A method for determining and distinguishing between methane ebullition flux and diffusion flux from a body of water

Abstract

The application discloses a method for determining and distinguishing methane bubble flux and diffusion flux released by water bodies, and belongs to the field of methane flux determination in environmental water bodies, and comprises the following steps: determining the gas content of CH4 and N2O in the gas after the water body at a sampling point and surrounding atmosphere are shaken together and in the surrounding atmosphere of the water body at the sampling point, calculating the gas concentration of CH4 and N2O in the water body when the water body and the surrounding atmosphere are balanced and in the water body at the actual sampling point; determining the release flux of N2O and the total release flux of CH4 in the water body; calculating and comparing the gas mass transfer coefficients of diffusion type CH4 and total CH4; and calculating the CH4 diffusion and bubble flux. The application utilizes N2O to calculate the CH4 diffusion flux, realizes the rapid distinction of bubble type and diffusion type CH4 of water bodies, can collect and determine CH4 gas on a large scale in multiple environments, and solves the problems that CH4 determination is easily affected by the environment, time-consuming is relatively long, and it is difficult to capture occasional bubble events.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of methane flux determination in water body, and particularly relates to a method for determining and distinguishing bubble flux and diffusion flux of methane released by water body. BACKGROUND

[0002] Methane (CH4) is the second largest greenhouse gas after carbon dioxide (CO2), and aquatic ecosystems are one of the important sources of CH4 emission. Therefore, CH4 emission from water body has been the focus of research.

[0003] In aquatic ecosystems, CH4 is mainly produced by methanogenic bacteria using acetate or CO2 / H2 as substrate through fermentation. The emission pathways of CH4 in water body include diffusion and bubble. Diffusion type CH4 exists in dissolved molecular form and is easily oxidized and consumed during water transport. For example, about 80% of the diffusion type CH4 is oxidized in the Amazon floodplain lakes. Bubble type CH4 moves faster in water and is less oxidized. In some nutrient-rich, shallow, and anaerobic water bodies, bubble type CH4 emission flux is high, accounting for 50% - 90% of the total CH4 emission flux. Therefore, the emission pathway of CH4 has an important influence on the total emission flux, and it is necessary to distinguish and determine the two types of CH4.

[0004] At present, static chamber method is one of the common methods for determining diffusion type CH4 in water body. This method forms a closed space by setting a gas-tight chamber on the water-air interface, and analyzes the gas emission flux by determining the linear change rate of gas content in the chamber over time. However, in actual determination process, the static chamber method is often disturbed by bubble type CH4, and the gas content in the chamber is difficult to change linearly over time, which affects the calculation of diffusion type CH4 flux. The commonly used method for determining bubble type CH4 is inverted funnel method. This method uses funnel-shaped device inverted under water surface to capture CH4 bubbles, and estimates bubble type CH4 flux by recording the captured CH4 volume and determining its concentration. However, inverted funnel method takes a long time, usually several weeks or even longer, which limits the determination of multiple points, and it is difficult to capture occasional bubble events. In order to solve this problem, a method is needed that can quickly distinguish and determine bubble type and diffusion type CH4 at the same time. SUMMARY

[0005] Invention purposes: In view of the problems existing in the prior art, the present application provides a method for simultaneously and rapidly distinguishing and measuring the bubble type and diffusion type CH4 release flux of water body. The present application calculates the diffusion type CH4 flux by using N2O, realizes the rapid distinction of the bubble type and diffusion type CH4 of water body, helps large-scale collection and measurement of CH4 gas in multiple environments, and provides valuable method support for the measurement of CH4 emission of aquatic ecological system. The problems that the current technology is easily affected by the environment, time-consuming, and difficult to capture occasional bubble events are solved.

[0006] Technical scheme: In order to achieve the above-mentioned purposes, the method for measuring and distinguishing the bubble type and diffusion type CH4 release flux of water body comprises the following steps:

[0007] (1) measuring the gas content of CH4 and N2O in the gas balanced between the water body of the sampling point and the surrounding atmosphere 、 , calculating the gas concentration 、 ; measuring the gas content of CH4 and N2O in the atmosphere surrounding the sampling point water body 、 , calculating the gas concentration , ; calculating the dissolved gas concentration of CH4 and N2O in the sampling point water body and , and the dissolved gas concentration of CH4 and N2O in the water when the atmosphere and the surface water body are balanced and ;

[0008] (2) measuring the release flux of N2O and the total release flux of CH4 in the water body;

[0009] (3) using 、 、 、 、 、 , based on the thin boundary layer model, the gas mass transfer coefficient of N2O and CH4 in the water body and are calculated, according to the stable proportional relationship of the mass transfer coefficients of different diffusion gases in the same water-gas interface, the gas mass transfer coefficient of the diffusion type CH4 is calculated by using , and the CH4 diffusion flux is calculated by using 、 and ;

[0010] (4) and If , then there is bubbling CH4 in the water body, and the CH4 bubbling flux is equal to the total CH4 release flux minus the CH4 diffusion flux ; if , then there is no bubbling, and the CH4 diffusion flux is equal to the total CH4 release flux .

[0011] wherein the gas content in step (1) , is determined by the oscillation equilibrium method, 20 ml of surface water sample is collected by a 50 ml syringe with a three-way valve, 20 ml of ambient air (preferably overhead air) is then sucked, the three-way valve is closed, and the syringe is shaken to balance the water and ambient air. After standing, the gas is injected into a vacuum headspace bottle for preservation, and the CH4 and N2O gas contents in the balanced gas of the water body and ambient air at the sampling point are analyzed by a gas chromatograph , The ambient air sample (preferably overhead air) around the water body at the sampling point is collected by a syringe with a three-way valve, injected into a vacuum headspace bottle, and the CH4 and N2O gas contents in the ambient air around the water body at the sampling point are analyzed by a gas chromatograph , ;

[0012] , According to the ideal gas state equation, it is calculated by formula (1):

[0013]

[0014] wherein C h represents or , with a unit of 10 -6 mol L -1 ; c h represents or , with a unit of 10 -6 mol mol -1 (volumetric fraction unit ppm = 10 -6 mol / mol), T is the water temperature, with a unit of K;

[0015] , According to the ideal gas state equation, it is calculated by formula (2):

[0016]

[0017] Wherein C 0 represents or , unit is 10 -6 mol L -1 ; c 0 represents or , unit is 10 -6 mol mol -1 ; T Water temperature, unit is K;

[0018] And It is calculated by formula (3):

[0019]

[0020] Wherein C w represents or , unit is 10 -6 mol L -1 ; C h represents or , unit is 10 -6 mol L -1 ; C 0 represents or , unit is 10 -6 mol L -1 ; V h And V w The volume of gas and water in the syringe of the oscillation equilibrium method, both are equal volume, unit is L; β The Bunsen coefficient, for CH4, N2O is 0.03211, 0.6221 respectively;

[0021] And It is calculated by formula (4) using Henry's law:

[0022] (4)

[0023] Wherein C eq represents or , in units of 10 -6 mol L -1 ; P A denotes the partial pressure of CH4or N20 in the atmosphere, numerically equal to or ;

[0024] wherein, P A in units of atm; K H is the Henry's coefficient, in units of mol L -1 atm -1 whose value is determined according to the actual water temperature, as shown in equation (5):

[0025]

[0026] wherein, is the standard Henry's coefficient, for CH4, N20 respectively: 0.0014, 0.025, in units of mol L -1 atm -1 ; K T is the constant of temperature, for CH4, N20 respectively: 1600, 2600, in units of K; T is the water temperature, in units of K; T θ is the standard temperature, 298 K.

