An integrated system and method for online observation of stable isotopes of methane emission pathways in rice fields

Abstract

The application discloses an integrated system and method for online observation of stable isotopes of multiple methane emission pathways in rice fields, collects methane gas emitted by plants and non-plant mediation respectively, pre-processes the gas by using a Nafion membrane drying tube and a correction algorithm, realizes continuous measurement of data by using a cavity ring-down spectrum-based analyzer, controls semi-automatic or full-automatic switching of different cavities by using a multi-channel switching and control module, and finally analyzes stable isotope characteristics of plant-mediated and non-plant-mediated emission by using a data processing module combined with a Keeling plot method, so that integrated, continuous and online observation of methane emission pathways in rice fields is realized, and real-time performance, comparability and model verification capability of data are significantly improved.

Description

Technical Field

[0001] This invention relates to the field of greenhouse gas observation and ecological environment monitoring technology, and in particular to an integrated system and method for online observation of stable isotopes of methane through multiple emission pathways in paddy fields. Background Technology

[0002] methane ( ) is second only to carbon dioxide ( The second longest-lived greenhouse gas, with a warming potential of approximately [missing information] per unit timescale over a century. Methane emissions are 28 times higher than normal, significantly impacting global climate change and atmospheric oxidation capacity. In recent years, atmospheric methane concentrations have continued to rise, exacerbating climate change and significantly affecting atmospheric chemical processes such as ozone formation and hydroxyl radical (OH) concentration. Due to the complex sources of methane, encompassing natural wetlands, paddy fields, livestock farming, fossil fuel extraction and use, and landfills, accurately identifying and quantifying these emission sources has become a core scientific issue in global methane research and greenhouse gas inventory compilation. In this process, stable isotope analysis methods, especially carbon isotope composition (CIC), are crucial. Different methanogenic pathways (such as acetic acid fermentation, etc.) play a unique role. Reduction typically exhibits different isotopic fractionation effects, and the oxidation process of methane also alters its... Value. (Through) Continuous or phased observations can elucidate the formation pathways, transport mechanisms, and transformation processes of methane, providing support for source apportionment, emission inventory optimization, and improvements to Earth system models. Therefore, It has become one of the important indicators for atmospheric methane research.

[0003] Paddy fields are one of the major contributors to global anthropogenic methane emissions, accounting for 8–12% of total anthropogenic emissions, particularly significant in rice-growing areas of Asia. Methane production in paddy fields primarily originates from the decomposition of organic matter in anaerobic soil environments, with microbial activity producing methane and accumulating in the soil-water system. Subsequently, methane is released into the atmosphere through three main pathways: (1) bubble escape, where methane forms bubbles in soil pores and is suddenly released, typically exhibiting instantaneous and strong pulse characteristics; (2) molecular diffusion, where methane dissolves in soil water and then diffuses across the water-air interface into the atmosphere, a relatively slow and continuous pathway; and (3) plant pathway, where methane is directly transported to the atmosphere through aerenchyma tissues within rice plant stems, a pathway that accounts for a significant proportion of methane emissions from paddy fields. The relative contributions of these three pathways not only vary with the rice growth stage but are also influenced by soil physicochemical properties, water level management, fertilization measures, and meteorological conditions, exhibiting significant spatiotemporal differences. Introducing stable isotope technology is of great significance in paddy field methane research. Plant-mediated pathways often exhibit different characteristics from non-plant pathways. Signal, therefore It can be used to distinguish pathway contributions, thereby improving the accuracy of emission process analysis. Although the isotopic differences between the two non-plant pathways of gas bubbles and diffusion are relatively small, it is still possible to separate their contributions to some extent through continuous observation with high temporal resolution and in combination with the instantaneous change characteristics of methane concentration.

[0004] However, current technologies lack a device capable of simultaneously sampling and conducting continuous online isotope analysis of both phytochemical and non-phytochemical pathways within the same system. Therefore, a new integrated system is urgently needed to achieve real-time differentiation and continuous observation of methane emission pathways in paddy fields, providing technical support for carbon cycle research and greenhouse gas emission reduction.

