Nitrogen and phosphorus co-management method for river-estuary continuum
By using the coastal eutrophication potential index and ecological threshold diagnosis, combined with the InVEST model and ArcGIS tools, key source areas were identified and cost-effective measures were set up. This solved the problem of whole-chain collaborative management of the river-estuary continuum system and achieved precise, economical and efficient nitrogen and phosphorus collaborative management.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- XIAMEN UNIV
- Filing Date
- 2026-04-28
- Publication Date
- 2026-05-29
AI Technical Summary
Existing technologies have failed to form a full-chain, iterative, and collaborative management system covering 'flux metering and diagnosis—zoning ecological thresholds—risk decision-making—key source area identification—cost-effective management,' which cannot meet the systemic governance needs of the river-estuary continuum. There are problems such as insufficient understanding of the ecological attributes of estuaries, lack of cost-effectiveness constraints on governance measures, and governance vacuum caused by land-sea separation management.
The coastal eutrophication potential index was used to diagnose the stoichiometry and flux of nutrients, the estuary zones were divided and ecological thresholds were determined, and key source areas were identified by combining the InVEST model and ArcGIS tools. Measures such as fertilizer reduction and grass-planted waterways were set up, and cost-benefit analysis was conducted to achieve coordinated management of nitrogen and phosphorus.
It enables integrated and coordinated management of river basins and estuaries, accurately identifies key source areas, improves governance efficiency and targeting, is economical and efficient, has the ability to identify eutrophication risks at an early stage, and is applicable to various river-estuary systems with significant land-sea interactions.
Smart Images
Figure CN122114684A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of ecological management technology, specifically relating to a method for the coordinated management of nitrogen and phosphorus in river-estuary continuums. Background Technology
[0002] Estuaries are crucial transitional zones between land and sea, where excessive input of terrestrial nitrogen and phosphorus can easily trigger ecological disasters such as eutrophication, harmful algal blooms, and bottom-level hypoxia. Current river-estuary nutrient management faces numerous bottlenecks: insufficient understanding of estuarine ecological attributes, with near-shore water quality standards largely applied without considering the nonlinear ecological response of the freshwater-seawater transition zone, hindering refined management; insufficient accuracy in identifying key terrestrial pollution sources, failing to couple water function zoning, environmental capacity, and water quality targets, resulting in a disconnect between governance priorities and ecological risks; governance measures focusing solely on reduction efficiency, lacking cost-effectiveness constraints, and exhibiting poor implementation; and fragmented land-sea management, with uncoordinated basin and estuary objectives, creating a governance vacuum. Therefore, existing technologies have not formed a comprehensive, iterative, and collaborative management system covering the entire chain—from flux measurement and diagnosis to zoning ecological thresholds, risk decision-making, key source area identification, and cost-effectiveness control—and cannot meet the systemic governance needs of the river-estuary continuum. Summary of the Invention
[0003] To address the aforementioned issues, this invention proposes a nitrogen and phosphorus synergistic management method for river-estuary continuums. This method achieves integrated land-sea management, precise zoning, accurate source tracing, and cost-effective full-chain nitrogen and phosphorus synergistic control. It can be iteratively optimized and applied to the comprehensive eutrophication management of various river-estuary continuums with significant land-sea interactions.
[0004] To achieve the above objectives, the present invention adopts the following technical solution: A method for the coordinated management of nitrogen and phosphorus in the river-estuary continuum includes the following steps: S1. Use the coastal eutrophication potential index to diagnose key nutrient elements that affect the stoichiometry and flux of nutrient salts. S2. Based on the relationship between nutrient concentration and ecological response indicators, determine the ecological thresholds for total nitrogen, total phosphorus, dissolved inorganic nitrogen, and dissolved inorganic phosphorus in different estuary zones. S3. Based on the coastal eutrophication potential index and ecological threshold, comprehensively diagnose eutrophication risk and determine whether to choose watershed management or estuary management. S4. Identify key nitrogen and phosphorus pollution source areas that substantially limit downstream water quality targets under water function zoning and environmental capacity constraints; S5. A nitrogen and phosphorus synergistic management strategy is proposed based on cost-benefit analysis.