[0027] wherein, the said and are determined by static chamber method. Before sampling, the static chamber is placed vertically on the water surface for 2 min to avoid the influence of water surface disturbance. After 50 ml plastic syringe is used to suck the gas in the chamber for three times, 20 ml gas is extracted at 0, 5, 10, 15, 20, 30, 60 min time points, and is transferred into a vacuum headspace bottle, which is stored at room temperature in dark. Gas chromatograph is used to analyze the gas content of CH4, N20 in the static chamber and , in units of 10 -6 molmol -1 , and the wind speed and in-situ water temperature on the water surface are measured simultaneously.

[0028] The static box is used to collect the gas produced by the water body. The static box is a cylindrical chamber for storing the greenhouse gas produced by the water body. The upper part of the static box is sealed, and a small opening is formed in the center for connecting an air outlet connector. A soft tube is connected to the air outlet connector at one end and connected to a three-way valve at the other end. When collecting gas, a syringe is connected to the three-way valve to collect the gas. The lower end of the static box is designed as an opening. The gas enters the chamber from the bottom. The outer side of the box is provided with an annular baffle for fixing the floating ring. The surface of the static box is covered with aluminum foil.

[0029] The static box is placed on the water surface. The water body enters the chamber, so that the water surface in the chamber is higher than the water surface outside. The actual gas capture chamber volume of the static box accounts for 2 / 5-4 / 5 of the total volume.

[0030] In step (2), the release flux of N2O in the water body is measured and the total release flux of CH4 is measured According to formula (6):

[0031]

[0032] Wherein F represents or , unit: mol m -2 d -1 ; t is the sampling time, unit: min; 1440 is the number of minutes in a day; A is the bottom area of the static box, unit: m 2 ; n t and n 0 is the number of moles of CH4 or N2O gas in the static box at the end and beginning of sampling, unit: mol;

[0033] According to the ideal gas state equation: PV = nRT , formula (6) is converted into formula (7):

[0034]

[0035] Wherein, the partial pressure of gas in the static box P is represented by the gas content of CH4, N2O in the static box or , formula (7) is converted into formula (8):

[0036]

[0037] Wherein, F represents or The unit is mol m -2 d -1 ; c express or The unit is 10 -6 mol mol -1 ; V This refers to the static headspace volume of the enclosure, in meters (m³). 3 ; T Water temperature, in Kelvin (K). R The gas constant is 8.314 m. 3 Pa K -1 mol -1 101325 is one standard atmosphere; in calculations hour, This represents the slope of the change in CH4 gas content within the chamber from the start (0 min) to the end (60 min) of each sampling period; calculation When sampling was performed at seven time points (0, 5, 10, 15, 20, 30, and 60 minutes), the linear fit of the N2O gas content in the chamber over time was the best, and the fitted line... r 2 For time periods greater than 0.95, The linear regression slope of the N2O gas content in the chamber over time ( ) r 2 > 0.95).

[0038] In step (3), based on the stable proportional relationship of the mass transfer coefficients of different diffusing gases at the same water-gas interface, the following steps are taken: Calculated The calculation process is as shown in formulas (9) and (10):

[0039]

[0040]

[0041] In the formula, and These are the Schmitt numbers for CH4 and N2O; n It is the Schmidt number index, which is used when the wind speed is > 3.6 m / s. -1 hour n It is 1 / 2, and the wind speed is < 3.6 m / s. -1 hour n 2 / 3; wind speed was measured in situ at the sampling point;

[0042] and Calculated using formulas (11) and (12):

[0043] (11)

[0044] (12)

[0045] In the formula, T is water temperature, unit: ℃; the water temperature is measured in situ at the sampling point;

[0046] Calculated by formula (13):

[0047]

[0048] Based on the TBL model, Calculated by formula (14):

[0049] In the formula, J is the CH4 diffusion flux of water-gas interface, unit: mol m -2 d -1 ; K is the gas mass transfer coefficient of diffusive CH4, unit: m d -1 ; C is the dissolved gas concentration of CH4 in water body at the sampling point, unit: 10 -6 mol L -1 ; C is the dissolved gas concentration of CH4 in water when the atmosphere and surface water are in equilibrium, unit: 10 -6 mol L -1 .

[0050] Wherein, if step (4) > , there is bubbling CH4 in the water body, and the bubbling CH4 flux is calculated by formula (15):

[0051] (15)

[0052] CH4 diffusion flux is equal to the value calculated in formula (14);

[0053] If < , there is no bubbling:

[0054] .

[0055] The method combines the static chamber method with the thin boundary layer model, and uses the water body release N2O flux to calibrate the CH4 diffusion flux to determine and distinguish the application of the water body release bubbling methane flux and the diffusive methane flux.

[0056] The present application firstly proposes a method of combining static chamber method with thin boundary layer model to distinguish between bubble and diffusion CH4 in water body by using N2O flux to calibrate CH4 diffusion flux. The method of the present application shows high success rate and accuracy in the presence of large aquatic plants during the day, in the absence of large aquatic plants during the day and at night, and is less affected by the photosynthesis of aquatic plants, showing good stability and less affected by the water environment. The method provided by the present application has great potential in distinguishing between the two CH4 fluxes in various water environments.

[0057] Meanwhile, the present application adopts specific sampling time points to more comprehensively record the dynamic changes of gas content. This high-frequency sampling strategy is particularly suitable for capturing the rapid changes of gas content at the initial stage of static chamber placement, thereby improving the accuracy and reliability of calibration to ensure that the changes of gas content at different stages can be captured, thereby improving the accuracy and scientificity of calibration.

[0058] The method of the present application has the following effects:

[0059] Accurate quantification of CH4 emission pathways: The present method can simultaneously quantify the diffusion and bubble emission pathways of CH4. This is of great significance for a comprehensive understanding of the emission characteristics and mechanisms of CH4 in water ecological systems, and helps to more accurately assess the contribution of CH4 to the greenhouse effect, and provides a scientific basis for developing emission reduction strategies.

[0060] Improved measurement efficiency: Compared with the traditional method of separately measuring diffusion and bubble CH4, the present method can simultaneously complete the measurement of the two emission modes in a shorter time, which greatly improves the measurement efficiency, making it possible to conduct high-frequency measurements at multiple sampling points, thereby enabling a more comprehensive understanding of the temporal and spatial variation characteristics of CH4 emission.

[0061] Providing technical support for automated monitoring: Based on the research results of the present method, an automatic monitoring system can be developed to realize long-term, continuous and automatic monitoring of CH4 emission, reducing the error and labor intensity of manual operation, and improving the accuracy and reliability of monitoring data. This plays an important role in long-term monitoring of the dynamic changes of CH4 emission in water ecological systems and evaluating the impact of environmental changes on CH4 emission.

[0062] Reducing environmental interference: Since the N2O method is not affected by factors such as photosynthesis of aquatic plants, it can more truly reflect the emission of CH4. This helps to improve the understanding of the emission process of CH4 in water ecological systems, avoid measurement errors and misunderstandings caused by environmental interference, and provide more accurate data support for in-depth study of the biogeochemical cycle of CH4.

