A method for evaluating nitrogen and phosphorus reduction effect of a coastal zone

Abstract

This invention discloses a method for evaluating the nitrogen and phosphorus reduction effect in riparian zones, comprising: acquiring multispectral image data and a digital surface model; obtaining actual slope, elevation, and long-term hydrological dynamic data through ground measurements, sampling, and surveys; extracting core parameters; correcting the digital surface model using ground-measured elevation data; constructing a precise digital elevation model of the target riparian zone; determining the slope and dividing the slope range; identifying the target riparian zone type and planting / slope protection combination structure by combining multispectral image data, ground survey data, and the digital surface model; obtaining the nitrogen and phosphorus reduction baseline value based on the core parameters; extracting the rainfall intensity correction coefficient and water level fluctuation correction coefficient by combining hydrological dynamic data; calculating the final nitrogen and phosphorus reduction ratio; and performing spatial visualization to achieve efficient, accurate, and standardized evaluation of the nitrogen and phosphorus reduction effect in riparian zones, providing a scientific basis for the design, optimization, and effectiveness verification of riparian zone ecological restoration projects.

Description

Technical Field

[0001] This invention belongs to the field of data processing and ecological environment assessment technology, and specifically relates to a method for assessing the nitrogen and phosphorus reduction effect in coastal zones. Background Technology

[0002] As a transitional zone between aquatic and terrestrial ecosystems, the riparian zone's nitrogen and phosphorus reduction capacity directly impacts aquatic environmental quality and is a core assessment indicator for ecological restoration projects. Existing methods for assessing the effectiveness of nitrogen and phosphorus reduction in riparian zones have significant shortcomings: First, slope data acquisition relies on manual measurement, which is inefficient and has limited accuracy, failing to reflect the spatial heterogeneity of riparian slopes. Second, identification of plant structure and riparian zone types largely depends on field surveys, resulting in limited coverage and an inability to quickly obtain distribution information over large areas. Third, the assessment process often fails to comprehensively consider corrections for hydrological factors such as rainfall intensity and water level fluctuations, or lacks a systematic application of correction coefficients, leading to significant biases in the assessment results. Fourth, a standardized process for data acquisition, parameter extraction, correction calculation, and effect assessment has not been established, making it difficult to meet the efficient and accurate assessment needs in engineering practice.

[0003] While some studies in the field utilize remote sensing data for shoreline extraction or land use classification, and others obtain nitrogen and phosphorus reduction baseline values ​​for different plant-soil combinations through indoor experiments, there has been no systematic integration of low-altitude multispectral UAV data, ground-based measured data, nitrogen and phosphorus reduction baselines, and hydrological correction coefficients. This hinders the rapid, accurate, and large-scale assessment of nitrogen and phosphorus reduction effects in riparian zones, thus restricting the optimization and promotion of riparian ecological restoration projects. Summary of the Invention

[0004] To address the problems of low data acquisition efficiency, insufficient parameter extraction accuracy, unsystematic hydrological correction, and non-standard assessment procedures in existing methods for evaluating nitrogen and phosphorus reduction effects in riparian zones, this invention proposes a new method for evaluating nitrogen and phosphorus reduction effects in riparian zones. This method aims to achieve efficient, accurate, and standardized assessment of nitrogen and phosphorus reduction effects in riparian zones, providing a scientific basis for the design, optimization, and effectiveness verification of riparian ecological restoration projects.

[0005] This invention adopts the following technical solution: a method for evaluating the nitrogen and phosphorus reduction effect in coastal zones, comprising the following steps:

[0006] Step 1, Data Acquisition: Use a low-altitude multispectral UAV to acquire multispectral image data and digital surface model (DSM) of the target coastal zone; conduct ground measurements, sampling and surveys to obtain the actual slope, elevation and long-term hydrological dynamic data of the target coastal zone;

[0007] Step 2, Core Parameter Extraction: Establish a lookup table for riparian zone type, slope, planting combination nitrogen and phosphorus reduction ratio, and hydrological correction coefficient; use ground-measured elevation data to correct the digital surface model, construct a precise digital elevation model (DEM) of the target riparian zone, determine the slope, divide the slope interval according to the lookup table, and combine multispectral image data, ground survey data, and digital surface model to identify the target riparian zone type and planting / slope protection combination structure;

[0008] Step 3, Calculation of nitrogen and phosphorus reduction ratio: Based on the core parameters, find the lookup table described in Step 2 to obtain the nitrogen and phosphorus reduction baseline values. Combine the hydrological dynamic data to extract the rainfall intensity correction coefficient and water level fluctuation correction coefficient, and calculate the final nitrogen and phosphorus reduction ratio.