[0005] Preferably, the specific process of step S1 is as follows: The coastal eutrophication potential index is used to assess the potential impact of river nutrient input on eutrophication of coastal waters. The coastal eutrophication potential index includes the coastal nitrogen eutrophication potential index and the coastal phosphorus eutrophication potential index, and the calculation formula is as follows: , ,in, The potential index for nitrogen eutrophication along the coast; The index of eutrophication potential along the coast; N Flux The daily nitrogen flux per unit watershed area; P Flux The daily flux of phosphorus per unit watershed area; Si Flux This represents the daily flux of silicon per unit watershed area. The formula for calculating the nutrient flux at the survey section is: F=C Q, where F is the nutrient flux at the survey section; C is the average nutrient concentration at the survey section; and Q is the average river runoff.
[0006] Preferably, the specific process of step S2 is as follows: S21. Estuarine ecological zoning: Based on salinity gradient, hydrodynamic characteristics and major biogeochemical processes, the estuary is divided into riverine zone, mixed zone and nearshore zone to reflect the nonlinear response of phytoplankton in different estuarine areas to nutrient changes. S22. Determination of ecological thresholds for different zones: Using chlorophyll a, which characterizes phytoplankton biomass, as the key ecological response indicator, a random forest model is used to assess the importance of environmental factors to phytoplankton abundance. Partial correlation analysis is used to establish the response relationship between chlorophyll a concentration and the concentration of each nutrient. By identifying the inflection point of chlorophyll a change with nutrient concentration, the ecological thresholds for total nitrogen, total phosphorus, dissolved inorganic nitrogen, and dissolved inorganic phosphorus in each zone are determined. The ecological thresholds characterize the critical response of the phytoplankton community to nutrient input.
[0007] Preferably, the specific process of step S3 is as follows: When the coastal eutrophication potential index is positive, it indicates that the content of nitrogen or phosphorus relative to dissolved silicon is too high, which is conducive to the proliferation of non-siliceous algae. At the watershed level, nitrogen or phosphorus emissions should be reduced first. When the measured values of nitrogen and phosphorus in a certain zone of the estuary exceed the corresponding ecological threshold, it indicates that the current nutrient load of the estuary exceeds the concentration required for normal algal growth, and zoned and targeted management should be implemented for the upstream basin and the surrounding areas of the estuary.
[0008] Preferably, the specific process of step S4 is as follows: S41. Watershed water yield simulation: Using the annual water yield module of the InVEST model, the annual water yield of the watershed grid is calculated based on the water-heat coupling balance to simulate the annual water resource supply of the regional ecosystem. S42. Watershed nitrogen and phosphorus pollution simulation: Using the water purification module of the InVEST model, the output of total nitrogen and total phosphorus after purification by the ecosystem is simulated, and the pollutant output load at the grid and sub-watershed scales is calculated. S43. Key Source Area Identification: Using ArcGIS hydrological analysis tools, extract river sections, runoff nodes, and sub-basins to construct the river topology; calculate the potential runoff nitrogen and phosphorus mass concentrations and exceedance risk scores for each sub-basin; combine the compliance concentrations of water function zones to calculate the pollution index, and delineate total nitrogen control areas, total phosphorus control areas, nitrogen-phosphorus composite control areas, and relatively safe areas; use the Getis-Ord Gi spatial statistical method to identify non-point source pollution hotspots, and spatially couple the nitrogen-phosphorus composite control areas with significant hotspots to determine key source areas of non-point source pollution.
