Method for calculating displacement of polder in large lake area and contribution of nitrogen and phosphorus to river / lake

Abstract

The invention relates to a large lake region polder displacement and nitrogen and phosphorus into-river / lake contribution accounting method, model improvement is realized by introducing a polder pit-pond suspended matter transportation module into PHPS and PHNS models, the improved model is utilized to simulate the polder displacement and nitrogen and phosphorus output, and the on-way degradation amount is estimated in combination with the nitrogen and phosphorus into-river / lake contribution accounting method. And finally obtaining the contribution of nitrogen and phosphorus entering the river / lake. The method can be applied to a large lake region polder, and the hydrological flux of the polder and the contribution of nitrogen and phosphorus into the lake are more accurately quantified by combining the improved model.

Description

Technical Field

[0001] The present invention belongs to the technical field of hydrology and non-point source pollution load simulation and assessment, and specifically relates to a method for calculating the drainage volume of dikes in large lake areas and the contribution of nitrogen and phosphorus into rivers / lakes. Background Art

[0002] Weiyuan is an artificially regulated water collection unit formed over a long period of time in the plain river network area of ​​the middle and lower reaches of the Yangtze River, mainly used for flood control, drainage and irrigation. It has the characteristics of wide distribution and large volume, and is an important carrier for water security construction in the plain river network area. Under strong artificial interference, Weiyuan faces problems such as blocked water system connectivity, poor water environment and poor water ecology.

[0003] In the past, the calculation of nitrogen and phosphorus entering the lake in the basin was mostly based on the entry path and its corresponding path removal coefficient (Cheng Wenhui et al., 2006), the calculation of nitrogen and phosphorus flux into the lake, or the simulation of nitrogen and phosphorus deposition process in the river by coupling with complex river network hydrodynamic and water quality models (Gao Junfeng et al., 2020; Wang Xiaoqing and Li Zhe, 2015). The former ignores the heterogeneity of degradation coefficients caused by differences in river spatial migration distance and deposition process, and the latter involves the acquisition of river profile data, lack of hydrodynamic and water quality boundary condition data, and low accuracy.

[0004] In addition, the existing hydrological models are difficult to fully reflect the specific hydrological characteristics and non-point source pollution transport mechanism of plain embankments, especially ignoring the suspended solids circulation process in ponds within the embankment, which will reduce the reliability of the simulation results. For example, previous studies have improved the SWAT and AGNPS models to extract plain river networks and reflect the hydrological controlled processes in plain embankments by modifying river networks and adding virtual reservoirs based on the characteristics of embankments in the southern river network area. However, the improved model still cannot reflect the mutual replenishment of surface water and groundwater in plain embankments, the rise of soil capillary water, and other characteristics, and there are many parameters and high data requirements. Yan et al. (2017) and Yan et al. (2021) coupled WALRUS-paddy with the MUSLE hydrological soil erosion model and the nitrogen and phosphorus transport process modules, and developed the PHNS and PHPS models of hydrological processes and phosphorus transport in plain embankments, which can better reflect the characteristics of embankments such as the tight coupling of surface water, groundwater and soil water in embankments, artificial irrigation and drainage, etc. However, since this model focuses on the simulation of the terrestrial transport of nitrogen and phosphorus, it ignores the sedimentation process of suspended matter in ponds within the dike and the accompanying biogeochemical processes of nitrogen and phosphorus, resulting in uncertainty in the simulation of the nitrogen and phosphorus transport process.

[0005] At the same time, due to the lack of data and methods on large-scale embankment areas in lake areas and their spatial complexity, there are few studies on the assessment of water volume and nitrogen and phosphorus inflows into lakes from multiple embankments in large lake areas. This makes it impossible to provide accurate data base for watershed management on embankment water volume and the contribution of nitrogen and phosphorus into rivers / lakes, affecting the accuracy of analysis of pollutant sources in rivers and lakes in plain river network areas. Summary of the invention

[0006] The purpose of the present invention is to provide a method for calculating the drainage volume of dikes and the contribution of nitrogen and phosphorus into rivers / lakes in large lake areas. The model is improved by introducing a dike pond suspended matter transport module into the PHPS and PHNS models. The improved model is used to simulate the drainage volume of dikes and the output of nitrogen and phosphorus. The degradation amount along the way is estimated in combination with the method for calculating the contribution of nitrogen and phosphorus into rivers / lakes, and finally the contribution of nitrogen and phosphorus into rivers / lakes is obtained.