[0063] Promote related research and application: The successful application of this method provides a new idea and tool for the study of CH4 emission in aquatic ecosystems. It will promote the research progress in related fields, promote the in-depth understanding of the mechanism of CH4 emission, and also provide strong technical support for environmental monitoring, climate change assessment and greenhouse gas emission reduction.

[0064] Advantages: Compared with the prior art, the present application has the following advantages:

[0065] High success rate: Through 120 tests, the success rate of the N2O method based on the present application reached 99.2%, while the success rate of the traditional CO2-based method was only 66.7%. This shows that the method of the present application can stably measure under various environmental conditions, and is not affected by interference factors such as photosynthesis of aquatic plants, thereby significantly improving the reliability of the measurement.

[0066] High accuracy: The linear fitting slope of the CH4 diffusion flux calibration value calculated by the N2O method based on the present application and the measured value is 0.87 ± 0.06 mol m -2 d -1 , the determination coefficient ( r 2 ) is 0.62, p < 0.0001. It shows high accuracy. In contrast, the linear fitting slope of the CH4 diffusion flux calibration value calculated by the CO2 calibration method and the measured value is 0.30 ± 0.36 mol m -2 d -1 , the determination coefficient ( r 2 ) is 0.01, and the p value is 0.4, indicating that the correlation between the calculated value and the measured value is poor, and the accuracy is low. This shows that the method of the present application can more accurately calibrate the emission flux of diffusive CH4.

[0067] Strong stability: Under different environmental conditions, the performance of the N2O method is relatively stable. Even in the presence of aquatic plants during the day, the accuracy of the N2O method of the present application is significantly better than that of the CO2 method. This makes the method applicable to a variety of complex water environments, providing strong support for long-term monitoring and research of CH4 emission.

[0068] Based on the proportional relationship of gas transfer coefficients: The method of the present application utilizes the proportional relationship between the transfer coefficients of different gases at the same water-air interface, and estimates the gas transfer coefficient of CH4 by measuring the gas transfer coefficient of N2O. This method based on the proportional relationship has a theoretical basis and can avoid the difficulties encountered in directly measuring the gas transfer coefficient of CH4, such as large measurement error, complex equipment requirements, etc.

[0069] Simple operation: the method of the present application combines static chamber method and thin boundary layer model, and the N2O emission flux generated by the water body is measured to calibrate the CH4 diffusion flux, without the need of complex equipment and cumbersome operation steps. This makes the method more convenient and fast in practical application, reduces the measurement cost and workload, and is conducive to the popularization and application in more research and monitoring projects.

[0070] Wide range of applications: the method of the present application is not only suitable for single water body ecological system, but also can be used for CH4 emission measurement of various types of water bodies. For example, rivers, lakes, reservoirs and other different types of water bodies will release both diffusion and bubbling CH4, and the method is expected to provide an effective measurement means for CH4 emission research in these environments. BRIEF DESCRIPTION OF DRAWINGS

[0071] Figure 1 It is a structural schematic diagram of the sampling device static chamber, in which 1 is a gas outlet joint, 2 is a hose, 3 is a three-way valve, 4 is a chamber, 4-1 is a first aluminum foil, 5 is an annular baffle, 5-1 is a second aluminum foil, and 6 is a float.

[0072] Figure 2 It is a comparison between the CH4 diffusion flux calibration value calculated by the CO2 calibration method and the N2O calibration method and the CH4 diffusion flux measured value in the pond environment with aquatic plants and without aquatic plants in the whole day.

[0073] Figure 3 It is a comparison between the CH4 diffusion flux calibration value calculated by the CO2 calibration method and the N2O calibration method and the CH4 diffusion flux measured value in the pond environment with aquatic plants in the daytime.

[0074] Figure 4 It is a comparison between the CH4 diffusion flux calibration value calculated by the CO2 calibration method and the N2O calibration method and the CH4 diffusion flux measured value in the pond environment without aquatic plants in the daytime.

[0075] Figure 5 It is a comparison between the CH4 diffusion flux calibration value calculated by the CO2 calibration method and the N2O calibration method and the CH4 diffusion flux measured value in the pond environment with aquatic plants and without aquatic plants in the night environment.

[0076] Figure 6 It is a comparison between the CH4 diffusion flux calibration value calculated by the N2O calibration method and the CH4 diffusion flux measured value in the lake environment in the daytime.

[0077] Figure 7 It is a comparison between the CH4 diffusion flux calibration value calculated by the N2O calibration method and the CH4 diffusion flux measured value in the reservoir environment in the daytime. DETAILED DESCRIPTION

[0078] The application will be further described below in conjunction with the accompanying drawings and examples. The experimental methods described in the examples are all conventional methods unless otherwise specified; the materials described are all commercially available unless otherwise specified.

[0079] Example 1

[0080] As shown in Figure 1 , a static chamber is used to capture the water body generated gas, and the static chamber body is a cylindrical chamber for storing greenhouse gases generated by the water body. The chamber volume is 13.6L, the bottom area is 4.52dm 2 , the upper part is sealed and a small hole is opened in the center for connecting a gas outlet connector 1 with a length of 24.5mm and an outer diameter of 8mm. A 25cm long, 5mm outer diameter, 3mm inner diameter PVC hose 2 is connected to the gas outlet connector 1, and the other end is connected to a three-way valve 3. When collecting gas, a syringe is connected to the three-way valve 3 to collect gas. The entire lower end of the static chamber is designed as an open design, and the gas enters the chamber 4 from the lower bottom. An annular baffle 5 with a diameter of 12cm is installed 18cm from the top of the chamber body to fix the inner filling of polyurethane foam floating ring 6, so that the static chamber can stably float on the water surface. The surface of each static chamber is also covered with a first aluminum foil 4-1 and a second aluminum foil 5-1 to reflect sunlight and minimize internal heating. Since the static chamber is placed on the water surface, the water body will enter the chamber, so that the water surface in the chamber is higher than the outside water surface. Therefore, the actual gas capture chamber volume of the static chamber is 18 / 30 of the total volume.

[0081] Example 2

[0082] The experiment was conducted in the campus pond of Nanjing University of Information Engineering in China from March to November 2024. The pond is divided into two areas: one area has large aquatic plants, and the other area does not have large aquatic plants. This experiment randomly selects sampling points in these two pond areas during the day and at night for sampling. Daytime sampling is conducted between 9:00 am and 5:00 pm to cover the period of strongest light to evaluate the effect of plant photosynthesis on calibration. Night sampling is conducted between 7:00 pm and 10:00 pm to evaluate the effect of calibration after plant photosynthesis stops at night. In order to ensure the independence of the sampling points, the two sampling points are at least one meter apart.

[0083] 1. C w and C eq calculation

[0084] , The gas content of CH4 and N2O in the water and the surrounding atmosphere at the sampling point was measured by the method of shaking balance. 20 ml of surface water was collected using a 50 ml syringe with a three-way valve, and 20 ml of the surrounding atmosphere (headspace air) was also collected. After shaking the syringe for 1 min to balance the water and headspace air, the headspace air was injected into a 12 ml evacuated headspace vial (839W, labco Exetainer® Vial, UK) and stored. The gas content of CH4 and N2O in the vial was analyzed by gas chromatography , The gas content of CH4 and N2O in the water and the surrounding atmosphere at the sampling point was measured by the method of shaking balance. 20 ml of surface water was collected using a 50 ml syringe with a three-way valve, and 20 ml of the surrounding atmosphere (headspace air) was also collected. After shaking the syringe for 1 min to balance the water and headspace air, the headspace air was injected into a 12 ml evacuated headspace vial (839W, labco Exetainer® Vial, UK) and stored. The gas content of CH4 and N2O in the vial was analyzed by gas chromatography , .

