A method and device for calculating a reference value of soil carbon flux in a wind-turbulent environment

Abstract

The present invention discloses a method and device for calculating the reference value of soil carbon flux in a wind-turbulence environment, relating to the field of measurement technology. Compared with the previous method of measuring soil respiration value, i.e., the chamber method, the present invention solves the problem of how to avoid the influence of wind turbulence on the reliability of measurement values. In terms of the calculation principle, the principle of mass conservation is used, and on the basis of the previous generation, the influence of wind turbulence on chamber measurement is considered, so that the device can also be used normally in the field environment and can provide more accurate values in terms of measurement results. In terms of structural design, the device is light-weighted, and the analysis device and the diffusion chamber are separated, making the device convenient to operate during the processes of carrying, using and later maintenance. And all function keys of the device are integrated on the control main board, various functions are visualized, and the operation is simple and easy to master, having certain commercial promotion value.

Description

Technical Field

[0001] The present invention relates to the field of measurement technology, and particularly to a method and device for calculating a reference value of soil carbon flux in a wind-turbulent environment. Background Art

[0002] Global warming is one of the important environmental problems faced by the world today. Global warming not only threatens biodiversity and the stability of ecosystems, but also poses a huge threat to human society, economic development and people's lives. An important cause of global warming is the excessive greenhouse gases such as methane (CH4), carbon dioxide (CO2) and nitrous oxide (N2O), which accumulate in the atmospheric system, and the excessive heat generated by surface radiation cannot dissipate, resulting in an increase in atmospheric temperature. Among them, CO2 is the most important long-lived greenhouse gas, making a significant contribution to the greenhouse effect of the earth. CO2 accounts for about 66% of the climate warming effect. In addition, from 1990 to 2020, the radiative forcing (warming effect on climate) of long-lived greenhouse gases increased by 47%, and CO2 accounted for about 80% of this increase. This shows that CO2 plays an extremely important role in the greenhouse effect. Soil is one of the main sources of these greenhouse gases, and the amount of CO2 released from the soil globally each year reaches 98±12 Pg C, about 15 times the current annual release amount from fossil fuel combustion. Soil respiration is an important mechanism for the exchange of CO2 between terrestrial ecosystems and the atmospheric system. Even a small change in soil respiration may significantly change the atmospheric CO2 concentration level and directly affect the global climate. How to measure soil respiration is a challenging task because it involves a variety of complex biological, chemical and physical processes, and the accuracy and reliability of its measured values directly affect the estimation of soil carbon flux and the understanding of the dynamics of ecosystem carbon cycling.

[0003] In order to estimate the flux generated by soil respiration in terrestrial ecosystems and understand the soil CO2 emission situation, in the past few decades, researchers have developed many methods to measure soil respiration, including: chamber method, isotope labeling method, box method, gas well method, eddy covariance method, etc. Each method has its advantages, disadvantages and scope of application. In actual measurement, the chamber method has the highest usage rate due to its simplicity and speed, accounting for more than 95%. Currently, the commonly used methods are the closed dynamic chamber method and the open chamber method. The closed dynamic chamber method calculates the soil CO2 flux by fitting the model according to the change rate of CO2 concentration in the chamber over time. The open chamber method calculates the soil CO2 flux based on the gas flow rate and the CO2 concentration difference between the inlet and outlet of the chamber. However, in terms of the current usage quantity, the closed dynamic chamber method still accounts for the vast majority of the usage. However, using the chamber method to measure soil respiration value is a challenging task. Because during the measurement process, due to the interference of external environmental factors, the measurement results will be biased, especially in the wind-turbulent environment. Because currently it is generally believed that the gas movement in the soil is mainly controlled by molecular diffusion, however, advection can also change the soil gas transport. In addition, during high wind speed periods, the soil gas transport is enhanced, and this enhancement is due to the dynamic change of the air pressure field above the soil, which enhances the advection-dispersion of the soil gas transport in the soil pores, called the wind-induced pressure pump effect. Since the gas transport induced by wind-turbulence often has the characteristics of high frequency and short duration, for the closed chamber with short-period measurement, wind-turbulence is the most important influencing factor. Therefore, under the influence of wind-turbulence, we cannot consider the flux value obtained by fitting calculation of the flux model to be effective, and this phenomenon is difficult to avoid during field measurement.