[0007] To achieve the above object, the present invention adopts the following technical solution:

[0008] The calculation method of drainage volume of large lake areas and contribution of nitrogen and phosphorus to rivers / lakes includes:

[0009] The geospatial data of each polder in the lake area were obtained, and a single polder was used as the calculation unit. The polder drainage and nitrogen and phosphorus concentrations were simulated based on the PHNS model and PHPS model with the polder pond suspended solids module added. The control equation of the polder pond suspended solids module included the TSS mass balance equation, as follows:

[0010]

[0011] In the formula, It is the amount of suspended matter in the water bodies of embankments, ponds and ponds; is the initial value of the suspended matter in the pond on a certain day; It is the amount of suspended matter collected in ponds due to erosion and transportation of rainfall runoff on land surface, calculated by PHPS / PHNS model; It is the amount of suspended matter reduced by sedimentation in water. It is the amount of suspended matter transported to the river outside the dike with the outflow of the dike area. The amount of suspended matter reduced by the water body due to sedimentation obtained by simulating the suspended matter module of the dike area pond is used as the input of the suspended matter sedimentation parameter in the PHPS and PHNS models, and the PHNS model and PHPS model are used to simulate the nitrogen and phosphorus concentrations.

[0012] According to the simulation results of drainage volume and nitrogen and phosphorus concentration of each embankment, the total nitrogen and phosphorus output flux of all embankments in the lake area were obtained;

[0013] Obtain the degradation amount of nitrogen and phosphorus entering the lake along the river network, and calculate the difference between the total nitrogen and phosphorus output flux of the dike and the degradation amount, that is, the contribution of nitrogen and phosphorus into the river / lake.

[0014] As a preferred embodiment, the amount of suspended solids reduced by the water body due to sedimentation is determined based on the following formula:

[0015]

[0016]

[0017]

[0018] In the formula, It is the initial concentration of suspended matter in water after the influx of sediment produced by land erosion; It is the final suspended matter content of the water body after considering sedimentation; is the equilibrium suspended matter concentration in the water column; is the decay constant; is the median particle size of the sediment produced on the land surface of the polder area; is the initial water storage capacity of the pond; is the amount of water that flows into the pond from land surface. , Obtained by PHNS / PHPS model calculation.

[0019] Furthermore, the amount of suspended matter transported to the river outside the polder area with the outflow is obtained based on the following formula:

[0020]

[0021] In the formula, is the discharge of the polder area, calculated by the PHPS or PHNS model.

[0022] As a preferred embodiment, the degradation amount of nitrogen and phosphorus entering the lake and river network is calculated based on the following formula:

[0023]

[0024] Where D is the degradation amount along the way; C is the nitrogen and phosphorus concentration of the water body; V is the volume of the water body; q is the comprehensive degradation coefficient of the pollutant; is the acceleration due to gravity.

[0025] As a preferred implementation, the method further includes performing outlier inspection and correction according to the simulation results, including:

[0026] The water surface rate of the model was adjusted with a step size of 0.5% until the model output value was normal at a certain water surface rate. The water surface rate at this time was used as the model water surface rate setting value for numerical simulation.

[0027] As a preferred implementation, during model calculation, multiple calculation units are calculated in parallel.

[0028] As a preferred implementation, the method also includes, based on the simulation results of the drainage volume and nitrogen and phosphorus concentrations of each dike, drawing a spatial distribution map of the lake drainage and the output intensity of nitrogen and phosphorus into the river, identifying the high and low distribution areas of nitrogen and phosphorus output intensity, comparing the interannual differences of wet, normal and dry hydrological years, and identifying the high and low distribution hot spots of nitrogen and phosphorus output intensity.

[0029] The present invention also provides a computer device, comprising a memory, a processor and a computer program stored in the memory, wherein the processor executes the computer program to implement the steps of the above method.

[0030] The present invention also provides a computer-readable storage medium having a computer program / instruction stored thereon, which implements the steps of the above method when the computer program / instruction is executed by a processor.

[0031] The present invention also provides a computer program product, comprising a computer program / instruction, characterized in that the computer program / instruction implements the steps of the above method when executed by a processor.

[0032] The present invention has the following beneficial effects:

[0033] (1) The present invention can be applied to large lake area embankments. Combined with the improved model, the hydrological flux of the embankments and the contribution of the embankments into the lake can be more accurately quantified. The contribution of the embankments into the river can also be combined to further calculate the contribution rate of the embankments into the lake.

