A method and system for multi-scale coupling simulation and precise tracing evaluation of nitrogen in a river basin

Abstract

The application discloses a kind of basin nitrogen multi-scale coupling simulation and accurate traceability evaluation method and system, belong to the technical field of basin water environment simulation and non-point source pollution control, method includes: based on the soil, weather, land use and nitrogen deposition data of research area, the runoff of each grid, runoff nitrogen concentration, deep leakage and nitrogen leaching amount are calculated;D8 flow direction method and triangular unit line method are used to calculate the flow rate of basin outlet;The amount of nitrogen transport of surface path is calculated using the first-order kinetic method;Based on deep leakage and nitrogen leaching amount, the kinetic model coupled with organic nitrogen mineralization, microbial assimilation and denitrification process is used to calculate the amount of nitrogen transport of underground path;Comprehensive above result, output grid scale water nitrogen flux spatial distribution map, identify the key source area of nitrogen loss.The application realizes the multi-scale integrated simulation and accurate traceability of nitrogen migration and transformation by closely coupling grid scale biogeochemical process and watershed scale hydrological process.

Description

Technical Field

[0001] This invention relates to a method and system for multi-scale coupled simulation and precise source tracing assessment of nitrogen in watersheds, belonging to the field of watershed water environment simulation and non-point source pollution control technology. Background Technology

[0002] Nitrogen is a major contributor to non-point source pollution in watersheds, and its migration and transformation processes are complex, involving multi-scale coupling of soil biogeochemical processes and hydrological transport processes. Existing watershed nitrogen simulation technologies fall into two main but fragmented categories: one is grid-scale biogeochemical models, such as DNDC and WHCNS, which can accurately simulate nitrogen transformation and vertical migration within the soil, but completely ignore the hydrological connectivity between grid points, failing to capture the horizontal transport path and time lag effects of nitrogen from source to outlet; the other is watershed-scale hydrological models, such as SWAT and MIKE SHE, which excel at simulating water flow and physical transport of pollutants, but oversimplify the description of key biogeochemical processes such as underground nitrogen transformation, resulting in a severe deficiency in simulating long-term "biogeochemical lags." Recent "loosely coupled" methods (such as the combined use of DNDC and SWAT) attempt to bridge this gap, but due to problems such as spatiotemporal scale mismatch, process decoupling, and spatial resolution degradation, they still cannot achieve high-resolution, mechanistically complete, and accurate watershed nitrogen source tracing. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method and system for multi-scale coupled simulation and accurate source assessment of nitrogen in watersheds. By effectively coupling the vertical biogeochemical processes at the grid scale with the horizontal hydrological transport processes at the watershed scale, the invention overcomes the defect of the separation of the two types of processes in traditional models.

[0004] To achieve the above objectives, the present invention is implemented using the following technical solution:

[0005] In a first aspect, the present invention provides a method for multi-scale coupled simulation and accurate source tracing assessment of nitrogen in watersheds, comprising:

[0006] Based on the soil property data, meteorological data, land use raster map and nitrogen deposition raster map obtained in the study area, the runoff, runoff nitrogen concentration, deep infiltration and deep nitrogen leaching of each raster were calculated.

[0007] Based on the aforementioned production flow rate, the flow path is determined using the D8 flow direction method, and the watershed outlet flow rate is calculated using the triangular unit line method.

[0008] Based on the aforementioned runoff and runoff nitrogen concentration, the amount of nitrogen removed during the migration process is calculated using a first-order kinetic method, thereby calculating the amount of nitrogen transported via the surface pathway at the watershed outlet.

[0009] Based on the deep seepage and deep nitrogen leaching, a kinetic model coupled with organic nitrogen mineralization, microbial assimilation, and denitrification processes was used to calculate the amount of nitrogen transported via the underground pathway at the watershed outlet.

[0010] Based on the watershed outlet flow, the amount of nitrogen transported via surface pathways at the watershed outlet, and the amount of nitrogen transported via underground pathways at the watershed outlet, a grid-scale spatial distribution map of water and nitrogen flux is generated to identify key source areas of nitrogen loss and their spatial distribution characteristics.

