Method for measuring pore water carbon exchange flux of mangrove forest in large-scale estuary area

Abstract

The invention relates to the technical field of mangrove forest pore water carbon exchange determination, in particular to a method for determining the pore water carbon exchange flux of a mangrove forest in a large-scale estuary area. Comprising the following steps: selecting a plurality of monitoring communities: selecting mangrove forest communities with the same age as the monitoring communities, wherein the mangrove forest communities are located along the estuary and in the upstream, downstream and downstream regions of the estuary and have the same geographic space distance; collecting a surface water sample and a pore water sample, and collecting and culturing a sediment sample; respectively measuring the activity of 222Rn in surface water, the activity of 222Rn in pore water, the activity of 222Rn diffused from sediments, and the activity of 226Ra in surface water; calculating the pore water exchange rate; and measuring the soluble carbon content of the water body, and calculating the pore water carbon exchange flux. According to the method, the accuracy of large-scale estuary pore water carbon exchange flux measurement can be improved, and the influence of sampling habitat, various composition and spatial scale difference on estuary carbon income and expenditure estimation is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of mangrove pore water carbon exchange determination, in particular to a method for determining the pore water carbon exchange flux of mangroves in a large-scale estuary area. Background Art

[0002] As an important "blue carbon" ecosystem, mangroves play a vital role in the biogeochemical processes of various substances including carbon in coastal waters. As people pay more and more attention to the carbon cycle regulation of mangrove ecosystems and the importance of carbon sink capacity in regulating the global carbon balance, in recent decades, estimation studies on carbon storage in mangrove ecosystems in different regions and at different scales have been widely carried out around the world. There is a complex biogeochemical connection between mangroves and adjacent waters. During the tidal cycle, pore water exchange carries DIC and DOC. Tide-driven pore water exchange is one of the main ways for mangrove ecosystems to exchange carbon with the outside world. However, the current quantitative research system for the carbon exchange process of mangrove pore water is not perfect, which has greatly underestimated the role of mangrove ecosystems in the global carbon cycle.

[0003] At present, the relevant research on mangroves is mainly focused on the mangrove areas within a specific range in the estuarine ecosystem, or the overall quantification of the carbon exchange of mangrove pore water within the small-scale estuarine basin. The heterogeneity of the spatial distribution of water and soil environment in different sections of the estuary in different seasons has not been studied, which may lead to the dynamic changes in the spatial and temporal patterns of the quantitative results of pore water exchange rate and carbon exchange flux. In addition, the current academic community generally believes that the main river channel of the mangrove tidal gully or estuary is the main channel for water to enter and exit the mangrove during tidal fluctuations, and the research sites are mostly selected from tidal gullies or rivers where no mangrove plants are settled. In fact, the closer the sampling is to the mangrove vegetation, the more it can minimize the data and information loss caused by the pore water transport process, such as the overflow of CO2 after DIC mineralization and the flocculation of DOC. The results of sampling in the mangrove vegetation distribution area are more representative of the overall carbon dynamics of the mangrove community than the results of sampling in the river channel or tidal gully. Therefore, existing studies on the quantification of mangrove carbon exchange flux mostly use the pore water exchange rate and carbon content in tidal channels or river channels to reflect the carbon exchange between the pore water and the nearshore in a certain mangrove area or a small estuary area. They cannot effectively distinguish and quantify the pore water carbon exchange flux of mangrove communities composed of specific tree species, nor can they fully represent the pore water carbon exchange within the mangrove community. Summary of the invention

[0004] The purpose of the present invention is to overcome the above-mentioned defects of the prior art and propose a method for determining the carbon exchange flux of mangrove pore water in a large-scale estuarine area, which can improve the accuracy of the determination of the carbon exchange flux of pore water in large-scale estuaries and reduce the influence of sampling habitats, several compositions, and spatial scale differences on the estimation of estuarine carbon budget.