[0009] Preferably, the formula for calculating the water production in step S41 is: , , , ,in, Let x be the annual water production of the x-th grid; x is the grid number. Let x be the annual actual evapotranspiration of the x-th grid. Let x be the annual precipitation of the x-th grid cell; The potential evapotranspiration of the x-th grid cell; These are non-physical parameters relating to climate and soil properties; Let x be the evapotranspiration coefficient of the x-th grid cell; This is the reference evaporation rate for the x-th grid cell; Let x be the solar radiation in the x-th grid cell; This represents the average of the daily average maximum and minimum temperatures of the x-th grid cell. This is the difference between the daily average maximum temperature and the daily average minimum temperature of the x-th grid.
[0010] Preferably, the formula for calculating the pollutant output of the x-th grid in step S42 is: ,in, The pollutant output of the x-th grid after water purification by the ecosystem; The hydrological sensitivity score for the x-th raster. The output coefficient of the x-th grid; , where λ x Let λ be the flow rate of the x-th grid cell; W The runoff index for the study area; , where ∑ U Y U This represents the sum of water production from all grids along the flow path of the x-th grid in the study area.
[0011] Preferably, the specific process of step S5 is as follows: S51. Management Scenario Setting: Set up non-engineering measures and engineering measures. Non-engineering measures include fertilizer reduction of 10% and fertilizer reduction of 20%; engineering measures include grassed waterways, returning farmland to forest, and vegetation filter belts; combine engineering measures and non-engineering measures to form a combined scheme. S52. Pollution Load Reduction Efficiency Assessment: The reduction effect of total nitrogen and total phosphorus is calculated using the load reduction rate. The calculation formula is as follows: , Where R is the total phosphorus load reduction efficiency at the sub-basin scale; TP BAS The total phosphorus load output by the model under the baseline scenario; TP BMPS The model output represents the total phosphorus load after incorporating optimal management practices; M represents the total nitrogen load reduction efficiency at the sub-basin scale; TN BAS The total nitrogen load (TN) is the model output under the baseline scenario. BMPS The total nitrogen load output by the model after incorporating optimal management practices; S53. Cost accounting for measures: separately account for the construction and operation costs of fertilizer reduction, grassed waterways, returning farmland to forest, vegetation filter belts and combined measures; S54. Cost-benefit analysis: Using the difference in pollution load between the baseline scenario and the implementation of the measures as the benefit, calculate the cost-benefit value. The calculation formula is as follows: Where CE is the cost-benefit value; Cost is the cost of implementing the measure; LOAD BAS The total pollution load of the study area under the baseline scenario; LOAD BMP The total pollution load of the study area after the best management measures are implemented.
[0012] By adopting the above technical solution, the present invention has the following beneficial effects: 1. This invention closely integrates the process of nutrient transport in the watershed with the ecological response of the estuary, breaking through the limitations of traditional land and sea area segmented management, forming an integrated management logic covering the "river-estuary-nearshore" continuum, realizing full-chain risk management from the source to the recipient, coordinating land and sea, and eliminating governance vacuums.
[0013] 2. This invention divides estuaries into riverine, mixed, and nearshore zones based on salinity gradients and hydrodynamic characteristics. Using chlorophyll a as an ecological indicator, it determines the ecological thresholds for each zone, overcoming the shortcomings of traditional uniform water quality standards that are unsuitable for estuarine transition zones. This achieves refined and differentiated nutrient management, enabling precise estuarine zone management that adapts to nonlinear ecological characteristics. Furthermore, this invention couples the InVEST model, water function zoning, environmental capacity, standardized pollution indices, and Getis-Ord Gi hotspot analysis to accurately locate key source areas of nitrogen and phosphorus compound pollution. This avoids extensive, comprehensive treatment across the entire area, significantly improving management efficiency and targeting, achieving precise identification of key source areas, and providing highly targeted management.