[0011] Furthermore, based on the aforementioned production flow rate, the flow path is determined using the D8 flow direction method, and the watershed outlet flow rate is calculated using the triangular unit line method, including:

[0012] The flow path is determined using the D8 flow direction method, and the total convergence time is calculated using the trigonometric unit line method, as shown in the following formula:

[0013] ;

[0014] in, Represents the total convergence time. This represents the hydrological lag time of all land use pixels upstream of the flow path. This represents the hydrological lag time for all river channel pixels. This indicates the number of land use types involved upstream of the flow path. Let be the total number of pixels corresponding to the i-th land use category. The number of pixels in the upstream river channel of the flow path;

[0015] The flow rate based on the nth grid and total convergence time Calculate the outflow of the watershed. The calculation formula is as follows:

[0016] ;

[0017] in, The triangular unit line function for the nth grid cell. This represents the total number of raster cells.

[0018] Furthermore, based on the aforementioned runoff and runoff nitrogen concentration, a first-order kinetic method is used to calculate the amount of nitrogen removed during migration, thereby calculating the amount of nitrogen transported via the surface pathway at the watershed outlet, including:

[0019] The nitrogen removal process during surface transport is simulated based on a first-order kinetic equation, as shown in the following formula:

[0020] ;

[0021] in, This represents the amount of nitrogen removed from the runoff at pixel n after the confluence process. The initial runoff nitrogen concentration, The nitrogen removal rate parameter is the nitrogen removal rate as it flows through each land use pixel. These are the corresponding parameters for pixels flowing through the river channel;

[0022] The flow rate based on the nth grid and nitrogen removal rate Calculate the amount of nitrogen transported via surface pathways at the watershed outlet. The formula is as follows:

[0023] .

[0024] Furthermore, based on the aforementioned deep seepage and deep nitrogen leaching, a kinetic model coupling organic nitrogen mineralization, microbial assimilation, and denitrification processes is used to calculate the nitrogen transport rate via the underground pathway at the watershed outlet, as shown in the following formula:

[0025] A two-layer linear reservoir model is used to simulate the outflow of fast and slow groundwater reservoirs. The dynamic changes in water volume are described by the following formula:

[0026] ;

[0027] ;

[0028] in, and Let be the water volume of the fast reservoir at times t and t-1, respectively. For time step, and Let be the water volume in the slow reservoir at times t and t-1, respectively. express Time Grid The amount of deep leakage; and These are the decay coefficients for the fast and slow inventory, respectively; This is the diversion coefficient;

[0029] A kinetic model coupling organic nitrogen mineralization, microbial assimilation, and denitrification processes was used to calculate the nitrogen transport rate via the subsurface pathway at the watershed outlet, as shown in the following formula:

[0030] ;

[0031] ;

[0032] in, and The mineral nitrogen concentrations in the fast reservoir at times t and t-1 are respectively. and The mineral nitrogen concentrations in the slow reservoir at times t and t-1 are respectively. for Time Grid The amount of deep nitrogen leaching; and The organic nitrogen decomposition rates are for the slow and fast libraries, respectively. The distribution coefficient of organic nitrogen mineralization products in the fast-release library; and These represent the soil organic nitrogen content in the fast and slow reservoirs, respectively. For the maximum assimilation rate, It is the half-saturation constant; Denitrification rate coefficient

[0033] The amount of nitrogen transported via the underground pathway at the watershed outlet is calculated by multiplying the water volume of the fast and slow reservoirs by the mineral nitrogen concentrations of the fast and slow reservoirs.

[0034] Furthermore, the method also includes:

[0035] The calculated watershed outlet flow, surface path nitrogen transport, and subsurface path nitrogen transport are compared with the pre-acquired measured watershed outlet flow data and measured watershed outlet nitrogen flux data.

[0036] The Manning coefficient was determined using measured watershed outlet flow data. Groundwater retention time , and diversion coefficient Calibration was performed; surface nitrogen removal rate was calculated using measured nitrogen flux data at the watershed outlet. Groundwater nitrogen assimilation parameters Denitrification rate Perform calibration and output a set of optimized model parameters;

[0037] Using the optimized model parameter set, the watershed nitrogen multi-scale coupled simulation and precise source tracing assessment method is re-executed to obtain optimized result data.

[0038] Furthermore, the identification of key nitrogen loss source regions and their spatial distribution characteristics includes:

[0039] Based on the simulated grid-scale spatial distribution map of water nitrogen flux, high nitrogen output regions are extracted as key source areas of nitrogen loss.