[0005] Current research methods for methane emissions from paddy fields mainly include static chambers, automated chambers, funnel sampling, and laboratory analysis. Static chambers and automated chambers are mature and widely used, capable of estimating total methane emissions. However, these methods are limited by their inability to distinguish between three different release pathways: bubble emission, diffusion, and plant channel emission. For bubble emission, a common method is to use a funnel to capture bubbles in water and send them for laboratory mass spectrometry analysis. While this can obtain the isotopic composition of methane in the bubbles, it suffers from strong sampling intermittency, significant environmental influence, and laboratory analysis lag, making it difficult to reflect the dynamic characteristics of bubble release. Studies of the plant channel pathway often rely on bagging experiments or model extrapolation, lacking direct real-time observation and resulting in insufficient validation. Furthermore, existing studies often employ different devices and analytical methods for different pathways, with variations in sampling time, gas path conditions, and instrument accuracy, leading to a lack of data uniformity and comparability. This not only increases the uncertainty in distinguishing emission pathways but also limits the application of data in process model validation and regional emission constraints. Therefore, existing technologies suffer from discontinuity, indistinguishable pathways, and a lack of uniform comparability. There is an urgent need for an integrated device that can perform alternating sampling and unified gas path processing of plant and non-plant pathways within the same system, combined with high-precision online isotope analysis, to continuously monitor the methane emission process in paddy fields and achieve pathway differentiation. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing studies on methane emissions from paddy fields, such as indistinguishable emission pathways, discontinuous observations, and a lack of data uniformity. This invention proposes an integrated system and method for online stable isotope observation of multiple methane emission pathways in paddy fields. Through a unified gas path design and online isotope analysis, this system achieves alternating sampling and cyclical observation of plant-mediated and non-plant-mediated emissions, thereby obtaining continuous time-series data. Furthermore, by combining isotope characteristics and data processing methods, emission pathways can be distinguished.

[0007] This invention provides a method for online observation of stable isotopes of methane emitted through multiple pathways in paddy fields, the specific steps of which are as follows:

[0008] Step S1: Collect methane gas emitted from the rice plant channel using a transparent plant chamber, and collect non-plant mediated emission gas, including bubbles and diffusion, using a non-plant chamber.

[0009] Step S2: Remove water vapor from the collected gas using a Nafion membrane drying tube, and combine... The correction formula corrects for residual interference;

[0010] The correction function is as follows:

[0011] (1)

[0012] (2)

[0013] (3)

[0014] Where wet represents the measurement value under water content, and dry represents the value under dry baseline conditions. The parameter represents the water vapor volume fraction (%) measured by the instrument. , , , , It is the correction factor.

[0015] Furthermore, flow control can be performed during the gas passage through the Nafion membrane drying tube to control the flow rate of the gas entering the Nafion membrane drying tube.

[0016] Step S3: Continuously measure methane concentration and... value;

[0017] The cavity ring-down spectroscopy (CRDS) analyzer can be either the Picarro G2201-i or G2210-i analyzer, used for real-time continuous measurement of methane concentration and... value;

[0018] Step S4: Switch between different sampling chambers using the multi-channel switching control module to achieve sequential measurement of emissions through multiple pathways;

[0019] The sampling chamber can be selected from the LI-8100-104 series sealed chamber or other sealed chambers with the same function; the sampling chamber can be divided into plant chamber and non-plant chamber.

[0020] Step S5: Record concentration and isotope data using the data acquisition and processing module, analyze the end-member characteristics of plant-mediated and non-plant-mediated emissions using the Keeling plot method, and further identify bubble and diffusion contributions through instantaneous changes in methane concentration.

[0021] Specifically, data processing also includes the following steps:

[0022] Step S51: Preprocess the collected data, including removing transitional data points and abnormal data points at the moment of switching, and detecting and correcting gas path lag.

[0023] Step S52: Perform linear correction on the observed gas data using the working standard gas;

[0024] Step S53: Based on the obtained corrected data, establish a Keeling plot using the Keeling plot method. With total methane concentration The linear relationship between the reciprocals is used to calculate the intercept and obtain the emission end-member characteristics.

[0025] Step S54: Output the source data calculated from the keeling plot for each sampling window. Values, the ratio of bubble contribution to diffusion contribution, the number of bubble events, and / or the results of their interaction with environmental factors.

