Karst wetland water-carbon cycle model construction method

Abstract

The application discloses a karst wetland water-carbon cycle model construction method, and belongs to the technical field of karst hydrogeochemistry and ecological environment monitoring. The method takes an event section as a basic calculation unit, obtains rainfall, soil water, surface karst zone water, surface runoff and underground river flow data, and establishes a five-water water quantity conservation relationship; determines a first infiltration recharge K1 according to soil water migration, constructs a drip water response kernel according to a rainfall pulse and a cave drip water flow, and generates a second infiltration recharge K2 dynamic recharge item; combines water temperature, pH value and isotope end member constraints to determine dissolved inorganic carbon concentration and carbon sink correction coefficients, and calculates carbon sink flux; according to the closed error, the drip water response kernel parameters are back substituted and corrected, and a surface-underground water coupling numerical model is constructed, and a calibrated karst wetland water-carbon cycle model is formed. The application realizes integrated construction and dynamic calibration of the karst wetland water cycle and carbon cycle process.

Description

Technical Field

[0001] This invention relates to the field of karst hydrogeochemistry and ecological environment monitoring technology, and in particular to a method for constructing a water-carbon cycle model for karst wetlands. Background Technology

[0002] Karst wetlands serve as crucial transitional zones connecting the atmosphere, hydrosphere, lithosphere, and ecosystems. They simultaneously experience various hydrological processes, including rainfall infiltration, soil water migration, surface karst water recharge, surface runoff confluence, and underground river discharge. These processes are accompanied by complex carbon cycle processes such as carbonate karst erosion, dissolved inorganic carbon migration, and carbon sink formation. Therefore, karst wetlands are not only important carriers for regional water resource regulation but also a vital component of terrestrial ecosystem carbon sinks.

[0003] Currently, research on water and carbon cycles in karst wetlands mainly employs a combination of field monitoring, statistical analysis, and numerical simulation. Existing technologies typically involve deploying rainfall monitoring equipment, soil moisture sensors, groundwater level monitoring equipment, and underground river flow monitoring equipment to collect data on rainfall, soil water, karst zone water, surface runoff, and underground river flow. Water balance analysis, hydrochemical analysis, or isotope tracing methods are then used to study hydrological processes and carbon migration patterns. Simultaneously, some studies have employed a coupled approach of surface water models and groundwater models to simulate water cycle processes in karst areas, aiming to improve the ability to describe complex karst hydrological systems.

[0004] However, existing technologies still have the following shortcomings: Most existing models analyze surface water or groundwater processes separately, making it difficult to uniformly express the coupling relationships between rainfall, soil water, surface runoff, karst water, and underground river flow at the same time and volume scale.

[0005] Karst areas are characterized by unique water flow paths such as fissure flow, conduit flow, and preferential flow. The rapid infiltration process reflected by cave dripping exhibits significant time lag and memory characteristics. Existing technologies typically treat this as static monitoring data for analysis, making it difficult to effectively characterize the dynamic response relationship between rainfall events and underground recharge processes.

[0006] Current carbon sink calculations mostly rely on water chemistry parameters to directly calculate carbon sink flux. However, they have limited ability to characterize the contribution ratio of different carbon sources, isotopic end-member mixing processes, and carbon sink changes at event scales, which can easily lead to discrepancies between carbon sink estimation results and actual processes.

[0007] Existing methods lack a unified closed-loop feedback mechanism, and model parameters usually need to be manually adjusted or calibrated multiple times, making it difficult to achieve coordinated optimization of water processes and carbon cycle processes.

[0008] Therefore, there is an urgent need for a method to construct a karst wetland water-carbon cycle model that can uniformly describe the water transformation and carbon cycle processes in karst wetlands and enable dynamic calibration and coupling of model parameters, so as to improve the model's ability to express the actual hydrogeochemical processes in karst wetlands. Summary of the Invention

