt-jointed flange plates 22. Two rubber gaskets 24 are arranged between the two flange plates 22. The bubble barrier structure is located between the two rubber gaskets 24.

[0069] The whole acrylic column 1 is spliced by two sections of acrylic columns. First, the water overflow port on the upper acrylic column is modified, and a three-way valve 7, a PU air pipe 8 and a waterproof joint are installed for it, and hot melt adhesive is welded on the inner and outer walls to ensure its sealing performance; then the two sections of acrylic columns are spliced, and the splicing sequence in the middle is as Figure 5 shown in Figure [ID]. Rubber gaskets 24 are installed on both the upper and lower parts to ensure the airtightness of the connection section and prevent the leakage of gas and liquid.

[0070] A stainless steel screen 26 is fixed below the silk screen 25 to prevent the silk screen from breaking. The silk screen 25 is tightly clamped in the middle to play a role in blocking the release of bubbles in the sediment.

[0071] As shown in Figure 1 and Figure 2 Figure [ID]. The flux box 6 is cylindrical. The top of the flux box 6 is a closed end. A hanging hook 20 is arranged on the top of the flux box 6. A string 19 connected to the hanging hook 20 passes through the acrylic cover plate 23 at the top end of the acrylic column 2. The top end of the string 19 is wound around a wooden stick 21 placed on the acrylic cover plate 23.

[0072] As shown in Figure 1 and Figure 2 Figure [ID]. A fan 16 is installed inside the top of the flux box 6. The fan 16 is powered by an external mobile power supply. An air inlet 17 and an air outlet 18 are opened on the top of the acrylic cover plate 23. PU air pipes 8 communicating with the flux box 6 are fixedly arranged inside the air inlet 17 and the air outlet 18, and a three-way valve 7 is arranged at the top end of the PU air pipe 8. The input end of the gas analyzer 5 is connected to the PU air pipe 8 inside the air outlet 18 through a pipeline, and the output end is connected to the PU air pipe 8 inside the air inlet 17 through a pipeline, and a vacuum filter 9 is installed on the pipeline at the input end of the gas analyzer 5.

[0073] As shown in Figure 7 Figure [ID]. The water-air balance device includes a support column and a gas exchange pipe. The support column is arranged vertically, and the gas exchange pipe is wound around the periphery of the support column. Syringes are connected to both ends of the gas exchange pipe. The output pipeline of the gas supply tank 11 is connected to an aeration head, and the aeration head is located in the syringe at the input end of the gas exchange pipe. The output end of the peristaltic pump 3 is connected to the syringe at the input end of the gas exchange pipe. The input end of the gas analyzer 5 is located in the syringe at the output end of the gas exchange pipe. A water collecting hopper is arranged below the drain port at the bottom end of the syringe at the output end of the gas exchange pipe.

[0074] The water-air balance device 4 is composed of a support column and a gas exchange pipe. 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 pipe is a PC transparent hose tightly wound around the periphery of the support column. The length of the trachea is controlled to be 6 m, and 100-ml syringes are connected to both ends respectively. The trachea and the water pipe are connected and tightly fixed with a rubber stopper. An aeration head is connected to the air inlet end to ensure full mixing of gas and liquid, and a receiving basin is used at the drainage port to collect the overlying water.

[0075] A gas flowmeter 12 is provided on the output pipeline of the gas supply tank 11.

[0076] Such as Figure 8 As shown, a method for using a device for identifying the relationship between sediment bubble methane and water body dissolved methane includes the following steps:

[0077] Step 1, preliminary exploration;