[0085] , According to the ideal gas equation of state, formula (1) was used to calculate:

[0086]

[0087] wherein C h represents or , the gas concentration of CH4 and N2O in the water and the surrounding atmosphere at the sampling point, with a unit of 10 -6 mol L -1 ; c h represents or , with a unit of 10 -6 mol mol -1 ; T is the water temperature, with a unit of K;

[0088] , According to the ideal gas equation of state, formula (2) was used to calculate:

[0089]

[0090] wherein C 0 represents or , the gas concentration of CH4 and N2O in the water and the surrounding atmosphere at the sampling point, with a unit of 10 -6mol L -1 ; c 0 represents or , unit is 10 -6 mol mol -1 ; T is water temperature, unit is K;

[0091] and calculated by formula (3):

[0092]

[0093] wherein C w represents or , unit is 10 -6 mol L -1 ; C h represents or , unit is 10 -6 mol L -1 ; C 0 represents or , unit is 10 -6 mol L -1 ; V h and V w is the volume of headspace gas and water in the syringe of the oscillation equilibrium method, both are equal volume, unit is L; β is the Bunsen coefficient, for CH4, N2O is 0.03211, 0.6221 respectively;

[0094] and according to the gas concentration in the atmosphere around the sampling point water body, using Henry law calculated by formula (4):

[0095] (4)

[0096] wherein C eq represents or , unit is 10 -6 mol L -1 ; P Arepresents the partial pressure of CH4or N20 in the atmosphere, numerically equal to or ;

[0097] wherein P A in atm; K H is the Henry’s coefficient, in mol L -1 atm -1 whose value is determined according to the actual water temperature, as shown in equation (5):

[0098]

[0099] wherein is the standard Henry’s coefficient, equal to 0.0014 and 0.025 for CH4and N20, respectively, in mol L -1 atm -1 ; K T is a constant for the temperature, equal to 1600 and 2600 for CH4and N20, respectively, in K; T is the water temperature, in K; T θ is the temperature at standard conditions, 298 K.

[0100] 2. Calculation , and the measured values of CH4diffusion flux

[0101] 2.1 Collection and analysis of the gases

[0102] The static chamber sampling of Example 1 was used. CH4and N20 released by the water body were trapped using the static chamber. Before sampling, the static chamber was placed vertically on the water surface for 2 min to avoid the influence of water surface disturbance. After the gas in the chamber was mixed and aspirated three times with a 50 ml plastic syringe, 20 ml of gas was extracted at 0, 5, 10, 15, 20, 30 and 60 min, and was filled into a 12 ml headspace bottle (839W, labco Exetainer® Vial, UK) under vacuum, which was stored at room temperature in the dark. The gas content of CH4and N20 in the static chamber was analyzed using a gas chromatograph (7890B, Agilent Technologies, USA) and The water temperature was measured in situ using a portable pH meter (PHBJ-260, Shanghai Yilian Scientific Instrument Co., Ltd., China).

[0103] 2.2 Determination of the N20 release flux from the water body Total flux of CH4 release According to equation (6):

[0104]

[0105] Wherein F represents or or the measured value of CH4 diffusion flux. The unit is mol m -2 d -1 ; t is the sampling time, the unit is min; 1440 is the number of minutes contained in a day; A is the bottom area of the static chamber, the unit is m 2 ; n t and n 0 is the number of moles of CH4 or N2O gas in the static chamber at the end and beginning of sampling (0, 5, 10, 15, 20, 30, 60 min, 7 time points), the unit is mol;

[0106] According to the ideal gas equation of state: PV = nRT , equation (6) is converted to equation (7):

[0107]

[0108] Wherein, the partial pressure of gas in the static chamber P is represented by the gas content of CH4, N2O in the static chamber or , equation (7) is converted to equation (8):

[0109]

[0110] Wherein F represents or or the measured value of CH4 diffusion flux, the unit is mol m -2 d -1 ; c represents or , the unit is 10 -6 mol mol -1 . In the formula, V is the headspace volume of the static chamber, the unit is m 3 ; A is the bottom area of the static chamber, the unit is m 2 ; T is the water temperature, the unit is K; R is the gas constant, 8.314 m 3Pa K -1 mol -1 101325 is one standard atmosphere; in calculations hour, This represents the slope of the change in CH4 content within the chamber from the start (0 min) to the end (60 min) of each sampling period; calculation When sampling was performed at seven time points (0, 5, 10, 15, 20, 30, and 60 minutes), the linear fit of the N2O gas content in the chamber over time was the best, and the fitted line... r 2 For time periods greater than 0.95, The linear regression slope of the N2O gas content in the chamber over time ( ) r 2 > 0.95); when calculating the measured CH4 diffusion flux, the difference between the calculated and the actual values ​​is as follows: At the same time, sampling times of 0, 5, 10, 15, 20, 30, and 60 minutes were selected. The linear fit of the CH4 gas content in the chamber over time was the best, and the fitted line... r 2 For time periods greater than 0.95, The linear regression slope of the CH4 gas content in the chamber over time ( r 2 > 0.95).

[0111] 3. Calculation and Comparison:

[0112] use Calculated The calculation process is as shown in formulas (9) and (10):

[0113]

[0114]

[0115] In the formula, To calculate the gas mass transfer coefficient of N2O in water based on the thin boundary layer model, and These are the Schmitt numbers for CH4 and N2O; n It is the Schmidt number index, which is used when the wind speed is > 3.6 m / s. -1 hour n It is 1 / 2, and the wind speed is < 3.6 m / s. -1 hour n The wind speed was 2 / 3; the wind speed was measured in situ using a portable anemometer (Testo 480, Testo AG, Germany).

[0116] and Calculated from equation (11) and equation (12):

[0117] (11)

[0118] (12)

[0119] where T is water temperature in °C. Measured in situ by a portable pH meter (PHBJ-260, Shanghai Instrumentation & Electronics Scientific Instruments Co., Ltd., China);

[0120] Calculated from equation (13), is the gas mass transfer coefficient of CH4 in water calculated based on the thin boundary layer model:

[0121]

[0122] Based on the TBL model, calculated from equation (14):

[0123] where, is the CH4 diffusion flux at the water-air interface in mol m -2 d -1 ; is the gas mass transfer coefficient of diffusive CH4 in m d -1 ; is the dissolved gas concentration of CH4 in water at the sampling point in 10 -6 mol L -1 ; is the dissolved gas concentration of CH4 in water when the atmosphere and surface water are in equilibrium in 10 -6 mol L -1 ;

[0124] If > , then there is bubbling CH4 in the water, and the flux of bubbling CH4 is calculated from equation (15):

[0125] (15)

[0126] The CH4 diffusion flux is equal to the calculated value in equation (14);

[0127] If < , then there is no bubbling:

[0128] .

[0129] Example 3

[0130] The experiment was conducted in Meiliang Bay of West Taihu Lake in Wuxi City, Jiangsu Province and East Taihu Lake in Suzhou City, Jiangsu Province, China from April 2024 to January 2025. Meiliang Bay is a lake area without large aquatic plants, while East Taihu Lake is a lake area with large aquatic plants. Sampling was conducted between 9:00 am and 5:00 pm to cover the period of strongest light to evaluate the impact of plant photosynthesis on calibration. To ensure the independence of sampling points, a distance of more than 5 km was set between each sampling point.