[0009] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0010] Therefore, to solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for constructing a water-carbon cycle model for karst wetlands, comprising the following steps: Using event segments as the basic calculation unit, five water monitoring data are acquired and a water quantity conservation relationship of five waters with the event segment volume as the unified caliber is established. The five waters include rainfall, soil water, surface karst zone water, surface runoff, and underground river outlet flow. The event segment is a continuous time period from the start of a rainfall pulse to the hydrological response tending to stabilize. The first infiltration recharge K1 is determined based on soil moisture transport. A drip response kernel is constructed based on rainfall pulses and cave drip flow rate, and a second infiltration recharge dynamic recharge term K2 is generated after event correction. The dissolved inorganic carbon concentration and carbon sink correction factor were determined based on the event segment water temperature, pH and isotopic end-member constraints. Calculate the carbon sink flux and carbon sink intensity per unit area during the event segment; The closure error is calculated based on the five water conservation relationships, and the parameters of the dripping response kernel are substituted back to correct the error. The modified second infiltration recharge K2 dynamic recharge term, carbon sink correction coefficient, and carbon sink intensity per unit area are input into the surface-groundwater coupled numerical model to form a calibrated karst wetland water-carbon cycle model.

[0011] As a preferred embodiment of the karst wetland water-carbon cycle model construction method of the present invention, the five water monitoring data include rainfall data, soil water data, surface karst zone water data, surface runoff data, and underground river outlet flow data; the rainfall data is converted into rainfall volume by combining rainfall depth with the corresponding catchment area; the soil water data, surface karst zone water data, surface runoff data, and underground river outlet flow data are all converted into volume based on the catchment area corresponding to the event segment; the water conservation relationship of the five waters uses the event segment volume as the unified calculation caliber; by uniformly converting rainfall depth and other hydrological monitoring quantities into event segment volume, data of different dimensions can be calculated under the same conservation relationship, providing a consistent input for subsequent error back-substitution and replenishment decomposition.

[0012] As a preferred embodiment of the karst wetland water-carbon cycle model construction method of the present invention, wherein: the first infiltration recharge K1 is calculated from the soil moisture flux and the water volume per unit area of ​​the groundwater surface, and converted into a volume based on the corresponding catchment area; the first infiltration recharge K1, together with the surface runoff volume and the underground river outlet flow volume, constitutes a component of the five-water conservation relationship; K1 is used to characterize the basic recharge process of soil water to surface karst zone water, and together with surface runoff and underground river outlet flow, constitutes a key component in the five-water conservation relationship, so that soil moisture transport and karst zone recharge are clearly correlated.

[0013] As a preferred embodiment of the karst wetland water-carbon cycle model construction method of the present invention, the event-corrected second infiltration recharge K2 dynamic recharge term is obtained by multiplying the rainfall pulse by the catchment area and convolving it with the dripping response kernel, and then weighted and fused with the measured cave dripping flow rate; the catchment area is the surface runoff area corresponding to the event segment; by convolving the rainfall pulse with the dripping response kernel and fusing the convolution result with the measured dripping flow rate, the priority flow response of cave dripping can be transformed into a calculable dynamic recharge term, which is convenient for subsequent closure correction.

[0014] As a preferred embodiment of the karst wetland water-carbon cycle model construction method of the present invention, the dripping response kernel includes shape parameters and time scale parameters; the shape parameters and time scale parameters are determined by the phase lag time from the rainfall peak to the dripping peak and the duration of the event; the phase lag time is used to characterize the time memory features of the preferential flow response; the shape parameters and time scale parameters are associated with the phase lag time and the duration of the event, so that the response kernel can reflect the time lag and duration characteristics of the preferential flow process, and provide an adjustable time structure for the K2 dynamic replenishment term.

[0015] As a preferred embodiment of the karst wetland water-carbon cycle model construction method of the present invention, the dissolved inorganic carbon concentration is determined based on the water temperature, pH value, carbon dioxide partial pressure, and carbonic acid balance constant as the water temperature changes during the event period; the carbon sink correction coefficient is generated based on the mixing ratio of isotopic endmembers of fresh carbonate rocks, soil organic carbon, deep groundwater, and modern recharge water; the dissolved inorganic carbon concentration (DIC) is determined based on the water temperature, pH value, and carbonic acid balance relationship during the event period, and the carbon sink correction coefficient is generated based on the mixing ratio of different isotopic endmembers, thereby making the carbon sink calculation subject to both water chemistry and carbon source composition.

[0016] As a preferred embodiment of the karst wetland water-carbon cycle model construction method of the present invention, the carbon sink correction coefficient is obtained by multiplying the soil end-member contribution factor, the young carbon contribution factor, and the time-delay decay factor; the reference time-delay constant of the time-delay decay factor is 1.5 to 3 times the average time delay of the event; incorporating the soil end-member contribution, the young carbon contribution, and the time-delay decay into the same correction coefficient helps to uniformly map the influence of carbon from different sources into the carbon sink calculation and maintain the correspondence with the event process.

