Method for monitoring gas fluxes of different components in situ in a wetland ecosystem

Abstract

This invention belongs to the field of gas measurement technology, specifically providing a method for in-situ monitoring of gas fluxes of different components in wetland ecosystems. First, before in-situ monitoring, all plant roots and benthic organisms in the sediment of the sample plot to be monitored are removed. Then, flux loops A, B, C, D, and E are fixed in the sample plot according to the method described in this invention. Finally, with simple calculations, the gas fluxes of five components in the wetland ecosystem—sediment, roots, plants, aquatic microorganisms, and aquatic plankton—can be monitored and evaluated. This invention provides a new technology for long-term, fixed-location ecological field monitoring. The method overcomes the limitation of macroscopic monitoring in determining the specific gas fluxes of individual components, providing a scientific basis for formulating protection and management strategies for components such as plants, soil, water, atmosphere, aquatic microorganisms, and plankton in wetland ecosystems.

Description

Technical Field

[0001] This invention belongs to the field of gas measurement technology, specifically relating to a method for in-situ monitoring of the flux of different components of gases in a wetland ecosystem. Background Technology

[0002] Wetlands are transitional zones between land and water. Wetland ecosystems are special transitional ecosystems that lie between terrestrial and aquatic ecosystems. Therefore, they possess abundant resources from both terrestrial and aquatic ecosystems, including plants, soil, water, atmosphere, aquatic microorganisms, and plankton. They have diverse functions and play an irreplaceable role in both human beings and the natural environment.

[0003] The organic carbon pool stored in wetland ecosystems accounts for 20%-30% of the total surface carbon pool in terrestrial ecosystems, and its carbon storage per unit area is three times that of forests. Understanding the CO2 and CH4 gas fluxes of components such as plants, soil, water, atmosphere, aquatic microorganisms, and plankton in wetland ecosystems is particularly important for monitoring wetland carbon sources and sinks.

[0004] Currently, the measurement and assessment of greenhouse gas fluxes (CO2, CH4, etc.) in wetland ecosystems mainly employ macroscopic methods. For example, portable trace gas analyzers (LI-COR, Li-7810, USA) are used to measure greenhouse gas fluxes at the water-air interface, or eddy tower analysis systems (LI-COR, Li-7700, USA) are used to assess greenhouse gas fluxes in the wetland atmosphere. These methods measure gas fluxes in wetland ecosystems macroscopically and cannot determine the CO2 and CH4 fluxes of specific components such as plants, soil, water, atmosphere, aquatic microorganisms, and plankton. However, gas fluxes in wetland ecosystems are composed of multiple components (including sediment components (microbial respiration in sediment), root components (plant root respiration in sediment), plant components (submerged plant respiration), aquatic microbial components (microbial respiration in aquatic bodies), and aquatic plankton components (respiration of planktonic plants and animals in aquatic bodies)). The components of a wetland ecosystem, such as plants, soil, water, atmosphere, aquatic microorganisms, and plankton, are not isolated entities but are interconnected and interact with each other. Without measuring the CO2 and CH4 fluxes of specific components in a wetland ecosystem, it is impossible to further analyze the relationship between environmental variables and greenhouse gas fluxes, and their influencing factors. Therefore, providing a method for measuring the gas fluxes of various components in a wetland ecosystem is of great significance for the protection and management of wetland ecosystems. Summary of the Invention

[0005] The purpose of this invention is to provide a method for in-situ monitoring of gas fluxes of different components in wetland ecosystems, so as to overcome the shortcomings of macroscopic monitoring in determining the specific gas fluxes of components in wetland ecosystems.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for in-situ monitoring of gas fluxes of different components in a wetland ecosystem includes the following steps:

[0008] (1) Select a grid with uniform species diversity in the wetland to be monitored as the test plot. In the year before the in-situ monitoring, drain the water in the test plot, dig out all the bottom mud with plant roots, and remove the plant roots and benthic organisms in the bottom mud. In the spring of the year of in-situ monitoring, backfill the dug bottom mud into the test plot and inject water with a depth of ≥0.5m into it.

[0009] Preferably, the bottom mud is excavated in the winter of the year preceding the in-situ monitoring; plant roots and benthic organisms in the bottom mud can be removed by sequentially drying, air-drying, crushing, and sieving.