[0009] Step 4: Output of evaluation results: Visualize the nitrogen and phosphorus reduction ratio spatially, generate a spatial distribution map of the nitrogen and phosphorus reduction effect of the target coastal zone, and output a statistical report.

[0010] As a preferred embodiment, the data acquisition in step 1 includes:

[0011] Low-altitude multispectral UAV data acquisition was conducted on the target coastal zone to obtain image data and digital surface models including green, red, and near-infrared bands. The aerial survey accuracy met the requirements for slope calculation and plant identification (this invention recommends a ground resolution of ≤5cm to ensure that the slope calculation error is ≤5%).

[0012] Typical sampling points were set up in the target coastal zone to collect ground survey data, collect soil samples, record plant species and structures, and measure the actual slope and elevation data of the sampling points. Simultaneously, long-term rainfall intensity data (low ≤20mm / h, medium 20~50mm / h, high ≥50mm / h) and water level fluctuation data (small ≤0.5m, medium 0.5~1.5m, large ≥1.5m) in the area were recorded.

[0013] Among them, rainfall intensity data must be recorded continuously for at least one hydrological year, and water level fluctuation data must cover the wet, normal, and dry seasons.

[0014] As a preferred option, in the lookup table of riparian zone type-slope-planting combination nitrogen and phosphorus reduction ratio and hydrological correction coefficient, the slope level, planting / slope protection combination type, total nitrogen (TN) reduction ratio, total phosphorus (TP) reduction ratio, rainfall intensity correction coefficient, and water level fluctuation correction coefficient are determined according to the riparian zone type.

[0015] The types of coastal zones include: slope type and nearshore water type;

[0016] The slope grades include:

[0017] Gentle slope: The ratio between the vertical height and horizontal width of the slope is ≤1:2;

[0018] Medium slope: The ratio between the vertical height and horizontal width of the slope is 1:1.5 to 1:2;

[0019] Steep slopes: The ratio between the vertical height and horizontal width of the slope is ≥1:1.5;

[0020] Calm waters: No obvious slope.

[0021] As a preferred embodiment, the extraction of core parameters in step 2 includes the following sub-steps:

[0022] Step 2.1, Digital Elevation Model Construction: The digital surface model obtained by the UAV is corrected using ground-measured elevation data, and the interference of vegetation canopy is eliminated. For areas with multiple layers of trees, shrubs and grasses, the vegetation height is measured in the field to assist in the correction, so as to obtain an accurate digital elevation model of the target coastal zone.

[0023] Step 2.2, Determination of slope and slope intervals: Based on the digital elevation model, geographic information software is used to obtain the slope distribution data of the target coastal zone, and slope intervals are divided in combination with the slope classification standard;

[0024] Step 2.3, Identification of Coastal Zone Type and Plant Structure: Combining UAV multispectral imagery (green band reflects vegetation chlorophyll content, near-infrared band distinguishes vegetation vitality), ground survey photos, and digital surface models, the Normalized Difference Vegetation Index (NDVI) is used to assist in identifying plant coverage areas. Combined with field survey records, the target coastal zone type (slope type, near-shore water type) and planting / slope protection combination structure (such as multilayered trees, shrubs, and grasses, gabion slope protection, submerged plant communities, etc.) are determined.