[0017] As a preferred embodiment of the karst wetland water-carbon cycle model construction method of the present invention, the step of correcting the parameters of the dripping response kernel based on the closure error includes: adjusting at least one parameter of the dripping response kernel based on the closure error calculated according to the five-water conservation relationship, and re-inputting the corrected parameters into the dripping response kernel to update the second infiltration recharge K2 dynamic recharge term; calculating the closure error according to the five-water conservation relationship, adjusting the dripping response kernel parameters according to the sign and magnitude of the closure error, and then re-inputting the corrected parameters into the K2 dynamic recharge term calculation process to realize the feedback constraint of the conservation relationship on the model parameters.

[0018] As a preferred embodiment of the karst wetland water-carbon cycle model construction method of the present invention, the surface-groundwater coupled numerical model consists of a distributed surface water model, a groundwater model, and a communication module for data transmission; the distributed surface water model is an SWMM model, and the groundwater model is a MODFLOW-CFP model; by combining the distributed surface water model, the groundwater model, and the communication module into a surface-groundwater coupled numerical model, the corrected recharge terms and carbon sink parameters can be incorporated into a unified numerical calculation framework.

[0019] As a preferred embodiment of the karst wetland water-carbon cycle model construction method of the present invention, the calibrated karst wetland water-carbon cycle model is operated under different rainfall conditions, different water resource extraction conditions, and different land use conditions, and the regulation coefficient is calculated according to the five water conservation relationships to output the water distribution and carbon flux change characteristics; the model is used for scenario simulation under different rainfall, extraction, and land use conditions to output the corresponding water distribution and carbon flux change characteristics, and is used to evaluate the wetland regulation capacity.

[0020] The beneficial effects of this invention are: 1. This invention uses event segments as a unified calculation unit, incorporating rainfall, soil water, surface karst water, surface runoff, and underground river flow into the same volume calculation framework, establishing a five-water conservation relationship, enabling monitoring data from different sources and at different scales to participate in model construction under a unified caliber, thereby improving the consistency of water process expression.

[0021] 2. This invention abstracts the preferential flow process in karst areas into a dynamic recharge term of the second infiltration recharge K2, and describes the time lag relationship and memory characteristics between rainfall pulses and underground recharge through a drip response kernel, enabling the model to reflect the dynamic response process of karst fissure flow and conduit flow, thereby improving the ability to characterize the special hydrological behavior of karst.

[0022] 3. This invention introduces an isotope end-member constraint mechanism, which incorporates carbon from carbonate rocks, soil, deep groundwater, and modern recharge sources into a unified analytical framework. It uses a carbon sink correction coefficient to constrain the carbon sink calculation results, making the carbon sink estimation process match the actual carbon source contribution relationship and improving the explanatory power of the carbon cycle process.

[0023] 4. This invention utilizes the water conservation relationship of the five waters to calculate the closure error and feeds the closure error back to the drip response kernel parameter correction process, so as to realize the simultaneous construction of model and parameter optimization, and make the determination of model parameters have a clear water conservation basis, forming a closed-loop construction mechanism in which water calculation, carbon sink calculation and parameter optimization are interconnected.

[0024] 5. This invention integrates the dynamic replenishment process, carbon sink correction process, and parameter optimization process into the construction process of the surface-groundwater coupled model. It establishes data transmission and feedback relationships between various technical links under a unified event scale, forming a karst wetland water-carbon cycle model that takes into account water conversion, carbon sink evolution, and scenario simulation capabilities, thus overcoming the shortcomings of the disconnect between various links in the existing technology. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein: Figure 1 This is a flowchart illustrating the overall workflow of the present invention.

[0026] Figure 2 This is a sub-flowchart for establishing the five-water data acquisition and basic water conservation relationship of the present invention.

[0027] Figure 3 This is a sub-flowchart of the construction of the dripping response kernel and the K2 correction of the present invention.

[0028] Figure 4 This is a flowchart of the calculation of isotope end-member constraints and carbon sink correction coefficients in this invention.