[0026] Environmental factors include parameters such as soil temperature and moisture content.

[0027] This invention also proposes an integrated system for online observation of stable isotopes of methane from multiple emission pathways in paddy fields, used to perform the methods described above. The system includes:

[0028] The sampling module includes a transparent plant chamber and a non-plant chamber;

[0029] The gas pretreatment module includes a Nafion membrane drying tube and a flow control unit;

[0030] The online stable isotope analysis module uses a Picarro G2201-i or G2210-i CRDS analyzer;

[0031] A multi-channel switching and control module, including a solenoid valve array or manifold device, is used to achieve semi-automatic or fully automatic switching between different chambers.

[0032] The data acquisition and processing module is used to record methane concentration. and The values ​​were calculated, and the emission characteristics of different pathways were analyzed using the Keelingplot method.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] This invention is the first to achieve integrated observation of methane emissions from paddy fields through multiple pathways. It connects plant chambers and non-plant chambers to the same online isotope analysis platform, and enables real-time monitoring of gas data from different sources by switching gas pathways. This ensures the comparability and continuity of data from different pathways, and realizes integrated, continuous, and online observation of methane emission pathways in paddy fields, significantly improving the real-time performance, comparability, and model validation capabilities of the data.

[0035] Secondly, a Nafion membrane drying tube is used to remove water vapor, and a calibration formula is used to correct and judge the measurement results. This reduces the interference of water vapor on the instrument's measurement signal and corrects measurement deviations that may be caused by the presence of water vapor, ensuring that the measurement results are not affected by the potential interference of water vapor. At the same time, a quality control mechanism is also set up, such as outlier removal and threshold setting, to promptly detect and deal with abnormal situations, ensuring the accuracy and reliability of the obtained measurement results, as well as the consistency and comparability of the obtained data with subsequent measurement data.

[0036] High temporal resolution CRDS technology enables continuous operation at the minute level. The instrument can capture instantaneous and rapid signals such as bubble emission, and can simultaneously retain the original measurement sequence with high temporal resolution and the low-frequency aggregated sequence, thus taking into account both rapid event identification and long-term trend analysis, and overcoming the intermittency and delay of traditional mass spectrometry methods.

[0037] Finally, path differentiation was achieved using gas path unification and data processing methods. The Keeling plot method was employed to... For total methane concentration Linear regression of the reciprocal of the equation provides direct validation for plant-mediated emission simulation. It also has good scalability and can be extended to greenhouse gas emission research in ecosystems such as wetlands and lakes, providing support for regional carbon cycle research and greenhouse gas inventory compilation. Attached Figure Description

[0038] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 This is a schematic diagram of the overall framework of the integrated online observation system for stable isotopes of methane multiple emission pathways in paddy fields as described in this invention;

[0040] Figure 2 This is a schematic diagram of the plant cavity structure described in this invention;

[0041] Figure 3 This is a schematic diagram of the non-plant chamber structure described in this invention;

[0042] Figure 4 This is a schematic diagram of the gas pretreatment and gas path connection process described in this invention;

[0043] Figure 5 This is a schematic diagram of the structure of the multi-channel switching and control module described in this invention;

[0044] Figure 6 This is a flowchart of the data acquisition and processing module described in this invention;

[0045] Figure 7 This is a schematic diagram of the deployment of the system of the present invention in a paddy field. Detailed Implementation

[0046] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0047] This invention provides a method for online observation of stable isotopes of methane emitted through multiple pathways in paddy fields, the specific steps of which are as follows:

[0048] Step S1: Collect methane gas emitted from the rice plant channel using a transparent plant chamber, and collect non-plant mediated emission gas, including bubbles and diffusion, using a non-plant chamber.

[0049] Step S2: Remove water vapor from the collected gas using a Nafion membrane drying tube, and combine... The correction formula corrects for residual interference;

[0050] Furthermore, flow control can be performed during the gas passage through the Nafion membrane drying tube to control the flow rate of the gas entering the Nafion membrane drying tube.