[0034] (2) The method of the present invention can also be used to effectively identify the hotspot areas and times of nitrogen and phosphorus pollution sources entering the lake from the dikes, providing a basis for precise regulation of the plain river network in different levels and periods. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a flow chart of the method of the present invention.

[0036] Figure 2 This is the land use distribution map of the Poyang Lake area.

[0037] Figure 3 This is the spatial distribution map of the drainage volume of the Poyang Lake area.

[0038] Figure 4 This is the spatial distribution map of nitrogen entering the river / lake from the embankments in the Poyang Lake area.

[0039] Figure 5 This is the spatial distribution map of phosphorus entering the river / lake from the embankment in the Poyang Lake area. DETAILED DESCRIPTION

[0040] In order to make the technical solution more clearly understood by those skilled in the art, the method of the present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0041] The large lake area referred to in this invention refers to lakes with an area greater than 500km 2 of the Lake District.

[0042] Example 1

[0043] This embodiment takes the calculation of the contribution of nitrogen and phosphorus from the dikes in the Poyang Lake Basin to the river / lake as an example to specifically illustrate the implementation of the method of the present invention, and the steps are as follows:

[0044] Construction of S100 embankment geospatial dataset;

[0045] (1) Acquisition of dike location data;

[0046] Based on the distribution atlas of embankments in various provinces, cities and prefectures, ArcGIS was used to draw the boundaries of embankments to form a vector distribution layer, and points were selected for verification. ArcGIS was used to calculate the longitude, latitude and area of ​​each embankment.

[0047] (2) Obtain the data required for model calculation and construct a geospatial dataset of the dikes, which mainly includes land information data, meteorological monitoring data, hydrological data, and water quality data;

[0048] Land information data include land use data, DEM data and soil physical and chemical properties data. The land use data can use Globeland30 global land cover data. First, ArcGIS is used to reclassify the data, including paddy fields, dry land, water bodies and construction land. Then, the area of ​​land classification in each dike is statistically divided according to the dike vector layer.

[0049] Meteorological monitoring data are obtained from the National Meteorological Science Data Center, including temperature, precipitation, humidity, air pressure, wind speed, and sunshine duration data.

[0050] The hydrological data were obtained from the hydrological yearbook, including the discharge of pumping stations and culverts, irrigation water volume, and groundwater level data.

[0051] Water quality data were obtained from the National Automatic Integrated Water Quality Monitoring Platform, including total nitrogen and total phosphorus concentration data.

[0052] Other data include fertilizer application amount, planting system, population and livestock and poultry breeding data. Fertilizer application amount and planting system are derived from references. Population data can be selected from Worldpop's global 100-meter population distribution data. Livestock and poultry breeding data are derived from local statistical yearbooks.

[0053] Through the distribution data vectors of the dikes, sharing of scientific data platforms, data reclassification and projection, and resolution consistency conversion, the geospatial dataset of the dikes is constructed. The coordinate system of each spatial distribution data can be unified into GCS_WGS_1984.

[0054] Improvement of hydrological and nitrogen and phosphorus models for S200 single-weir embankment

[0055] (1) Construction of suspended solids module in ponds and dikes

[0056] This application constructs a dike suspended solids module based on the existing PHNS model and PHPS model, couples the dike suspended solids module with the existing PHPS model and PHNS model modules respectively, and constructs a dike area hydrology and phosphorus migration model, as well as a dike area hydrology and nitrogen migration model for dike hydrology and nitrogen and phosphorus simulation.

[0057] The PHNS model is formed by coupling the WALRUS-paddy model (simulating rainfall runoff), the MUSLE model (simulating erosion and sediment production) and the INCA model, and the PHPS model is formed by coupling the WALRUS-padd model, the MUSLE model and the INCA-P model. The amount of particulate nitrogen (phosphorus) deposition in ponds in the PHNS (PHPS) model is the amount of suspended solids deposition simulated by the pond suspended solids module ( ) and nitrogen (phosphorus) content in suspended matter.

[0058] The relevant contents of PHNS and PHPS models have been disclosed in the articles previously published by the inventor of this application (cited below), and will not be repeated in this application.

[0059] [1]Yan, R., Huang, J., Li, L., Gao, J., 2017. Hydrology and phosphorus transport simulation in a lowland polder by a coupled modeling system. Environ. Pollut. 227, 613–625.