[0131] 1. C w and C eq Calculation of

[0132] According to the method in step 1 of Example 2.

[0133] 2. Calculation of , and measured CH4 diffusion flux

[0134] According to the method in step 2 of Example 2.

[0135] 3. Calculation of and Comparison

[0136] According to the method in step 3 of Example 2.

[0137] Example 4

[0138] The experiment was conducted in Liuchuan County, Heyuan City, Guangdong Province, China in August and December 2024. Seven reservoirs in the basin were selected for sampling, with few large aquatic plants in the reservoirs. Sampling was conducted between 9:00 am and 5:00 pm to cover the period of strongest light to evaluate the impact of plant photosynthesis on calibration. To ensure the independence of sampling points, a distance of more than 1 km was set between each sampling point.

[0139] 1. C w and C eq Calculation of

[0140] According to the method in step 1 of Example 2.

[0141] 2. Calculation of , and measured CH4 diffusion flux

[0142] According to the method in step 2 of Example 2.

[0143] 3. Calculation and Comparison

[0144] By the method in step 3 in Example 2.

[0145] Comparative Example 1

[0146] Comparative Example 1 was determined by the method of Example 2, except that the water body CH4diffusion flux was calibrated by the CO2release flux, so as to distinguish the water body CH4diffusion and bubbling flux, and the specific process was as follows:

[0147] The experiment was carried out in the pond of Nanjing University of Information Engineering in China from March to November 2024. The pond was divided into two areas: one area had large aquatic plants, and the other area did not have large aquatic plants. The experiment randomly selected sampling points in these two pond areas during the day and at night. Day sampling was carried out between 9:00 am and 5:00 pm to cover the period of strongest light, in order to evaluate the effect of plant photosynthesis on calibration. Night sampling was carried out between 7:00 pm and 10:00 pm to evaluate the effect of calibration after plant photosynthesis stopped at night. In order to ensure the independence of the sampling points, the two sampling points were at least one meter apart.

[0148] 1. C w and C eq Calculation of

[0149] and Determined by the oscillation equilibrium method. 20 mL of surface water sample was collected using a 50 ml plastic syringe with a three-way valve, and 20 mL of surrounding atmosphere (head air) was also taken. After closing the three-way valve, the syringe was shaken for 1 min to balance the water and headspace gas. After standing, the headspace gas was filled into a vacuum 12 mL headspace bottle (839W, labco Exetainer®Vial, UK) for preservation, and the gas content in the shaken headspace was analyzed by gas chromatograph (7890B, Agilent Technologies, USA) , (i.e., the CH4 and CO2 gas content in the gas after the water body and surrounding atmosphere at the sampling point are balanced). Atmospheric samples (head-down air) around the water body at the sampling point were collected using a syringe with a three-way valve and filled into a vacuum-sealed 12 mL headspace vial (839W, labco Exetainer® Vial, UK). The CH4 and CO2 gas content in the atmosphere surrounding the water body at the sampling point was analyzed using a gas chromatograph (7890B, Agilent Technologies, USA). , .

[0150] , Calculated using the ideal gas law by formula (1):

[0151]

[0152] in C h express or , represents the gas concentrations of CH4 and CO2 in the water and surrounding atmosphere at the sampling point after equilibrium is reached, in units of 10. -6 mol L -1 ; c h express or The unit is 10 -6 mol mol -1 ; T Water temperature, in Kelvin (K).

[0153] , Calculated using formula (2) based on the ideal gas law:

[0154]

[0155] in C 0 represents or , represents the concentrations of CH4 and CO2 gases in the atmosphere surrounding the water body at the sampling point, in units of 10. -6 mol L -1 ; c 0 represents or The unit is 10. -6 mol mol -1 , T Water temperature, in Kelvin (K).

[0156] and Calculated using formula (3):

[0157]

[0158] where C w represents or , the dissolved gas concentration of CH4and CO2in the water body at the sampling point, in units of 10 -6 mol L -1 ; C h represents or , in units of 10 -6 mol L -1 ; C 0represents or , in units of 10 -6 mol L -1 ; V h and V w is the volume of headspace gas and water in the syringe of the oscillation equilibrium method, both in equal volume, in units of L; β is the Bunsen coefficient, which is 0.03211 and 0.8511 for CH4and CO2, respectively.

[0159] and According to the gas concentration in the atmosphere around the water body at the sampling point, the Henry's law is used to calculate from formula (4):

[0160] (4)

[0161] where C eq represents or , the dissolved gas concentration of CH4and CO2in the water when the atmosphere and the surface water body are in equilibrium, in units of 10 -6 mol L -1 ; P A represents the partial pressure of CH4and CO2in the atmosphere, which is equal in value to and ;

[0162] In the formula, P A in units of atm; K H is the Henry coefficient, in units of mol L -1 atm -1whose value is determined according to the actual water temperature, as shown in equation (5):

[0163]

[0164] wherein, are standard Henry's coefficients, 0.0014 and 0.034 for CH4and CO2, respectively, with units of mol L -1 atm -1 ; K T are constants for temperature, 1600 and 2400 for CH4and CO2, respectively, with units of K; T is the water temperature, with units of K; T θ is the standard temperature, 298 K.

[0165] 2. Calculation , and the measured value of CH4diffusion flux

[0166] 2.1 Collection and analysis of gas

[0167] Static chamber sampling in Example 1 was used. CH4and CO2released by the water body were captured using the static chamber. Before sampling, the static chamber was placed vertically on the water surface for 2 min to avoid the influence of water surface disturbance. After three times of mixing the cavity gas with a 50 ml plastic syringe, 20 ml of gas was extracted at 0, 5, 10, 15, 20, 30, and 60 min, respectively, and filled into a vacuum 12 ml headspace bottle (839W, labco Exetainer® Vial, UK), which was stored at room temperature in the dark. Gas chromatography (7890B, Agilent Technologies, USA) was used to analyze the gas content of CH4and CO2in the static chamber and . A portable pH meter (PHBJ-260, Shanghai Yilian Scientific Instrument Co., Ltd., China) was used to measure the water temperature in situ.

[0168] 2.2 Determination of CO2release flux from the water body and the total flux of CH4release , calculated according to equation (6):

[0169]

[0170] wherein F represents or or the measured value of CH4diffusion flux, with units of mol m -2 d -1In the formula t Sampling time, in minutes; 1440 is the number of minutes in a day; A This refers to the static bottom area of ​​the box, in square meters. 2 ; n t and n 0 represents the number of moles of CH4 or CO2 gas in the static chamber at the start and end of sampling, in mol.