[0051] The correction function is as follows:

[0052] (1)

[0053] (2)

[0054] (3)

[0055] Where wet represents the measurement value under water content, and dry represents the value under dry baseline conditions. The parameter represents the water vapor volume fraction (%) measured by the instrument. , , , , It is the correction factor.

[0056] The aforementioned correction factors were obtained through experimental calibration using a reference gas. Specifically, they were calculated using known concentrations and... The standard gas with the value was repeatedly sampled under different humidity conditions to obtain... , and The wet / dry ratio was obtained, and the experimental data were then fitted to a quadratic polynomial (formula (1), (2)) and a linear function (formula (3)) to obtain the corresponding regression coefficients.

[0057] The Nafion membrane drying tube is a highly efficient water vapor removal structure. This structure can achieve drying by absorbing and transferring water molecules at the molecular level. The above water removal process is fast and does not require external energy drive. It can be carried out solely by the difference in water concentration on both sides of the tube wall.

[0058] However, in practical applications, Nafion membrane drying tubes struggle to completely reduce the water vapor concentration to zero, failing to achieve the theoretically desired drying result. Actual experiments revealed that Nafion membrane drying tubes exhibit significant dehumidification effects, with gas humidity gradually decreasing over time and typically stabilizing after 3-6 minutes. Lower flow rates of the test gas within the tube result in better dehumidification, as longer residence time leads to greater moisture removal. Conversely, increasing the test gas flow rate relatively decreases dehumidification efficiency. Furthermore, excessively high humidity in the test gas can also affect the water removal capacity of the Nafion membrane drying tube. If the humidity is too high and the Nafion membrane drying tube is insufficient in length, water molecules in the test gas may not have had time to migrate from the inner wall to the outer wall before flowing out of the tube, resulting in incomplete removal. In conclusion, in practical applications, factors such as gas flow rate, gas humidity, and the length of the Nafion membrane drying tube all influence its water vapor removal efficiency. Even if the Nafion membrane drying tube effectively reduces the water vapor concentration, it cannot guarantee the complete removal of all water vapor.

[0059] The main purpose of step S2 is to remove water vapor from the gas to reduce its potential impact on subsequent isotope analysis. However, in practice, the Nafion membrane drying tube sometimes cannot completely remove water vapor to achieve the theoretically complete drying. The presence of residual trace amounts of water vapor may affect the accuracy of instrument measurements. Even after complete removal of water vapor, it may still have a slight impact on the measurement results of the CRDS analyzer, such as historical residues or instrument memory effects. This impact may not be due to the physical presence of water vapor, but rather to its interference with the instrument's measurement signal.

[0060] Therefore, a correction formula is used to correct and evaluate the measurement results, further correcting measurement deviations that may be caused by the presence of water vapor. This ensures that the measurement results are not affected by potential water vapor interference, guaranteeing the accuracy and reliability of the obtained results, and ensuring the consistency and comparability of the obtained data with subsequent measurement data. The above correction steps can improve the accuracy and reliability of the entire measurement system.

[0061] Specifically, in order to quantify and correct the effect of water vapor on Regarding the impact of measurements, the above experimental calibration process was a controlled experiment conducted under laboratory conditions. The specific experimental calibration process is as follows:

[0062] The experiment used a Picarro G2201-i isotope analyzer, continuously introducing methane of known concentration and A reference gas was used, and a humidifier was installed at the inlet to gradually vary the water vapor concentration in the gas sample within the range of approximately 3% to 0.02%. Throughout the process, the analyzer continuously sampled at a constant flow rate and recorded the data in real time. , as well as By observing the values, a complete data sequence at different humidity levels is obtained. Based on these experimental data, this invention establishes the systematic dependence between water vapor concentration and the observed signal.

[0063] Furthermore, the calibration process for establishing the water vapor correction equation in a real laboratory can cover a water vapor concentration range of 0.1% to 4.0%, ensuring a wide applicability of the parameters. Moreover, the obtained parameters can be dynamically updated periodically to adapt to changes in instrument conditions or gas path conditions, while avoiding the impact of water vapor on the instrument and preventing abnormalities in measurement accuracy due to long-term use.

[0064] Furthermore, this invention provides two correction paths:

[0065] a) Path A: Directly use formula (3) for... The value can be corrected in a simple and real-time manner.