[0010] (2) Flux rings A, B, C, D, and E are fixed in the sample plot to be tested as follows: Flux rings A, B, C, D, and E are all elongated cylindrical tubes with the same radius and wall thickness and open at the top. Each of them has two holes on opposite sidewalls at the same height between the bottom sediment and the water surface. The two holes on each flux ring are the same size and opposite in position so that the water can flow normally in the ring and keep the water level consistent with the outside water level.

[0011] ① Inspect and remove the aboveground parts and all roots of the submerged plants germinating in the seed bank of the sediment at the location of flux loop A, and insert flux loop A into the sediment; the depth to which flux loop A is inserted into the sediment is greater than the maximum growth length of the submerged plant roots in the test plot (to prevent the submerged plant roots in the test plot from entering).

[0012] ② Inspect and remove the above-ground parts of the submerged plants that have germinated in the seed bank of the sediment at the location of flux ring B, and insert flux ring B into the sediment; the depth to which flux ring B is inserted into the sediment should be such that it does not obstruct the lateral root growth of the submerged plants.

[0013] ③ Insert flux ring C into the bottom sediment. The depth to which flux ring C is inserted into the bottom sediment should be such that it does not obstruct the lateral root growth of submerged plants.

[0014] ④ Seal the bottom ends of flux ring D and flux ring E, place them on the bottom sediment surface, and seal the two holes on the side wall of flux ring E with a plankton net;

[0015] (3) 24 hours before the start of in-situ monitoring, filter the water in flux loop E with a plankton net and add it;

[0016] (4) The gas fluxes in flux loops A, B, C, D, and E were measured using a gas flux measuring instrument, and the gas fluxes of different components in the wetland ecosystem under test were calculated using the following formula:

[0017] Sediment component gas flux = Gas flux in flux loop A - Gas flux in flux loop D;

[0018] Root component gas flux = Flux loop B gas flux - Flux loop A gas flux;

[0019] Plant component gas flux = Gas flux in flux loop C - Gas flux in flux loop B;

[0020] Aquatic microbial component gas flux = flux ring E gas flux;

[0021] Gas flux of phytoplankton components in water = Gas flux of flux loop D - Gas flux of flux loop E

[0022] The specific composition of the wetland ecosystem and the settings of each gas flux loop are as follows: Figure 1 As shown, the specific gas flux composition of each flux loop is as follows:

[0023] The gas flux in flux loop A consists of three parts: the gas flux of sediment components, the gas flux of aquatic microorganism components, and the gas flux of aquatic plankton components.

[0024] The gas flux in the flux loop B consists of four parts: sediment components, root components, aquatic microbial components, and aquatic planktonic components.

[0025] The gas flux in flux loop C consists of five components: sediment component, root component, plant component, aquatic microbial component, and aquatic planktonic component.

[0026] The gas flux in flux loop D consists of two parts: the gas flux of the aquatic microbial component and the aquatic planktonic component.

[0027] The gas flux in flux loop E consists solely of the gas flux from the aquatic microbial components.

[0028] Furthermore, flux rings A, B, C, D, and E are all made of highly transparent acrylic material to eliminate the influence of light on gas flux measurement.

[0029] Furthermore, flux rings A, B, C, D, and E each have two holes on their opposite sidewalls at half the water depth.

[0030] Furthermore, flux loops A, B, C, D, and E all protrude above the water surface, with the same or different heights above the water surface.

[0031] Furthermore, before measuring the gas flux in flux rings A, B, C, D, and E using a gas flux measuring instrument, a wooden stick is used to pry open the outer wall of each flux ring, removing any plants that have entered the ring through the side wall openings, and then the side wall openings are sealed. Preferably, a rubber band is used to cover the openings of the flux rings to seal them.

[0032] Furthermore, in step (2), the fixation time of flux loop A is before the bottom sediment backfill, and the fixation time of flux loops B, C, D, and E is after the bottom sediment backfill.

[0033] Furthermore, in step (2), the flux rings B and C are inserted into the sediment to a depth of 5-10 cm.

[0034] Furthermore, in step (2), the fixed intervals of flux rings A, B, C, D, and E are 10-20 cm.

[0035] Furthermore, the aperture size of the planktonic net is designed to intercept planktonic organisms, preferably 0.064 mm.