[0040] By combining the pre-obtained land use type map, the land cover type and its spatial distribution characteristics corresponding to the key source areas of nitrogen loss are determined.

[0041] Secondly, the present invention provides a watershed nitrogen multi-scale coupled simulation and precise source tracing assessment system, used to implement the watershed nitrogen multi-scale coupled simulation and precise source tracing assessment method described in any of the preceding claims, including:

[0042] The first calculation module is used to calculate the runoff, runoff nitrogen concentration, deep infiltration and deep nitrogen leaching of each grid cell based on the soil property data, meteorological data, land use grid map and nitrogen deposition grid map obtained in the study area.

[0043] The second calculation module is used to determine the flow path based on the output flow rate using the D8 flow direction method and to calculate the watershed outlet flow rate using the triangular unit line method.

[0044] The third calculation module is used to calculate the amount of nitrogen removed during the migration process based on the runoff and runoff nitrogen concentration using a first-order kinetic method, and then calculate the amount of nitrogen transported through the surface pathway at the watershed outlet.

[0045] The fourth calculation module is used to calculate the amount of nitrogen transported through the underground pathway at the watershed outlet, based on the deep seepage and deep nitrogen leaching, using a kinetic model that couples organic nitrogen mineralization, microbial assimilation, and denitrification processes.

[0046] The output module is used to output a grid-scale spatial distribution map of water and nitrogen flux based on the watershed outlet flow, the amount of nitrogen transported via surface pathways at the watershed outlet, and the amount of nitrogen transported via underground pathways at the watershed outlet. This map is used to identify key source areas of nitrogen loss and their spatial distribution characteristics.

[0047] Thirdly, the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of any of the methods described above.

[0048] Fourthly, the present invention provides an electronic device, comprising:

[0049] Memory, used to store computer programs / instructions;

[0050] A processor for executing the computer program / instructions to implement the steps of any of the methods described above.

[0051] Fifthly, the present invention provides a computer program product, including a computer program / instructions that, when executed by a processor, implement the steps of any of the methods described above.

[0052] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0053] 1. This invention provides a method and system for multi-scale coupled simulation and precise source assessment of nitrogen in watersheds. By first calculating the runoff, runoff nitrogen concentration, deep seepage, and deep nitrogen leaching of each grid, and then simulating the hydrological connectivity and nitrogen migration and transformation processes of surface and subsurface pathways, this method effectively couples the vertical biogeochemical processes at the grid scale with the horizontal hydrological transport processes at the watershed scale, overcoming the defect of traditional models that separate the two types of processes.

[0054] 2. This invention comprehensively utilizes the D8 flow direction method, the triangular unit line method, the first-order kinetic removal model, and a kinetic model coupled with multiple processes. It can more accurately characterize the time lag effect of water flow convergence and the complex transformation of nitrogen during migration, thereby achieving high-precision simulation of watershed outlet flow and nitrogen transport through surface and subsurface pathways, providing a reliable data foundation for watershed management decisions.

[0055] 3. By outputting a spatial distribution map of water and nitrogen flux at the grid scale, this invention, based on a multi-scale computational framework from the grid to the watershed, can reveal the spatial heterogeneity of nitrogen loss and accurately locate key source areas with high contribution rates, rather than just providing the average situation of the entire watershed, thereby supporting more targeted and precise governance measures.

[0056] 4. This invention, by calculating and outputting the nitrogen transport rates via surface and subsurface pathways respectively, can quantitatively analyze the relative contributions of different hydrological pathways, such as surface runoff and groundwater, to total nitrogen output. This helps to reveal whether nitrogen is lost through rapid surface runoff or migrates via slow subsurface pathways, deepening the understanding of the lag effect and fate patterns of nitrogen cycling in watersheds, and is of great significance for assessing the long-term effectiveness of remediation measures. Attached Figure Description

[0057] Figure 1 This is a schematic diagram of the research area provided in an embodiment of the present invention;

[0058] Figure 2 This is a schematic diagram of the model provided in the embodiment of the present invention;

[0059] Figure 3 This is a simulation diagram of the model provided in this embodiment of the invention for daily flow, monthly flow, evapotranspiration, and nitrogen emissions at the watershed outlet;

[0060] Figure 4 This is a schematic diagram illustrating the contribution of different high-resolution pixels to nitrogen emissions at the outlet via surface, subsurface, and soil pathways, as simulated by the model provided in this embodiment of the invention. Detailed Implementation

[0061] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0062] Example 1: This example introduces a method for multi-scale coupled simulation and accurate source tracing assessment of nitrogen in watersheds, including:

[0063] Based on the soil property data, meteorological data, land use raster map and nitrogen deposition raster map obtained in the study area, the runoff, runoff nitrogen concentration, deep infiltration and deep nitrogen leaching of each raster were calculated.