[0066] b) Path B: First, use formulas (1) and (2) respectively to... , The volume fraction is corrected, then the ratio is calculated and converted to... This results in more stable and consistent correction results;

[0067] in, ;

[0068] in It is the gas obtained from actual testing or after calibration. and The ratio, and It is in the VPDB standard and The ratio.

[0069] Furthermore, to avoid measurement deviations caused by moisture, the present invention can also introduce a quality control mechanism during the data processing stage, as detailed below:

[0070] 1. Baseline Definition: Optional When <0.1% The value is used as a drying baseline to monitor drift.

[0071] 2. Outlier removal: Methods such as median filtering or robust regression are used to remove abrupt changes that occur during the measurement process;

[0072] 3. Threshold setting: Set the concentration threshold A and / or the residual correction threshold B.

[0073] when When the concentration exceeds the concentration threshold A, the data points measured under this condition are marked as anomalies and removed.

[0074] When the corrected residual exceeds the corrected residual threshold B, the measured data point is marked as an anomaly and removed.

[0075] Furthermore, if the corrected residual shows an anomaly N times consecutively, the system will warn that the measuring instrument may be faulty and requires further debugging and correction, where N is an integer greater than or equal to 1.

[0076] Among them, the concentration threshold A can be 4%, the corrected residual threshold B can be 5%, and N can be 3.

[0077] The formula for calculating the corrected residual threshold B is as follows:

[0078] ;

[0079] Through the above experimental design, correction function, and parameter acquisition method, this invention can effectively correct water vapor interference under different humidity conditions, ensuring... , and The measurement results are consistent and comparable, providing a reliable data basis for subsequent methane emission pathway identification and flux estimation.

[0080] Step S3: Continuously measure methane concentration and... value;

[0081] The cavity ring-down spectroscopy (CRDS) analyzer can be either the Picarro G2201-i or G2210-i analyzer, used for real-time continuous measurement of methane concentration and... value;

[0082] Specifically, during the sampling process, a Picarro analyzer can be selected as the core measurement device to continuously record data in real time. , and The value, and simultaneously obtain It can collect gas path parameters such as concentration, optical cavity temperature, optical cavity pressure, flow rate, valve position and channel status, and can also integrate soil temperature and soil moisture probes into the measuring equipment to achieve synchronous acquisition of environmental factors.

[0083] The preferred sampling frequency for the raw data in the Picaro correlation sampling is 0.5 Hz to ensure the capture of instantaneous, rapid signals such as bubble emission. For slow processes such as diffusion, the raw measurement data can be further averaged over 10 or 60 seconds to obtain smoother trend data. In this way, both high-temporal-resolution raw measurement sequences and low-frequency aggregated sequences can be preserved simultaneously, thus achieving both rapid event identification and long-term trend analysis.

[0084] Step S4: Switch between different sampling chambers using the multi-channel switching control module to achieve sequential measurement of emissions through multiple pathways;

[0085] Furthermore, automated sampling controlled by a program can be selected during the measurement process;

[0086] The sampling chamber can be selected from the LI-8100-104 series sealed chamber or other sealed chambers with the same function;

[0087] Sampling chambers can be divided into plant chambers and non-plant chambers;

[0088] Step S5: Record concentration and isotope data using the data acquisition and processing module, analyze the end-member characteristics of plant-mediated and non-plant-mediated emissions using the Keeling plot method, and further identify bubble and diffusion contributions through instantaneous changes in methane concentration.

[0089] The data acquisition and processing module records the methane concentration and isotope data measured in step S3, and analyzes the acquired data.

[0090] In terms of data processing, this invention uses a closed-chamber sampling window for endmember analysis. The sampling window is defined as a complete closed cycle, with the first 2 minutes after closure defined as the mixing period and excluded. The effective analysis period is preferably from the 5th to the 10th minute, and it is necessary to ensure that the methane concentration has a certain dynamic range.

[0091] Specifically, data processing also includes the following steps:

[0092] Step S51: Preprocess the collected data, including removing transitional data points and abnormal data points at the moment of switching, and detecting and correcting gas path lag.