[0171] According to the ideal gas law: PV = nRT Transform formula (6) into formula (7):

[0172]

[0173] The partial pressure P of the gas in the static chamber is determined by the gas content of CH4 and CO2 in the static chamber. or This means that formula (7) is transformed into formula (8):

[0174]

[0175] in F express or Alternatively, the measured CH4 diffusion flux, in mol / m³. -2 d -1 ; c express or The unit is 10 -6 mol mol -1 In the formula, V The static headspace volume of the box is in meters. 3 ; T Temperature, in Kelvin (K). R The gas constant is 8.314 m. 3 Pa K -1 mol -1 101325 is one standard atmosphere; in calculations hour, This represents the slope of the change in CH4 content within the chamber from the beginning to the end of each sampling cycle; calculation When sampling was performed at seven time points (0, 5, 10, 15, 20, 30, and 60 minutes), the linear fit of the CO2 gas content in the chamber over time was the best, and the fitted line showed the best linearity. r 2 For time periods greater than 0.95, The linear regression slope of the CO2 gas content in the chamber over time ( ) r2 > 0.95); when calculating the measured CH4 diffusion flux, the difference between the calculated and the actual values ​​is as follows: At the same time, sampling times of 0, 5, 10, 15, 20, 30, and 60 minutes were selected. The linear fit of the CH4 gas content in the chamber over time was the best, and the fitted line... r 2 For time periods greater than 0.95, The linear regression slope of the CH4 gas content in the chamber over time ( r 2 > 0.95).

[0176] 3. Calculation and To make a comparison,

[0177] use Calculated The calculation process is shown in formulas (9-1) and (10-1):

[0178] (9-1)

[0179]

[0180] In the formula, To calculate the gas mass transfer coefficient of CO2 in water based on the thin boundary layer model, and These are the Schmidt numbers for CH4 and CO2; n It is the Schmidt number index, which is used when the wind speed is > 3.6 m / s. -1 hour n It is 1 / 2, and the wind speed is < 3.6 m / s. -1 hour n The value is 2 / 3. Wind speed was measured in situ using a portable anemometer (Testo 480, Testo AG, Germany).

[0181] and Calculated using formulas (11) and (12-1):

[0182] (11)

[0183] (12-1)

[0184] In the formula, T represents the water temperature in °C. The temperature was measured in situ using a portable pH meter (PHBJ-260, Shanghai Instrument & Electronics Scientific Instruments Co., Ltd., China).

[0185] calculated from equation (13), The gas mass transfer coefficient of CH4 in water was calculated based on the thin boundary layer model:

[0186]

[0187] Based on the TBL model, calculated from equation (14):

[0188] where, is the CH4 diffusion flux at the water-air interface, with the unit of mol m -2 d -1 ; is the gas mass transfer coefficient of CH4, with the unit of m d -1 ; is the dissolved CH4 gas concentration in water at the sampling point, with the unit of 10 -6 molL -1 ; is the dissolved CH4 gas concentration in water when the atmosphere and the surface water are in equilibrium, with the unit of 10 -6 mol L -1 .

[0189] If > , then there is bubbling CH4 in the water, and the bubbling CH4 flux is calculated from equation (15):

[0190] (15)

[0191] wherein the CH4 diffusion flux is equal to the calculated value in equation (14);

[0192] If < , then there is no bubbling:

[0193] .

[0194] Comparative Example 2

[0195] Comparative Example 2 was determined according to the determination method of Example 2, except that in step 2.1, 20 ml of gas was drawn at 0, 10, 20, 30, and 60 min, and the specific process was as follows:

[0196] The experiment was conducted in the campus pond of Nanjing University of Information Science & Technology in March to November 2024. The pond was divided into two areas: one area had large aquatic plants, and the other area did not have large aquatic plants. The sampling points were randomly selected in the two pond areas during the day. The sampling was conducted between 9:00 am and 5:00 pm to cover the period of strongest light to evaluate the influence of plant photosynthesis on calibration. To ensure the independence of the sampling points, the two sampling points were at least one meter apart.

[0197] 1. C w and C eq The calculation of

[0198] According to the method in step 1 of Example 2.

[0199] 2. The calculation of , and the measured value of CH4 diffusion flux

[0200] 2.1 Collection and analysis of gases

[0201] Static chamber sampling was used in Example 1. Static chambers were used to capture CH4 and N2O released by water. Before sampling, the static chamber was placed vertically on the water surface for 2 minutes to avoid the influence of water disturbance. After stirring the cavity three times with a 50 ml plastic syringe, 20 ml of gas was extracted at 0, 10, 20, 30, and 60 minutes, and filled into a 12 ml headspace bottle (839W, labco Exetainer® Vial, UK) under vacuum. The gas content of CH4 and N2O in the static chamber was analyzed using a gas chromatograph (7890B, Agilent Technologies, USA) and . The water temperature was measured in situ using a portable pH meter (PHBJ-260, Shanghai Yilian Scientific Instrument Co., Ltd., China).

[0202] 2.2 Determination of N2O release flux in water and CH4 release total flux , according to formula (6):

[0203]

[0204] wherein F represents or or the measured value of CH4 diffusion flux. The unit is mol m -2 d -1 ; tis the sampling time, unit: min; 1440 is the number of minutes in a day; A is the bottom area of the static chamber, unit: m 2 ; n t and n 0 is the number of moles of CH4 or N2O gas in the static chamber at the end and beginning of sampling (0, 10, 20, 30, 60 min, 5 time points), unit: mol;

[0205] According to the ideal gas state equation: PV = nRT , formula (6) is converted to formula (7):

[0206]

[0207] wherein the partial pressure of the gas in the static chamber P is represented by the gas content of CH4, N2O in the static chamber or , formula (7) is converted to formula (8):

[0208]

[0209] wherein F represents or or the measured value of CH4 diffusion flux, unit: mol m -2 d -1 ; c represents or , unit: 10 -6 mol mol -1 . In the formula, V is the headspace volume of the static chamber, unit: m 3 ; A is the bottom area of the static chamber, unit: m 2 ; T is the water temperature, unit: K; R is the gas constant, 8.314 m 3 Pa K -1 mol -1 ; 101325 is one standard atmosphere; when calculating , represents the slope of the change of CH4 content in the chamber from the beginning (0 min) to the end (60 min) of each sampling period; when calculating , the sampling time is selected from 0, 10, 20, 30, 60 min 5 time points, the linear fitting degree of N2O gas content in the chamber with time is the best and the fitting line r2 a time period greater than 0.95, a linear regression slope of N2O gas content in the chamber over time (S2) r 2 a time period greater than 0.95, a linear regression slope of N2O gas content in the chamber over time (S2) r 2 a time period greater than 0.95, a linear regression slope of N2O gas content in the chamber over time (S2) r 2 a time period greater than 0.95.

[0210] 3. Calculate and for comparison:

[0211] According to the method in step 3 in Example 2.

[0212] Example 5

[0213] Analysis results

[0214] 1. Success rate of method for methane calibration

[0215] According to Example 2 and Comparative Example 1, sampling was performed in a pond on the campus of Nanjing University of Information Engineering in China, and 40 groups of CH4, N2O, and CO2 gas content data produced by water in a static chamber under the environment of aquatic plants in the daytime, 40 groups of CH4, N2O, and CO2 gas content data produced by water in the environment without aquatic plants in the daytime, and 40 groups of CH4, N2O, and CO2 gas content data produced by water in the environment at night were obtained. The obtained data was first pretreated to remove abnormal values and repeated data, then the N2O and CO2 gas content data was used to draw a scatter plot by Microsoft Excel and select an appropriate linear fitting to calculate the flux of CH4 for calibration. The CH4 gas content data obtained by sampling was used to draw a scatter plot by Microsoft Excel and select an appropriate linear fitting to calculate the measured value of CH4 diffusion flux. If the calibration value is negative and the measured value is positive, it is considered as a failed calibration. The results are shown in Table 1. Overall, the success rate of N2O calibration of CH4 flux of the present application is much higher than that of CO2 calibration method. In the environment with aquatic plants in the daytime, the success rate of CO2 calibration method is very low: in the environment without aquatic plants in the daytime, the success rate of CO2 calibration method will also be affected. The success rate of the N2O calibration method of the present application is always stable and maintained at a high level.