[0005] The technical solution of the present invention is: a method for determining the carbon exchange flux of mangrove pore water in a large-scale estuary area, which comprises the following steps:

[0006] S1. Select several monitoring communities: select mangrove communities along the estuary, upstream, downstream and downstream areas of the estuary with the same geographical distance and the same tree age as the monitoring communities;

[0007] S2. Collect surface water samples, collect pore water samples, and collect and culture sediment samples;

[0008] S3. For surface water 222 Rn activity, pore water 222 Rn activity, diffusion from sediments 222 Rn activity, and 226 Ra activities were measured respectively;

[0009] S4. Calculation of pore water exchange rate;

[0010] S5. Determine the soluble carbon content of the water body and calculate the pore water carbon exchange flux.

[0011] In the present invention, in the process of collecting surface water samples, each monitoring sampling lasts for one day and night, including two consecutive tidal cycles. Surface water samples are collected every 2-3 hours from the time when the tide rushes in and submerges the surface of the sediment under the forest, until the tide exits the mangrove community and the sediment under the forest is exposed again;

[0012] Use the overflow method to slowly inject surface water into the radon bottle, ensuring that there are no residual bubbles in the surface water sample and that the bottle cap is tightly pressed.

[0013] In the process of collecting pore water samples, several PVC pipes are respectively installed in the monitoring communities determined in step S1, and the PVC pipes are inserted deep into the ground. At fixed time intervals, pore water samples are extracted from the PVC pipes;

[0014] The pore water in the PVC pipe is collected into the radon bottle by the peristaltic pump and the overflow method.

[0015] During the collection and cultivation of sediment samples, several sediment core samples were randomly collected around the pore water sampling points. The sediment core samples were cultivated according to a water-soil volume ratio of 5:1 and sealed in a storage box for 30 days. 222 After Rn reaches equilibrium, the overlying water is taken by overflow method.

[0016] The radon gas detector was used to measure the surface water samples. 222 Rn activity, pore water samples 222 Rn activity, and overlying water 222 Rn activity.

[0017] Determination of surface water samples 226 When measuring the Ra activity, first evenly load the manganese fiber into the adsorption column. The upper end of the adsorption column is connected to the valve of the bucket containing the surface water sample. The bucket valve is opened, and the surface water sample passes through the adsorption column from top to bottom. The manganese fiber in the adsorption column reacts with the surface water sample. 226 Ra is absorbed and enriched;

[0018] After the enrichment was completed, the manganese fiber was washed with deionized water and measured using the synchronous delay counter method. 226 Ra concentration.

[0019] Pore ​​water input 222 Rn Flux F SGD The calculation formula is:

[0020] F SGD =(F out -F in )+F atm +F dec –F Ra -F sed ,

[0021] Among them, F out Represents the output of seawater at low tide 222 Rn flux, F in Represents the amount of seawater input during high tide 222 Rn flux, F atm Represents the amount of surface water escaping through the atmosphere 222 Rn flux, F dec represents the flux of 222Rn lost in surface waters through isotope decay, F Ra represent 226 Ra decay contribution 222 Rn flux, F sed Represents the contribution of sediment diffusion 222 Rn flux;

[0022] The calculation formula of pore water exchange rate Q is:

[0023]

[0024] Among them, C GW Represents groundwater 222 Rn activity.

[0025] Tidal contribution 222 Rn Flux F out -F in The calculation process is:

[0026]

[0027] Among them, Rn WC Represents surface water in the forest 222 Rn activity, unit is Bq·m -3 ; ΔWat vol Represents the change in the volume of overlying water in the mangrove community caused by tides within a time step, in m 3 ; A represents the area of ​​mangrove community, unit is m 2 ; Δt represents the duration of a time step, in h;

[0028] Loss of surface water through atmospheric escape 222 Rn Flux F atm The calculation formula is:

[0029] F atm = k(Rn WC -α×C air ),

[0030] Where k represents the gas transmission speed in m·s -1 ; Rn WC represent 222 The activity of Rn in surface water, in Bq·m -3 ; α represents 222 Rn is the distribution coefficient between gas phase and water phase; C air represent 222 The activity of Rn in the atmosphere, in Bq·m -3 ;

[0031] k can be calculated by the following empirical formula:

[0032]

[0033] Where u represents wind speed in m·s -1 ; S c Represents the temperature at a specified 222 Schmidt constant of Rn;

[0034] The calculation formula of α is:

[0035] α=0.105+0.405e -0.0502T ,

[0036] Where T represents the surface water temperature of the mangrove community, in °C;

[0037] Contribution of sediment diffusion to 222 Rn Flux F sed The calculation formula is:

[0038]

[0039] Among them, λ Rn represent 222 The decay constant of Rn is 0.181d -1 ; represents the porosity of the bottom sediment, with a value of 0.38 or 0.35; D m represents the molecular diffusion coefficient, which is calculated as:

[0040]

[0041] C eq Represents sediment pore water 222 The activity of Rn, in Bq·m -3 ; C0 represents the overlying water in the mangrove community 222 The average activity of Rn, in Bq·m -3 ;

[0042] In the water 222 Rn decay loss 222 Rn Flux F Dec The calculation formula is:

[0043]

[0044] In the water 226 Ra decay contribution 222 Rn Flux F Ra The calculation formula is:

[0045] F Ra =λ Ra ×C 226Ra ×H,

[0046] Among them, λ Ra represent 226 The decay constant of Ra is 1.37×10 -11 d -1 ; C 226Ra Represents surface water 226 The activity of Ra, in Bq·m -3; H represents water depth, in meters.

[0047] In step S5, first, after filtering the collected surface water sample and pore water sample, the DIC concentration and DOC concentration of the surface water sample and the pore water sample are measured respectively;

[0048] Then, the pore water carbon exchange flux can be obtained by multiplying the pore water exchange rate obtained in step S4 by the pore water soluble carbon concentration, wherein the pore water soluble carbon concentration is equal to the sum of the DIC concentration and the DOC concentration obtained by the above measurement.

[0049] The beneficial effects of the present invention are as follows: the present application quantifies the carbon exchange flux in large-scale estuarine basins and conducts a quantitative study on the pore water carbon exchange status in mangrove vegetation distribution areas, which can reduce the deviation in the carbon budget assessment of the estuarine mangrove system ecosystem. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 is a schematic diagram of pore water sample collection;

[0051] Figure 2 This is a comparison of the pore water exchange rates of various mangrove communities in the Pearl River Estuary at different water stages;

[0052] Figure 3 This is a comparison of pore water soluble inorganic carbon concentration (DIC) of various mangrove communities in the Pearl River Estuary at different water stages;

[0053] Figure 4 This is a comparison of pore water dissolved organic carbon concentration (DOC) of various mangrove communities in the Pearl River Estuary at different water stages;

[0054] Figure 5 This is a comparison chart of the soluble carbon exchange flux in the pore water of various mangrove communities in the Pearl River Estuary at different water stages.

[0055] In the picture: 1 PVC pipe; 2 peristaltic pump; 3 radon bottle. DETAILED DESCRIPTION

[0056] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0057] In the following description, specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in a variety of other ways than those described herein, and those skilled in the art can make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0058] The present application discloses a method for determining the carbon exchange flux of mangrove pore water in a large-scale estuarine area, and the method comprises the following steps.

[0059] The first step is to monitor community selection.

[0060] The research objects are mangrove communities of the same age distributed in the upper, middle and lower reaches of the estuary at a geographical distance of 100 km along the estuary.

[0061] In this embodiment, the addresses of the monitoring communities are selected to be distributed in the upstream area of ​​the estuary, i.e., Hualong Town, Panyu District, Guangzhou City, the midstream area, i.e., Hengmen Waterway, Zhongshan City, and the downstream area, i.e., Hezhou North, Doumen District, Zhuhai City, with a geographical distance of 100 km along the coast of the Pearl River Estuary. The research object selected for the monitoring community is the Sonneratia apetala community with a tree age of 12 years.

[0062] The second step is to collect surface water samples.

[0063] Each monitoring sampling lasts for one day and night, including two consecutive tidal cycles. Surface water samples are collected every 2-3 hours from the time when the tide floods the surface of the understory sediments until the tide retreats from the mangrove community and the understory sediments are exposed again.

[0064] During the sampling process, the surface water is slowly injected into the radon bottle using the overflow method. The radon bottle in this embodiment is a 40ml glass bottle to prevent 222 Rn escapes into the air, ensure that there are no residual bubbles in the water sample and tighten the bottle cap to determine the 222 Rn concentration.

