A method and system for analyzing nitrogen and phosphorus pollution loads of water quality in a large watershed

Abstract

The present application relates to the technical field of environmental engineering, in particular to a method and system for analyzing nitrogen and phosphorus pollution load of a large-scale watershed water quality. The present application obtains a current detected soil sub-region and water sub-region; obtains pollution accommodation degree according to the nitrogen and phosphorus content fluctuation degree of the soil sub-region and the nitrogen and phosphorus content fluctuation degree of the neighborhood; merges the soil sub-regions according to the difference between the nitrogen and phosphorus diffusion direction and the nitrogen and phosphorus content fluctuation degree, obtains a pollution migration region, and determines a nitrogen and phosphorus pollution migration path; obtains water pollution influence degree according to the pollution accommodation degree of the soil sub-region in the pollution migration region and the consistency degree between the nitrogen and phosphorus migration direction, and the nitrogen and phosphorus attenuation degree on the pollution migration path, and obtains water pollution load value combined with the nitrogen and phosphorus content. The present application comprehensively considers spatial heterogeneity, dynamic accommodation and transmission effect, and improves the accuracy of nitrogen and phosphorus pollution load analysis.

Description

Technical Field

[0001] This invention relates to the field of environmental engineering technology, specifically to a method and system for analyzing nitrogen and phosphorus pollution loads in water quality over a large area of ​​a river basin. Background Technology

[0002] Nitrogen and phosphorus pollution in river basins and lake catchments is a major challenge in current water environment management. The sources of nitrogen and phosphorus pollution are complex, mainly including agricultural runoff, livestock and poultry wastewater, and scattered domestic sewage. These pollution sources flow into water bodies with surface runoff, leading to water quality deterioration and promoting eutrophication. Therefore, it is necessary to analyze the nitrogen and phosphorus pollution load of watersheds in order to implement pollution control measures.

[0003] In existing technologies, two types of methods are typically used to analyze and predict nitrogen and phosphorus pollution loads in watersheds: one is to construct mechanistic models such as the SWAT model based on hydrological and meteorological data, and the other is to use machine learning algorithms such as extreme gradient boosting (XGBoost) for data-driven prediction to predict the nitrogen and phosphorus pollution loads at each monitoring point in the watershed, determine the pollution risk level of each area, and thus provide a basis for differentiated prevention and control measures.

[0004] However, actual nitrogen and phosphorus pollution in watersheds is usually "inflowed" from surrounding soils and tributaries, and this inflow process may pass through different regions and is profoundly influenced by the characteristics of the underlying surface. Typically, nitrogen and phosphorus pollution in the soil is dynamic, and the geological conditions within the watershed are complex. Soil type and land use patterns jointly determine the soil's capacity to contain and transfer nitrogen and phosphorus pollution, resulting in a difference between the contribution of pollution sources to nitrogen and phosphorus pollution in the watershed and the initial pollution. However, existing methods lack sufficient consideration of the dynamic attenuation mechanisms of pollutants in the soil, making it impossible to accurately assess the dynamic nitrogen and phosphorus pollution risk and its resulting pollution load in different areas of the watershed. Summary of the Invention

[0005] To address the technical problem of inaccurate nitrogen and phosphorus pollution load analysis caused by the dynamic containment and transfer of nitrogen and phosphorus pollution in different regions of a watershed due to the heterogeneity of underlying surface characteristics, this invention aims to provide a method and system for analyzing nitrogen and phosphorus pollution loads in watersheds over a large area. The specific technical solution adopted is as follows:

[0006] In a first aspect, one embodiment of the present invention provides a method for analyzing nitrogen and phosphorus pollution loads in water quality over a large area of ​​a river basin, the method comprising:

[0007] Obtain the watershed extent map of the watershed to be analyzed and the actual nitrogen and phosphorus content of each pixel in the current and previous several tests; the extent map is divided into soil area and water area, which are denoted as the analysis area;

[0008] Based on the environmental similarity and nitrogen and phosphorus content difference between any two pixels in the current detection area, the analysis area is divided into sub-regions; the sub-regions corresponding to the soil area and the water body area are respectively recorded as the soil sub-region and the water body sub-region currently being detected.

[0009] Based on the degree of co-fluctuation of nitrogen and phosphorus content in previously detected pixels within each soil sub-region and the degree of fluctuation of nitrogen and phosphorus content in their neighboring areas, the pollution carrying capacity of the corresponding soil sub-region is obtained.

[0010] Based on the differences in the direction of nitrogen and phosphorus diffusion and the degree of fluctuation in nitrogen and phosphorus content between any two soil sub-regions currently being tested, the soil sub-regions currently being tested are merged to obtain different pollution migration areas, and the nitrogen and phosphorus pollution migration paths of the pollution migration areas are determined.

[0011] Based on the degree of consistency between the pollution carrying capacity and the nitrogen and phosphorus migration direction of each soil sub-region within the pollution migration area currently being detected, and the degree of nitrogen and phosphorus attenuation along the nitrogen and phosphorus pollution migration path, the water pollution impact degree of the corresponding soil sub-region is obtained.

[0012] Based on the nitrogen and phosphorus content of each pixel in each soil sub-region currently detected and the degree of water pollution impact, the water pollution load value of the corresponding soil sub-region is obtained.

[0013] Furthermore, dividing the analysis region into sub-regions includes:

[0014] Obtain the time series of vegetation index, baseline nitrogen content, baseline phosphorus content and various meteorological indicators for each pixel at the current detection;

[0015] The correlation coefficient of the time series of the two pixels for each meteorological indicator detected at the present time is calculated respectively. The correlation coefficients of all types of environmental indicators are averaged to obtain the meteorological similarity of the two pixels detected at the present time. The environmental similarity of the two pixels detected at the present time is obtained based on the difference in vegetation index of the two pixels detected at the present time and the meteorological similarity.

[0016] Based on the difference in actual nitrogen content and actual phosphorus content between the two pixels in the current detection and the similarity to the environment, the probability that the two pixels are in the same area in the current detection is obtained.

[0017] Based on the probability of the same region, region growing is performed on all pixels within the same analysis region to obtain several sub-regions.

[0018] Furthermore, obtaining the probability of two pixels in the same detected region includes:

[0019] The differences between the current measured baseline nitrogen content and the actual nitrogen content, and the differences between the current measured baseline phosphorus content and the actual phosphorus content, for each pixel within the soil region are recorded as nitrogen fluctuation amplitude and phosphorus fluctuation amplitude, respectively. Negative correlation mapping is performed on the differences in nitrogen fluctuation amplitude and phosphorus fluctuation amplitude between any two pixels within the soil region. The product of the two mapping results and the environmental similarity is normalized to obtain the probability of the two corresponding pixels being in the same region in the current detection.

[0020] For any two pixels within the water body area, negative correlation mapping is performed on the actual nitrogen content difference and the actual phosphorus content difference detected at the current time. The product of the two mapping results and the environmental similarity is normalized to obtain the probability of the two corresponding pixels being in the same area at the current time.

[0021] Furthermore, obtaining the pollution carrying capacity of the corresponding soil sub-region includes:

[0022] Select any soil sub-region currently being tested as the example region; average the actual nitrogen content of all pixels within the example region in each test to obtain the overall nitrogen content of the example region in each test; calculate the difference between the overall nitrogen content of the example region in each of the two adjacent tests before the current test, and use this as the nitrogen content fluctuation value of the example region in the corresponding subsequent test; obtain the phosphorus content fluctuation values ​​of the example region in several tests before the current test.