[0064] Based on the aforementioned production flow rate, the flow path is determined using the D8 flow direction method, and the watershed outlet flow rate is calculated using the triangular unit line method.

[0065] Based on the aforementioned runoff and runoff nitrogen concentration, the amount of nitrogen removed during the migration process is calculated using a first-order kinetic method, thereby calculating the amount of nitrogen transported via the surface pathway at the watershed outlet.

[0066] Based on the deep seepage and deep nitrogen leaching, a kinetic model coupled with organic nitrogen mineralization, microbial assimilation, and denitrification processes was used to calculate the amount of nitrogen transported via the underground pathway at the watershed outlet.

[0067] Based on the watershed outlet flow, the surface pathway nitrogen transport at the watershed outlet, and the subsurface pathway nitrogen transport at the watershed outlet, the daily flow, monthly flow, evapotranspiration, and watershed outlet nitrogen emissions simulated by the model are calibrated and validated. Figure 3 Based on the validated model system, a grid-scale spatial distribution map of water and nitrogen flux is output. Figure 4 (a) is used to identify key source areas of nitrogen loss and their spatial distribution characteristics.

[0068] The watershed nitrogen multi-scale coupled simulation and accurate source tracing assessment method provided in this embodiment involves the following steps in its application:

[0069] Step 1: Model framework construction;

[0070] like Figure 2 As shown, a coupled simulation framework for a multi-scale hydrological-nitrogen biogeochemical model is constructed to achieve:

[0071] (1) Vertical process module: collects data such as... Figure 1 The raster maps of soil, meteorology, land use, and nitrogen deposition within the study area are shown. These maps drive an existing raster-scale soil biogeochemical model (RegWHCNS) to calculate the runoff generation of the i-th grid cell within the study area. ), runoff nitrogen loss ( ), deep leakage ( ) and deep nitrogen leaching amount ( These variables serve as inputs for subsequent horizontal transport modules to calculate water flow and nitrogen flux at the watershed outlet.

[0072] (2) Horizontal transmission module;

[0073] The output of the vertical process module is used as the input of the horizontal transmission module, which is divided into two sub-modules: surface flow and subsurface flow.

[0074] a. Surface flow and nitrogen migration;

[0075] The flow path is determined using the D8 flow direction method, and the convergence time is calculated using the trigonometric unit line method.

[0076] ;

[0077] ;

[0078] This formula is used to calculate the total time for runoff from the nth pixel to reach the watershed outlet. Represents the total confluence time (seconds), its value is derived from the hydrological lag time of all land use pixels upstream of the flow path. (seconds) hydrological lag time for all river channel pixels (seconds) are accumulated to obtain; in the formula This indicates the number of land use types involved upstream of the flow path. Let be the total number of pixels corresponding to the i-th land use category. This represents the number of pixels in the upstream river channel. Calculated based on the NRCS TR-55 method, Calculated based on Manning's formula; This is the Manning coefficient. The spatial step size; Slope; "For" refers to the 24-hour rainfall within the recurrence period of the event under consideration.

[0079] The flow rate based on the nth grid and total convergence time Calculate the outflow of the watershed. The calculation formula is as follows:

[0080] ;

[0081] in, The triangular unit line function for the nth grid cell. This represents the total number of raster cells.

[0082] Nitrogen is removed via first-order kinetics during surface transport:

[0083] ;

[0084] This formula quantifies the amount of nitrogen removed by surface runoff during the runoff process. In the formula... This represents the amount of nitrogen (mg / L) removed from the runoff of the nth pixel during its confluence process, calculated based on the initial runoff nitrogen concentration. (mg / L), and taking into account the nitrogen removal rate parameter as it flows through each land use pixel. (hours⁻¹) and length of stay The product of the two, and the corresponding parameters when the pixel flows through the river channel. (hours⁻¹) and The product of these is then accumulated over all upstream pixels.