[0065] To determine the surface water 226 To determine the Ra content, 20L of surface water was drawn from each sampling site into a specially made bucket with a scale and a valve.

[0066] The third step is to collect pore water samples.

[0067] Several PVC pipes were installed in each of the three Sonneratia apetala communities identified in the first step. The PVC pipes were inserted deep underground, and pore water samples were extracted from the PVC pipes at fixed time intervals. To reduce the interference of residual water in the PVC pipes, the residual water in the PVC pipes was emptied several times before collecting samples.

[0068] In this embodiment, four PVC pipes 1 were installed in the three Sonneratia apetala communities determined in the first step to a depth of 0.5-2.0 m underground. The pore water samples in the PVC pipes were extracted every 2-3 hours by a peristaltic pump 2, which was connected to the PVC pipes through a thin hose. The pore water in the PVC pipes was collected into a radon bottle 3 by the peristaltic pump and the overflow method. Figure 1 shown.

[0069] The fourth step is to collect and culture sediment samples, and to 222 Rn activity and226 Determination of Ra Activity.

[0070] Sediment columns with a height of 0-20 cm and a diameter of 8 cm were randomly collected around five pore water sampling points. The sediment samples were cultured at a water-soil volume ratio of 5:1. In this embodiment, the volume of each column sediment was about 1 L. 5 L of radium-free water was added to each column sediment and sealed in a storage box. After being placed in the storage box for 30 days, the pore water and the overlying water 222 After Rn reaches equilibrium, the overlying water is taken by overflow method.

[0071] Using radon detector to measure the radon in surface water and pore water samples 222 Rn activity and diffusion from sediments 222 Rn activity. Before the measurement begins, the instrument must be purified for more than 5 minutes, and the measurement must be performed after setting the cycle time, number of cycles, pump body and other parameters. Surface water and pore water samples and sediment overlying water must be filtered.

[0072] The surface water extracted in the second step 226 When measuring the Ra activity, first use clean tweezers to evenly load 15g of manganese fiber with good appearance into the adsorption column. Connect one end of the adsorption column to the flow meter and then to the bucket valve. Open the bucket valve and let the surface water sample pass through the entire adsorption column from top to bottom. 226 Ra was adsorbed and enriched. Start to enrich 20L of surface water in the bucket 226 When Ra is reached, slowly open the valve at the bottom of the bucket to allow the surface water sample to flow at a rate of less than 1 L min -1 The flow rate of the surface water sample through the manganese fiber tube is 226 After the enrichment, the residual particles and salt on the manganese fiber were washed with deionized water, wrung out, and put into a marked ziplock bag, and brought back to the laboratory for determination using the synchronous delay counter method. 226 Ra concentration.

[0073] Step 5: Calculation of pore water exchange rate.

[0074] pass 222 The Rn mass balance model is used to calculate the pore water exchange rate of mangroves. 222 The source and sink balance of Rn can be obtained in water 222 The mass balance equation for Rn flux is:

[0075] F SGD +F in +F Ra +F sed =F out +F atm +F dec, (1)

[0076] Thus, the pore water input 222 Rn Flux F SGD The calculation formula is:

[0077] F SGD =(F out -F in )+F atm +F dec –F Ra -F sed , (2)

[0078] Among them, F SGD Represents the pore water input 222 Rn flux, F out Represents the output of seawater at low tide 222 Rn flux, F in Represents the amount of seawater input during high tide 222 Rn flux, F atm Represents the amount of surface water escaping through the atmosphere 222 Rn flux, F dec represents the flux of 222Rn lost in surface waters through isotope decay, F Ra represent 226 Ra decay contribution 222 Rn flux, F sed Represents the contribution of sediment diffusion 222 Rn flux. The units of each source and sink term are Bq·m -2 ·h -1 .