[0029] Figure 5 This is a flowchart of the back-substitution correction of closure error in the present invention.

[0030] Figure 6 This is a flowchart illustrating the construction of the coupled model and the multi-scenario simulation of the present invention. Detailed Implementation

[0031] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0032] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0033] Secondly, the term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention; the phrase "in an embodiment" appearing in different places in this specification does not all refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0034] Example 1 Reference Figure 1This is the first embodiment of the present invention, which aims to solve the problems of complex boundary conditions, delayed preferential flow response, difficulty in quantifying carbon source mixing, and insufficient model closure in the existing technology when coupling modeling of hydrological processes and carbon cycle processes in karst wetlands. The method is based on the transformation dynamics constraints of five waters (atmospheric precipitation, soil water, surface runoff, surface karst zone water, and karst groundwater), introduces the event response kernel of cave drip preferential flow, combines isotope endmember mixing correction, and achieves model self-consistency through water volume closure back substitution. The water-carbon cycle coupling model skeleton and its calibration parameter set that can be used for karst wetland water volume evolution, carbon sink flux calculation and scenario simulation are constructed in sequence.

[0035] It should be noted that this embodiment only focuses on the coupled modeling of hydrological processes and carbon cycle processes.

[0036] This method uses event segments as the basic calculation unit and aligns all monitoring data according to a unified common time step; the preferred common time step is 15 minutes; each step sequentially completes the model skeleton establishment, key parameter identification, response verification, carbon source constraint, closed-loop replacement and coupling integration, and finally forms a calibrated karst wetland water-carbon cycle model.

[0037] S1. Obtain water monitoring data and establish basic water quantity constraints; like Figure 2 As shown, the specific steps are as follows: S11. Acquire rainfall data, soil moisture data, surface karst zone water data, surface runoff data, and karst underground river outlet flow data of the karst wetland to be monitored; convert the above raw monitoring data into a time series dataset with a preset time step.

[0038] S12. Based on the catchment area corresponding to each event segment, convert each data point from the original water depth or flow rate data into the event volume under the same diameter, so as a unified input for subsequent water balance calculations; among which, rainfall data is usually expressed as rainfall depth, denoted as... Unit: mm; based on the catchment area corresponding to the event segment. (Unit: m²) Converted to rainfall volume Rainfall volume The calculation formula is: ; Soil moisture content increase volume Surface runoff volume Surface karst zone water volume underground river outlet flow volume All according to the same catchment area Converted to volume, thus ensuring dimensional consistency.

[0039] The above five waters satisfy the following event-scale water balance expression: ;in, ; This refers to the volume of soil water infiltrating into the surface karst zone (piston-type infiltration). This refers to the preferential flow volume of surface runoff to surface karst water (cave drips).

[0040] S13. Calculate the rainfall infiltration process; This embodiment uses the Philip infiltration model to calculate the instantaneous rainfall infiltration rate. Unit: mm / h The calculation formula is: In the above formula, t is time, in hours (h); S is the percolation coefficient, in seconds (h). A represents the stable soil infiltration rate, in mm / h, preferably taken as the saturated hydraulic conductivity. Equivalent expression; The cumulative infiltration volume within the event segment is obtained through time integration, and the specific calculation formula is as follows: ;in, The corresponding catchment area is expressed in square meters (m²). The calculation result of the above formula serves as the input boundary for the soil water module.

[0041] S14. Establish the dynamic relationship of soil moisture transport; Define the volume of soil moisture increment With soil volumetric water content and total soil volume The relationship is: In the above formula, This refers to the total soil volume within the corresponding catchment unit, in m³. Soil volumetric water content, unit: cm³ / cm³.

[0042] Vertical water movement satisfies the following continuity equation: In the above formula, Vertical water flux, unit: cm / h; These are depth coordinates, in meters (m), with downwards being positive.

[0043] S15. For soil moisture transport, the Richards equation is used for calculation: ;in, Soil volumetric water content, unit: cm³ / cm³; The diffusivity of unsaturated soil is expressed in cm² / h. Unsaturated hydraulic conductivity, unit: cm / h; Root water absorption rate, unit: ; t represents depth coordinates in meters (m), with downwards being positive; t represents time in hours (h). The above relationship is used to constrain the spatiotemporal evolution of soil moisture.