[0060] [2]Yan, R., Brunner P., Gao*, J., 2021. Simulation of nitrogendynamics in lowland polders using a new coupled modeling approach: Insights into management. Journal of Cleaner Production, 313: 127753.

[0061] The constructed embankment suspended solids module is as follows:

[0062] Due to the interception of the embankment and pumping station, and the gentle terrain, the water in the pond in front of the pumping station is almost static most of the time, the sedimentation of suspended matter is obvious, and the resuspension effect can be ignored. Therefore, the amount of suspended matter in the pond in front of the pump in the embankment area is mainly caused by the input of rainfall runoff, sedimentation, and outflow from the embankment area. The suspended matter module of the pond (water collection pit) in front of the pump is added to the PHPS model and PHNS model, and its control equation is the TSS mass balance equation, as follows:

[0063] (1)

[0064] In the formula, is the amount of suspended matter in the pond water, t (ton); is the initial value of the initial suspended matter content of the pond water body, t; It is the amount of suspended matter collected in ponds due to erosion and sediment production from land surface rainfall runoff, t, which is simulated and output by the rainfall runoff and erosion sediment production modules of the PHNS or PHPS model; is the amount of suspended matter reduced by sedimentation in the water body, t, It is the amount of suspended matter transported from ponds to the river outside the dike along with the outflow of the dike area, t.

[0065] a) Sedimentation

[0066] The amount of suspended matter removed from a water body by sedimentation is calculated as follows:

[0067] (2)

[0068] In the formula, is the initial concentration of suspended matter in water after the influx of sand produced by land erosion, t / m 3 ; is the final suspended solids content of the water body after considering the sedimentation effect, t / m 3 ; V represents the water storage capacity of the pond, m 3 , calculated by the rainfall runoff module of the PHNS or PHPS model.

[0069] (3)

[0070] In the formula, is the initial water storage capacity of the pond, m 3 ,; is the amount of water flowing into the pond from land surface, m 3 . and All are calculated by the rainfall runoff module of the PHNS or PHPS model.

[0071] The sedimentation of suspended solids depends on the equilibrium suspended solids concentration. and the median particle size of suspended solids. When the suspended solids concentration in the pond water is greater than the equilibrium suspended solids concentration Suspended matter sedimentation occurs when:

[0072] (4)

[0073] In the formula, is the equilibrium suspended matter concentration in the water body ,t / m 3 , after preliminary assignment based on field test data and reference to relevant literature, it is determined by model calibration; k s is the attenuation constant, 1 / d, generally taken as 0.184; d 50 is the median particle size of land-based sediment production, , according to the composition ratio of clay, silt and sand in the surface soil layer of the polder area, the method in Neitsche et al. (2011) was used to determine it.

[0074] b) Suspended matter control outflow in the polder area

[0075] (5)

[0076] Where: is the drainage volume of the polder area, m 3 , calculated by the PHPS or PHNS model of the polder area.

[0077] (2) Parameter calibration and verification

[0078] The calibration of model parameters is divided into two steps. First, the drainage runoff is calibrated and the hydrological parameters related to drainage are adjusted to make the simulated runoff consistent with the measured drainage data. Secondly, the water quality parameters are calibrated on the basis of the calibrated hydrological parameters to make the simulated nutrient concentration and the measured concentration reach a good fitting level. The Nash coefficient NS (Nash–Sutcliffe coefficient) and the determination coefficient R are selected. 2 Evaluate the simulation effect.

[0079] S300 Lake Area Multi-Weir Model Computation Framework

[0080] Model data file preparation: Use the geospatial attribute dataset constructed in step 1 to perform model calculations.

[0081] The files required for the polder area model mainly include input data text, parameter files, and driver files, which are mainly stored in csv and text formats as model input. There are i text files for input data, one for each polder area, including data variables such as date, precipitation, potential evapotranspiration, and measured flow, which are derived from the geospatial attribute data set; there is one parameter file, and each polder area corresponds to a row of records, which include land use type area ratio, soil physical and chemical properties, model calibration parameters, pump gate drainage level, etc. The land use information and soil physical and chemical properties of each polder area are obtained based on the superposition of different land use type distribution raster layers and polder area distribution vector data. The pump gate drainage level is determined according to the collected polder area gate pump scheduling rules; there is one driver file, including information such as the start model command, the initial state of key variables, the definition of the water level-flow function relationship, and the drawing of result charts.