[0093] Step S52: Perform linear correction on the observed gas data using the working standard gas. The specific correction process is as follows:

[0094] by Taking observational data as an example, in order to correct Instrument drift and proportional / translational deviation during parameter measurement can be selected. Two reference gases with significantly different characteristics were established. The linear relationship between (drying conditions) and the calibration scale was established, and the obtained coefficients m and n were applied to field observations to obtain the values ​​on the VPDB scale. value:

[0095] ;

[0096] in, Drying after moisture correction value, For the standardization of the scale .

[0097] Step S53: Based on the obtained corrected data, establish a Keeling plot using the Keeling plot method. With total methane concentration The linear relationship between the reciprocals is used to calculate the intercept and obtain the emission end-member characteristics.

[0098] Endmembers obtained from plant chambers using this method The value can characterize endmembers mediated by the plant, rather than those obtained from the plant chamber. The value represents non-plant-mediated emissions.

[0099] Specifically, the Keeling plot method is used to... For total methane concentration A linear regression is performed using the reciprocal of the value, and the intercept corresponds to the emission source. Values ​​that satisfy the following relationship:

[0100] ;

[0101] in, The total methane concentration can be directly observed or calculated from the observation results of 12CH4 and 13CH4. The above linear relationship is constructed for each closed window.

[0102] In the non-plant chamber, the instantaneous changes in methane concentration are used to further distinguish between bubble emissions and diffusion emissions. Specifically, the first derivative of the original sequence sampled at a frequency of 0.5 Hz is calculated, and the median absolute deviation method is used to determine the judgment threshold C. When the rate of concentration increase exceeds the judgment threshold C and persists for a certain period of time, it is determined to be a bubble event. At the same time, the bubble contribution can be obtained by integrating the bubble peak area; while the remaining slow concentration increase is defined as the diffusion contribution.

[0103] Step S54: Output the source data calculated from the keeling plot for each sampling window. Values, the ratio of bubble contribution to diffusion contribution, the number of bubble events, and / or the results of their interaction with environmental factors.

[0104] Environmental factors include parameters such as soil temperature and moisture content.

[0105] Furthermore, the keeling plot can be applied to diffusion-dominated or stable emission phases.

[0106] This invention also proposes an integrated system for online observation of stable isotopes of methane from multiple emission pathways in paddy fields, used to perform the methods described above. The system includes:

[0107] The sampling module includes a transparent plant chamber and a non-plant chamber;

[0108] The gas pretreatment module includes a Nafion membrane drying tube and a flow control unit;

[0109] The online stable isotope analysis module uses a Picarro G2201-i or G2210-i CRDS analyzer;

[0110] A multi-channel switching and control module, including a solenoid valve array or manifold device, is used to achieve semi-automatic or fully automatic switching between different chambers.

[0111] The data acquisition and processing module is used to record methane concentration. and The values ​​were calculated, and the emission characteristics of different pathways were analyzed using the Keelingplot method.

[0112] As an extended application, the system of this invention is not only suitable for the study of methane emissions from paddy fields, but can also be extended to typical ecosystems such as wetlands and lakes to realize online isotope observation of methane emissions through multiple pathways, and has broad scientific research and application value.

[0113] like Figure 1As shown, the integrated system for online observation of stable isotopes of methane emission pathways in paddy fields provided by the present invention includes a sampling module, a gas pretreatment module, a stable isotope online analysis module, a multi-channel switching and control module, and a data acquisition and processing module. The sampling module includes a plant sampling device and a non-plant sampling device.

[0114] The data collected in the rice paddies can be used as a reference. Figure 2-3 ,like Figure 2 As shown, the plant cavity covers part of the rice plant to collect methane emissions via the plant-mediated pathway; Figure 3 As shown, the non-plant chambers are located in areas free of rice plants and are used to collect non-plant-mediated emissions, including bubbles and diffusion. Each chamber is connected to the gas pretreatment module via a conduit.