[0044] S2. Calculate the infiltration recharge of soil water into the surface karst zone. and surface runoff exchange; The specific steps are as follows: S21: Receive soil moisture movement data and determine piston-type infiltration conditions; Receive soil moisture movement data output from step S1, including soil volumetric water content. Vertical water flux In addition to soil hydraulic parameters; under one-dimensional vertical flow conditions, based on the piston-type infiltration flow assumption, the infiltration recharge of soil water to surface karst zone water is calculated. .

[0045] S22: Calculate the infiltration rate per unit area and convert it to volume; The infiltration rate per unit area is calculated using the soil moisture movement equation and flux integral, and then converted into a volumetric value based on the corresponding catchment area. Unit: m³; Calculation process is as follows: ; ; ; In the above formula, , They are respectively height and Soil moisture flux at the location, unit: cm / h; , For time period to The volume of water passing through a unit area at a given location, expressed in cm². The water level is in meters (m). The water catchment area corresponding to this event segment is expressed in square meters (m²).

[0046] S23. Determine the infiltration recharge of surface runoff to surface karst water. ; for The solution is obtained by combining measured flow rate with response kernel correction; the original drip flow rate sequence is obtained from cave drip water collection and flow measurement devices. By combining the rainfall pulse and drip response kernel calculation correction terms, the effective replenishment amount for the event segment is obtained. The specific calculation process is shown in step S3 below.

[0047] S24. Calculate the surface runoff D and the karst water exchange rate W; The surface runoff D is calculated using a segmented flow formula: the rectangular weir formula is used for low water levels and small flow rates, while the cross-sectional method is used for high water levels and large flow rates.

[0048] The calculation of the exchange rate W between surface karst water and pipe water adopts the fracture cubic law, the Hagen-Poiseuille equation for laminar flow in pipes, and the Darcy-Weisbach form for turbulent flow, combined with the linear equation for the exchange rate between fracture water and pipe water. The specific calculation formula is as follows: ;in, The amount of water exchanged is expressed in m³ / s. The pipe conductivity is expressed in square meters per second. Fracture head, unit: m; The water head inside the pipe, in meters (m).

[0049] S3. Construct the cave dripping response and calculate the event-corrected response. ; like Figure 3 As shown, the specific steps are as follows: S31. Align the timing of rainfall and dripping water and divide the event segments; Received rainfall sequence and cave drip flow sequence After aligning the timing, the event segment is divided into event segments e. The specific rules for dividing the event segments are as follows: the start time of the rainfall pulse is taken as the start of the event, and the end time is taken as the drip flow rate drops back to the baseline before the event and continues to maintain a preset time interval. The preset time interval is adapted to the monitoring resolution period and is not shorter than multiple consecutive sampling steps (e.g., 30 minutes to 1 hour) to avoid artificially cutting the same priority flow process. For cases where the interval between two adjacent rainfall pulses is short, they can be merged into the same event segment.

[0050] S32: Construct a Gamma-distributed kernel for the water droplet response; For each event segment, a drip response kernel is constructed, using a Gamma distribution: , ;in, represents the shape parameter of the Gamma nucleus, which is dimensionless; The timescale parameter for the Gamma kernel, in hours; For gamma function; Response time, in hours (h).

[0051] The above two kernel parameters , The event characteristics are determined using the following formulas: In the above formula, Phase lag time from peak rainfall to peak drip rate, in hours; Duration of the event, in hours (h). , These are calibration coefficients, dimensionless; To prevent tiny positive numbers with a denominator of zero, for example: .

[0052] Preferably, the and The calibration method is as follows: select at least 5 typical historical events, aim to minimize the squared error between the measured drip flow rate and the convolutional reconstructed value, and obtain the result using least squares regression; after calibration... The value range is usually 0.5 to 2.0. The value ranges from 0.2 to 1.0, and the specific value is determined based on the field data.

[0053] S33: Calculate the theoretical response flow rate; Multiplying the rainfall intensity by the catchment area yields the volumetric input rate, which is then convolved with the response kernel to obtain the theoretical drip flow rate. The calculation formula is as follows: ;in, Input the rainfall pulse within the event segment, unit: mm / h; The start time of the event, in hours (h). The catchment area is measured in square meters (m²). The dimension is m³ / h.