[0085] The flow rate based on the nth grid and nitrogen removal rate Calculate the amount of nitrogen transported via surface pathways at the watershed outlet. The formula is as follows:

[0086] .

[0087] b. Subsurface flows and nitrogen migration;

[0088] A two-layer linear reservoir model is used to simulate fast and slow groundwater reservoirs:

[0089] ;

[0090] ;

[0091] This equation describes the dynamic changes in water volume in fast and slow groundwater reservoirs. The left side of the equation represents the rate of change of the outflow from the fast reservoir over time. and The values ​​are the water volume (in cubic meters) of the fast reservoir at times t and t-1, respectively. For time step, This represents the decay coefficient of the slow library. The first term on the right... The first term represents the sum of deep seepage or lateral water flow (cubic meters / time step) flowing into the fast reservoir from all grids, output by the grid-scale model; the second term represents the fast reservoir's own decay coefficient. The outflow process is as follows. The input source for the slow library is the outflow from the fast library, calculated according to the splitting coefficient. The divided part, namely The output is the slow library itself through the decay coefficient. The outflow process; and The values ​​are the water volume (in cubic meters) in the slow reservoir at times t and t-1, respectively.

[0092] ;

[0093] ;

[0094] This formula describes the dynamic changes in mineral nitrogen concentration in the fast reservoir; and The mineral nitrogen concentrations in the fast reservoir at times t and t-1 are respectively. and These represent the mineral nitrogen concentrations in the slow reservoir at times t and t-1, respectively. The first term on the right-hand side of the equation is the external input, namely the deep nitrogen leaching amount fed in from the grid. The concentration increment is obtained by dividing (kg / time step) by the volume of water in the fast reservoir; the second and third terms represent the sources of organic nitrogen mineralization, indicating the decomposition rate of the slow SON reservoir. (hours⁻¹) and the fast SON library by decomposition rate (hours⁻¹) and product partition coefficient (0-1) Mineral nitrogen generated by transformation; and These represent the soil organic nitrogen content in the fast and slow reservoirs, respectively. The fourth term is microbial assimilation consumption, described using the Michaelis-Menten equation, in which... The maximum assimilation rate is (mg / L·h). The term represents the half-saturation constant (mg / L); the last term represents the denitrification loss, which is related to the mineral nitrogen concentration and the denitrification rate coefficient. (hours⁻¹) is directly proportional.

[0095] The amount of nitrogen transported via the underground pathway at the watershed outlet is calculated by multiplying the water volume of the fast and slow reservoirs by the mineral nitrogen concentrations of the fast and slow reservoirs.

[0096] Step 2: Constraints on multi-scale data fusion;

[0097] (1) Vertical constraints: Soil samples were collected within the region to obtain the basic physicochemical properties of the soil. The grid soil hydraulic parameters were derived using the Pedotransfer Functions (Vereecken, Wosten, Weynants). Combined with meteorological and irrigation data, the water submodule in the vertical model was driven to output the grid-scale water balance term. The vertical nitrogen submodule was driven based on the existing field fertilization survey and nitrogen deposition dataset to further output the grid-scale nitrogen destination. Finally, the soil nitrogen transformation parameters (nitrification, denitrification, mineralization rate, etc.) were calibrated using in-situ soil moisture and nitrogen concentration data. The key parameters of the water and nitrogen modules were calibrated by combining remote sensing ET data (GLEAM, PML_V2, MODIS) to make the simulated vertical flux match the existing dataset.

[0098] (2) Horizontal constraints: First, based on the watershed outlet flow data, the Manning coefficient is calibrated. Groundwater retention time , and diversion coefficient Then, based on the nitrogen transport data at the watershed outlet, the surface nitrogen removal rate was calibrated. Groundwater nitrogen assimilation parameters Denitrification rate Finally, parameter calibration is implemented based on the Bayesian DREAM algorithm.

[0099] Step 3: Spatiotemporal dynamic simulation and output;

[0100] Based on the constrained vertical and horizontal models, a grid-scale spatial distribution map of water and nitrogen fluxes can be output, identifying key source areas of nitrogen loss and their spatial heterogeneity. The contribution of outlet nitrogen flux is analyzed based on the transport volumes from different hydrological pathways, including surface runoff and groundwater (baseflow and lateral flow). Figure 4 (bd) and its temporal dynamics. Based on the relationship between raster output and underlying surfaces such as land use, an attribution model of land use type and nitrogen output response is constructed. This model can accurately assess the contribution ratio of different cover types such as tea gardens, forests, and paddy fields to the total nitrogen output of the watershed, and locate key pollution sources in high-fertilization areas such as tea gardens. Combined with the time lag analysis module, the system evaluates the transport time of nitrogen from the source area to the outlet, revealing the interannual and seasonal lag patterns of nitrogen flux under different transport pathways. This establishes a comprehensive source identification and contribution rate assessment system that integrates spatial source identification, transport pathway analysis, land use attribution, and time lag evaluation.