[0023] The product of the nitrogen content fluctuation value and the phosphorus content fluctuation value of the example region in each detection before the current detection is normalized to obtain the nitrogen and phosphorus fluctuation value of the example region in the corresponding detection; a pulse detection of the example region is selected from several detections before the current detection, wherein the nitrogen content fluctuation value and the phosphorus content fluctuation value of the example region in the pulse detection are both positive, and the nitrogen and phosphorus fluctuation values ​​are greater than a preset fluctuation threshold.

[0024] The differences in actual nitrogen content and actual phosphorus content in the example region before and after each pulse detection are calculated, and the average of the two differences is used as the nitrogen and phosphorus neighborhood fluctuation value of the example region in each pulse.

[0025] The mean of the nitrogen and phosphorus fluctuation values ​​and the mean of the nitrogen and phosphorus neighborhood fluctuation values ​​of the example area are calculated separately. The product of the two means is negatively correlated and normalized to obtain the pollution tolerance of the example area.

[0026] Furthermore, the obtained different pollution migration areas include:

[0027] Obtain the nitrogen gradient vector and phosphorus gradient vector of each pixel in the currently detected soil sub-region; obtain the combined vector of nitrogen gradient vectors and the combined vector of phosphorus gradient vectors of all pixels in the currently detected soil sub-region, and denot them as nitrogen migration vector and phosphorus migration vector respectively; take the combined vector of nitrogen migration vector and phosphorus migration vector as the overall nitrogen and phosphorus migration vector of the currently detected soil sub-region.

[0028] The nitrogen and phosphorus fluctuation values ​​of each soil sub-region currently being detected are arranged in chronological order from previous detections to obtain a fluctuation sequence;

[0029] The correlation coefficient of the fluctuation sequence and the cosine similarity of the overall nitrogen and phosphorus migration vectors of any two soil sub-regions currently detected are obtained respectively. The product of the correlation coefficient and the cosine similarity is normalized to obtain the migration feature similarity of the corresponding two soil sub-regions.

[0030] Based on the migration feature similarity, region growing is performed on all currently detected soil sub-regions to obtain the currently detected pollution migration regions.

[0031] Furthermore, determining the nitrogen and phosphorus pollution migration pathways in the pollution migration area includes:

[0032] For each pollution migration area currently detected, the sum vector of the overall nitrogen and phosphorus migration vectors of all soil sub-regions within the pollution migration area is obtained and denoted as the pollution migration vector;

[0033] Draw a straight line passing through the center point of the pollution migration area and parallel to the direction of the pollution migration vector, and denote it as the baseline of the pollution migration area; project the center points of all soil sub-regions within the pollution migration area onto the baseline, and connect the center points of each soil sub-region in order of the direction of the pollution migration vector according to the projection position of each center point on the baseline to obtain the nitrogen and phosphorus pollution migration path.

[0034] Furthermore, obtaining the water pollution impact degree of the corresponding soil sub-region includes:

[0035] For each pollution migration area currently detected, the soil sub-regions located at the upstream and downstream positions in the nitrogen and phosphorus pollution migration path of the pollution migration area are successively recorded as the path start area and path end area; the average of the actual phosphorus content of all pixels in the sub-region currently detected is calculated to obtain the overall phosphorus content;

[0036] Calculate the distance between the center point of each of the currently detected water body sub-regions and the center point of the end region of the path of the pollution migration region, and select the water body sub-region corresponding to the minimum distance as the water body analysis region of the pollution migration region; calculate the absolute value of the overall nitrogen content difference and the absolute value of the overall phosphorus content difference between the starting region of the path of the pollution migration region and the water body analysis region, and use the product of the two absolute values ​​of difference as the path pollution attenuation index;

[0037] The mean cosine similarity between the overall nitrogen and phosphorus migration vectors of all soil sub-regions within the pollution migration area and the pollution migration vectors is used as the migration direction stability.

[0038] The average pollution carrying capacity of all soil sub-regions within the pollution migration area is taken as the overall carrying capacity;

[0039] Based on the distance between the center point of each soil sub-region currently being detected and the center point of the water analysis region in the pollution migration area, the migration direction stability, the overall carrying capacity, and the path pollution attenuation index, the water pollution impact value of the corresponding soil sub-region is obtained.

[0040] Furthermore, obtaining the water pollution load value of the corresponding soil sub-region includes:

[0041] Calculate the mean of the overall nitrogen content and the overall phosphorus content of all pixels in each soil sub-region currently being detected, and normalize the product of the mean and the water pollution impact degree to obtain the water pollution load value of the corresponding soil sub-region.

[0042] Furthermore, the stability of the migration direction is positively correlated with the degree of water pollution impact, while the path pollution attenuation index and the overall carrying capacity are both negatively correlated with the degree of water pollution impact.

[0043] Secondly, another embodiment of the present invention provides a nitrogen and phosphorus pollution load analysis system for a large-scale watershed, the system comprising:

[0044] The data acquisition module is used to acquire the watershed extent map of the watershed to be analyzed and the actual nitrogen and phosphorus content of each pixel in the current detection and several previous detections; the extent map is divided into soil area and water area, which are denoted as the analysis area;

[0045] The sub-region division module is used to divide the analysis area into sub-regions based on the environmental similarity and nitrogen and phosphorus content difference between any two pixels in the analysis area at the current detection time; the sub-regions corresponding to the soil area and the water body area are respectively recorded as the soil sub-region and the water body sub-region currently detected;

[0046] The pollution carrying capacity analysis module is used to obtain the pollution carrying capacity of the corresponding soil sub-region based on the degree of co-fluctuation of nitrogen and phosphorus content of the pixels in the currently detected soil sub-region in previous tests and the degree of fluctuation of nitrogen and phosphorus content in their neighboring areas.

[0047] The pollution migration analysis module is used to merge the currently detected soil sub-regions based on the differences in the direction of nitrogen and phosphorus diffusion and the differences in the degree of fluctuation of nitrogen and phosphorus content between any two currently detected soil sub-regions, to obtain different pollution migration regions, and to determine the nitrogen and phosphorus pollution migration paths in the pollution migration regions.

[0048] The water pollution impact analysis module is used to obtain the water pollution impact degree of the corresponding soil sub-region based on the degree of consistency between the pollution carrying capacity and the nitrogen and phosphorus migration direction of the soil sub-region in the pollution migration area where each soil sub-region is located, as well as the degree of nitrogen and phosphorus attenuation on the nitrogen and phosphorus pollution migration path.

[0049] The pollution load analysis module is used to obtain the water pollution load value of the corresponding soil sub-region based on the nitrogen and phosphorus content of each pixel in the currently detected soil sub-region and the degree of water pollution impact.