[0036] Furthermore, during the experimental measurement, the instrument can only be operated around the sample site to be tested, and the water body must not be disturbed. The entire measurement process must be kept quiet to reduce interference with the surrounding environment of the gas flux loop and affect the measurement data of gas flux in each loop, so as to ensure that the obtained measurement data is true and reliable.

[0037] The beneficial effects of this invention are as follows:

[0038] This invention provides a method for in-situ monitoring of gas fluxes of different components in wetland ecosystems. By fixing five flux loops according to this method, gas fluxes of five components—sediment, roots, plants, aquatic microorganisms, and aquatic plankton—in the wetland ecosystem can be monitored and assessed with simple calculations. Flux data of different components in wetland ecosystems will help us to accurately assess the fluxes of gases such as CO2 and CH4 for each component, deepen our understanding of wetlands, and provide a scientific basis for formulating protection and management strategies for components such as plants, soil, water, atmosphere, aquatic microorganisms, and plankton in wetland ecosystems. This invention will provide a new technology for long-term, fixed-location ecological field monitoring. Attached Figure Description

[0039] Figure 1 A schematic diagram showing the composition of the wetland ecosystem and the various gas flux loops.

[0040] Figure 2This is a schematic diagram illustrating the in-situ monitoring of gas fluxes of different components in a wetland ecosystem. Detailed Implementation

[0041] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0042] The method for in-situ monitoring of different component gas fluxes in wetland ecosystems using the present invention includes the following steps:

[0043] (1) Setting up fixed sample plots and fixed quadrats

[0044] In the wetland to be tested, a 4×4 m square with uniform species diversity was selected as the test plot. A 0.5×2 m fixed quadrat was set up in the test plot to fix flux loops A, B, C, D and E, with each gas flux loop spaced 20 cm apart.

[0045] (2) Sample plot treatment

[0046] A 4×4 m enclosure with a height of 1.5 m was set up around the sample plot to be tested. In the winter of the year preceding in-situ monitoring, the water within the enclosure was pumped out, and the bottom sediment within the enclosure was excavated 2 m underground and completely removed. The sediment was then dried, air-dried, broken up, and passed through a 4 mm mesh sieve to remove plant roots and benthic organisms. The sieved soil was then thoroughly mixed and set aside for later use.

[0047] Submerged plants were not sown in the soil of the test plots; instead, germplasm resources from the seed bank of the bottom sediment germplasm were used for germination.

[0048] (3) Sample plot backfilling and gas flux loop setup.

[0049] In the spring of the same year as the in-situ monitoring, the soil from step (2) was backfilled into the enclosure of the 4×4 m test plot, and the water level inside the enclosure was controlled to be 0.5 m using an automatic water inlet device. Five flux loops were fixed as follows:

[0050] ① Inspect and remove any submerged plants germinating in the seed bank of the sediment where flux loop A is located, and remove the above-ground parts and all roots of the submerged plants with a small rake; before backfilling the sediment, insert flux loop A into the sediment to a depth of 90 cm (i.e., the bottom of flux loop A is 90 cm from the surface of the sediment).

[0051] ② Inspect and remove any submerged plants germinating in the seed bank of the substrate where flux ring B is located, and remove the above-ground parts of the submerged plants with a small rake; after backfilling the substrate, insert flux ring B 10 cm into the substrate (so as not to obstruct the lateral root growth of the submerged plants).

[0052] ③ After backfilling the bottom mud, insert the flux ring C 10 cm into the bottom mud (so as not to block the horizontal root growth of submerged plants).

[0053] ④ After backfilling the bottom sediment, seal the bottom ends of flux rings D and E and place them on the surface of the bottom sediment; and use a plankton net to seal the two holes on the side wall of flux ring E.

[0054] The flux rings A, B, C, D, and E are all long, round tubes made of transparent acrylic material, with an outer diameter of 20 cm, a wall thickness of 0.3 cm, and an inner diameter of 19.4 cm. When fixed, each ring protrudes 10 cm above the water surface (flux ring A is 150 cm high, flux rings B and C are 70 cm high, and flux rings D and E are 60 cm high). At a water depth of 25 cm, each ring has two holes on its opposite sidewall to allow water to flow normally within the ring and maintain the same water level as the outside water.