[0079] Tidal effect on seawater 222 Rn concentration has a strong influence: at high tide, the seawater will 222 Rn is transported into the estuary, at low tide 222 Rn is exported from the estuary along with the seawater. 222 Rn flux is F out -F in The calculation process is shown in formula (3):

[0080]

[0081] Among them, Rn WC Represents surface water in the forest 222 Rn concentration, unit is Bq·m -3 ; ΔWat vol Represents the change in the volume of overlying water in the mangrove community caused by tides within a time step, in m 3 ; A represents the area of ​​mangrove community, unit is m 2; Δt represents the duration of a time step, in h.

[0082] 222 Rn is slightly soluble in water. 222 When Rn is in an unbalanced state, 222 The process of Rn escaping from water to the atmosphere. 222 Rn Flux F atm The calculation process is shown in formula (4):

[0083] F atm = k(Rn WC -α×C air ), (4)

[0084] Where k represents the gas transmission speed in m·s -1 ; Rn WC represent 222 The concentration of Rn in surface water, in Bq·m -3 ; α represents 222 Rn is the distribution coefficient between gas phase and water phase; C air represent 222 The concentration of Rn in the atmosphere, in Bq·m -3 .

[0085] According to the literature, k can be calculated by the empirical formula (5):

[0086]

[0087] Where u represents wind speed in m·s -1 ; S c Represents the temperature at a specified 222 Schmidt constant of Rn.

[0088] According to the Fritz Weigel equation, the calculation formula of α can be obtained:

[0089] α=0.105+0.405e -0.0502T , (6)

[0090] Where T represents the surface water temperature of the mangrove community in °C.

[0091] Pore ​​water is rich in 222 Rn, therefore 222 Rn will continue to diffuse from the sediment-water interface into the overlying water. Without considering the disturbance effect of organisms, the contribution of bottom sediment diffusion can be calculated according to the following formula (7): 222 Rn Flux F sed :

[0092]

[0093] Among them, λ Rn represent 222 The decay constant of Rn is 0.181d -1 ; Represents the porosity of the bottom sediment, which can be calculated from the bulk density and density of the sediment. The average porosity of the bottom sediment can be taken as 0.38 or 0.35; D m represents the molecular diffusion coefficient, which is calculated as:

[0094]

[0095] C eq Represents sediment pore water 222 The concentration of Rn is obtained from the sediment pore water by sediment culture equilibrium experiment. 222 Rn concentration, unit is Bq·m -3 ; C0 represents the overlying water in the mangrove community 222 The average concentration of Rn, in Bq·m -3 .

[0096] because 222 Rn is a radioactive element and will undergo the following decay reactions in surface water:

[0097] 222 Rn→ 218 Po+ 4 He.

[0098] In the water 222 Rn decay loss 222 Rn Flux F Dec The calculation formula is:

[0099]

[0100] In surface water 226 Ra is also a radioactive element, and the following decay reactions will occur in surface water: 226 Ra → 222 Rn+ 4 He. In the water 226 Ra decay contribution 222 Rn Flux F Ra The calculation formula is:

[0101]

[0102] Among them, λ Ra represent 226 The decay constant of Ra is 1.37×10 -11 d-1 ; C 226Ra Represents surface water 226 The concentration of Ra, in Bq·m -3 ; H represents water depth, in meters.

[0103] In fact, 226 The half-life of Ra in water is 1620a, which is much longer than the sampling measurement time interval. 226 Ra decay pair 222 The contribution of Rn flux is negligible, so in this embodiment, F Ra The value of is 0.

[0104] According to formula (2), the pore water input 222 Rn Flux F SGD Then, the pore water exchange rate Q is calculated according to formula (11), and its unit is m·d -1 .

[0105]

[0106] Among them, C GW Represents groundwater 222 Rn activity.

[0107] Step 6: Calculation of pore water carbon exchange flux.

[0108] First, the soluble carbon content of the water body was measured. The pore water samples collected in the above steps were filtered with a 0.45 μm filter membrane, and the DIC concentration and DOC concentration in the pore water samples were measured using a Shimadzu TOC-VCPH total organic carbon analyzer.

[0109] Then, the pore water carbon exchange flux can be obtained by multiplying the pore water exchange rate obtained in step 5 by the pore water soluble carbon concentration, which is equal to the sum of the DIC concentration and the DOC concentration obtained by the above measurement.