[0025] As a preferred embodiment, the Normalized Difference Vegetation Index (NDVI) in step 2.3 is calculated as follows:

[0026] NDVI = (Near-infrared band - Red band) / (Near-infrared band + Red band);

[0027] When NDVI ≥ 0.3, it is considered as effective vegetation cover;

[0028] As a preferred embodiment, the calculation of the nitrogen and phosphorus reduction ratio in step 3 includes the following sub-steps:

[0029] Step 3.1, Benchmark Value Lookup: Based on the target riparian zone type, slope range, and planting / slope protection combination structure extracted in Step 2, obtain the benchmark values ​​for total nitrogen reduction ratio and total phosphorus reduction ratio from the lookup table;

[0030] For example, for a multi-layered slope of trees, shrubs and grasses, the corresponding TN benchmark value is ≥30% and the TP benchmark value is ≥25%.

[0031] Step 3.2, Hydrological Correction: Based on the rainfall intensity level and water level fluctuation level of the target coastal zone, extract the corresponding rainfall intensity correction coefficient and water level fluctuation correction coefficient from the lookup table. Multiply the baseline values ​​of total nitrogen reduction ratio and total phosphorus reduction ratio by the rainfall intensity correction coefficient and water level fluctuation correction coefficient respectively to obtain the final nitrogen and phosphorus reduction ratio, which is expressed as: Final reduction ratio = baseline value × rainfall intensity correction coefficient × water level fluctuation correction coefficient.

[0032] As a preferred option, in step 3.2, if there are spatial differences in rainfall or water level within the target coastal zone, correction coefficients are extracted for each sub-region to perform hydrological correction, thus avoiding errors caused by overall averaging.

[0033] As a preferred option, the spatial distribution map of nitrogen and phosphorus reduction effect in step 4 adopts a graded color method, and the reduction effect is divided into four levels according to the reduction ratio: excellent (≥30%), good (20%~30%), medium (10%~20%), and poor (<10%); the statistical report clarifies the differences in reduction effect and key influencing factors.

[0034] The present invention also provides: an electronic device, comprising:

[0035] One or more processors;

[0036] A storage device on which one or more programs are stored;

[0037] When the one or more programs are executed by the one or more processors, the one or more processors implement the aforementioned method for evaluating the nitrogen and phosphorus reduction effect in the coastal zone.

[0038] The present invention also provides a computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements the steps in the aforementioned method for evaluating the nitrogen and phosphorus reduction effect in coastal zones.

[0039] Compared with the prior art, the present invention, employing the above technical solution, has the following technical effects:

[0040] 1. The method of this invention enables rapid data collection over large areas of coastal zones using low-altitude multispectral UAVs, significantly reducing the workload of manual field surveys and greatly improving assessment efficiency. Ground data is used to correct the UAV DSM to obtain a precise DEM; combining the accuracy of plant structure identification with multispectral imagery and field surveys, and then overlaying hydrological correction coefficients, reduces the assessment error of nitrogen and phosphorus reduction ratios, meeting the accuracy requirements of ecological restoration projects.

[0041] 2. The method of this invention establishes a standardized process of data acquisition, parameter extraction, correction calculation and result output, clarifies the technical requirements of each step, ensures the comparability of evaluation results in different regions and batches, and avoids evaluation deviations caused by differences in methods.

[0042] 3. The evaluation results of this invention can directly reflect the differences in nitrogen and phosphorus reduction capacity in different coastal areas, providing precise guidance for ecological restoration projects such as planting structure optimization (e.g., in medium-slope areas, single herbaceous plants can be replaced with a multi-layered tree-shrub-grass structure), slope adjustment (e.g., in steep-slope areas, slope reduction can be achieved by cutting the slope down to a medium slope to improve the reduction effect), and hydrological regulation (e.g., in areas with high water level fluctuations, water-blocking facilities can be added to control the fluctuation ≤0.5m), thus helping to improve the ecological restoration effect of coastal areas. Attached Figure Description

[0043] Figure 1 This is a flowchart of the method for evaluating the nitrogen and phosphorus reduction effect in coastal zones according to the present invention. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of the application will be further described in detail below with reference to the accompanying drawings. The described embodiments are only a part of the embodiments involved in this invention. All non-innovative embodiments based on these embodiments by other researchers in the art are within the protection scope of this invention. Furthermore, the step numbers in the embodiments of this invention are only set for ease of explanation and do not limit the order of the steps. The execution order of each step in the embodiments can be adaptively adjusted according to the understanding of those skilled in the art.