[0054] S34: Weighted fusion of measured and theoretical flow rates yields the corrected drip flow rate; Confidence weights are defined based on sampling integrity, orifice condition, sensor saturation, and local dripping stability. The range of values ​​is The measured drip flow rate is weighted and fused with the convolutional theoretical flow rate to obtain the event-corrected drip flow rate. The calculation formula is as follows: .

[0055] S34: Integrate to obtain the effective supply amount for the event segment; The effective supply amount for the event segment is calculated using the following formula. : The calculated results are used as inputs for subsequent isotope correction and closed-loop substitution.

[0056] S4. Introduce isotopic end-member constraints to correct the composition of DIC and carbon sink coefficient; like Figure 4 As shown, the specific steps are as follows: S41: Receive water droplet data and calculate hydrogen ion concentration; Receive the on-site pH value and water temperature from the event segment drip data output by S3. (Unit: °C) Calculate the hydrogen ion concentration: ;in, The unit is mol / L, and the subscript j indicates the j-th time slice within the event segment.

[0057] S42. Calculate the concentration of dissolved inorganic carbon based on the carbonic acid equilibrium relationship. ; The carbonic acid system satisfies the following constraints: ; ; ; ; In the above formula, Henry's constant, unit: mol / L ;、 and The first and second ionization constants of carbonic acid, respectively, in mol / L; For soil Pressure divider (atm), unit: atm, can be set according to actual measurement or empirical value in practical applications.

[0058] Preferably, the Henry's constant is calculated using the standard thermodynamic form, and the formula is as follows: ;in, ; This is a constant under conditions of 25℃; The enthalpy change corresponds to the reaction, in J / mol; R is the gas constant (8.314 J / mol). ); T is represented by Kelvin.

[0059] S43: Calculate the endmember mixing ratio based on isotope test data; Let the stable isotopic endmembers of fresh carbonate rocks be... Unit: ‰; Soil organic carbon end-member is Unit: ‰; deep groundwater end element is Unit: ‰; Modern supply end-unit is ,unit:‰; Based on actual measurements and The endmember mixing ratio is calculated as follows: ; ; ; in, Limit the value to between 0 and 1; The reference time delay constant, in hours, can be 1.5 to 3 times the average time delay of the event; the average time delay is the average time difference between the peak rainfall and the peak dripping. The above end-member values ​​were determined by a combination of field measurements and baseline values: It can be obtained from testing fresh carbonate rock samples. It can be produced by surface soil organic carbon or soil gas The sample was measured. and It can be obtained from deep groundwater and modern precipitation or shallow recharge water samples, respectively.

[0060] S44: Calculate the carbon sink correction factor; Carbon Sequestration Correction Factor (Dimensionless) is used to characterize the combined effects of soil end-member contributions, young carbon contributions, and event-dependent decay. The calculation formula is as follows: ;in, This is the time corresponding to the current time slice.

[0061] S5. Calculate the carbon sink flux and carbon sink intensity per unit area during the event segment; The specific steps are as follows: S51: Calculate carbon flux during the event segment; Receive the corrected drip flow rate output in step S3 The dissolved inorganic carbon concentration output in step S4 and carbon sink correction factor The carbon flux of the event segment is calculated by summing up all time slices within the event segment using the following formula. : ;in, The number of time slices within an event segment; Let j be the length of the j-th time slice, in seconds; to ensure dimensional consistency, Expressed in m³ / s, Expressed in mol / m³, Let 's' represent it, therefore, The unit is mol C.

[0062] S52, Calculate carbon sequestration intensity per unit area ; The calculation formula is: ;in, The area of ​​the catchment area corresponding to the event segment is expressed in square meters. The unit is mol C / m².

[0063] S6, will The correction amount is returned to the five-water equilibrium and the closure error is corrected. like Figure 5 As shown, the specific steps are as follows: S61. Receive each water component and calculate the closure error. ; Specifically, closure error The calculation formula is: .

[0064] S62. Determine whether the error exceeds the preset allowable range; Define relative error When relative error When the error exceeds the preset tolerance range (e.g., relative error greater than 5%), step S63 is executed to perform physical callback correction; otherwise, the effective supply amount of the event segment is directly output. Carbon flux during the event segment and current carbon sequestration intensity per unit area Proceed to the next step, S7.