[0115] Figure 4 This is a schematic diagram of the gas pretreatment and gas path connection process described in this invention. The collected gas first enters a gas pretreatment module, which includes a Nafion membrane drying tube and a flow control unit to remove water vapor from the gas and stabilize the flow rate. The pretreated gas is then sent to a high-precision greenhouse gas analyzer, specifically a Picarro G2201-i or G2210-i analyzer based on cavity ring-down spectroscopy (CRDS), to analyze methane concentration and... Continuous measurement.

[0116] Furthermore, a calcium sulfate drying tube is also provided to dry the purge gas.

[0117] Figure 5 This is a schematic diagram of the multi-channel switching and control module described in this invention. The module uses an array of solenoid valves or a manifold device to achieve alternating switching of gases in different chambers, supporting semi-automatic or fully automatic modes. Gas path switching can be set to a timed cycle, such as switching every 5 minutes, or it can be triggered by a concentration mutation signal when a bubble event occurs. In specific applications, the sampling chamber typically operates according to the following procedure: after the chamber is closed, the gas inside the chamber fully interacts with the rice plants or water and mixes evenly. Then, stable observation is maintained for approximately 10 minutes to obtain reliable methane concentration and... After the data observation is completed, the chamber is opened to mix with the outside environment to complete the emptying process, and then the next round of sampling begins. If the channel is switched, the other chamber will be observed in sequence; otherwise, the observation can continue in the same chamber.

[0118] Figure 6 This is a flowchart of the data acquisition and processing module described in this invention. The data acquisition and processing module is responsible for recording methane concentration and... Data was collected and the Keeling plot method was used for emission endmember analysis to distinguish between plant-mediated and non-plant-mediated pathways. In the non-plant chamber data, bubble emissions and diffusion emissions were further distinguished by instantaneous concentration mutation characteristics.

[0119] The system can run continuously throughout the entire growth period of rice paddies, outputting data at the minute level. The data is combined with meteorological and hydrological parameters to form a complete emissions dataset.

[0120] Based on Example 1, this example provides an observation method in a semi-automatic switching mode. In this mode, the multi-channel switching and control module consists of several solenoid valves and manual control switches. The operator can manually or periodically switch between plant chambers and non-plant chambers according to experimental needs, thereby achieving alternating sampling of different emission pathways.

[0121] During semi-automatic operation, the system is typically set to change the sampling channel every 5–10 minutes to ensure that the methane concentration from different pathways is consistent. The data are highly comparable over time. During the switching process, the operator can determine whether a bubble event has occurred by observing changes in gas concentration (sudden surges), and switch to a non-plant chamber for observation if necessary, thereby capturing bubble emission signals.

[0122] To reduce the impact of residual gas during the switching process, the gas path in this embodiment is briefly flushed after each switch to ensure that the gas source entering the analyzer is singular, thereby improving the accuracy and repeatability of the data.

[0123] This embodiment also provides a preferred solution, which can be further configured with a program control unit on the basis of semi-automatic operation to realize timed switching or event-triggered sampling, so as to reduce manual intervention and improve long-term operation capability.

[0124] Through the aforementioned semi-automatic switching mode, the device of the present invention can ensure observation stability while also taking into account the need for path differentiation, making it particularly suitable for long-term field experiments and multi-point synchronous comparative studies by researchers.

[0125] Based on Examples 1 and 2, this example provides the application of the system in a paddy field. The test site is a typical rice-growing area in Jurong City, Jiangsu Province, with a field area of ​​about several acres, which has the conditions for long-term irrigation and rice management.

[0126] During field deployment, transparent plant chambers are installed in areas with concentrated rice plants, covering the stems and some leaves, to collect plant-mediated methane emissions. Non-plant chambers are deployed in water areas without plants to collect non-plant-mediated emissions, including bubbles and diffusion. All chambers are connected to the gas pretreatment module via corrosion-resistant conduits.

[0127] The sampled gas is dried by a Nafion membrane drying tube to remove water vapor, and then corrected using a calibration formula. Residual interference was then detected and analyzed using a Picaro G2201-i analyzer for online measurement. The instrument remained stable throughout the observation period, with a measurement time resolution on the order of minutes.

[0128] During operation, operators switched channels every 5–10 minutes to ensure the continuity and comparability of data from different emission pathways. Several bubble events, characterized by instantaneous spikes in methane concentration, were also recorded during observation; the system was able to capture the corresponding events. The signal provides raw data support for subsequent path differentiation.