[0050] The present invention has the following beneficial effects:

[0051] In this embodiment of the invention, sub-regions are dynamically divided based on environmental similarity and differences in nitrogen and phosphorus content, effectively identifying the spatial heterogeneity of soil and water bodies within the watershed and making the spatial differentiation characteristics of pollution clearer. The pollution carrying capacity is determined by combining the degree of coordinated fluctuation of nitrogen and phosphorus content in historically detected soil sub-regions with the fluctuation of nitrogen and phosphorus content in their neighboring areas, assessing the soil's buffering and resilience to pollution and solving the problem of existing analyses neglecting the soil's own carrying capacity characteristics. Sub-regions are merged based on differences in diffusion direction and fluctuations in nitrogen and phosphorus content, and the nitrogen and phosphorus pollution migration paths in the pollution migration area are determined, thereby more accurately simulating the impact of underlying surface heterogeneity on pollution transmission. The pollution carrying capacity of soil sub-regions within the pollution migration area is integrated with the consistency of nitrogen and phosphorus migration direction, as well as the degree of nitrogen and phosphorus attenuation along the nitrogen and phosphorus pollution migration paths. The pollution impact of soil sub-regions on water bodies in the watershed is analyzed comprehensively based on spatial heterogeneity, dynamic carrying capacity, and transmission effects. The pollution load value of the water body is determined by combining nitrogen and phosphorus content, realizing a full-process analysis from soil to water body, ensuring that the load assessment considers both the existing pollution and dynamic output, and significantly improving the accuracy of nitrogen and phosphorus pollution load analysis. Attached Figure Description

[0052] To more clearly illustrate the technical solutions and advantages in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0053] Figure 1 The flowchart illustrates the steps of a method for analyzing nitrogen and phosphorus pollution loads in a large-scale watershed according to an embodiment of the present invention.

[0054] Figure 2 This is a flowchart of a method for obtaining a sub-region according to an embodiment of the present invention;

[0055] Figure 3 This is a flowchart illustrating a method for obtaining a contamination migration area according to an embodiment of the present invention.

[0056] Figure 4 This is a system structure diagram of a large-scale watershed nitrogen and phosphorus pollution load analysis system provided in one embodiment of the present invention;

[0057] Figure 5 This is a schematic diagram of a computer device for analyzing nitrogen and phosphorus pollution loads in a large-scale watershed, as provided in one embodiment of the present invention. Detailed Implementation

[0058] To further illustrate the technical means and effects adopted by the present invention to achieve its intended purpose, the following, in conjunction with the accompanying drawings and preferred embodiments, details the specific implementation, structure, features, and effects of a method and system for analyzing nitrogen and phosphorus pollution loads in a large-scale watershed according to the present invention. In the following description, different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0059] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0060] The following description, in conjunction with the accompanying drawings, details the specific scheme of the nitrogen and phosphorus pollution load analysis method and system for large-scale watershed water quality provided by this invention.

[0061] Example 1:

[0062] This invention proposes a method for analyzing nitrogen and phosphorus pollution loads in watersheds over a large area. Please refer to [link / reference]. Figure 1The diagram illustrates a flowchart of a method for analyzing nitrogen and phosphorus pollution loads in a large-scale watershed according to an embodiment of the present invention. The method includes:

[0063] Step S1: Obtain the watershed extent map of the watershed to be analyzed and the actual nitrogen and phosphorus content of each pixel in the current and previous several tests; the extent map is divided into soil area and water area, which are denoted as the analysis area.

[0064] The watershed to be analyzed should include surface water bodies such as rivers and lakes, and the surrounding soil areas. These soil areas may be classified based on their application function as agricultural soil, residential soil, or natural environment soil. Several sampling points should be randomly set up within the watershed to be analyzed, with at least one sampling point set up within each typical land cover type. The GPS coordinates and elevation values ​​of each sampling point should be measured using a GPS locator and altimeter.

[0065] During each test, soil samples were collected at stratified locations at the monitoring points. The nitrogen and phosphorus contents in these samples were determined in the laboratory using the Kjeldahl method and the molybdenum-antimony colorimetric-ultraviolet spectrophotometric method, and recorded as the actual nitrogen and phosphorus contents for each monitoring point in each test. Nitrogen and phosphorus pollution in the soil and surface water of the watershed under analysis was monitored using a drone-mounted hyperspectral camera. To minimize the impact of light interference on hyperspectral detection, drone hyperspectral monitoring was conducted at fixed times each week, such as Wednesdays from 12:00 to 14:00. From the hyperspectral images acquired by the drone, the complete spectral curves of the pixels corresponding to each sampling point were extracted. The nitrogen and phosphorus contents measured in the laboratory were matched with their corresponding spectral data. A nitrogen and phosphorus inversion model was constructed using machine learning or statistical analysis methods. This model can describe the quantitative relationship between spectral features and nitrogen and phosphorus contents. Simultaneously, the Normalized Difference Vegetation Index (NDVI) for each pixel in each test was calculated using the red and near-infrared bands of the hyperspectral data as an auxiliary parameter reflecting vegetation cover and biomass.

[0066] The trained nitrogen and phosphorus inversion model was applied to each pixel of the hyperspectral image to calculate the nitrogen and phosphorus content at the location represented by each pixel. A spatial interpolation algorithm was then used to generate a watershed nitrogen and phosphorus content distribution map that spatially matches the hyperspectral image. The nitrogen and phosphorus content of each pixel in the distribution map were then used as the baseline nitrogen and phosphorus content, respectively.

[0067] A watershed map of the watershed to be analyzed is obtained using digital elevation model (DEM) data, which provides the elevation value of each pixel within the watershed. To ensure correspondence with the pixel meaning of the watershed nitrogen and phosphorus content distribution map, the elevation model data should be preprocessed to ensure its spatial resolution, projected coordinate system, and geographic extent are consistent with the hyperspectral imagery, typically achieved through resampling or spatial alignment. The corresponding pixels of the monitoring points on the watershed map are designated as monitoring pixels. Temperature and humidity values ​​for the corresponding monitoring pixels are collected at each monitoring point using temperature and humidity sensors installed at each monitoring point. The actual nitrogen and phosphorus contents of each monitoring pixel are also collected using laboratory methods for each measurement. The distances between each pixel on the watershed map and all monitoring pixels are calculated. The temperature, humidity, actual nitrogen, and actual phosphorus contents of the monitoring pixel with the smallest distance are used as the temperature, humidity, actual nitrogen, and actual phosphorus contents for each pixel in each measurement.

[0068] Step S2: Based on the environmental similarity and nitrogen and phosphorus content difference between any two pixels in the analysis area during the current detection, divide the analysis area into sub-regions; and record the corresponding sub-regions of the soil area and water body area as the soil sub-region and water body sub-region of the current detection, respectively.

[0069] Typically, nitrogen and phosphorus pollution in soil exhibits dynamic changes, and the geological conditions within a watershed are complex. Different soil regions have varying soil structures and land use types, which influence the nitrogen and phosphorus pollution load on water bodies within the watershed. The environmental similarity and nitrogen and phosphorus content differences between two pixels reflect the degree of similarity in pollution status and environmental conditions at corresponding locations, respectively. By combining both factors, the likelihood of two pixels being classified into the same sub-region is analyzed, thus dividing the soil region and the water body region into separate zones.

[0070] Step S3: Based on the degree of co-fluctuation of nitrogen and phosphorus content in the previously detected pixels within each soil sub-region and the degree of fluctuation of nitrogen and phosphorus content in their neighboring areas, obtain the pollution carrying capacity of the corresponding soil sub-region.

[0071] Different soil types are used in different ways, resulting in variations in the capacity of different soil types to hold nitrogen and phosphorus ions. Carrying capacity refers to the ability of environmental systems such as soil or water bodies to absorb, decompose, transform, or store pollutants without impairing their own functions. Soil areas with higher carrying capacity have stronger resistance and resilience, resulting in smaller unidirectional fluctuations in nitrogen and phosphorus content when affected by pollution, and smaller changes in nitrogen and phosphorus content before and after pollution, thus maintaining their stability. Therefore, by comprehensively analyzing the degree of synergistic fluctuation of nitrogen and phosphorus content in previously detected pixels within the currently detected soil sub-regions and the fluctuations in nitrogen and phosphorus content in their neighboring areas, the carrying capacity of soil sub-regions to nitrogen and phosphorus pollution is analyzed to obtain the pollution carrying capacity. This addresses the problem of existing methods neglecting the soil's own buffering capacity, making pollution load analysis more consistent with actual ecological processes.