[0014] 3. This invention sets out measures such as fertilizer reduction, grassed waterways, reforestation, vegetation filter belts, and combinations thereof. It quantifies reduction efficiency, construction and operation costs, and cost-benefit values, and selects the most economical and efficient solutions, taking into account both ecological effects and economic feasibility, thus facilitating management decision-making and engineering implementation. Furthermore, this method is based on a general ecological model, index algorithm, and management elements, and is not dependent on specific watershed conditions. It can periodically update indicators, evaluate effectiveness, and optimize strategies, making it applicable to various river-estuary systems with strong land-sea interactions and clearly defined water quality targets and water function zoning.
[0015] 4. This invention uses the Coastal Eutrophication Potential Index (ICEP Index) to quantify the risk of nutrient structure imbalance, identify the proliferation potential of non-siliceous algae in advance, and combine it with measured concentration thresholds for dual diagnosis to achieve early identification, early warning, and early control of eutrophication, thereby improving the ecological security guarantee capacity, conducting pre-diagnosis of ecological risks, and making prevention and control more proactive. Attached Figure Description
[0016] Figure 1 This is a flowchart of the method of the present invention. Detailed Implementation
[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.
[0018] like Figure 1 As shown, the nitrogen and phosphorus synergistic management method for the river-estuary continuum includes the following steps: S1. Use the coastal eutrophication potential index to diagnose key nutrient elements that affect the stoichiometry and flux of nutrient salts. The specific process of step S1 is as follows: The coastal eutrophication potential index is used to assess the potential impact of river nutrient input on eutrophication of coastal waters. The coastal eutrophication potential index includes the coastal nitrogen eutrophication potential index and the coastal phosphorus eutrophication potential index. The calculation formula is as follows: , ,in, The potential index for nitrogen eutrophication along the coast; The index of eutrophication potential along the coast; N Flux The daily nitrogen flux per unit watershed area; P Flux The daily flux of phosphorus per unit watershed area; Si Flux This represents the daily flux of silicon per unit watershed area. The formula for calculating the nutrient flux at the survey section is: F=C Q, where F is the nutrient flux at the survey section; C is the average nutrient concentration at the survey section; and Q is the average river runoff. S2. Based on the relationship between nutrient concentration and ecological response indicators, determine the ecological thresholds for total nitrogen, total phosphorus, dissolved inorganic nitrogen, and dissolved inorganic phosphorus in different estuary zones. The specific process of step S2 is as follows: S21. Estuarine ecological zoning: Based on salinity gradient, hydrodynamic characteristics and major biogeochemical processes, the estuary is divided into riverine zone, mixed zone and nearshore zone to reflect the nonlinear response of phytoplankton in different estuarine areas to nutrient changes. S22. Determination of Regional Ecological Thresholds: Using chlorophyll a, which characterizes phytoplankton biomass, as the key ecological response indicator, a random forest model is used to assess the importance of environmental factors to phytoplankton abundance. Partial correlation analysis is used to establish the response relationship between chlorophyll a concentration and the concentration of each nutrient. By identifying the inflection point of chlorophyll a change with nutrient concentration, the ecological thresholds of total nitrogen, total phosphorus, dissolved inorganic nitrogen, and dissolved inorganic phosphorus in each region are determined. These ecological thresholds characterize the critical response of the phytoplankton community to nutrient input. S3. Based on the coastal eutrophication potential index and ecological threshold, comprehensively diagnose eutrophication risk and determine whether to choose watershed management or estuary management. The specific process of step S3 is as follows: When the coastal eutrophication potential index is positive, it indicates that the content of nitrogen or phosphorus relative to dissolved silicon is too high, which is conducive to the proliferation of non-siliceous algae. At the watershed level, nitrogen or phosphorus emissions should be reduced first. When the measured values of nitrogen and phosphorus in a certain zone of the estuary exceed the corresponding ecological threshold, it indicates that the current nutrient load of the estuary exceeds the concentration required for normal algal growth, and zoned and targeted