[0078] Use silk meshes 25 with different mesh numbers for blocking. A total of 5 groups of gradients are designed, namely no silk mesh, 50-mesh, 100-mesh, 500-mesh, and 900-mesh silk meshes. Each group has three parallel samples, and a blank control sample is added to each silk mesh group. There are a total of 19 sets of devices. Before cultivation, cover the modified stainless steel screen 26 on the sediment surface and evenly lay white gravel on it to ensure the uniform release of sediment bubbles. Then insert the 19 assembled sets of devices into the corresponding 5 groups of cultivation boxes 1 filled with sediment, connect water to the cultivation boxes 1 for cultivation, and close the three-way stopcock at the overflow port 15 after the water level of the overlying water layer 13 is stable; the top of the parallel group acrylic device is open and sealed with double layers of plastic wrap and a shower cap and then sealed with an acrylic cover 23. The top of the blank control group is open and sealed with double layers of plastic wrap and a shower cap and then tied tightly with a string to ensure the airtightness of the device, thus completing the device assembly and cultivation work.

[0079] S1.1. Explore the change law of the headspace methane release flux. First, dig out the black and odorous water body sediment into the cultivation box 1 for cultivation; control the depth of the sediment 14 in the 6 groups of cultivation boxes to be about 15 cm, set an overlying water layer 13 above the sediment 14, cover the modified stainless steel screen 26 on the sediment 14 surface and evenly lay white gravel on it before cultivation to ensure the uniform release of sediment bubbles. After obvious bubbles accumulate below the gas barrier structure, hang the flux box 6 at the top of the acrylic column 2 and ensure that the lower edge is completely immersed in the overlying water layer 13 in the acrylic column 2;

[0080] S1.2. Turn on the fan 16 so that the gas in the flux chamber 6 flows into the gas analyzer 5 through the circulation pipeline. Use the gas analyzer 5 to measure the change in the methane gas concentration in the headspace of the overlying water layer 13 in the flux chamber 6 for ten minutes continuously. Use this device to measure the methane gas release fluxes in the headspace of the overlying water of the 900, 500, 100, 50-mesh silk screens and the group without silk screen. From Figure 9 it can be seen that there are obvious gradient changes in the methane gas release fluxes in the headspace among different silk screen groups. Thus, it can be determined that the feasibility of this device is good.

[0081] Step 2. When the methane gas concentration in the headspace shows an obvious and stable gradient, use the peristaltic pump 3 to pump the water in the overlying water layer 13 cultured in the acrylic column 2 into the water-air equilibrium device 4. Use the gas supply tank 10 to input nitrogen into the water-air equilibrium device 4 to purge the pumped water and blow out the dissolved methane gas in it. Use another gas analyzer 5 to measure the concentration of the blown-out gas, thus completing the measurement of the dissolved methane concentration in the overlying water layer 13.

[0082] The methane concentration value in the overlying water layer 13 on the sediment 14 The calculation formula is:

[0083] According to Fick's law, the model estimation method is calculated as follows:

[0084] F = K ( )(1);

[0085] In the formula: F is the water-air interface diffusion flux, ;

[0086] is the original concentration of the greenhouse gas on the water surface;

[0087] The concentration when the greenhouse gas on the water surface reaches equilibrium with the greenhouse gas in the atmosphere at a specific temperature. Use the average concentration of the greenhouse gas in the atmosphere and the measured water temperature;

[0088] K is the gas exchange coefficient, cm / h, and its calculation formula is:

[0089] = ;

[0090] In the formula: is the gas exchange coefficient of sulfur hexafluoride, cm / h;

[0091] is the Schmidt number, is the Schmidt number 600 at 20 °C;

[0092] 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;

[0093] The Schmidt number calculation formula for methane gas in freshwater ecosystems is:

[0094] =1897.8 114.258t 3.2902 0.039061 ;

[0095] Where t is the water temperature;

[0096] =2.07+0.215× ;

[0097] In the formula is the wind speed 10m above the water surface (m / s). Just take 0;

[0098] 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:

[0099] F= (2);

[0100] Where: F is the greenhouse gas flux to be measured at the water-air interface, mmol / ( );

[0101] k is the slope of the greenhouse gas concentration in the flux box over time, ;

[0102] , are conversion coefficients, representing volume fractions ( )-mass concentration (mg / ) and the conversion factors between minutes and days;

[0103] V is the volume of air in the box when it is placed on the water surface. ;

[0104] A is the water surface area covered by the box, ;

[0105] M is the molar mass of the measured greenhouse gas, g / mol;

[0106] Combining the above two equations (1) and (2), the methane concentration in the water body above the sediment can be calculated: .