[0072] Step S4: Based on the differences in the direction of nitrogen and phosphorus diffusion and the differences in the degree of fluctuation of nitrogen and phosphorus content between any two soil sub-regions currently being tested, merge the soil sub-regions currently being tested to obtain different pollution migration areas, and determine the nitrogen and phosphorus pollution migration paths in the pollution migration areas.

[0073] Nitrogen and phosphorus pollution migration in soil within a watershed typically follows a specific direction, moving from upstream to downstream and ultimately into adjacent water bodies. Differences in the direction of nitrogen and phosphorus diffusion and variations in nitrogen and phosphorus content between two soil sub-regions reflect the consistency of pollution migration directions and the likelihood of similar pollution sources. By combining these two factors to analyze the similarity of pollution migration characteristics between the two soil sub-regions, soil sub-regions with similar migration characteristics are merged to obtain the pollution migration region. The migration pathways of nitrogen and phosphorus pollution are then determined, revealing the migration patterns of nitrogen and phosphorus pollution within the soil and clarifying the migration path from upstream to downstream. This allows for a more accurate simulation of the impact of underlying surface heterogeneity on pollution transfer.

[0074] Step S5: Based on the degree of consistency between the pollution carrying capacity and the nitrogen and phosphorus migration direction of each soil sub-region within the pollution migration area currently being detected, as well as the degree of nitrogen and phosphorus attenuation along the nitrogen and phosphorus pollution migration path, obtain the water pollution impact degree of the corresponding soil sub-region.

[0075] Pollution carrying capacity reflects the ability of a soil subregion to retain nitrogen and phosphorus pollution. The consistency of nitrogen and phosphorus migration direction in soil subregions within the pollution migration area reflects the ease or difficulty of transporting pollution to water bodies. Combined with the degree of nitrogen and phosphorus attenuation along the nitrogen and phosphorus pollution migration path, the pollution impact of soil subregions on watershed water bodies is comprehensively analyzed to obtain the water pollution impact degree.

[0076] Step S6: Based on the nitrogen and phosphorus content of each cell in the currently detected soil sub-region and the degree of water pollution impact, obtain the water pollution load value of the corresponding soil sub-region.

[0077] The nitrogen and phosphorus content of pixels within a soil sub-region represents the overall pollution status of the soil sub-region, while the water pollution impact reflects the degree of influence of the soil sub-region on the water pollution of the basin. By comprehensively analyzing both, the contribution of the soil sub-region to the water pollution of the basin can be assessed, and the water pollution load value can be obtained. This solves the load estimation bias caused by the neglect of dynamic carrying capacity and transmission in existing methods, and provides accurate decision-making basis for watershed management.

[0078] The water pollution load values ​​of all currently detected soil sub-regions are transmitted to the output device, and the location of each soil sub-region and its corresponding water pollution load value are visualized and output. The larger the water pollution load value, the darker the color of the region.

[0079] Preferably, in some possible implementations of the embodiments of the present invention, the method for obtaining the sub-region is described in [reference needed]. Figure 2 The diagram illustrates a flowchart of a method for obtaining a sub-region according to an embodiment of the present invention, the method comprising:

[0080] Step S210: Obtain the time series of vegetation index, baseline nitrogen content, baseline phosphorus content and various meteorological indicators for each pixel in the current detection.

[0081] It should be noted that meteorological indicators include temperature and humidity values. The time sequence of each meteorological indicator for each pixel during the period from the end of the (i-1)th detection to the start of the ith detection is arranged chronologically to obtain the time sequence of each meteorological indicator for each pixel during the ith detection.

[0082] Step S220: Calculate the correlation coefficient of the time series of each meteorological indicator for the two pixels in the current detection, and average the correlation coefficients of all types of environmental indicators to obtain the meteorological similarity of the two pixels in the current detection; obtain the environmental similarity of the two pixels in the current detection based on the difference in vegetation index and meteorological similarity of the two pixels in the current detection.

[0083] It should be noted that a higher meteorological similarity indicates a higher degree of synchronicity in the meteorological change patterns of the corresponding locations of the two pixels, and thus a more similar meteorological environment. The vegetation index reflects vegetation cover density; a smaller difference in the vegetation index between the corresponding locations of two pixels indicates a more similar vegetation environment. Therefore, the difference in the currently detected vegetation index between two pixels is negatively correlated with environmental similarity, while meteorological similarity is positively correlated with environmental similarity. In this embodiment of the invention, a negative correlation mapping is performed on the absolute value of the difference in the currently detected vegetation index between two pixels, and the product of the mapping result and the meteorological similarity is taken as the environmental similarity between the two pixels in the current detection.

[0084] In this embodiment of the invention, the data to be processed is used as the exponent of an exponential function with the natural constant as the base to achieve a negative correlation mapping of the data to be processed. Alternatively, the reciprocal of the sum of the data to be processed and a very small positive number can be taken, which is not limited here.

[0085] In one implementation of this invention, the correlation coefficient is the Pearson correlation coefficient.

[0086] Step S230: Based on the difference in actual nitrogen content, the difference in actual phosphorus content, and the environmental similarity between the two pixels in the current detection, obtain the probability that the two pixels are in the same area in the current detection.

[0087] Preferably, in some possible implementations of the embodiments of the present invention, the method for obtaining the probability of the same region includes: recording the difference between the currently detected baseline nitrogen content and the actual nitrogen content, and the difference between the baseline phosphorus content and the actual phosphorus content of each pixel in the soil region as nitrogen fluctuation amplitude and phosphorus fluctuation amplitude, respectively; performing negative correlation mapping on the differences in nitrogen fluctuation amplitude and phosphorus fluctuation amplitude of any two pixels in the soil region, and normalizing the product of the two mapping results and the environmental similarity to obtain the probability of the two pixels being in the same region in the current detection; performing negative correlation mapping on the currently detected actual nitrogen content and actual phosphorus content of any two pixels in the water body region, and normalizing the product of the two mapping results and the environmental similarity to obtain the probability of the two pixels being in the same region in the current detection. Here, "difference" refers to the absolute value of the difference.

[0088] It should be noted that due to the adsorption, fixation, and long-term accumulation of soil particles, the nitrogen and phosphorus content in soil usually has a relatively stable baseline value. Using the difference between the measured nitrogen and phosphorus content and the baseline nitrogen and phosphorus content can effectively identify areas affected by temporary pollution events. The nitrogen and phosphorus content in surface water is highly dynamic. Directly using the actual nitrogen and phosphorus content can better capture the instantaneous pollution level of the water body and avoid biases introduced by inaccurate baseline nitrogen and phosphorus content. If the difference in the amplitude of nitrogen and phosphorus fluctuations or the difference in actual nitrogen and phosphorus content between two pixels is smaller, and the environmental similarity is greater, it indicates that the pollution status and environmental conditions at the corresponding locations of the two pixels are more similar. Therefore, the two pixels are more likely to be classified into the same sub-region, i.e., the probability of being in the same region is greater.