management should be implemented in the upstream basin and the surrounding areas of the estuary. S4. Identify key nitrogen and phosphorus pollution source areas that substantially limit downstream water quality targets under water function zoning and environmental capacity constraints; The specific process of step S4 is as follows: S41. Watershed water yield simulation: Using the annual water yield module of the InVEST model, the annual water yield of the watershed grid is calculated based on the water-heat coupling balance to simulate the annual water resource supply of the regional ecosystem. The formula for calculating the water production in step S41 is: , , , ,in, Let x be the annual water production of the x-th grid; x is the grid number. Let x be the annual actual evapotranspiration of the x-th grid. Let x be the annual precipitation of the x-th grid cell; The potential evapotranspiration of the x-th grid cell; These are non-physical parameters relating to climate and soil properties; Let x be the evapotranspiration coefficient of the x-th grid cell; This is the reference evaporation rate for the x-th grid cell; Let x be the solar radiation in the x-th grid cell; This represents the average of the daily average maximum and minimum temperatures of the x-th grid cell. This represents the difference between the daily average maximum temperature and the daily average minimum temperature of the x-th grid cell. S42. Watershed nitrogen and phosphorus pollution simulation: Using the water purification module of the InVEST model, the output of total nitrogen and total phosphorus after purification by the ecosystem is simulated, and the pollutant output load at the grid and sub-watershed scales is calculated. In step S42, the formula for calculating the pollutant output of the x-th grid in the water purification module is: ,in, The pollutant output of the x-th grid after water purification by the ecosystem; The hydrological sensitivity score for the x-th raster. The output coefficient of the x-th grid; , where λ x Let λ be the flow rate of the x-th grid cell; W The runoff index for the study area; , where ∑ U Y U This represents the sum of the water production of each cell along the flow path of the x-th cell in the study area; S43. Key Source Area Identification: Using ArcGIS hydrological analysis tools, extract river sections, runoff nodes, and sub-basins to construct the river topology; calculate the potential runoff nitrogen and phosphorus mass concentrations and exceedance risk scores for each sub-basin; combine the compliance concentrations of water function zones to calculate the pollution index, and delineate total nitrogen control areas, total phosphorus control areas, nitrogen and phosphorus combined control areas, and relatively safe areas; use the Getis-Ord Gi spatial statistical method to identify non-point source pollution hotspots, and spatially couple the nitrogen and phosphorus combined control areas with significant hotspots to determine key source areas of non-point source pollution. S5. Based on cost-benefit analysis, a nitrogen and phosphorus synergistic management strategy is proposed. The specific process of step S5 is as follows: S51. Management Scenario Setting: Set up non-engineering measures and engineering measures. Non-engineering measures include fertilizer reduction of 10% and fertilizer reduction of 20%; engineering measures include grassed waterways, returning farmland to forest, and vegetation filter belts; combine engineering measures and non-engineering measures to form a combined scheme. S52. Pollution Load Reduction Efficiency Assessment: The reduction effect of total nitrogen and total phosphorus is calculated using the load reduction rate. The calculation formula is as follows: , Where R is the total phosphorus load reduction efficiency at the sub-basin scale; TP BAS The total phosphorus load output by the model under the baseline scenario; TP BMPS The model output represents the total phosphorus load after incorporating optimal management practices; M represents the total nitrogen load reduction efficiency at the sub-basin scale; TN BAS The total nitrogen load (TN) is the model output under the baseline scenario. BMPS The total nitrogen load output by the model after incorporating optimal management practices; S53. Cost accounting for measures: separately account for the construction and operation costs of fertilizer reduction, grassed waterways, returning farmland to forest, vegetation filter belts and combined measures; S54. Cost-benefit analysis: Using the difference in pollution load between the baseline scenario and the implementation of the measures as the benefit, calculate the cost-benefit value. The calculation formula is as follows: Where CE is the cost-benefit value; Cost is the cost of implementing the measure; LOAD BAS The total pollution load of the study area under the baseline scenario; LOAD BMP The total pollution load of the study area after the best management measures are implemented.