[0055] (4) 24 hours before the measurement, filter the water in flux loop E with a plankton net and add it;

[0056] (5) Measurement of gas flux values ​​for each ring (specifically, the in-situ monitoring diagram at the sample site is shown in the figure below). Figure 2 (As shown)

[0057] Before measuring the gas flux data, use a wooden stick to move around the outer wall of the gas flux ring to remove the plants that have entered the ring through the opening, and then use a 10 cm wide rubber band to cover the opening of the flux ring to seal it.

[0058] The CO2 and CH4 fluxes of each flux loop were measured three times a month using a Li-7810 (LI-COR, Lincoln, Nebraska, USA) instrument (usually around the 5th, 15th, and 25th). Each measurement was taken on a clear morning between 9:00 and 11:00.

[0059] During the experiment, the instrument should only be operated around the sample site to be tested. The water body should not be disturbed. The entire measurement process should be kept quiet to reduce interference with the surrounding environment of the gas flux loop and affect the measurement data of gas flux in each loop, so as to ensure that the obtained measurement data is true and reliable.

[0060] step:

[0061] a. The Li-7810 main unit and Smart Chamber should be powered on and warmed up for 30 minutes to ensure stable instrument readings;

[0062] b. Set the measurement parameters: pipeline length 200 cm, gas flow loop cross-sectional area 295.59 cm². 2 The gas flux loop was 10 cm above the water surface. The measurement duration was 60 s, with a 15 s interval between air changes.

[0063] c. Gently place the modified gas chamber on top of the gas flux loop (avoid vibration affecting the measurement data), click start, and begin measurement;

[0064] d. Set tags and save data;

[0065] e. After the measurement is completed, remove the 10 cm wide rubber band loop to make the environment inside and outside the loop the same.

[0066] (6) Gas flux data processing

[0067] The monthly average is calculated by averaging multiple measurements of gas flux in each flux loop for the same month. The annual average is calculated by averaging the values ​​of the nine months of the same year (in northern my country, water bodies freeze in winter; in southern China, measurements can be taken for all 12 months). Seasonal values ​​are calculated by averaging the corresponding monthly averages: spring values ​​are the average from March to May, summer values ​​are the average from June to August, and autumn values ​​are the average from September to November. Specific gas flux measurement results are shown in Tables 1 and 2.

[0068] Table 1. Quarterly average CO2 flux for each flux ring

[0069]

[0070] Table 2. Quarterly average CH4 flux for each flux ring

[0071]

[0072] The gas flux in flux loop A consists of three components: sediment, aquatic microorganisms, and phytoplankton. The gas flux in flux loop B consists of four components: sediment, root system, aquatic microorganisms, and phytoplankton. The gas flux in flux loop C consists of five components: sediment, root system, plant, aquatic microorganisms, and phytoplankton. The gas flux in flux loop D consists of two components: aquatic microorganisms and phytoplankton. The gas flux in flux loop E consists solely of the gas flux from aquatic microorganisms.

[0073] The gas fluxes of different components in the wetland ecosystem under test were calculated using the following formulas, and the results are shown in Tables 3 and 4:

[0074] Sediment component gas flux = Gas flux in flux loop A - Gas flux in flux loop D;

[0075] Root component gas flux = Flux loop B gas flux - Flux loop A gas flux;

[0076] Plant component gas flux = Gas flux in flux loop C - Gas flux in flux loop B;

[0077] Aquatic microbial component gas flux = flux ring E gas flux;

[0078] Gas flux of phytoplankton components in water = Gas flux of flux loop D - Gas flux of flux loop E

[0079] Table 3. Quarterly average CO2 flux of each component

[0080]

[0081] Table 4. Quarterly average CH4 flux of each component

[0082]

[0083] The results in Tables 1 and 3 show that in wetland ecosystems, sediment, root system, and aquatic microorganisms emit CO2, which serves as carbon sources; plant components and aquatic plankton absorb CO2, which serves as carbon sinks; and the total CO2 absorption of the entire wetland ecosystem exceeds its emissions, which also serves as a carbon sink.

[0084] The results in Tables 2 and 4 show that in wetland ecosystems, sediment, plant, root, plankton, and microbial components all emit CH4, which serves as a carbon source. CH4 emissions in wetland ecosystems mainly originate from sediment and root components, and plant components promote CH4 emissions.

[0085] The above embodiments are only used to illustrate the present invention. Any equivalent modifications and improvements made based on the technical solutions of the present invention should not be excluded from the protection scope of the present invention.