[0216] Table 1 Comparison of success rates of CO2 calibration method and N2O calibration method in pond environment

[0217]

[0218] 2. Comparison of total accuracy of the method for methane calibration

[0219] In combination with Example 2 and Comparative Example 1, sampling was performed in a pond on the campus of Nanjing University of Information Engineering in China to obtain 40 groups of data of CH4, N2O and CO2 gas content collected by static boxes in water bodies in the daytime in the presence of aquatic plants, 40 groups of data of CH4, N2O and CO2 gas content collected by static boxes in water bodies in the daytime in the absence of aquatic plants, and 40 groups of data of CH4, N2O and CO2 gas content collected by static boxes in water bodies at night. The obtained data were first pretreated to remove abnormal values and repeated data, then the N2O and CO2 gas content data were used to draw a scatter plot by Microsoft Excel and a suitable linear fitting was selected to be substituted into the calculation of flux to calibrate the diffusion type CH4. The CH4 concentration data obtained by sampling were used to draw a scatter plot by Microsoft Excel and a suitable linear fitting was selected to be substituted into the calculation to obtain the measured value of CH4 diffusion flux. The calibrated value and the measured value of CH4 diffusion flux were used to generate a graph of the data by Origin 2023 software to compare the accuracy. The results are shown in Figure 2 Compared with the CO2 calibration method, the flux obtained by the N2O calibration method of the present application is closer to the measured value and has higher accuracy under the three environmental conditions. The linear fitting slopes of the calibrated value and the measured value of CH4 diffusion flux obtained by the CO2 calibration method and the N2O calibration method are 0.30 ± 0.36 mol m -2 d -1 and 0.87 ± 0.06 mol m -2 d -1 , respectively, and the determination coefficients (R r 2 ) are 0.01 and 0.62, respectively, and the P values are 0.4 and < 0.0001, respectively. p 3. Comparison of accuracy of the method for methane calibration under different scenarios

[0220] In combination with Example 2 and Comparative Example 1, the accuracy of the CO2 calibration method varies under different environments. However, the accuracy of the N2O calibration method of the present application remains stable and is not affected by the environment. As shown in

[0221] Figure 3 ​The results show that, under daytime conditions with aquatic plants, the accuracy of the N2O calibration method is higher than that of the CO2 calibration method. The linear fitting slopes between the calibrated and measured CH4 diffusion flux values ​​obtained by the CO2 and N2O calibration methods are -1.09 ± 0.64 mol m⁻¹, respectively. -2 d -1 and 0.94 ± 0.14 mol m -2 d -1 coefficient of determination ( r 2 The values ​​were 0.13 and 0.52 respectively. p The values ​​are 0.11 and < 0.0001, respectively.

[0222] like Figure 4 The results show that, under daytime conditions without aquatic plants, both calibration methods have high accuracy. The linear fitting slopes between the calibrated and measured CH4 diffusion flux values ​​obtained by the CO2 calibration method and the N2O calibration method of this invention are 3.41 ± 2.93 mol m⁻¹, respectively. -2 d -1 and 0.93 ± 0.13 mol m -2 d -1 coefficient of determination ( r 2 The values ​​are 0.02 and 0.55 respectively. p The values ​​are 0.26 and < 0.0001, respectively. For example... Figure 5 The results show that in nighttime environments, both calibration methods have high accuracy, with the N2O calibration method of this invention showing slightly higher accuracy than the CO2 calibration method. The linear fitting slopes between the CH4 diffusion flux calibrations obtained by the CO2 and N2O calibration methods and the measured values ​​are 0.78 ± 0.16 mol m⁻¹, respectively. -2 d -1 and 0.81 ± 0.12 molm -2 d -1 coefficient of determination ( r 2 The values ​​were 0.39 and 0.57, respectively. p All values ​​are < 0.0001.

[0223] 4. The impact of sampling time interval on calibration results

[0224] When using the static chamber method to capture greenhouse gases produced in water bodies, the rate of change in gas concentration varies significantly across different time periods. Specifically, when the static chamber is first placed on the water surface, the gas concentration inside the chamber rises rapidly, and the rate of change is relatively fast during this initial stage. However, as the gas concentration in the chamber gradually approaches saturation, the rate of change slows down significantly. Therefore, the selection of the sampling time interval is crucial for more accurately capturing the dramatic changes in gas concentration in the early stages.

[0225] Combining Example 2 and Comparative Example 2, selecting 0, 5, 10, 15, 20, 30, and 60 minutes as sampling time points allows for a more comprehensive recording of the dynamic changes in gas content. This high-frequency sampling strategy is particularly suitable for capturing rapid changes in gas content during the initial placement of the static chamber, thereby improving the accuracy and reliability of the calibration. This ensures that the changing characteristics of gas content at different stages are captured, thus enhancing the accuracy and scientific rigor of the calibration. In contrast, selecting only 0, 10, 20, 30, and 60 minutes as sampling time points would miss crucial data during the initial rapid change phase of gas content, affecting the accuracy and completeness of the calibration results.

[0226] 5. Evaluation of the success rate and accuracy of N2O calibration for diffuse CH4 in lake environments

[0227] In accordance with Example 3, samples were collected from Meiliang Bay in West Taihu Lake, Wuxi City, Jiangsu Province, and East Taihu Lake, Suzhou City, Jiangsu Province, China. 36 sets of data each on CH4 and N2O gas content were obtained under daytime conditions with aquatic plants, and 27 sets of data each under daytime conditions without aquatic plants. The data were first preprocessed to remove outliers and duplicates. Then, using the N2O gas content data, scatter plots were created in Microsoft Excel, and a suitable linear fit was selected to calculate the flux for calibrating diffuse CH4. The measured CH4 diffusion flux was obtained by using the sampled CH4 gas content data to create scatter plots in Microsoft Excel and selecting a suitable linear fit. If the calibrated value was negative and the measured value was positive, the calibration was considered a failure. The results are shown in Table 2. The success rate of the N2O calibration method of this invention remained consistently high in lake environments. The accuracy of the calibrated and measured CH4 diffusion flux data was compared using graphs generated by Origin 2023 software. The results are as follows: Figure 6 As shown, the accuracy of the N2O calibration method in lake environments remains consistently high. The linear fit slope between the calibrated and measured values ​​of CH4 diffusion flux obtained by the N2O calibration method of this invention is 0.67 ± 0.14 mol m -2 d -1 coefficient of determination ( r2 The value is 0.28. p Value < 0.0001.

[0228] Table 2 Success Rate of N2O Calibration Method in Lake Environment

[0229]

[0230] 6. Evaluation of the success rate and accuracy of N2O calibration for diffuse CH4 in reservoir environments.