[0065] S63. Perform physical callback correction on the response kernel parameters; like This indicates that there is still an unexplained portion of the event's water volume, and the response timescale parameter can be appropriately increased to prolong the tail response of the dripping water; if This indicates that the current model overestimates the dripping response, in which case the time-scale parameter can be appropriately reduced; The revised formula uses a damped hyperbolic tangent function to prevent abrupt parameter changes: ; ; In the above formula, , The correction coefficient (dimensionless) is preferably in the range of 0.1 to 0.5, and can be specifically determined based on historical event samples. In this embodiment, the preferred value is 0.3. Let be the hyperbolic tangent function, with a range of . This makes the correction amount gradual; , These are the upper and lower limits of the scale parameter, in h, set based on the 5th and 95th percentiles of the statistical distribution of historical event samples, combined with physical rationality. For example... , ; , These are the upper and lower limits of the shape parameter, dimensionless, for example... , ; To prevent tiny positive numbers with a denominator of zero, for example: .

[0066] S64. Re-enter the corrected parameters into step S3; Repeat steps S31 to S35 and S4 and S5 to form a closed-loop correction. Respond to kernel parameters and output the effective supply amount of the event segment after closure correction. Carbon flux during the event segment and current carbon sequestration intensity per unit area Set the maximum number of iterations to 5. If the iteration exceeds 5 and the error still has not converged, retain the current parameters and output a warning.

[0067] S7. Construct a coupled surface-groundwater numerical model and conduct multi-scenario evolution simulation and storage capacity evaluation; like Figure 6 As shown, the specific steps are as follows: S71, Receive the corrected data and input it into the coupling model; Receive the corrected data output from step S6, and input the corrected data as boundary conditions, calibration parameters or coupling constraints into the surface-groundwater coupled numerical model.

[0068] S72. Construct the coupled model structure; The coupled numerical model is used to introduce the aforementioned event segment K2 dynamic correction results, isotope correction results and closure error correction results into the coupling framework of the SWMM distributed surface water model and the MODFLOW-CFP groundwater model, so that the coupled model simultaneously includes the calibration relationships of surface runoff, infiltration recharge, underground pipeline flow and karst water exchange. Preferably, the coupled numerical model consists of an SWMM module, a MODFLOW-CFP module, and a Broker module for data transmission, and considers the direct connection between karst conduits and sinkholes as well as the characteristics of inclined channels; by using the corrected recharge amount, corrected carbon sink coefficient, and event-scale carbon sink flux obtained in step S6 as model parameter update inputs, the dynamic construction and iterative calibration of the surface-groundwater coupling structure are completed.

[0069] S73. Conduct multi-scenario evolution simulation; Evolutionary simulations were performed under different scenarios for the following conditions: Different hydrodynamic conditions: light rain, moderate rain, heavy rain, and rainstorm levels; Different water resource extraction conditions: altering groundwater extraction volume, surface water extraction volume, and ecological water demand; Different land use conditions: wetland area shrinks or expands.

[0070] The simulation yielded the corresponding characteristics of water distribution and carbon sink flux changes.

[0071] S74: Calculate the storage coefficient and evaluate the carbon sink potential; The formula for calculating the regulation coefficient is: In the above formula, The water storage capacity during the event period is expressed in m³. and These represent changes in surface runoff and karst groundwater, respectively, in m³; based on simulation results and storage coefficients. This study aims to further evaluate the carbon sequestration potential and carbon sequestration function effects of karst wetlands, providing model support for wetland recharge regulation, carbon sequestration accounting, and protection management.

[0072] This embodiment improves the cave drip recharge rate from traditional discrete measured values ​​to a dynamic recharge term driven by event pulse convolution. By using isotope endmember constraints and water volume closure back substitution correction, it enhances the physical consistency, interpretability, and carbon sink quantification accuracy of the model. Compared with existing technologies, this method can more accurately characterize the contribution of preferential flow to the water-carbon cycle in karst wetlands and has adaptive closure correction capability, making it suitable for wetland simulation and carbon sink assessment under different hydrogeological conditions.