[0110] The experimental results obtained by the method described in this embodiment are as follows Figures 2 to 5 As shown, Figure 2 This is a comparison of the pore water exchange rates of various mangrove communities in the Pearl River Estuary at different water stages. Figure 3 This is a comparison of pore water soluble inorganic carbon concentration (DIC) of various mangrove communities in the Pearl River Estuary at different water stages. Figure 4 This is a comparison of pore water dissolved organic carbon concentration (DOC) of various mangrove communities in the Pearl River Estuary at different water stages. Figure 5 This is a comparison chart of the soluble carbon exchange flux in the pore water of various mangrove communities in the Pearl River Estuary at different water stages.

[0111] The experimental results show that there is a temporal and spatial difference in the pore water exchange rate of the Sonneratia apetala community in the Pearl River Estuary. There are significant differences in the pore water exchange rates in the upstream, midstream and downstream, and the trends in different periods are consistent, all showing that the pore water exchange rate in the upstream is less than the pore water exchange rate in the midstream and less than the pore water exchange rate in the downstream.

[0112] In addition, there are significant differences in soluble carbon concentration and soluble carbon exchange flux in different regions, which shows that it is meaningful to measure the pore water carbon exchange flux in different areas of the estuary, which can more accurately evaluate the carbon balance of the estuary.

[0113] The above is a detailed introduction to the method for determining the carbon exchange flux of mangrove pore water in a large-scale estuarine area provided by the present invention. Specific examples are used in this article to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of the present invention, the present invention can also be improved and modified in a number of ways, and these improvements and modifications also fall within the scope of protection of the claims of the present invention. The above description of the disclosed embodiments enables professionals and technicians in this field to implement or use the present invention. Various modifications to these embodiments will be obvious to professionals and technicians in this field, and the general principles defined in this article can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown in this article, but will conform to the widest scope consistent with the principles and novel features disclosed in this article.

Claims

1. A method for determining the carbon exchange flux of mangrove pore water in a large-scale estuarine area, characterized in that: The following steps are involved: S1. Select several monitoring communities: select mangrove communities along the estuary, upstream, downstream and downstream areas of the estuary with the same geographical distance and the same tree age as the monitoring communities; S2. Collect surface water samples, collect pore water samples, and collect and culture sediment samples; S3. For surface water 222 Rn activity, pore water 222 Rn activity, diffusion from sediments 222 Rn activity, and 226 Ra activities were measured respectively; S4. Calculation of pore water exchange rate; S5. Determine the soluble carbon content of the water body and calculate the pore water carbon exchange flux.

2. The method for determining the carbon exchange flux of mangrove pore water in a large-scale estuarine region according to claim 1, characterized in that: During the collection of surface water samples, each monitoring sampling lasts for one day and night, including two consecutive tidal cycles. Surface water samples are collected every 2-3 hours from the time when the tide floods the surface of the understory sediments until the tide exits the mangrove community and the understory sediments are exposed again; Use the overflow method to slowly inject surface water into the radon bottle, ensuring that there are no residual bubbles in the surface water sample and that the bottle cap is tightly pressed.

3. The method for determining the carbon exchange flux of mangrove pore water in a large-scale estuarine region according to claim 1, characterized in that: In the process of collecting pore water samples, several PVC pipes are respectively installed in the monitoring communities determined in step S1, and the PVC pipes are inserted deep into the ground. At fixed time intervals, pore water samples are extracted from the PVC pipes; The pore water in the PVC pipe is collected into the radon bottle by the peristaltic pump and the overflow method.

4. The method for determining the carbon exchange flux of mangrove pore water in a large-scale estuarine region according to claim 1, characterized in that: During the collection and cultivation of sediment samples, several sediment core samples were randomly collected around the pore water sampling points. The sediment core samples were cultivated according to a water-soil volume ratio of 5:1 and sealed in a storage box for 30 days. 222 After Rn reaches equilibrium, the overlying water is taken by overflow method.

5. The method for determining the carbon exchange flux of mangrove pore water in a large-scale estuary region according to claim 1, characterized in that: The radon gas detector was used to measure the surface water samples. 222 Rn activity, pore water samples 222 Rn activity, and overlying water 222 Rn activity.