[0004] To solve the above problems, the present invention proposes a method and device for calculating the reference value of soil carbon flux in a wind-turbulent environment. Summary of the Invention

[0005] The purpose of the present invention is to propose a method and device for calculating the reference value of soil carbon flux in a wind-turbulent environment to solve the problems raised in the background technology:

[0006] How to avoid the influence of wind-turbulence on the reliability of measurement values.

[0007] To achieve the above purpose, the present invention adopts the following technical solutions:

[0008] A device for calculating the reference value of soil carbon flux in a wind-turbulent environment, comprising: an analysis device with a frustum structure on the upper part and a diffusion chamber with a cylindrical structure on the lower part; the analysis device includes a measurement part and a display part, and the diffusion chamber includes a medium layer and a chamber layer, separated by a layer of fine wire mesh in the middle.

[0009] Preferably, the interior of the measurement part is an empty cylinder for connecting to the diffusion gas chamber of the lower cylinder structure. The measurement part further includes a gas storage cylinder, an air pump, and a flow meter connected in sequence. The left and right sides of the measurement part are provided with air inlet and outlet ports.

[0010] Preferably, the display part is composed of a display screen, a knob, buttons, and a control main board. The display screen is arranged at the upper left of the display part for displaying the flow rate indication of the internal CO2 concentration sensor and the flow meter and the flux calculation result. The knob is arranged on the right side of the display screen for adjusting the air pump flow rate. The buttons are arranged below the display screen for controlling the display screen switch. The control main board is arranged inside the display part.

[0011] Preferably, the medium layer is used for placing a porous medium. Three CO2 concentration sensors are arranged in a stepped manner at different heights inside the medium layer for measuring the change of CO2 concentration inside the porous medium.

[0012] Preferably, five CO2 concentration sensors are arranged in a stepped manner at different heights inside the gas chamber layer to monitor the change of CO2 concentration inside the gas chamber layer in real time. A differential pressure sensor is arranged at the bottom of the inner side of the gas chamber layer. Two air inlet and outlet holes are arranged on each of the left and right sides of the gas chamber layer. The air inlet and outlet holes are all connected to the internal air pipe. The upper hole is the air inlet, which is connected to the gas storage cylinder through a hose. The lower hole is the air outlet, which is connected to the air pump inlet through a hose. The CO2 concentration sensors are all connected to the control main board of the display part.

[0013] A method for calculating the reference value of soil carbon flux in a wind-turbulent environment includes the following steps:

[0014] Taking molecular diffusion as the gas exchange mechanism between the soil and the atmosphere, CO2 diffuses from the area with high concentration to the area with low concentration. According to Fick's first law, the CO2 flux at this time is:

[0015]

[0016] where F is the CO2 flux; D is the diffusion coefficient of CO2 in the soil; C is the CO2 concentration in the soil; is the gradient operator;

[0017] When the diffusion process is unsteady, the concentration of a substance at any position in space changes with time and is calculated by Fick's second law:

[0018]

[0019] where t is time; div() and grad() are both operation functions;

[0020] When the environmental variables affect the diffusion process, the mechanism controlling gas exchange changes to molecular diffusion and convective diffusion. At this time, the flux is calculated by the convective diffusion equation:

[0021]

[0022] where u is the gas velocity; S is the source term;

[0023] The experimental soil treated by high-temperature drying and sterilization does not produce CO2, so S = 0; the CO2 concentration in the chamber to be verified is uniformly distributed in space, and the diffusion process is continuous; and the lateral transport of gas in the chamber to be verified and in the soil does not affect the flux value measured in the chamber; therefore, the gas diffusion in the vertical direction is calculated, and the above equation is simplified to the following equation;

[0024]

[0025] where x is the effective distance;

[0026] The gas transport equations in the soil and in the chamber to be verified are derived from the above equation, and a system of equations is constructed to obtain the following equation:

[0027]

[0028] where C S is the CO2 concentration in the soil; D S is the CO2 diffusion coefficient in the soil; h is the soil thickness; C a is the CO2 concentration in the chamber to be verified; D a is the CO2 diffusion coefficient in the chamber to be verified; H is the height of the chamber to be verified; Integrate both sides of the system of equations and combine with the above equation to get:

[0029]

[0030] where V S is the soil volume; V a is the volume of the chamber to be verified; Δ is the change;

[0031]

[0032] where A S is the effective area of the soil; is the CO2 flux at the lower surface of the soil; is the CO2 flux at the upper surface of the soil; A a is the effective area of the chamber to be verified; is the CO2 flux at the lower surface of the chamber to be verified; is the CO2 flux at the upper surface of the chamber to be verified; is the CO2 concentration entering the chamber to be verified; is the CO2 concentration leaving the chamber to be verified; where:

[0033]

[0034]

[0035] A S = A a

[0036] Obtained:

[0037]

[0038] From this, the reference value of soil carbon flux is calculated

[0039] Compared with the prior art, the present invention provides a method and device for calculating the reference value of soil carbon flux in a wind-turbulence environment, having the following beneficial effects:

[0040] In the calculation principle, the present invention uses the principle of mass conservation and, on the basis of the predecessors, considers the influence of wind turbulence on chamber measurement, enabling the normal use of this device in the field environment and providing a more accurate value in the measurement result. In the structural design, the device is light-weighted and the analysis device and the diffusion chamber are separated, making the device convenient to operate during the carrying process, use process, and later maintenance process. And all function keys of this device are integrated on the control main board, with various functions visualized and simple to operate, having a certain commercial promotion value. Brief Description of the Drawings

[0041] Figure 1 is a schematic diagram of the device mentioned in Embodiment 1 of the present invention.

[0042] Meanings of the marks in the figure:

[0043] 1. Analysis device; 2. Diffusion chamber; 3. Measurement part; 4. Display part; 5. Gas storage cylinder; 6. Air pump; 7. Flowmeter; 8. Display screen; 9. Knob; 10. Button; 11. Medium layer; 12. Chamber layer; 13. Fine wire mesh; 14. CO2 concentration sensor; 15. Differential pressure sensor; 16. Air hole; 17. Internal air pipe. Detailed Embodiments

[0044] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0045] The present invention uses the principle of mass conservation in its calculation principle and takes into account the influence of wind turbulence on the measurement of the gas chamber on the basis of previous generations, enabling the device to be used normally in the field environment and providing more accurate values in the measurement results. In terms of structural design, the device is lightweight and the analysis device and the diffusion gas chamber are separated, making the device convenient to operate during the carrying process, use process, and later maintenance process. And all function keys of the device are integrated on the control main board, various functions are visualized, and the operation is simple and easy to master, having certain commercial promotion value. The specific contents are as follows.

[0046] Embodiment 1:

[0047] Please refer to Figure 1 , a method and device for calculating the reference value of soil carbon flux in a wind turbulence environment according to the present invention, including: an analysis device 1 with a quadrangular frustum structure on the upper part and a diffusion gas chamber 2 with a cylindrical structure on the lower part; the inside of the analysis device 1 is an empty cylinder for connecting with the diffusion gas chamber 2 with a cylindrical structure below. The upper surface of the quadrangular frustum structure is 10 cm long and 10 cm wide, and the inside is a hollow circle with a diameter of 10 cm; the lower surface is 10 cm long and 20 cm wide, and the inside is a hollow circle with a diameter of 10 cm; the upper bottom of the side is 10 cm long, the lower bottom is 20 cm long, and the height is 10 cm. The upper surface of the cylindrical structure is a circle with a diameter of 10 cm, and the height of the cylinder is 20 cm.

[0048] The analysis device 1 includes a measurement part 3 and a display part 4.

[0049] Above the measurement part 3, a gas chamber device to be calibrated can be placed. The inside of the measurement part 3 is an empty cylinder for connecting with the diffusion gas chamber 2 with a cylindrical structure below. The measurement part 3 further includes a gas storage bottle 5, an air pump 6, and a flowmeter 7 connected in sequence. Air inlet and outlet ports are also provided on the left and right sides of the measurement part 3.

[0050] The display part 4 consists of a display screen 8, a knob 9, a button 10, and a control main board; the display screen 8 is arranged in the upper left corner of the display part 4 for displaying the flow readings of the internal CO2 concentration sensor 14 and the flowmeter 7 and the flux calculation result. The knob 9 is arranged on the right side of the display screen 8 for adjusting the flow of the air pump 6. The button 10 is arranged below the display screen 8 for controlling the switch of the display screen 8. The control main board is arranged inside the display part 4.

[0051] The diffusion gas chamber 2 includes a medium layer 11 and a gas chamber layer 12, separated by a layer of fine wire mesh 13 in the middle. The fine wire mesh 13 is a circle with a diameter of 10 cm and is at a height of 10 cm in the cylinder.

[0052] The medium layer 11 is used to place porous media. Three CO2 concentration sensors 14 are arranged in a stepped manner at different heights inside the medium layer 11 for measuring the change of CO2 concentration inside the porous media.