[0019] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.
Claims
1. A method for coordinated nitrogen and phosphorus management in a river-estuary continuum, characterized in that, Includes the following steps: S1. Use the coastal eutrophication potential index to diagnose key nutrient elements that affect the stoichiometry and flux of nutrient salts. S2. Based on the relationship between nutrient concentration and ecological response indicators, determine the ecological thresholds for total nitrogen, total phosphorus, dissolved inorganic nitrogen, and dissolved inorganic phosphorus in different estuary zones. S3. Based on the coastal eutrophication potential index and ecological threshold, comprehensively diagnose eutrophication risk and determine whether to choose watershed management or estuary management. S4. Identify key nitrogen and phosphorus pollution source areas that substantially limit downstream water quality targets under water function zoning and environmental capacity constraints; S5. A nitrogen and phosphorus synergistic management strategy is proposed based on cost-benefit analysis.
2. The nitrogen and phosphorus synergistic management method for river-estuary continuums as described in claim 1, characterized in that, The specific process of step S1 is as follows: The coastal eutrophication potential index is used to assess the potential impact of river nutrient input on eutrophication of coastal waters. The coastal eutrophication potential index includes the coastal nitrogen eutrophication potential index and the coastal phosphorus eutrophication potential index. The calculation formula is as follows: , ,in, The potential index for nitrogen eutrophication along the coast; The index of eutrophication potential along the coast; N Flux The daily nitrogen flux per unit watershed area; P Flux The daily flux of phosphorus per unit watershed area; Si Flux This represents the daily flux of silicon per unit watershed area. The formula for calculating the nutrient flux at the survey section is: F=C Q, where F is the nutrient flux at the survey section; C is the average nutrient concentration at the survey section; and Q is the average river runoff.
3. The nitrogen and phosphorus synergistic management method for river-estuary continuum as described in claim 1, characterized in that, The specific process of step S2 is as follows: S21. Estuarine ecological zoning: Based on salinity gradient, hydrodynamic characteristics and major biogeochemical processes, the estuary is divided into riverine zone, mixed zone and nearshore zone to reflect the nonlinear response of phytoplankton in different estuarine areas to nutrient changes. S22. Determination of ecological thresholds for different zones: Using chlorophyll a, which characterizes phytoplankton biomass, as the key ecological response indicator, a random forest model is used to assess the importance of environmental factors to phytoplankton abundance. Partial correlation analysis is used to establish the response relationship between chlorophyll a concentration and the concentration of each nutrient. By identifying the inflection point of chlorophyll a change with nutrient concentration, the ecological thresholds for total nitrogen, total phosphorus, dissolved inorganic nitrogen, and dissolved inorganic phosphorus in each zone are determined. The ecological thresholds characterize the critical response of the phytoplankton community to nutrient input.
4. The nitrogen and phosphorus synergistic management method for river-estuary continuum as described in claim 1, characterized in that: The specific process of step S3 is as follows: When the coastal eutrophication potential index is positive, it indicates that the content of nitrogen or phosphorus relative to dissolved silicon is too high, which is conducive to the proliferation of non-siliceous algae. At the watershed level, nitrogen or phosphorus emissions should be reduced first. When the measured values of nitrogen and phosphorus in a certain zone of the estuary exceed the corresponding ecological threshold, it indicates that the current nutrient load of the estuary exceeds the concentration required for normal algal growth, and zoned and targeted management should be implemented for the upstream basin and the surrounding areas of the estuary.