6. The method for determining the carbon exchange flux of mangrove pore water in a large-scale estuarine region according to claim 1, characterized in that: Determination of surface water samples 226 When measuring the Ra activity, first evenly load the manganese fiber into the adsorption column. The upper end of the adsorption column is connected to the valve of the bucket containing the surface water sample. The bucket valve is opened, and the surface water sample passes through the adsorption column from top to bottom. The manganese fiber in the adsorption column reacts with the surface water sample. 226 Ra is absorbed and enriched; After the enrichment was completed, the manganese fiber was washed with deionized water and measured using the synchronous delay counter method. 226 Ra concentration.

7. The method for determining the carbon exchange flux of mangrove pore water in a large-scale estuary region according to claim 1, characterized in that: Pore ​​water input 222 Rn Flux F SGD The calculation formula is: F SGD =(F out -F in )+F atm +F dec –F Ra -F sed , Among them, F out Represents the output of seawater at low tide 222 Rn flux, F in Represents the amount of seawater input during high tide 222 Rn flux, F atm Represents the amount of surface water escaping through the atmosphere 222 Rn flux, F dec represents the flux of 222Rn lost in surface waters through isotope decay, F Ra represent 226 Ra decay contribution 222 Rn flux, F sed Represents the contribution of sediment diffusion 222 Rn flux; The calculation formula of pore water exchange rate Q is: Among them, C GW Represents groundwater 222 Rn activity.

8. The method for determining the carbon exchange flux of mangrove pore water in a large-scale estuarine region according to claim 7, characterized in that: Tidal contribution 222 Rn Flux F out -F in The calculation process is: Among them, Rn WC Represents surface water in the forest 222 Rn activity, unit is Bq·m -3 ; ΔWat vol Represents the change in the volume of overlying water in the mangrove community caused by tides within a time step, in m 3 ; A represents the area of ​​mangrove community, unit is m 2 ; Δt represents the duration of a time step, in h; Loss of surface water through atmospheric escape 222 Rn Flux F atm The calculation formula is: F atm =k(Rn WC -α×C air ), Where k represents the gas transmission speed in m·s -1 ; Rn WC represent 222 The activity of Rn in surface water, in Bq·m -3 ; α represents 222 Rn is the distribution coefficient between gas phase and water phase; C air represent 222 The activity of Rn in the atmosphere, in Bq·m -3 ; k can be calculated by the following empirical formula: Where u represents the wind speed in m·s -1 ; S c Represents the temperature at a specified 222 Schmidt constant of Rn; The calculation formula of α is: α＝0.105+0.405e -0.0502T ， Where T represents the surface water temperature of the mangrove community, in °C; Contribution of sediment diffusion to 222 Rn Flux F sed The calculation formula is: Among them, λ Rn represent 222 The decay constant of Rn is 0.181d -1 ; represents the porosity of the bottom sediment, with a value of 0.38 or 0.35; D m represents the molecular diffusion coefficient, which is calculated as: C eq Represents sediment pore water 222 The activity of Rn, in Bq·m -3 ; C0 represents the overlying water in the mangrove community 222 The average activity of Rn, in Bq·m -3 ; In the water 222 Rn decay loss 222 Rn Flux F Dec The calculation formula is: In the water 226 Ra decay contribution 222 Rn Flux F Ra The calculation formula is: F Ra =λ Ra ×C 226Ra ×H, Among them, λ Ra represent 226 The decay constant of Ra is 1.37×10 -11 d -1 ; C 226Ra Represents surface water 226 The activity of Ra, in Bq·m -3 ; H represents water depth, in meters.

9. The method for determining the carbon exchange flux of mangrove pore water in a large-scale estuary region according to claim 1, characterized in that: In step S5, first, after filtering the collected surface water sample and pore water sample, the DIC concentration and DOC concentration of the surface water sample and the pore water sample are measured respectively; Then, the pore water carbon exchange flux can be obtained by multiplying the pore water exchange rate obtained in step S4 by the pore water soluble carbon concentration, and the pore water soluble carbon concentration is equal to the sum of the DIC concentration and the DOC concentration obtained by the above measurement.

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