Claims

1. A method for in-situ monitoring of gas fluxes of different components in a wetland ecosystem, characterized in that, Includes the following steps: (1) Select a grid with uniform species diversity in the wetland to be monitored as the test plot. In the year before the in-situ monitoring, drain the water in the test plot, dig out all the bottom mud with plant roots, and remove the plant roots and benthic organisms in the bottom mud. In the spring of the year of in-situ monitoring, backfill the dug bottom mud into the test plot and inject water with a depth of ≥0.5m into it. (2) Flux rings A, B, C, D, and E are fixed in the sample plot to be tested as follows: Flux rings A, B, C, D, and E are all elongated cylindrical tubes with the same radius and wall thickness and open at the top. Each tube has two holes on its opposite sidewall at the same height between the bottom sediment and the water surface. The two holes on each flux ring are the same size and are positioned opposite each other. ① Inspect and remove the aboveground parts and all roots of the submerged plants germinating in the seed bank of the sediment at the location of flux loop A, and insert flux loop A into the sediment; the depth to which flux loop A is inserted into the sediment is greater than the maximum growth length of the submerged plant roots in the sample plot to be tested. ② Inspect and remove the above-ground parts of the submerged plants germinating in the seed bank of the sediment at the location of flux ring B, and insert flux ring B into the sediment; the depth to which flux ring B is inserted into the sediment does not obstruct the lateral root growth of the submerged plants. ③ Insert flux ring C into the bottom sediment, wherein the depth to which flux ring C is inserted into the bottom sediment does not obstruct the lateral root growth of submerged plants. ④ Seal the bottom ends of flux ring D and flux ring E, place them on the bottom sediment surface, and use a plankton net to seal the two holes on the side wall of flux ring E; (3) 24 hours before the start of in-situ monitoring, filter the water in flux loop E with a plankton net and add it; (4) The gas fluxes in flux loops A, B, C, D, and E were measured using a gas flux measuring instrument, and the gas fluxes of different components in the wetland ecosystem under test were calculated using the following formula: Sediment component gas flux = Gas flux in flux loop A - Gas flux in flux loop D; Root component gas flux = Flux loop B gas flux - Flux loop A gas flux; Plant component gas flux = Gas flux in flux loop C - Gas flux in flux loop B; Aquatic microbial component gas flux = flux ring E gas flux; Gas flux of phytoplankton components in water = Gas flux of flux loop D - Gas flux of flux loop E 2. The method for in-situ monitoring of gas fluxes of different components in a wetland ecosystem according to claim 1, characterized in that, Flux rings A, B, C, D, and E are all made of high-transmittance acrylic material.

3. The method for in-situ monitoring of gas fluxes of different components in a wetland ecosystem according to claim 1, characterized in that, Flux rings A, B, C, D, and E each have two holes on their opposite sidewalls at half the water depth.

4. The method for in-situ monitoring of gas fluxes of different components in a wetland ecosystem according to claim 1, characterized in that, Flux loops A, B, C, D, and E are all above the water surface, and the heights above the water surface may be the same or different.

5. The method for in-situ monitoring of gas fluxes of different components in a wetland ecosystem according to claim 1, characterized in that, Before measuring the gas flux in flux rings A, B, C, D, and E using a gas flux measuring instrument, use a wooden stick to poke around the outer wall of each flux ring to remove the plants that have entered the ring through the side wall openings, and then seal the side wall openings.

6. The method for in-situ monitoring of gas fluxes of different components in a wetland ecosystem according to claim 1, characterized in that, In step (2), the fixation time of flux loop A is before the bottom sediment backfill, and the fixation time of flux loops B, C, D and E is after the bottom sediment backfill.

7. The method for in-situ monitoring of gas fluxes of different components in a wetland ecosystem according to claim 1, characterized in that, In step (2), the flux rings B and C are inserted into the sediment to a depth of 5-10 cm.

8. The method for in-situ monitoring of gas fluxes of different components in a wetland ecosystem according to claim 1, characterized in that, In step (2), the fixed intervals of flux loops A, B, C, D, and E are 10-20 cm.

9. The method for in-situ monitoring of gas fluxes of different components in a wetland ecosystem according to claim 1, characterized in that, The aperture size of the planktonic net is designed to intercept planktonic organisms.

10. A method for in-situ monitoring of gas fluxes of different components in a wetland ecosystem according to claim 9, characterized in that, The pore size of the planktonic net is 0.064 mm.

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