[0101] The specific beneficial effects of this embodiment are as follows:

[0102] In watershed hydrology and nitrogen flux simulation, the model demonstrated good simulation performance at both daily and monthly scales. The daily-scale flow simulation achieved a coefficient of determination (R²) of 0.505, a consistency index (IA) of 0.801, and a Nash efficiency coefficient (NSE) of 0.953. The monthly-scale simulation performance further improved, with an R² of 0.906. The monthly-scale evapotranspiration simulation showed good agreement with multi-source remote sensing products, with an R² of 0.965. Based on accurate hydrological simulation, the model successfully reproduced the monthly-scale nitrogen flux dynamics at the watershed outlet, with a high degree of consistency between simulated and observed values, a coefficient of determination (R²) of 0.730, and an average monthly nitrogen output error of less than 0.5%. It successfully identified tea plantations (14.1% of the area) contributing 28.2% of nitrogen output and forests (60.9% of the area) contributing 48.3%.

[0103] Regarding the analysis of water and nitrogen flux pathways, the model accurately quantified the contribution of different hydrological pathways to the total flux. Simulation results show that surface runoff, baseflow, and lateral flow contribute 45.7%, 43.8%, and 10.5% of the total flow, respectively. In terms of nitrogen output, although baseflow contributes only 43.8% of the water volume, it accounts for 62.4% of the nitrogen output, while surface runoff contributes 27.0% of the nitrogen output, highlighting the dominant role of groundwater pathways in nitrogen transport and the importance of biogeochemical retention.

[0104] In terms of spatial heterogeneity characterization, the model successfully captured the differences in water and nitrogen dynamics across different land use types. Simulations of three typical ecosystems—tea plantations, forests, and paddy fields—showed simulation determination coefficients (R²) for soil moisture and nitrogen concentration dynamics both exceeding 0.897, and consistency indices (IA) exceeding 0.803. Spatial contribution analysis further revealed that tea plantations, accounting for only 14.1% of the watershed area, contributed 28.2% of nitrogen output, while forests, covering 60.9% of the area, contributed 48.3%, demonstrating the model's accurate identification capability in spatial source tracing.

[0105] Example 2: This example provides a watershed nitrogen multi-scale coupled simulation and precise source tracing assessment system, including:

[0106] The first calculation module is used to calculate the runoff, runoff nitrogen concentration, deep infiltration and deep nitrogen leaching of each grid cell based on the soil property data, meteorological data, land use grid map and nitrogen deposition grid map obtained in the study area.

[0107] The second calculation module is used to determine the flow path based on the output flow rate using the D8 flow direction method and to calculate the watershed outlet flow rate using the triangular unit line method.

[0108] The third calculation module is used to calculate the amount of nitrogen removed during the migration process based on the runoff and runoff nitrogen concentration using a first-order kinetic method, and then calculate the amount of nitrogen transported through the surface pathway at the watershed outlet.

[0109] The fourth calculation module is used to calculate the amount of nitrogen transported through the underground pathway at the watershed outlet, based on the deep seepage and deep nitrogen leaching, using a kinetic model that couples organic nitrogen mineralization, microbial assimilation, and denitrification processes.

[0110] The output module is used to output a grid-scale spatial distribution map of water and nitrogen flux based on the watershed outlet flow, the amount of nitrogen transported via surface pathways at the watershed outlet, and the amount of nitrogen transported via underground pathways at the watershed outlet. This map is used to identify key source areas of nitrogen loss and their spatial distribution characteristics.

[0111] The specific functions of each module described above are explained in the relevant content of the method in Embodiment 1, and will not be repeated here.

[0112] Example 3: This example provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of any of the methods described in Example 1.

[0113] Example 4: This example provides an electronic device, including:

[0114] Memory, used to store computer programs / instructions;

[0115] A processor for executing the computer program / instructions to implement the steps of any of the methods described in Embodiment 1.