[0082] Model parallel operation: Due to the large number of lake embankments, a parallel computing framework was used to improve operation efficiency and reduce operation time costs, giving full play to the advantages of multi-core CPU servers. According to the model data file prepared in step 1, enter the start command to run the embankment nitrogen transport process model for each embankment, and run it a total of i times.

[0083] Estimation of nitrogen and phosphorus loss fluxes of dikes: Based on the model output results of drainage volume, nitrogen and phosphorus concentrations of each dike, program to extract the simulation results of nitrogen and phosphorus loss fluxes of each dike, and finally summarize the nitrogen and phosphorus loss fluxes and output intensity of all dikes in the lake area. The nitrogen (IN) and phosphorus (IP) output intensity are calculated by the following formula:

[0084] (6)

[0085] (7)

[0086] Where TN is the nitrogen loss flux of the dike (kg / yr), TP is the phosphorus loss flux (kg / yr), which are calculated by PHNS and PHPS models respectively; A is the dike area (ha).

[0087] Inspection and correction of outliers in S400 simulation results

[0088] The simulation results of daily drainage and nitrogen and phosphorus loss in wet, normal and dry years of each dike are tested for abnormal values. The method for determining the wet, normal and dry year type is to determine the wet, normal and dry year type based on precipitation data for more than 20 years. The empirical frequency method or the deviation percentage method in the "Hydrological Information Forecast Specification" can be used to determine the design value of each frequency as the precipitation standard for dividing wet, normal and dry years.

[0089] If an abnormal value is found, the cause of the abnormal value is traced back and the problem is eliminated until a reasonable simulation result is obtained. In particular, due to the resolution and uncertainty of the remote sensing image of large-scale land use in the lake area, some embankments will present an unreal result that the water surface rate (the percentage of water surface in the total area of ​​the embankment) is lower than 1%. The embankment model is mainly developed based on a certain water surface rate, which will cause the embankment model to output too much or too little water volume and nitrogen and phosphorus simulation results. To solve this problem, the present invention adjusts the water surface rate by +0.5% each time, and finds that when the water surface rate is adjusted to about 5% at the lowest, the model output can be guaranteed to be reasonable, and close to the actual situation with a lower water surface rate. For this reason, the embankments with a water surface rate lower than 5% are selected, and the input data of their land use spatial distribution is corrected according to the water surface rate of 5%, which is converted from the paddy field area according to the actual situation in the lake area.

[0090] Calculation of nitrogen and phosphorus contribution from embankments to rivers / lakes in S500 lake area

[0091] Identification of spatiotemporal hotspots of nitrogen and phosphorus inflows into rivers from embankments in S510 lake area

[0092] Water cycle and nitrogen and phosphorus transport play an important role in the aquatic ecosystem and nutrient cycle of the dike. Monitoring and management of them are crucial to preventing eutrophication of water bodies and protecting biodiversity.

[0093] Based on the output results of the model, spatial geostatistical methods (spatial autocorrelation) were used to draw the spatial distribution map of lake drainage and nitrogen and phosphorus output intensity into the river, identify the high and low distribution areas of nitrogen and phosphorus output intensity, compare the interannual differences in wet, normal and dry hydrological years, and identify the high and low distribution hot spots of nitrogen and phosphorus output intensity.

[0094] Analysis on the contribution rate of nitrogen and phosphorus from S520 dike to the lake

[0095] When the water from the embankment flows into the surrounding rivers, it will gradually flow into the main river channel, accompanied by the sedimentation and decomposition of pollutants along the way, and eventually part of it will enter the large lakes downstream. The present invention comprehensively considers accuracy and convenience, and proposes to calculate the comprehensive degradation amount D of nitrogen and phosphorus along the river network entering the lake according to the following method:

[0096] (8)

[0097] Where C is the nitrogen and phosphorus concentration of the water body (mg / L), V is the volume of the river water (m 3 ), q is the comprehensive degradation coefficient of pollutants (1 / d), 10 -3 is the unit conversion coefficient, q can be obtained through field monitoring experiments or relevant regional research literature, and g is the gravitational acceleration.

[0098] Calculate the difference between the total nitrogen and phosphorus output flux of the dike and the degradation along the way, that is, the amount of nitrogen and phosphorus entering the river / lake from the dike, and take the ratio of the amount of nitrogen and phosphorus entering the river / lake from the dike to the total nitrogen and phosphorus load of all rivers entering the river / lake of the corresponding river (lake) as the contribution rate of nitrogen and phosphorus entering the lake from the dike. In the future, the contribution rate of nitrogen and phosphorus entering the lake from the dike in each region and the reasons can be further compared.