[0231] In accordance with Example 4, samples were collected from seven reservoirs in the Liutian River Basin, Longchuan County, Heyuan City, Guangdong Province, China, yielding 72 sets of data each on the CH4 and N2O gas content in the water. The data were first preprocessed to remove outliers and duplicates. Then, using the N2O gas content data, a scatter plot was created in Microsoft Excel, and a suitable linear fit was selected to calculate the flux for calibrating diffuse CH4. The measured CH4 diffusion flux was obtained by using the sampled CH4 gas content data to create a scatter plot in Microsoft Excel and selecting a suitable linear fit. If the calibrated value was negative while the measured value was positive, the calibration was considered a failure. Ultimately, the N2O calibration method of this invention achieved a success rate of 98.6% in the reservoir environment, demonstrating that the N2O calibration method maintains a consistently high success rate in reservoir environments. The accuracy of the calibrated and measured CH4 diffusion flux data was compared using graphs generated by Origin 2023 software. The results are as follows. Figure 7 As shown, the accuracy of the N2O calibration method remains stable at a high level in the reservoir environment. The slope of the linear fit between the calibrated value and the measured value of CH4 diffusion flux obtained by the N2O calibration method is 0.87 ± 0.04 mol m -2 d -1 coefficient of determination ( r 2 The value is 0.86. p Value < 0.0001.

Claims

1. A method of determining and distinguishing between methane ebullition flux and diffusion flux released from a body of water, characterized by, It comprises the following steps: (1) The gas content of CH4 and N20 in the water body and the surrounding atmosphere after equilibrium is determined , , the calculated gas concentration , ; Measuring the gas content of CH4 and N2O in the atmosphere around the sampling point of water body , , calculating the gas concentration , ; Dissolved gas concentrations of CH4 and N2O in water at sampling points and Dissolved gas concentrations of CH4 and N2O in water at equilibrium with the atmosphere and Dissolved gas concentrations of CH4 and N2O in water at equilibrium with the atmosphere (2) Determining the release flux of N20 in water body and the total flux of CH4 ; (3) Utilization , , , , , The gas mass transfer coefficients of N2O and CH4 in water were calculated based on the thin boundary layer model. and Based on the stable proportional relationship between the mass transfer coefficients of different diffusing gases at the same water-gas interface, using... The gas mass transfer coefficient of diffuse CH4 was calculated. ,use , and Calculate CH4 diffusion flux ; (4) If and are compared, if > , there is bubbling CH4 in the water body, and the CH4 bubbling flux is equal to the total CH4 release flux minus the CH4 diffusion flux ; if < , there is no bubbling, and the CH4 diffusion flux is equal to the total CH4 release flux ; Gas content in step (1) , The gas content of CH4 and N2O in the water body and the surrounding atmosphere at the sampling point after equilibrium was analyzed by gas chromatography 、 The gas content of CH4 and N2O in the water body and the surrounding atmosphere at the sampling point after equilibrium was analyzed by gas chromatography 、 ; , According to the ideal gas state equation, calculated from equation (1): ， wherein C h represents or , in units of 10 -6 mol L -1 ; c h represents or , in units of 10 -6 mol mol -1 ; T T is the water temperature, in units of K; , According to the ideal gas state equation, calculated from equation (2): ， wherein C 0 represents or , in units of 10 -6 mol L -1 ; c 0 represents or , in units of 10 -6 mol mol -1 ; T T is the water temperature, in units of K; and Calculated from equation (3): ， wherein C w represents or , in units of 10 -6 mol L -1 ; C h represents or , in units of 10 -6 mol L -1 ; C 0 represents or , in units of 10 -6 mol L -1 ; V h and V w is the volume of gas and water in an injector of the oscillation equilibrium method, both in equal volume, in units of L; β is the Bunsen coefficient, 0.03211 and 0.6221 for CH4 and N2O, respectively; and Using Henry's law, from equation (4): （4）， wherein C eq represents or in units of 10 -6 mol L -1 ; P A represents the partial pressure of CH4or N20 in the atmosphere, numerically equal to or ; wherein P A in atm; K H H is the Henry's coefficient in mol L -1 atm -1 The value is determined based on the actual water temperature, as shown in equation (5): ， wherein GCH4, GCH4= 0.0014, GCH4= 0.025, unit: mol L -1 atm -1 ; K T GCH4, GCH4= 1600, GCH4= 2600, unit: K; T Twater, unit: K; T θ Tref, 298 K; The release flux of N2O in the water body was determined in step (2) and the total flux of CH4 release According to formula (6): ， wherein F represents or , in mol m -2 d -1 ; t is the sampling time, in min; 1440 is the number of minutes in a day; A is the static chamber bottom area, in m 2 ; n t and n 0 is the number of moles of CH4or N20 gas in the static chamber at the end and beginning of the sampling, in mol; According to the ideal gas state equation: PV = nRT Equation (6) is converted to equation (7): ， where the gas partial pressure in the static chamber P Gas content of CH4, N20 in static chamber or denotes, equation (7) is transformed into equation (8): ， wherein F represents or , in mol m -2 d -1 ; c represents or , in 10 -6 mol mol -1 ; V is the static chamber headspace volume, in m 3 ; T is the water temperature, in K; R is the gas constant, 8.314 m 3 Pa K -1 mol -1 ; 101325 is one standard atmosphere; in calculating , represents the slope of the change in CH4gas content within the chamber from the beginning to the end of each sampling period; in calculating , represents the linear regression slope of N2O gas content within the chamber over time, r 2 > 0.95; The mass transfer coefficient of different diffusion gases based on the same water-gas interface in step (3) has a stable proportional relationship, and the calculation formula is as follows: The calculation results are as follows: The calculation process is as shown in formula (9) and formula (10): ， ， wherein and is the Schmidt number for CH4and N20; n is the Schmidt number exponent, when wind speed > 3.6 m s -1 n is 1 / 2, when wind speed < 3.6 m s -1 n is 2 / 3;​​ and From equation (11) and equation (12), it is calculated that: （11）， （12）， In the formula, T is water temperature, unit is ℃; Calculated from equation (13): ， is calculated from equation (14): .

2. The method of determining and distinguishing between methane ebullition and diffusion fluxes released from a body of water according to claim 1, wherein, In step (2), CH4 and N2O released from the water body are captured by using a static chamber. Before sampling, the static chamber is vertically placed on the water surface. After the cavity gas is mixed by a syringe for three to four times, the gas in the chamber is extracted at time points of 0, 5, 10, 15, 20, 30 and 60 min, and is transferred to a vacuum headspace bottle for analysis by using a gas chromatograph to obtain the gas content of CH4 and N2O in the static chamber and , 10 -6 mol mol -1 At the same time, the wind speed on the water surface and the in-situ water temperature are measured.

3. The method of determining and distinguishing between methane ebullition and diffusion fluxes released from a body of water according to claim 2, wherein, The static box body is a cylindrical chamber for storing greenhouse gases generated by water body, the upper part is sealed and a small opening is provided at the center for connecting the gas outlet connector, a hose is connected to the gas outlet connector at one end and connected to a three-way valve at the other end, and the syringe is connected to the three-way valve to collect gas when gas is collected; the lower end of the whole static box is designed as an opening, and the gas enters the chamber from the lower bottom, the annular baffle is installed on the outside of the box body to fix the floating ring, and the surface of the static box is also covered with aluminum foil.

4. The method of determining and distinguishing between methane ebullition and diffusion fluxes released from a body of water according to claim 2, wherein, When the static box is placed on the water surface, the water body enters the chamber, so that the water surface in the chamber is higher than the water surface outside, and the actual gas capturing chamber volume of the static box accounts for 2 / 5-4 / 5 of the total volume.

5. The application of calibrating CH4 diffusion flux with N2O flux based on the method of claim 1 to determine and distinguish the bubble methane flux and the diffusion methane flux released by water body.

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