[0073] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for constructing a water-carbon cycle model for karst wetlands, characterized by: Includes the following steps: Using event segments as the basic calculation unit, five water monitoring data are acquired and a water quantity conservation relationship of five waters with the event segment volume as the unified caliber is established. The five waters include rainfall, soil water, surface karst zone water, surface runoff, and underground river outlet flow. The event segment is a continuous time period from the start of a rainfall pulse to the hydrological response tending to stabilize. The first infiltration recharge K1 is determined based on soil moisture transport. A drip response kernel is constructed based on rainfall pulses and cave drip flow rate, and a second infiltration recharge dynamic recharge term K2 is generated after event correction. The dissolved inorganic carbon concentration and carbon sink correction factor were determined based on the event segment water temperature, pH and isotopic end-member constraints. Calculate the carbon sink flux and carbon sink intensity per unit area during the event segment; The closure error is calculated based on the five water conservation relationships, and the parameters of the dripping response kernel are substituted back to correct the error. The modified second infiltration recharge K2 dynamic recharge term, carbon sink correction coefficient, and carbon sink intensity per unit area are input into the surface-groundwater coupled numerical model to form a calibrated karst wetland water-carbon cycle model.

2. The method for constructing a karst wetland water-carbon cycle model as described in claim 1, characterized in that: The five water monitoring data include rainfall data, soil water data, surface karst zone water data, surface runoff data, and underground river outlet flow data. The rainfall data is converted into rainfall volume by combining rainfall depth with the corresponding catchment area. Soil water data, surface karst zone water data, surface runoff data, and underground river outlet flow data are all converted into volume based on the catchment area corresponding to the event segment. The water conservation relationship of the five waters uses the volume of the event segment as the unified calculation caliber.

3. The method for constructing a karst wetland water-carbon cycle model as described in claim 2, characterized in that: The first infiltration recharge K1 is calculated from the soil moisture flux and the water volume per unit area of ​​the groundwater surface, and converted into a volume based on the corresponding catchment area; the first infiltration recharge K1, together with the surface runoff volume and the underground river outlet flow volume, constitute the components of the water conservation relationship of the five waters.

4. The method for constructing a karst wetland water-carbon cycle model as described in claim 3, characterized in that: The event-corrected second infiltration recharge quantity K2 dynamic recharge term is obtained by multiplying the rainfall pulse by the catchment area and convolving it with the drip response kernel, and then weighted and fused with the measured cave drip flow rate; the conversion coefficient is obtained by calibrating the error between the measured recharge quantity of historical events and the convolutional reconstruction value.

5. The method for constructing a karst wetland water-carbon cycle model as described in claim 4, characterized in that: The dripping response kernel includes shape parameters and time scale parameters; the shape parameters and the time scale parameters are determined by the phase lag time from the rainfall peak to the dripping peak and the duration of the event; the phase lag time is used to characterize the temporal memory features of the preferential flow response.

6. The method for constructing a karst wetland water-carbon cycle model as described in claim 5, characterized in that: The dissolved inorganic carbon concentration is determined based on the water temperature, pH value, carbon dioxide partial pressure, and carbon dioxide equilibrium constant as a function of water temperature during the event period; the carbon sink correction coefficient is generated based on the isotopic end-member mixing ratio of fresh carbonate rocks, soil organic carbon, deep groundwater, and modern recharge water.

7. The method for constructing a karst wetland water-carbon cycle model as described in claim 6, characterized in that: The carbon sink correction coefficient is obtained by multiplying the soil end-member contribution factor, the young carbon contribution factor, and the time-delay decay factor; the reference time-delay constant of the time-delay decay factor is 1.5 to 3 times the average time delay of the event.

8. The method for constructing a karst wetland water-carbon cycle model as described in claim 7, characterized in that: The parameter correction of the drip response kernel based on the closure error includes: adjusting at least one parameter of the drip response kernel based on the closure error calculated according to the five water conservation relationship, and re-inputting the corrected parameter into the drip response kernel to update the dynamic replenishment item of the second infiltration replenishment K2.

9. The method for constructing a karst wetland water-carbon cycle model as described in claim 8, characterized in that: The surface-groundwater coupled numerical model consists of a distributed surface water model, a groundwater model, and a communication module for data transmission; the distributed surface water model is an SWMM model, and the groundwater model is a MODFLOW-CFP model.

10. The method for constructing a karst wetland water-carbon cycle model as described in claim 9, characterized in that: The calibrated karst wetland water-carbon cycle model operates under different rainfall conditions, different water resource extraction conditions, and different land use conditions, and calculates the regulation coefficient based on the five water conservation relationships to output the characteristics of water distribution and carbon flux changes.

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