[0116] Example 5: This example provides a computer program product, including a computer program / instructions, which, when executed by a processor, implement the steps of the method described in any one of Examples 1.

[0117] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

[0118] Those skilled in the art will understand that embodiments of this disclosure can be provided as methods, systems, or computer program products. Therefore, this disclosure can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this disclosure can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0119] This disclosure is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this disclosure. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create a machine for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0120] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0121] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0122] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this disclosure and not to limit its protection scope. Although this disclosure has been described in detail with reference to the above embodiments, those skilled in the art should understand that after reading this disclosure, they can still make various changes, modifications or equivalent substitutions to the specific implementation of the invention, but these changes, modifications or equivalent substitutions are all within the protection scope of the pending claims.

Claims

1. A method for multi-scale coupled simulation and precise source tracing assessment of nitrogen in watersheds, characterized in that, include: Based on the soil property data, meteorological data, land use raster map and nitrogen deposition raster map obtained in the study area, the runoff, runoff nitrogen concentration, deep infiltration and deep nitrogen leaching of each raster were calculated. Based on the aforementioned production flow rate, the flow path is determined using the D8 flow direction method, and the watershed outlet flow rate is calculated using the triangular unit line method. Based on the aforementioned runoff and runoff nitrogen concentration, the amount of nitrogen removed during the migration process is calculated using a first-order kinetic method, thereby calculating the amount of nitrogen transported via the surface pathway at the watershed outlet. Based on the deep seepage and deep nitrogen leaching, a kinetic model coupled with organic nitrogen mineralization, microbial assimilation, and denitrification processes was used to calculate the amount of nitrogen transported via the underground pathway at the watershed outlet. Based on the watershed outlet flow, the amount of nitrogen transported via surface pathways at the watershed outlet, and the amount of nitrogen transported via underground pathways at the watershed outlet, a grid-scale spatial distribution map of water and nitrogen flux is generated to identify key source areas of nitrogen loss and their spatial distribution characteristics.

2. The watershed nitrogen multi-scale coupled simulation and precise source tracing assessment method according to claim 1, characterized in that, Based on the aforementioned production volume, the flow path is determined using the D8 flow direction method, and the watershed outlet flow is calculated using the triangular unit line method, including: The flow path is determined using the D8 flow direction method, and the total convergence time is calculated using the trigonometric unit line method, as shown in the following formula: ； in, Represents the total convergence time. This represents the hydrological lag time of all land use pixels upstream of the flow path. This represents the hydrological lag time for all river channel pixels. This indicates the number of land use types involved upstream of the flow path. Let be the total number of pixels corresponding to the i-th land use category. The number of pixels in the upstream river channel of the flow path; The flow rate based on the nth grid and total convergence time Calculate the outflow of the watershed. The calculation formula is as follows: ； in, The triangular unit line function for the nth grid cell. This represents the total number of raster cells.

3. The watershed nitrogen multi-scale coupled simulation and precise source tracing assessment method according to claim 1, characterized in that, Based on the aforementioned runoff and runoff nitrogen concentration, the amount of nitrogen removed during migration is calculated using a first-order kinetic method, thereby calculating the amount of nitrogen transported via surface pathways at the watershed outlet, including: The nitrogen removal process during surface transport is simulated based on a first-order kinetic equation, as shown in the following formula: ； in, This represents the amount of nitrogen removed from the runoff at pixel n after the confluence process. The initial runoff nitrogen concentration, The nitrogen removal rate parameter is the nitrogen removal rate as it flows through each land use pixel. These are the corresponding parameters for pixels flowing through the river channel; The flow rate based on the nth grid and nitrogen removal rate Calculate the amount of nitrogen transported via surface pathways at the watershed outlet. The formula is as follows: 。 4. The watershed nitrogen multi-scale coupled simulation and precise source tracing assessment method according to claim 1, characterized in that, Based on the aforementioned deep seepage and deep nitrogen leaching, a kinetic model coupling organic nitrogen mineralization, microbial assimilation, and denitrification processes is used to calculate the nitrogen transport rate via the subsurface pathway at the watershed outlet, as shown in the following formula: A two-layer linear reservoir model is used to simulate the outflow of fast and slow groundwater reservoirs. The dynamic changes in water volume are described by the following formula: ； ； in, and Let be the water volume of the fast reservoir at times t and t-1, respectively. For time step, and Let be the water volume in the slow reservoir at times t and t-1, respectively. express Time Grid The amount of deep leakage; and These are the decay coefficients for the fast and slow inventory, respectively; This is the diversion coefficient; A kinetic model coupling organic nitrogen mineralization, microbial assimilation, and denitrification processes was used to calculate the nitrogen transport rate via the subsurface pathway at the watershed outlet, as shown in the following formula: ； ； in, and The mineral nitrogen concentrations in the fast reservoir at times t and t-1 are respectively. and The mineral nitrogen concentrations in the slow reservoir at times t and t-1 are respectively. for Time Grid The amount of deep nitrogen leaching; and The organic nitrogen decomposition rates are for the slow and fast libraries, respectively. The distribution coefficient of organic nitrogen mineralization products in the fast-release library; and These represent the soil organic nitrogen content in the fast and slow reservoirs, respectively. For the maximum assimilation rate, It is the half-saturation constant; This is the denitrification rate coefficient; The amount of nitrogen transported via the underground pathway at the watershed outlet is calculated by multiplying the water volume of the fast and slow reservoirs by the mineral nitrogen concentrations of the fast and slow reservoirs.