[0089] In this embodiment of the invention, the data to be processed is used as the exponent of an exponential function with the natural constant as the base to achieve negative correlation mapping of the data to be processed. The Sigmoid function is used for normalization processing, or negative correlation mapping can be achieved by taking the reciprocal. Normalization methods such as function transformation and max-min normalization are used, which are not limited here.

[0090] Step S240: Based on the probability of the same region, perform region growing on all pixels within the same analysis region to obtain several sub-regions.

[0091] In this embodiment of the invention, a pixel is randomly selected within the analysis area as a growth point for region growth. Within the preset neighborhood of the growth point, pixels with a probability of being in the same region as the growth point that is greater than a preset probability threshold are selected as new growth points for region growth. Region growth stops when the probability of being in the same region of all new growth points and all pixels within their preset neighborhood is less than or equal to the preset probability threshold, thus obtaining the sub-region corresponding to the analysis area.

[0092] In one implementation of this invention, the preset neighborhood is an eight-neighborhood, and the preset possible threshold is set to 0.5. The implementer can set it according to the specific circumstances.

[0093] Preferably, in some possible implementations of the embodiments of the present invention, the method for obtaining pollution carrying capacity includes: arbitrarily selecting a soil sub-region currently being tested as an example region; averaging the actual nitrogen content of all pixels within the example region in each test to obtain the overall nitrogen content of the example region in each test; calculating the difference between the overall nitrogen content of the example region in each of the two adjacent tests before the current test, as the nitrogen content fluctuation value of the example region in the corresponding subsequent test; obtaining the phosphorus content fluctuation values ​​of the example region in several tests before the current test; and normalizing the product of the nitrogen content fluctuation value and the phosphorus content fluctuation value of the example region in each test before the current test. The following steps are performed to obtain the nitrogen and phosphorus fluctuation values ​​of the example area in the corresponding detection: Pulse detection of the example area is selected from several previous detections. The nitrogen and phosphorus fluctuation values ​​of the example area in each pulse detection are positive and greater than a preset fluctuation threshold. The actual nitrogen and phosphorus content differences of the example area in each pulse detection are calculated, and the average of these two differences is taken as the nitrogen and phosphorus neighborhood fluctuation value of the example area in each pulse. The average nitrogen and phosphorus fluctuation values ​​and the average nitrogen and phosphorus neighborhood fluctuation values ​​of the example area in all pulse tests are calculated separately. The product of the two averages is negatively correlated and normalized to obtain the pollution carrying capacity of the example area. Here, "difference" refers to the absolute value of the difference.

[0094] It should be noted that the overall nitrogen content reflects the overall nitrogen pollution level of the example area at each detection, while the nitrogen content fluctuation value reflects the trend and amplitude of nitrogen pollution changes. Analyzing the combined nitrogen and phosphorus content fluctuation values ​​reveals the intensity of the coordinated fluctuations between nitrogen and phosphorus. A positive and larger nitrogen-phosphorus fluctuation value indicates a more significant co-directional change in nitrogen and phosphorus content, while a negative and smaller value indicates a more significant inverse change. Real pollution events typically lead to a simultaneous and significant increase in nitrogen and phosphorus content; pulse detection represents a significant pollution increase event. In this embodiment, the `premnmx` function is used for normalization, ensuring that the nitrogen-phosphorus fluctuation value ranges from -1 to 1, thus setting the preset fluctuation threshold to 0.

[0095] The nitrogen and phosphorus fluctuation values ​​and the nitrogen and phosphorus neighborhood fluctuation values ​​are used to assess the resistance and resilience of the sample area to nitrogen and phosphorus pollution, respectively. If the nitrogen and phosphorus fluctuation values ​​and the nitrogen and phosphorus neighborhood fluctuation values ​​of the sample area are smaller in all pulse tests, it indicates that the sample area has a stronger resistance and resilience to nitrogen and phosphorus pollution under multiple pollution shocks. The sample area can effectively handle pollution shocks, and the sample area has a stronger capacity to accommodate nitrogen and phosphorus pollution, resulting in a greater pollution tolerance.

[0096] In this embodiment of the invention, the product of the mean of nitrogen and phosphorus fluctuation values ​​in all pulse tests in the example region and the mean of nitrogen and phosphorus neighborhood fluctuation values ​​can be used as the exponent of an exponential function with the natural constant as the base, thereby achieving negative correlation and normalization of the product.

[0097] It is important to note that the methods for obtaining phosphorus content fluctuation values ​​are similar to those for nitrogen content fluctuation values; the difference is that the actual nitrogen content is replaced with the actual phosphorus content during the nitrogen content fluctuation value acquisition process. The method for obtaining the pollution carrying capacity of all currently tested soil sub-regions and the example region is the same.

[0098] Preferably, in some possible implementations of the embodiments of the present invention, the method for obtaining the sub-region is described in [reference needed]. Figure 3 The diagram illustrates a flowchart of a method for obtaining a contamination migration area according to an embodiment of the present invention, the method comprising:

[0099] Step S310: Obtain the nitrogen gradient vector and phosphorus gradient vector of each pixel in the currently detected soil sub-region; obtain the combined vector of nitrogen gradient vectors and the combined vector of phosphorus gradient vectors of all pixels in the currently detected soil sub-region, and denot them as nitrogen migration vector and phosphorus migration vector respectively; take the combined vector of nitrogen migration vector and phosphorus migration vector as the overall nitrogen and phosphorus migration vector of the currently detected soil sub-region.

[0100] It should be noted that the nitrogen migration vector and phosphorus migration vector represent the overall direction and trend of nitrogen and phosphorus pollution migration in the entire soil sub-region, respectively. The combined vector of the two, namely the overall nitrogen and phosphorus migration vector, reflects the overall migration situation of pollution.

[0101] It should be noted that the nitrogen gradient vector and phosphorus gradient vector are determined based on the actual nitrogen content and actual phosphorus content of each pixel in the current detection. The nitrogen gradient vector and phosphorus gradient vector are obtained in a similar way to the gradient vector, except that the gray value is replaced with the actual nitrogen content and actual phosphorus content in the gradient vector acquisition process.

[0102] Step S320: Arrange the nitrogen and phosphorus fluctuation values ​​of each soil sub-region detected in the previous several tests in chronological order to obtain the fluctuation sequence; obtain the correlation coefficient and cosine similarity of the overall nitrogen and phosphorus migration vector of any two soil sub-regions detected in the current test respectively, and normalize the product of the correlation coefficient and the cosine similarity to obtain the migration feature similarity of the corresponding two soil sub-regions.

[0103] It should be noted that the fluctuation sequence reflects the historical fluctuations in nitrogen and phosphorus pollution in soil sub-regions. A higher correlation coefficient between the fluctuation sequences of two soil sub-regions indicates a greater likelihood that the two regions are affected by similar pollution sources, and thus, a more similar pollution migration source characteristic. Similarly, a higher cosine similarity between the overall nitrogen and phosphorus migration vectors of two soil sub-regions indicates a more consistent direction of pollution migration in the current detection, and thus, a more similar pollution migration source characteristic. Therefore, both the correlation coefficient and cosine similarity are positively correlated with the similarity of migration characteristics.

[0104] In this embodiment of the invention, the maximum and minimum normalization is used for normalization processing. Alternatively, the sigmoid function, function transformation, or other normalization methods can be used, and no limitation is made here.

[0105] In one implementation of this invention, the correlation coefficient is the Pearson correlation coefficient.