[0053] Inside the gas chamber layer 12, five CO2 concentration sensors 14 are arranged in a stepped manner at different heights to monitor the change of CO2 concentration inside the gas chamber layer 12 in real time. A differential pressure sensor 15 is arranged at the inner bottom of the gas chamber layer 12. There are 2 air inlet and outlet holes 16 on each of the left and right sides of the gas chamber layer 12. A total of 4 air inlet and outlet holes 16 on the left and right sides are arranged at the same height. The air inlet and outlet holes 16 are all connected to the "∞"-shaped internal air pipe 17. The internal air pipes 17 are respectively distributed at 2.5 cm and 7.5 cm in height. The upper air hole 16 is the air inlet, which is connected to the gas storage cylinder 5 through a hose; the lower air hole 16 is the air outlet, which is connected to the air inlet of the air pump 6 through a hose. The CO2 concentration sensors 14 are all connected to the control main board of the display part 4.

[0054] This device can provide accurate CO2 flux, can test the accuracy of measuring instruments, and this device is convenient to carry and easy to operate, can display measurement data in real time, can be used in field experiments, and has certain popularization value and commercial value.

[0055] Example 2:

[0056] Before each measurement starts, first calibrate the readings of a total of 8 CO2 concentration sensors 14 in the gas chamber layer 12 and the medium layer 11. First, place a calibrated CO2 concentration sensor 14 in the gas storage cylinder 5 and connect it to the control main board, and then seal the upper part of the analysis device 1; then turn on the total power of the device. At this time, the readings of each CO2 concentration sensor 14 can be observed from the display screen 8; then turn on the switch of the air pump 6, adjust the air pump 6 through the knob 9 and observe the reading of the flowmeter 7 to control the flow rate at 0.3 L min -1 . After waiting for 5 minutes for the diffusion gas chamber 2 to reach a stable state, observe the readings of each CO2 concentration sensor 14. If its reading is different from that of the CO2 concentration sensor 14 in the gas storage cylinder 5, select the corresponding CO2 concentration sensor 14 and adjust it to the same value. If there are multiple abnormal values, all CO2 concentration sensors 14 can also be set to the same value at one time.

[0057] After calibration, turn off the air pump 6, open the diffusion gas chamber 2, and evenly fill it with porous media (such as quartz sand, soil, etc.) that have been sterilized at high temperature. The maximum height is 10 cm, and the filling volume can be adjusted according to experimental needs. At the same time, arrange 3 CO2 concentration sensors 14 inside the porous media.

[0058] Finally, connect the gas storage cylinder 5 to the air inlet of the device with a hose. After the device is installed, open the gas valve to introduce CO2 into the diffusion gas chamber 2, and at the same time turn on the switch of the air pump 6, adjust the knob 9 of the gas storage cylinder 5 and observe the dial reading to adjust it to 0.3 L min -1 . Similarly, adjust the knob 9 of the air pump 6 and observe the reading of the flowmeter 7 to adjust it to 0.3 L min-1 When the readings of the 5 CO₂ concentration sensors 14 in the gas chamber layer 12 change by less than 1% within 20 minutes, the diffusion gas chamber 2 reaches a stable state.

[0059] After placing the gas chamber to be verified, V a is the volume of the gas chamber, and C a is the CO₂ concentration in the gas chamber. A a is the bottom area of the gas chamber, which is equal to the cross-sectional area of the diffusion gas chamber 2. A S , that is, the area of a circle with a radius of 5 cm; Q is the flow rate equal to 0.3 L / min -1 , and at this time, the gas velocity u is obtained by dividing Q by A S . is the CO₂ concentration in the gas storage cylinder 5, is the reading of the CO₂ concentration sensor 14 in the gas storage cylinder 5, and V S is the filling volume of the porous medium, and C S is the average value of the 3 CO₂ concentration sensors 14 in the porous medium. At this time, the reference value of the flux can be calculated The control main board will display the calculated flux value on the display screen 8.

[0060] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and all should be covered within the protection scope of the present invention.