[0045] In one embodiment of the present invention, the riparian zone of Yiai Lake in Huanggang City was selected as the study area. The area is about 5 km², located on the north bank of the middle reaches of the Yangtze River, and belongs to the subtropical monsoon climate with an average annual rainfall of 1200-1400 mm. The terrain in the area includes three slope ranges: gentle slope, medium slope, and steep slope. The planting structure covers the types of trees, shrubs and grasses (weeping willow + Amorpha fruticosa + Zoysia japonica), single herb (Bermudagrass), and ecological concrete slope protection (with Zoysia japonica). According to the meteorological and hydrological station data of the past 3 years, the average annual rainfall intensity in the area is mainly medium (20-50 mm / h), accounting for 65%, and the water level fluctuation is at a medium level (average 0.8 m per year, fluctuation range 0.5-1.2 m).

[0046] The nitrogen and phosphorus reduction effect of the method of this invention in this coastal zone is evaluated, such as... Figure 1 As shown, it includes the following steps:

[0047] Step 1: Data Collection

[0048] In this embodiment, low-altitude multispectral UAV data acquisition: DJI P4 Multispectral UAV was selected, with a flight altitude of 100m, a forward overlap of 85%, and a lateral overlap of 70%, to acquire green light, red light, and near-infrared band images and DSM data of the study area.

[0049] Ground field survey data collection: Multiple sampling points were evenly distributed within the study area according to slope ranges, meeting the density requirement of 1 point / km². The coordinates of the sampling points were recorded using a handheld GPS. Three soil samples (0-20cm) were collected within 10m around each sampling point (mixed into one sample for testing). The plant species and planting structure of each sampling point were recorded (e.g., gentle slope sampling point 1: weeping willow (diameter at breast height 5-8cm) + Amorpha fruticosa (height 1.2-1.5m) + Zoysia japonica (coverage 80%)). Rainfall data (Yiai Lake meteorological station, data interval 1h) and water level data (Yiai Lake hydrological station, data interval 1d) for the past 3 years were collected. The rainfall intensity level was determined to be moderate (35mm / h, corresponding to the average intensity of moderate rain in the past 3 years), and the water level fluctuation level was determined to be moderate (0.8m, corresponding to the average annual fluctuation in the past 3 years).

[0050] Step 2, Parameter Extraction

[0051] First, a lookup table was constructed to determine the nitrogen and phosphorus reduction ratio and hydrological correction coefficient for riparian zone type, slope, and planting combination.

[0052] In this embodiment, based on the WOS core collection and CNKI database from 2000 to 2024, a systematic review of the rules for nitrogen and phosphorus interception technology in coastal zones was conducted through bibliometric analysis, as shown in Table 1 below.

[0053] Table 1: Lookup Table for Nitrogen and Phosphorus Reduction Ratio and Hydrological Correction Coefficients of Coastal Zone Type, Slope, and Planting Combination

[0054]

[0055] Specifically, the lookup table includes two types of coastal zones: slope type and nearshore water type.

[0056] In riparian zones with gentle slopes, planting / slope protection combinations include: plant slope protection (multilayered trees, shrubs, and grasses: weeping willow + Amorpha fruticosa + Zoysia japonica), gabion slope protection (coal ash filler + vegetation), eco-bag slope protection (ryegrass), and eco-concrete slope protection (with vegetation: Zoysia japonica); planting / slope protection combinations for medium slopes include: plant slope protection (single herb: Bermuda grass), and geocell slope protection (ryegrass + soil fill); planting / slope protection combinations for steep slopes include: eco-concrete slope protection (with vegetation: Bahia grass), and gabion slope protection (pebble filler + Bermuda grass).

[0057] In nearshore waters, planting / slope protection combinations in gentle water areas include: submerged plants (single Vallisneria natans community, 50% coverage), submerged plants (mixed community: Hydrilla verticillata + Vallisneria natans + Potamogeton malaianus, 50% coverage), ecological floating islands (mixed plants: Canna indica + Juncus effusus + Acorus calamus), and ecological floating islands (enhanced biofilm: Lythrum salicaria + Typha orientalis + Iris tectorum + bio-carbon fiber).