[0106] Step S330: Based on migration feature similarity, perform region growing on all currently detected soil sub-regions to obtain the currently detected pollution migration regions.

[0107] It should be noted that, in this embodiment of the invention, a currently detected soil sub-region is arbitrarily selected as a growth point for region growth. From the soil sub-regions adjacent to the growth point, soil sub-regions with a migration feature similarity greater than a preset similarity threshold are selected as new growth points for region growth. Region growth stops when the migration feature similarity between all new growth points and their adjacent soil sub-regions is less than or equal to the preset similarity threshold, resulting in different pollution migration regions. Within the pollution migration region, soil sub-regions possess similar migration characteristics.

[0108] In one implementation of this invention, the preset similarity threshold is set to 0.5, which can be set by the implementer according to specific circumstances.

[0109] Preferably, in some possible implementations of the embodiments of the present invention, the method for obtaining the nitrogen and phosphorus pollution migration path includes: for each pollution migration area currently detected, obtaining the sum vector of the overall nitrogen and phosphorus migration vectors of all soil sub-regions within the pollution migration area, denoted as the pollution migration vector; drawing a straight line passing through the center point of the pollution migration area and parallel to the direction of the pollution migration vector, denoted as the baseline of the pollution migration area; projecting the center points of all soil sub-regions within the pollution migration area onto the baseline, and connecting the center points of each soil sub-region in the order of the direction of the pollution migration vector according to the projection position of each center point on the baseline to obtain the nitrogen and phosphorus pollution migration path.

[0110] It should be noted that the pollution migration vector reflects the overall migration situation of the entire pollution migration area; by projecting the center point of the soil sub-region within the pollution migration area onto the baseline, the offset in the direction perpendicular to the migration can be ignored, and only the position information along the migration direction can be retained, highlighting the order of the migration path. The connected nitrogen and phosphorus pollution migration paths can show the migration trajectory of nitrogen and phosphorus pollutants within the pollution migration area.

[0111] In one implementation of this invention, spline curve interpolation is used to connect the center points of all soil sub-regions within the pollution migration area to generate a smooth curve path, namely the nitrogen and phosphorus pollution migration path.

[0112] Preferably, in some possible implementations of the embodiments of the present invention, the method for obtaining the degree of water pollution impact includes: for each currently detected pollution migration area, the soil sub-regions located at the upstream and downstream positions in the nitrogen and phosphorus pollution migration path of the pollution migration area are sequentially recorded as the path start area and path end area; the average of the actual phosphorus content of all pixels in the sub-region in the current detection is calculated to obtain the overall phosphorus content; the distance between the center point of all currently detected water sub-regions and the center point of the path end area of ​​the pollution migration area is calculated, and the water sub-region corresponding to the smallest distance is selected as the water analysis area of ​​the pollution migration area; the path of the pollution migration area is calculated respectively. The absolute values ​​of the overall nitrogen content difference and the overall phosphorus content difference between the starting area and the water analysis area are used as the product of the two absolute values ​​to obtain the path pollution attenuation index. The mean of the cosine similarity between the overall nitrogen and phosphorus migration vectors of all soil sub-regions within the pollution migration area and the pollution migration vector is used as the migration direction stability. The mean of the pollution carrying capacity of all soil sub-regions within the pollution migration area is used as the overall carrying capacity. Based on the distance between the center point of each soil sub-region currently being detected and the center point of the water analysis area within the pollution migration area, the migration direction stability, the overall carrying capacity, and the path pollution attenuation index, the water pollution impact value of the corresponding soil sub-region is obtained.

[0113] It should be noted that by using minimum distance correlation, the soil pollution pathway is connected to the most relevant water body, meaning the water body analysis area is where the pollution from the pollution migration area ultimately flows into the water body. The smaller the difference in overall nitrogen and phosphorus content between the starting area of ​​the pollution migration pathway and the water body analysis area, the smaller the difference in nitrogen and phosphorus pollution levels between the two areas. This results in a smaller attenuation of nitrogen and phosphorus pollution along the migration direction, a smaller path pollution attenuation index, and easier transport of pollution to the watershed, thus increasing the pollution impact on the watershed. Conversely, a higher migration direction stability indicates that the overall nitrogen and phosphorus migration direction of the pollution migration area is more consistent with the nitrogen and phosphorus migration directions of all soil sub-regions within it. This makes it easier for pollution to be directly transported to the water body, reducing pollution loss along the migration path and increasing the pollution impact on the watershed. Finally, a lower overall carrying capacity indicates a weaker ability of the soil sub-regions within the pollution migration area to retain nitrogen and phosphorus pollution, making the pollution more likely to migrate and thus having a greater pollution impact on the watershed. The smaller the distance between the center point of the currently detected soil sub-region and the center point of the water analysis area within its pollution migration zone, the higher the migration efficiency of pollution from the source to the watershed, and the greater the pollution impact on the watershed. Therefore, the stability of the migration direction is positively correlated with the water pollution impact value, while the path pollution attenuation index, overall carrying capacity, and the distance between the center point of the soil sub-region and the center point of the water analysis area within its pollution migration zone are all negatively correlated with the water pollution impact value.

[0114] In this embodiment of the invention, the distance between the center point of each soil sub-region currently being detected and the center point of the water analysis area of ​​the pollution migration area, the path pollution attenuation index, and the overall carrying capacity are respectively negatively correlated and mapped. The product of the three mapping results and the migration direction stability is taken as the water pollution influence degree of the corresponding soil sub-region.

[0115] In this embodiment of the invention, the data to be processed is used as the exponent of an exponential function with the natural constant as the base to achieve a negative correlation mapping of the data to be processed. Alternatively, the negative correlation mapping can be achieved by taking the reciprocal, and there is no limitation here.

[0116] Preferably, in some possible implementations of the embodiments of the present invention, the method for obtaining the water pollution load value includes: calculating the mean of the overall nitrogen content and the overall phosphorus content of all pixels in each soil sub-region currently being detected, normalizing the product of the mean and the water pollution impact degree, and obtaining the water pollution load value of the corresponding soil sub-region.

[0117] It should be noted that the average values ​​of overall nitrogen content and overall phosphorus content represent the overall pollution status of the soil sub-region; the water pollution impact reflects the degree of influence of the soil sub-region on the watershed water pollution and is a weighting factor; the water pollution load obtained by multiplying the two values ​​refers to the degree of contribution of the soil sub-region to the watershed water pollution.

[0118] In this embodiment of the invention, the maximum and minimum normalization is used for normalization processing. Alternatively, the sigmoid function, function transformation, or other normalization methods can be used, and no limitation is made here.

[0119] This invention is now complete.

[0120] Example 2:

[0121] This invention proposes a system for analyzing nitrogen and phosphorus pollution loads in watersheds over a large area. Please refer to [link / reference]. Figure 4 The diagram illustrates a system structure of a large-scale watershed nitrogen and phosphorus pollution load analysis system according to an embodiment of the present invention. The system includes:

[0122] The data acquisition module 710 is used to acquire the watershed extent map of the watershed to be analyzed and the actual nitrogen content and actual phosphorus content of each pixel in the current detection and several previous detections; the extent map is divided into soil area and water area, which are denoted as the analysis area;

[0123] The sub-region division module 720 is used to divide the analysis area into sub-regions based on the environmental similarity and nitrogen and phosphorus content difference between any two pixels in the analysis area at the current detection time; the sub-regions corresponding to the soil area and the water body area are respectively recorded as the soil sub-region and the water body sub-region at the current detection time.