[0107] The dissolved methane concentration in the overlying water of different silk screen groups was estimated using the above calculation method to obtain Table 1;

[0108] Table 1 Estimation of dissolved methane concentration in the overlying water of different silk screen groups

[0109]

[0110] It can be observed from Table 1 that there are obvious gradient changes between groups. As the silk screen mesh number increases, the dissolved methane concentration value in the water gradually decreases, laying a foundation for demonstrating important conclusions such as "dissolved methane in water mainly comes from sediment bubble release" and that under the consideration of bubble methane release, the methane release flux in shallow water bodies is much greater than the diffusion release flux.

Claims

1. An apparatus for identifying the relationship between bubble methane in sediment and dissolved methane in water body, characterized in that: It includes an incubator (1), an acrylic column (2) fixed inside the incubator (1), a flux chamber (6) hoisted at the inner top of the acrylic column (2), a gas analyzer (5) connected to the flux chamber (6) through a circulation pipeline, and a bubble barrier structure fixedly arranged in the middle of the acrylic column (2). There is sediment (14) filled below the bubble barrier structure and an overlying water layer (13) arranged above. An overflow port (15) is arranged on the side wall of the acrylic column (2) and is connected to a peristaltic pump (3) through the overflow port (15) and a pipeline. The output end of the peristaltic pump (3) is connected to a water-air balance device (4). The input end of the water-air balance device (4) is also connected to a gas supply tank (11) of inert gas. The output end of the water-air balance device (4) is connected to the gas analyzer (5). A fan (16) is installed at the inner top of the flux chamber (6), and the fan (16) is powered by an external mobile power supply.

2. The device for identifying the relationship between bubble methane and dissolved methane in water body according to claim 1, wherein: The bubble barrier structure is a silk mesh (25). The middle part of the acrylic column (2) is a splicing structure, including two butt-jointed flange plates (22). Two rubber gaskets (24) are arranged between the two flange plates (22). The bubble barrier structure is located between the two rubber gaskets (24).

3. The device for identifying the relationship between bubble methane in sediment and dissolved methane in water body according to claim 2, characterized in that: A stainless steel screen (26) is arranged at the bottom of the silk mesh (25).

4. The device for identifying the relationship between bubble methane and dissolved methane in water body according to claim 2, wherein: Reinforcing ribs are arranged at the connection between the acrylic column (2) and the flange plate (22), and the reinforcing ribs are evenly arranged around the acrylic column (2).

5. The device for identifying the relationship between bubble methane in sediment and dissolved methane in water body according to claim 1, characterized in that: The flux chamber (6) is cylindrical. The top of the flux chamber (6) is a closed end. A hanging hook (20) is arranged at the top of the flux chamber (6). A string (19) connected to the hanging hook (20) passes through the acrylic cover plate (23) at the top end of the acrylic column (2), and the top end of the string (19) is wound around a wooden stick (21) placed on the acrylic cover plate (23).

6. The device for identifying the relationship between bubble methane in sediment and dissolved methane in water body according to claim 5, wherein: An air inlet (17) and an air outlet (18) are arranged at the top of the flux chamber (6). PU air pipes (8) communicating with the flux chamber (6) are fixedly arranged inside the air inlet (17) and the air outlet (18). A three-way valve (7) is arranged at the top end of the PU air pipe (8). The input end of the gas analyzer (5) is connected to the PU air pipe (8) inside the air outlet (18) through a pipeline, and the output end is connected to the PU air pipe (8) inside the air inlet (17) through a pipeline. A vacuum filter (9) is installed on the pipeline at the input end of the gas analyzer (5).