5. The nitrogen and phosphorus synergistic management method for river-estuary continuums as described in claim 1, characterized in that, The specific process of step S4 is as follows: S41. Watershed water yield simulation: Using the annual water yield module of the InVEST model, the annual water yield of the watershed grid is calculated based on the water-heat coupling balance to simulate the annual water resource supply of the regional ecosystem. S42. Watershed nitrogen and phosphorus pollution simulation: Using the water purification module of the InVEST model, the output of total nitrogen and total phosphorus after purification by the ecosystem is simulated, and the pollutant output load at the grid and sub-watershed scales is calculated. S43. Key Source Area Identification: Using ArcGIS hydrological analysis tools, extract river sections, runoff nodes, and sub-basins to construct the river topology; calculate the potential runoff nitrogen and phosphorus mass concentrations and exceedance risk scores for each sub-basin; combine the compliance concentrations of water function zones to calculate the pollution index, and delineate total nitrogen control areas, total phosphorus control areas, nitrogen-phosphorus composite control areas, and relatively safe areas; use the Getis-Ord Gi spatial statistical method to identify non-point source pollution hotspots, and spatially couple the nitrogen-phosphorus composite control areas with significant hotspots to determine key source areas of non-point source pollution.
6. The nitrogen and phosphorus synergistic management method for river-estuary continuums as described in claim 5, characterized in that, The formula for calculating the water production in step S41 is: , , , ,in, Let x be the annual water production of the x-th grid; x is the grid number. Let x be the annual actual evapotranspiration of the x-th grid. Let x be the annual precipitation of the x-th grid cell; The potential evapotranspiration of the x-th grid cell; These are non-physical parameters relating to climate and soil properties; Let x be the evapotranspiration coefficient of the x-th grid cell; This is the reference evaporation rate for the x-th grid. Let x be the solar radiation in the x-th grid cell; This represents the average of the daily average maximum and minimum temperatures of the x-th grid cell. This is the difference between the daily average maximum temperature and the daily average minimum temperature of the x-th grid.
7. The nitrogen and phosphorus synergistic management method for river-estuary continuums as described in claim 6, characterized in that, In step S42, the formula for calculating the pollutant output of the x-th grid in the water purification module is: ,in, The pollutant output of the x-th grid after water purification by the ecosystem; The hydrological sensitivity score for the x-th grid; The output coefficient of the x-th grid; , where λ x Let λ be the flow rate of the x-th grid cell; W The runoff index for the study area; , where ∑ U Y U This represents the sum of water production from all grids along the flow path of the x-th grid in the study area.
8. The nitrogen and phosphorus synergistic management method for river-estuary continuum as described in claim 1, characterized in that, The specific process of step S5 is as follows: S51. Management Scenario Setting: Set up non-engineering measures and engineering measures. Non-engineering measures include fertilizer reduction of 10% and fertilizer reduction of 20%; engineering measures include grassed waterways, returning farmland to forest, and vegetation filter belts; combine engineering measures and non-engineering measures to form a combined scheme. S52. Pollution Load Reduction Efficiency Assessment: The reduction effect of total nitrogen and total phosphorus is calculated using the load reduction rate. The calculation formula is as follows: , Where R is the total phosphorus load reduction efficiency at the sub-basin scale; TP BAS The total phosphorus load output by the model under the baseline scenario; TP BMPS The model output represents the total phosphorus load after incorporating optimal management practices; M represents the total nitrogen load reduction efficiency at the sub-basin scale; TN BAS The total nitrogen load (TN) is the model output under the baseline scenario. BMPS The total nitrogen load output by the model after incorporating optimal management practices; S53. Cost accounting for measures: separately account for the construction and operation costs of fertilizer reduction, grassed waterways, returning farmland to forest, vegetation filter belts and combined measures; S54. Cost-benefit analysis: Using the difference in pollution load between the baseline scenario and the implementation of the measures as the benefit, calculate the cost-benefit value. The calculation formula is as follows: Where CE is the cost-benefit value; Cost is the cost of implementing the measure; LOAD BAS The total pollution load of the study area under the baseline scenario; LOAD BMP The total pollution load of the study area after the best management measures are implemented.