[0099] Although the present invention has provided optional implementation modes as above, they are not intended to limit the present invention. A person with ordinary knowledge in the technical field to which the present invention belongs can make various changes and modifications without departing from the spirit and scope of the present invention, including the program for applying the method, the computer storage medium containing the program, and the device should also be within the protection scope of the present invention.

Claims

1. A method for calculating the drainage volume of large lake areas and the contribution of nitrogen and phosphorus to rivers / lakes, characterized in that: include: The geospatial data of each polder in the lake area were obtained, and a single polder was used as the calculation unit. The polder drainage and nitrogen and phosphorus concentrations were simulated based on the PHNS model and PHPS model with the polder pond suspended solids module added. The control equation of the polder pond suspended solids module included the TSS mass balance equation, as follows: ； In the formula, It is the amount of suspended matter in the water bodies of embankments, ponds and ponds; is the initial value of the suspended matter in the pond on a certain day; It is the amount of suspended matter collected in ponds due to erosion and transportation of rainfall runoff on land surface, calculated by PHPS / PHNS model; It is the amount of suspended matter reduced by sedimentation in water. It is the amount of suspended matter transported to the river outside the dike with the outflow of the dike area. The amount of suspended matter reduced by the water body due to sedimentation obtained by simulating the suspended matter module of the dike area pond is used as the input of the suspended matter sedimentation parameter in the PHPS and PHNS models, and the PHNS model and PHPS model are used to simulate the nitrogen and phosphorus concentrations. According to the simulation results of drainage volume and nitrogen and phosphorus concentration of each embankment, the total nitrogen and phosphorus output flux of all embankments in the lake area were obtained; Obtain the degradation amount of nitrogen and phosphorus entering the lake along the river network, and calculate the difference between the total nitrogen and phosphorus output flux of the dike and the degradation amount, that is, the contribution of nitrogen and phosphorus into the river / lake.

2. The method according to claim 1, characterized in that The amount of suspended solids reduced by the water body due to sedimentation is determined based on the following formula: ； ； ； In the formula, It is the initial concentration of suspended matter in water after the influx of sediment produced by land erosion; It is the final suspended matter content of the water body after considering sedimentation; is the equilibrium suspended matter concentration in the water column; is the decay constant; is the median particle size of the land-surface sediment produced in the polder area; is the initial water storage capacity of the pond; is the amount of water that flows into the pond from land surface. , Obtained by PHNS / PHPS model calculation.

3. The method according to claim 2, characterized in that The amount of suspended matter transported to the river outside the polder area with the outflow is obtained based on the following formula: ； In the formula, is the discharge of the polder area, calculated by the PHPS or PHNS model.

4. The method according to claim 1, characterized in that: The amount of nitrogen and phosphorus entering the lake and degrading along the river network is calculated based on the following formula: ； Where D is the degradation amount along the way; C is the nitrogen and phosphorus concentration of the water body; V is the volume of the water body; q is the comprehensive degradation coefficient of the pollutant; is the acceleration due to gravity.

5. The method according to claim 1, characterized in that It also includes outlier testing and correction based on simulation results, including: The water surface rate of the model was adjusted with a step size of 0.5% until the model output value was normal at a certain water surface rate. The water surface rate at this time was used as the model water surface rate setting value for numerical simulation.

6. The method according to claim 1, characterized in that When calculating the model, multiple computing units are calculated in parallel.

7. The method according to claim 1, characterized in that It also includes drawing a spatial distribution map of lake drainage and nitrogen and phosphorus output intensity into the river based on the simulation results of each dike drainage and nitrogen and phosphorus concentration, identifying high and low distribution areas of nitrogen and phosphorus output intensity, comparing the interannual differences of wet, normal and dry hydrological years, and identifying the high and low distribution hotspot times of nitrogen and phosphorus output intensity.

8. A computer device comprising a memory, a processor and a computer program stored in the memory, characterized in that: The processor executes the computer program to implement the steps of the method according to any one of claims 1 to 7.

9. A computer-readable storage medium having a computer program / instruction stored thereon, characterized in that: When the computer program / instructions are executed by a processor, the steps of the method described in any one of claims 1 to 7 are implemented.

10. A computer program product comprising a computer program / instructions, characterized in that When the computer program / instructions are executed by a processor, the steps of the method described in any one of claims 1 to 7 are implemented.

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