5. The watershed nitrogen multi-scale coupled simulation and precise source tracing assessment method according to claim 1, characterized in that, The method further includes: The calculated watershed outlet flow, surface path nitrogen transport, and subsurface path nitrogen transport are compared with the pre-acquired measured watershed outlet flow data and measured watershed outlet nitrogen flux data. The Manning coefficient was determined using measured watershed outlet flow data. Groundwater retention time , and diversion coefficient Calibration was performed; surface nitrogen removal rate was calculated using measured nitrogen flux data at the watershed outlet. Groundwater nitrogen assimilation parameters Denitrification rate Perform calibration and output a set of optimized model parameters; Using the optimized model parameter set, the watershed nitrogen multi-scale coupled simulation and precise source tracing assessment method is re-executed to obtain optimized result data.

6. The watershed nitrogen multi-scale coupled simulation and precise source tracing assessment method according to claim 1, characterized in that, The identification of key nitrogen loss source regions and their spatial distribution characteristics includes: Based on the simulated grid-scale spatial distribution map of water nitrogen flux, high nitrogen output regions are extracted as key source areas of nitrogen loss. By combining the pre-obtained land use type map, the land cover type and its spatial distribution characteristics corresponding to the key source areas of nitrogen loss are determined.

7. A watershed nitrogen multi-scale coupled simulation and precise source tracing assessment system, used to implement the watershed nitrogen multi-scale coupled simulation and precise source tracing assessment method according to any one of claims 1-6, characterized in that, include: The first calculation module is used to calculate the runoff, runoff nitrogen concentration, deep infiltration and deep nitrogen leaching of each grid cell based on the soil property data, meteorological data, land use grid map and nitrogen deposition grid map obtained in the study area. The second calculation module is used to determine the flow path based on the output flow rate using the D8 flow direction method and to calculate the watershed outlet flow rate using the triangular unit line method. The third calculation module is used to calculate the amount of nitrogen removed during the migration process based on the runoff and runoff nitrogen concentration using a first-order kinetic method, and then calculate the amount of nitrogen transported through the surface pathway at the watershed outlet. The fourth calculation module is used to calculate the amount of nitrogen transported through the underground pathway at the watershed outlet, based on the deep seepage and deep nitrogen leaching, using a kinetic model that couples organic nitrogen mineralization, microbial assimilation, and denitrification processes. The output module is used to output a grid-scale spatial distribution map of water and nitrogen flux based on the watershed outlet flow, the amount of nitrogen transported via surface pathways at the watershed outlet, and the amount of nitrogen transported via underground pathways at the watershed outlet. This map is used to identify key source areas of nitrogen loss and their spatial distribution characteristics.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that: When executed by a processor, the computer program implements the steps of the method described in any one of claims 1-6.

9. An electronic device, characterized in that, include: Memory, used to store computer programs / instructions; A processor for executing the computer program / instructions to implement the steps of the method according to any one of claims 1-6.

10. A computer program product comprising a computer program / instructions, characterized in that, When the computer program / instructions are executed by the processor, they implement the steps of the method described in any one of claims 1-6.

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