[0129] This embodiment demonstrates that the integrated system of the present invention can operate stably in a paddy field environment for a long period of time, successfully achieving alternating sampling and cyclical observation of plant pathways and non-plant pathways, and obtaining continuous methane concentration and isotope data. This provides a solid experimental foundation for subsequent data analysis, pathway differentiation, and model validation.

[0130] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of this application.

[0131] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or terminal device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or terminal device. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or terminal device that includes said element.

Claims

1. A method for online observation of stable isotopes of methane from multiple emission pathways in paddy fields, characterized in that, Includes the following steps: Step S1: Collect methane gas emitted from the rice plant channel using a transparent plant chamber, and collect non-plant mediated emission gas, including bubbles and diffusion, using a non-plant chamber. Step S2: Remove water vapor from the collected gas using a Nafion membrane drying tube, and combine... The correction formula corrects for residual interference; where, The correction formulas include: （1） （2） （3） (4) Where wet represents the measurement value under water content, and dry represents the value under dry baseline conditions. Indicates the water vapor volume fraction (%) measured by the instrument; parameters , , , , It is a correction factor; The gas obtained after correction and The ratio, and It is in the VPDB standard and The ratio; Among them, directly using formula (3) to... The value is corrected; or formulas (1) and (2) are used to correct it first. , The volume fraction was corrected to obtain the corrected gas concentration. and Then, the ratio is calculated according to formula (4) to obtain the result. ; Step S3: Continuously measure methane concentration and... value; Step S4: Switch between different sampling chambers using the multi-channel switching control module to achieve sequential measurement of emissions through multiple pathways; Step S5: Record concentration and isotope data using the data acquisition and processing module, analyze the end-member characteristics of plant-mediated and non-plant-mediated emissions using the Keeling plot method, and identify bubble and diffusion contributions through instantaneous changes in methane concentration. Data processing includes the following steps: Step S51: Preprocess the collected data, including removing transitional data points and abnormal data points at the moment of switching, and detecting and correcting gas path hysteresis. Step S52: Perform linear correction on the observed gas data using the working standard gas; Step S53: Based on the obtained corrected data, establish a Keeling plot using the Keeling plot method. With total methane concentration The linear relationship between the reciprocals is used to calculate the intercept and obtain emission end-member characteristics. Step S54: Output the source data calculated from the keeling plot for each sampling window. Values, the ratio of bubble contribution to diffusion contribution, the number of bubble events, and / or the results of their interaction with environmental factors.

2. The method for online observation of stable isotopes of methane through multiple emission pathways in paddy fields according to claim 1, characterized in that, During the process of gas passing through the Nafion membrane drying tube, flow control is performed to control the flow rate of the gas entering the Nafion membrane drying tube.

3. The method for online observation of stable isotopes of methane through multiple emission pathways in paddy fields according to claim 1, characterized in that, Environmental factors include soil temperature and moisture content parameters.

4. The method for online observation of stable isotopes of methane emission through multiple pathways in paddy fields according to claim 1, characterized in that, The sampling chamber is selected from the LI-8100-104 series sealed chamber, which is divided into plant chamber and non-plant chamber.

5. The method for online observation of stable isotopes of methane emission through multiple pathways in paddy fields according to claim 1, characterized in that, For cavity ring-down spectroscopy (CRDS), the Picarro G2201-i or G2210-i analyzer is selected.

6. An integrated system for online observation of stable isotopes of methane emission through multiple pathways in paddy fields, characterized in that, The integrated system is used to perform the method according to any one of claims 1-5, and the integrated system includes the following modules: The sampling module includes a transparent plant chamber and a non-plant chamber; The gas pretreatment module includes a Nafion membrane drying tube and a flow control unit; The online stable isotope analysis module uses a Picarro G2201-i or G2210-i CRDS analyzer; A multi-channel switching and control module, including a solenoid valve array or manifold device, is used to achieve semi-automatic or fully automatic switching between different chambers. The data acquisition and processing module is used to record methane concentration. and The values ​​were determined, and the emission characteristics of different pathways were analyzed using the Keeling plot method.

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