7. The device for identifying the relationship between bubble methane in sediment and dissolved methane in water body according to claim 1, wherein: The water-air balance device includes a support column and a gas exchange pipe. The support column is arranged vertically, and the gas exchange pipe is wound around the periphery of the support column. Syringes are connected to both ends of the gas exchange pipe. The output pipeline of the gas supply tank (11) is connected to an aeration head, and the aeration head is located in the syringe at the input end of the gas exchange pipe. The output end of the peristaltic pump (3) is connected to the syringe at the input end of the gas exchange pipe. The input end of the gas analyzer (5) is located in the syringe at the output end of the gas exchange pipe. A water collecting hopper is arranged below the drainage port at the bottom end of the syringe at the output end of the gas exchange pipe.

8. The device for identifying the relationship between bubble methane in sediment and dissolved methane in water body according to claim 1, wherein: A gas flow meter (12) is arranged on the output pipeline of the gas supply tank (11).

9. The method of using a device for identifying the relationship between bubble methane in sediment and dissolved methane in water body according to claim 1, characterized in that, It includes the following steps: Step 1: Preliminary exploration; S1.

1. Explore the variation law of the headspace methane emission flux. Spread sediments (14) evenly on the bottom inside the incubator (1), set a water layer (13) above the sediments (14). After obvious bubbles accumulate below the gas barrier structure, hang the flux chamber at the top of the acrylic column and ensure that the lower edge is completely immersed in the water layer inside the acrylic column. S1.

2. Turn on the fan (16) so that the gas inside the flux chamber 6 flows into the gas analyzer (5) through the circulation pipeline. Use the gas analyzer (5) to measure the change in the concentration of methane gas in the headspace of the water layer (13) inside the flux chamber (6) for ten minutes continuously. Step 2. Accurately measure. When an obvious and stable gradient appears in the concentration of the headspace methane gas, use the peristaltic pump (3) to pump the water in the water layer (13) cultured in the acrylic column (2) into the water-air equilibrium device (4). Input nitrogen into the water-air equilibrium device (4) using the gas supply tank (11) to purge the pumped water and blow out the dissolved methane gas in it. Use the gas analyzer (5) to measure the concentration of the purged gas, thus completing the measurement of the dissolved methane concentration in the water layer (13).

10. The method of using the device for identifying the relationship between bubble methane in sediment and dissolved methane in water body as claimed in claim 9, characterized in that, The methane concentration value in the overlying water layer (13) of the sediment (14) is calculated by the formula: According to Fick's law, the model estimation method is calculated as follows: F = K ( )(1); Where: F is the diffusion flux at the water-air interface, ; is the original concentration of greenhouse gases at the water surface; The concentration when the greenhouse gases on the water surface reach equilibrium with the greenhouse gases in the atmosphere at a specific temperature, using the average concentration of greenhouse gases in the atmosphere and the measured water temperature; K is the gas exchange coefficient, cm / h, and its calculation formula is: = ； In the formula: is the gas exchange coefficient of sulfur hexafluoride, cm / h; is the Schmidt number, which is 600 at 20 °C; n is the wind speed coefficient, taking 0.67 when the wind speed is less than 3.7 m / s and taking 0.5 when it is greater than 3.7 m / s. The calculation formula for the Schmidt number of methane gas in the freshwater aquatic ecosystem: =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 (m / s) 10 m above the water surface. For this test it can be taken as 0; When using the flux chamber method to measure the greenhouse gas emission flux at the water-air interface, calculate according to the following formula: F= （2）； Where: F is the gas flux of the greenhouse gas to be measured at the water-air interface, mmol / ( ); k is the slope of the change in greenhouse gas concentration in the flux chamber over time, ; , is the conversion coefficient, representing respectively the conversion coefficient of volume fraction ( ) - mass concentration (mg / ), and the conversion coefficient between minutes and days; V is the volume of the air inside the box when the box is placed on the water surface, ; A is the water surface area covered by the box body, ; 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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