[0124] The pollution carrying capacity analysis module 730 is used to obtain the pollution carrying capacity of the corresponding soil sub-region based on the degree of co-fluctuation of nitrogen and phosphorus content of the pixels in the currently detected soil sub-region in previous tests and the degree of fluctuation of nitrogen and phosphorus content in their neighboring areas.

[0125] The pollution migration analysis module 740 is used to merge the currently detected soil sub-regions based on the differences in the direction of nitrogen and phosphorus diffusion and the differences in the degree of fluctuation of nitrogen and phosphorus content between any two currently detected soil sub-regions, to obtain different pollution migration regions, and to determine the nitrogen and phosphorus pollution migration paths of the pollution migration regions.

[0126] The water pollution impact analysis module 750 is used to obtain the water pollution impact degree of the corresponding soil sub-region based on the degree of consistency between the pollution carrying capacity and the nitrogen and phosphorus migration direction of the soil sub-region within the pollution migration area of ​​each soil sub-region currently being detected, as well as the degree of nitrogen and phosphorus attenuation on the nitrogen and phosphorus pollution migration path.

[0127] The pollution load analysis module 760 is used to obtain the water pollution load value of the corresponding soil sub-region based on the nitrogen and phosphorus content of each pixel in the currently detected soil sub-region and the degree of water pollution impact.

[0128] It should be noted that the equipment provided in the above embodiments is only an example of the division of the above functional modules. In actual applications, the above functions can be assigned to different functional modules as needed, that is, the internal structure of the computer equipment can be divided into different functional modules to complete all or part of the functions described above. In addition, the nitrogen and phosphorus pollution load analysis system for large-scale watershed water quality and the method embodiment for large-scale watershed water quality nitrogen and phosphorus pollution load analysis provided in the above embodiments belong to the same concept, and the specific implementation process is detailed in the method embodiment, which will not be repeated here.

[0129] Example 3:

[0130] Figure 5 This is a schematic diagram of a computer device for analyzing nitrogen and phosphorus pollution loads in a large-scale watershed according to an embodiment of the present invention. For example,... Figure 5 As shown, the computer device includes: a memory 801, a processor 802, and a computer program 803 stored in the memory 801 and running on the processor 802, wherein when the processor 802 executes the computer program 803, the computer device can execute any of the aforementioned methods for analyzing nitrogen and phosphorus pollution loads in large-scale watershed water quality.

[0131] Furthermore, embodiments of this application also protect an apparatus that may include a memory and a processor, wherein the memory stores executable program code, and the processor is used to call and execute the executable program code to perform a method for analyzing nitrogen and phosphorus pollution loads in a large-scale watershed provided in embodiments of this application.

[0132] This embodiment can divide the device into functional modules based on the above method example. For example, each module can correspond to a separate function, or two or more functions can be integrated into one processing module. The integrated module can be implemented in hardware. It should be noted that the module division in this embodiment is illustrative and only represents one logical functional division. In actual implementation, there may be other division methods.

[0133] It should be understood that the apparatus provided in this embodiment is used to perform the above-described method for analyzing nitrogen and phosphorus pollution loads in a large-scale watershed, and therefore can achieve the same effect as the above-described implementation method.

[0134] When using integrated units, the device may include a processing module and a storage module. When applied to a workpiece, the processing module can be used to control and manage the workpiece's operations. The storage module can be used to support the execution of program code by the workpiece.

[0135] The processing module may be a processor or a controller, which can implement or execute various exemplary logic blocks, modules, and circuits contained in conjunction with the disclosure of this application. The processor may also be a combination of functions that implement computing capabilities, such as a combination of one or more microprocessors, a combination of digital signal processing (DSP) and microprocessors, etc., and the storage module may be a memory.

[0136] It should be noted that the order of the above embodiments of the present invention is merely for descriptive purposes and does not represent the superiority or inferiority of the embodiments. The processes depicted in the accompanying drawings do not necessarily require a specific or sequential order to achieve the desired result. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0137] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0138] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for analyzing nitrogen and phosphorus pollution loads in a large-scale watershed, characterized in that, The method includes: Obtain the watershed extent map of the watershed to be analyzed and the actual nitrogen and phosphorus content of each pixel in the current and previous several tests; the extent map is divided into soil area and water area, which are denoted as the analysis area; Based on the environmental similarity and nitrogen and phosphorus content difference between any two pixels in the current detection area, the analysis area is divided into sub-regions; the sub-regions corresponding to the soil area and the water body area are respectively recorded as the soil sub-region and the water body sub-region currently being detected. Based on the degree of co-fluctuation of nitrogen and phosphorus content in previously detected pixels within each soil sub-region and the degree of fluctuation of nitrogen and phosphorus content in their neighboring areas, the pollution carrying capacity of the corresponding soil sub-region is obtained. Based on the differences in the direction of nitrogen and phosphorus diffusion and the degree of fluctuation in nitrogen and phosphorus content between any two soil sub-regions currently being tested, the soil sub-regions currently being tested are merged to obtain different pollution migration areas, and the nitrogen and phosphorus pollution migration paths of the pollution migration areas are determined. Based on the degree of consistency between the pollution carrying capacity and the nitrogen and phosphorus migration direction of each soil sub-region within the pollution migration area currently being detected, and the degree of nitrogen and phosphorus attenuation along the nitrogen and phosphorus pollution migration path, the water pollution impact degree of the corresponding soil sub-region is obtained. Based on the nitrogen and phosphorus content of each pixel in each soil sub-region currently detected and the degree of water pollution impact, the water pollution load value of the corresponding soil sub-region is obtained.

2. The method for analyzing nitrogen and phosphorus pollution loads in a large-scale watershed according to claim 1, characterized in that, The process of dividing the analysis region into sub-regions includes: Obtain the time series of vegetation index, baseline nitrogen content, baseline phosphorus content and various meteorological indicators for each pixel at the current detection; The correlation coefficient of the time series of the two pixels for each meteorological indicator detected at the present time is calculated respectively. The correlation coefficients of all types of environmental indicators are averaged to obtain the meteorological similarity of the two pixels detected at the present time. The environmental similarity of the two pixels detected at the present time is obtained based on the difference in vegetation index of the two pixels detected at the present time and the meteorological similarity. Based on the difference in actual nitrogen content and actual phosphorus content between the two pixels in the current detection and the similarity to the environment, the probability that the two pixels are in the same area in the current detection is obtained. Based on the probability of the same region, region growing is performed on all pixels within the same analysis region to obtain several sub-regions.

3. The method for analyzing nitrogen and phosphorus pollution loads in a large-scale watershed according to claim 2, characterized in that, The step of obtaining the probability of two pixels in the same detected region includes: The differences between the current measured baseline nitrogen content and the actual nitrogen content, and the differences between the current measured baseline phosphorus content and the actual phosphorus content, for each pixel within the soil region are recorded as nitrogen fluctuation amplitude and phosphorus fluctuation amplitude, respectively. Negative correlation mapping is performed on the differences in nitrogen fluctuation amplitude and phosphorus fluctuation amplitude between any two pixels within the soil region. The product of the two mapping results and the environmental similarity is normalized to obtain the probability of the two corresponding pixels being in the same region in the current detection. For any two pixels within the water body area, negative correlation mapping is performed on the actual nitrogen content difference and the actual phosphorus content difference detected at the current time. The product of the two mapping results and the environmental similarity is normalized to obtain the probability of the two corresponding pixels being in the same area at the current time.