Claims

1. A method for calculating the reference value of soil carbon flux in a wind-turbulent environment, characterized in that, The method is implemented based on a device for calculating the reference value of soil carbon flux in a wind-turbulent environment. The device includes an analysis device (1) with a frustum structure at the upper part and a diffusion chamber (2) with a cylindrical structure at the lower part. The analysis device (1) includes a measurement part (3) and a display part (4). The diffusion chamber (2) includes a medium layer (11) and a chamber layer (12), which are separated by a layer of fine wire mesh (13) in the middle. The method includes the following steps: Taking molecular diffusion as the gas exchange mechanism between the soil and the atmosphere, CO2 diffuses from the region with a high concentration to the region with a low concentration. According to Fick's first law, the CO2 flux at this time is: Among them, F is the CO2 flux; D is the diffusion coefficient of CO2 in the soil; C is the CO2 concentration in the soil; is the gradient operator; When the diffusion process is unsteady, the concentration of a substance at any position in space changes with time, which is calculated by Fick's second law: where t is time; div() and grad() are both operation functions. When environmental variables affect the diffusion process, the mechanism controlling gas exchange at this time changes to molecular diffusion and convective diffusion, and the flux is calculated by the convective diffusion equation at this time: where u is the gas velocity; S is the source term. The experimental soil treated by high-temperature drying and sterilization does not produce CO2, so S = 0; the CO2 concentration in the chamber to be verified is uniformly distributed in space, and the diffusion process is continuous; and the lateral transport of gas in the chamber to be verified and in the soil does not affect the flux value measured in the chamber. Therefore, when calculating the gas diffusion in the vertical direction, the above formula is simplified to the following formula: where x is the effective distance. The gas transport equations in the soil and in the chamber to be verified are derived from the above formula, and a system of equations is constructed to obtain the following formula: Among them, C S is the CO2 concentration in the soil; D S is the CO2 diffusion coefficient in the soil; h is the soil thickness; C a is the CO2 concentration in the air chamber to be verified; D a is the CO2 diffusion coefficient in the air chamber to be verified; H is the height of the air chamber to be verified; Solve the integral on both sides of the system of equations and combine the above formula to obtain: Among them, V S is the soil volume; V a is the volume of the air chamber to be verified; Δ is the change amount; Among them, A S is the effective area of the soil; is the CO2 flux on the lower surface of the soil; is the CO2 flux on the upper surface of the soil; A a is the effective area of the chamber to be verified; is the CO2 flux on the lower surface of the chamber to be verified; is the CO2 flux on the upper surface of the chamber to be verified; is the CO2 concentration entering the chamber to be verified; is the CO2 concentration leaving the chamber to be verified; Among them: Obtain: The reference value of soil carbon flux is calculated therefrom 2. The method for calculating the reference value of soil carbon flux in a wind-turbulent environment according to claim 1, wherein The interior of the measurement part (3) is an empty cylinder, which is used to connect with the diffusion chamber (2) with a cylindrical structure at the lower part. The measurement part (3) also includes a gas storage cylinder (5), an air pump (6) and a flowmeter (7) connected in sequence. The left and right sides of the measurement part (3) are provided with air inlets and outlets.

3. The method for calculating the reference value of soil carbon flux in a wind-turbulent environment according to claim 2, characterized in that, The display part (4) consists of a display screen (8), a knob (9), a button (10) and a control main board. The display screen (8) is arranged at the upper left of the display part (4), and is used to display the flow rate readings of the internal CO2 concentration sensor (14) and the flowmeter (7) and the flux calculation result. The knob (9) is arranged on the right side of the display screen (8) and is used to adjust the flow rate of the air pump (6). The button (10) is arranged below the display screen (8) and is used to control the switch of the display screen (8). The control main board is arranged inside the display part (4).

4. The method for calculating the reference value of soil carbon flux in a wind-turbulent environment according to claim 3, characterized in that, The medium layer (11) is used to place a porous medium. Three CO2 concentration sensors (14) are arranged in a stepped manner at different heights inside the medium layer (11) to measure the change of CO2 concentration inside the porous medium.

5. The method for calculating the reference value of soil carbon flux in a wind-turbulent environment according to claim 4, wherein Inside the air chamber layer (12), five CO2 concentration sensors (14) are arranged in a stepped manner at different heights to monitor the change of CO2 concentration inside the air chamber layer (12) in real time. A differential pressure sensor (15) is arranged at the inner bottom of the air chamber layer (12). Two air inlet and outlet holes (16) are arranged on each of the left and right sides of the air chamber layer (12). The air inlet and outlet holes (16) are all connected to the internal air pipe (17). The upper air hole (16) is the air inlet, which is connected to the gas storage cylinder (5) through a hose; the lower air hole (16) is the air outlet, which is connected to the air inlet of the air pump (6) through a hose. The CO2 concentration sensors (14) are all connected to the control main board of the display part (4).

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