4. The method for analyzing nitrogen and phosphorus pollution loads in a large-scale watershed according to claim 1, characterized in that, The process of obtaining the pollution carrying capacity of the corresponding soil sub-region includes: Select any soil sub-region currently being tested as the example region; average the actual nitrogen content of all pixels within the example region in each test to obtain the overall nitrogen content of the example region in each test; calculate the difference between the overall nitrogen content of the example region in each of the two adjacent tests before the current test, and use this as the nitrogen content fluctuation value of the example region in the corresponding subsequent test; obtain the phosphorus content fluctuation values ​​of the example region in several tests before the current test. The product of the nitrogen content fluctuation value and the phosphorus content fluctuation value of the example region in each detection before the current detection is normalized to obtain the nitrogen and phosphorus fluctuation value of the example region in the corresponding detection; a pulse detection of the example region is selected from several detections before the current detection, wherein the nitrogen content fluctuation value and the phosphorus content fluctuation value of the example region in the pulse detection are both positive, and the nitrogen and phosphorus fluctuation values ​​are greater than a preset fluctuation threshold. The differences in actual nitrogen content and actual phosphorus content in the example region before and after each pulse detection are calculated, and the average of the two differences is used as the nitrogen and phosphorus neighborhood fluctuation value of the example region in each pulse. The mean of the nitrogen and phosphorus fluctuation values ​​and the mean of the nitrogen and phosphorus neighborhood fluctuation values ​​of the example area are calculated separately. The product of the two means is negatively correlated and normalized to obtain the pollution tolerance of the example area.

5. The method for analyzing nitrogen and phosphorus pollution loads in a large-scale watershed according to claim 4, characterized in that, The obtained different pollution migration areas include: Obtain the nitrogen gradient vector and phosphorus gradient vector of each pixel in the currently detected soil sub-region; obtain the combined vector of nitrogen gradient vectors and the combined vector of phosphorus gradient vectors of all pixels in the currently detected soil sub-region, and denot them as nitrogen migration vector and phosphorus migration vector respectively; take the combined vector of nitrogen migration vector and phosphorus migration vector as the overall nitrogen and phosphorus migration vector of the currently detected soil sub-region. The nitrogen and phosphorus fluctuation values ​​of each soil sub-region currently being detected are arranged in chronological order from previous detections to obtain a fluctuation sequence; The correlation coefficient of the fluctuation sequence and the cosine similarity of the overall nitrogen and phosphorus migration vectors of any two soil sub-regions currently detected are obtained respectively. The product of the correlation coefficient and the cosine similarity is normalized to obtain the migration feature similarity of the corresponding two soil sub-regions. Based on the migration feature similarity, region growing is performed on all currently detected soil sub-regions to obtain the currently detected pollution migration regions.

6. The method for analyzing nitrogen and phosphorus pollution loads in a large-scale watershed according to claim 5, characterized in that, The determination of nitrogen and phosphorus pollution migration pathways in the pollution migration area includes: For each pollution migration area currently detected, obtain the sum vector of the overall nitrogen and phosphorus migration vectors of all soil sub-regions within the pollution migration area, denoted as the pollution migration vector; Draw a straight line passing through the center point of the pollution migration area and parallel to the direction of the pollution migration vector, and denote it as the baseline of the pollution migration area; project the center points of all soil sub-regions within the pollution migration area onto the baseline, and connect the center points of each soil sub-region in order of the direction of the pollution migration vector according to the projection position of each center point on the baseline to obtain the nitrogen and phosphorus pollution migration path.

7. The method for analyzing nitrogen and phosphorus pollution loads in a large-scale watershed according to claim 6, characterized in that, The acquisition of the water pollution impact degree of the corresponding soil sub-region includes: For each pollution migration area currently detected, the soil sub-regions located at the upstream and downstream positions in the nitrogen and phosphorus pollution migration path of the pollution migration area are successively recorded as the path start area and path end area; the average of the actual phosphorus content of all pixels in the sub-region currently detected is calculated to obtain the overall phosphorus content; Calculate the distance between the center point of each of the currently detected water body sub-regions and the center point of the end region of the path of the pollution migration region, and select the water body sub-region corresponding to the minimum distance as the water body analysis region of the pollution migration region; calculate the absolute value of the overall nitrogen content difference and the absolute value of the overall phosphorus content difference between the starting region of the path of the pollution migration region and the water body analysis region, and use the product of the two absolute values ​​of difference as the path pollution attenuation index; The mean cosine similarity between the overall nitrogen and phosphorus migration vectors of all soil sub-regions within the pollution migration area and the pollution migration vectors is used as the migration direction stability. The average pollution carrying capacity of all soil sub-regions within the pollution migration area is taken as the overall carrying capacity; Based on the distance between the center point of each soil sub-region currently being detected and the center point of the water analysis region in the pollution migration area, the migration direction stability, the overall carrying capacity, and the path pollution attenuation index, the water pollution impact value of the corresponding soil sub-region is obtained.

8. The method for analyzing nitrogen and phosphorus pollution loads in a large-scale watershed according to claim 7, characterized in that, The acquisition of the water pollution load value of the corresponding soil sub-region includes: Calculate the mean of the overall nitrogen content and the overall phosphorus content of all pixels in each soil sub-region currently being detected, and normalize the product of the mean and the water pollution impact degree to obtain the water pollution load value of the corresponding soil sub-region.

9. The method for analyzing nitrogen and phosphorus pollution loads in a large-scale watershed according to claim 7, characterized in that, The stability of the migration direction is positively correlated with the degree of water pollution impact, while the path pollution attenuation index and the overall carrying capacity are both negatively correlated with the degree of water pollution impact.

10. A system for analyzing nitrogen and phosphorus pollution loads in a large-scale watershed, characterized in that, The system includes: The data acquisition module is used to acquire the watershed extent map of the watershed to be analyzed and the actual nitrogen and phosphorus content of each pixel in the current detection and several previous detections; the extent map is divided into soil area and water area, which are denoted as the analysis area; The sub-region division module is used to divide the analysis area into sub-regions based on the environmental similarity and nitrogen and phosphorus content difference between any two pixels in the analysis area at the current detection time; the sub-regions corresponding to the soil area and the water body area are respectively recorded as the soil sub-region and the water body sub-region currently detected; The pollution carrying capacity analysis module is used to obtain the pollution carrying capacity of the corresponding soil sub-region based on the degree of co-fluctuation of nitrogen and phosphorus content of the pixels in the currently detected soil sub-region in previous tests and the degree of fluctuation of nitrogen and phosphorus content in their neighboring areas. The pollution migration analysis module is used to merge the currently detected soil sub-regions based on the differences in the direction of nitrogen and phosphorus diffusion and the differences in the degree of fluctuation of nitrogen and phosphorus content between any two currently detected soil sub-regions, to obtain different pollution migration regions, and to determine the nitrogen and phosphorus pollution migration paths in the pollution migration regions. The water pollution impact analysis module is used to obtain the water pollution impact degree of the corresponding soil sub-region based on the degree of consistency between the pollution carrying capacity and the nitrogen and phosphorus migration direction of the soil sub-region in the pollution migration area where each soil sub-region is located, as well as the degree of nitrogen and phosphorus attenuation on the nitrogen and phosphorus pollution migration path. The pollution load analysis module is used to obtain the water pollution load value of the corresponding soil sub-region based on the nitrogen and phosphorus content of each pixel in the currently detected soil sub-region and the degree of water pollution impact.

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