[0058] Based on the above planting / slope protection combination types, the corresponding total nitrogen (TN) reduction ratio, total phosphorus (TP) reduction ratio, rainfall intensity correction coefficient, and water level fluctuation correction coefficient are determined for subsequent reference.

[0059] Then, a DEM was constructed. Using measured elevation data from multiple sampling points, the UAV DSM was corrected using the georeferencing tool of geographic information software (using quadratic polynomial fitting, R²=0.98). Elevation interference from vegetation canopies such as weeping willow (canopy height 3~5m) and Amorpha fruticosa (canopy height 1.2~1.5m) was removed to obtain the DEM data. The DEM elevation error was verified by three ground control points to be ±0.08m, which meets the accuracy requirements.

[0060] Next, the slope ranges were divided. Based on the DEM, the slope was calculated using geographic information software. Combined with the classification standards in the lookup table of riparian zone type-slope-planting combination nitrogen and phosphorus reduction ratio and hydrological correction coefficient constructed in step 2, the following areas were divided: gentle slope area (≤1:2, corresponding to slope ≤50%, area 2.3km²), medium slope area (1:1.5~1:2, corresponding to slope 50%~66.7%, area 1.8km²), and steep slope area (≥1:1.5, corresponding to slope ≥66.7%, area 0.9km²).

[0061] Finally, type and plant structure identification was performed. NDVI was calculated using UAV imagery (formula: (B4-B3) / (B4+B3), where B4 is the near-infrared band and B3 is the red band). Areas with NDVI ≥ 0.3 were considered to have effective vegetation cover. Combining field photos and survey records, a multi-layered area of ​​trees, shrubs, and grasses (1.2 km², NDVI 0.6~0.8), a single herbaceous area (Bermudagrass) (1.5 km², NDVI 0.3~0.5), and an ecological concrete slope protection area (NDVI 0.2~0.3, Zoysia japonica coverage 30%) were identified. All riparian zones were of the riparian slope type (no near-shore water area).

[0062] Step 3: Calculation of nitrogen and phosphorus reduction ratio

[0063] Step 3.1, Benchmark Value Lookup: Based on the slope type, slope range, and planting structure combination, extract the benchmark value from the lookup table of nitrogen and phosphorus reduction ratio and hydrological correction coefficient for riparian zone type, slope, and planting combination in Step 2, as follows:

[0064] 1) Gentle slope + multi-layered tree, shrub and grass (weeping willow + purple locust + zoysia): Look up the corresponding entry in the table "bank slope type - gentle slope - vegetation slope protection (multi-layered tree, shrub and grass)", with TN benchmark value ≥30% and TP benchmark value ≥25%;

[0065] 2) Medium slope + single herbaceous plant (Bermudagrass): Refer to the entry "bank slope type - medium slope - vegetation slope protection (single herbaceous plant)" in the table, with TN baseline value of 15%~20% and TP baseline value of 12%~18%;

[0066] 3) Steep slope + ecological concrete slope protection (with Zoysia japonica): The corresponding entry in the lookup table is "bank slope type - steep slope - ecological concrete slope protection (with vegetation)" (the lookup table is "with Bahia grass". Since Zoysia japonica and Bahia grass are both herbaceous slope protection plants with similar reduction capacity, the benchmark value of this entry is used). The benchmark value of TN is 35%~40% and the benchmark value of TP is 55%~60%.

[0067] Step 3.2, Hydrological Correction: Based on the regional rainfall (35mm / h) and water level fluctuation (0.8m), extract the corresponding correction coefficients from the lookup table, as follows:

[0068] 1) Gentle slope + multi-layered trees, shrubs and grasses: medium rain correction factor 0.8 (look up the medium rain factor in the table "bank slope type - gentle slope - vegetation slope protection"), medium water level correction factor 0.9 (same as the water level factor in the entry);

[0069] 2) Medium slope + single herb (Bermudagrass): Medium rain correction factor 0.75 (look up the medium rain factor in the table "bank slope type - medium slope - plant slope protection"), medium water level correction factor 0.85 (same as the water level factor in the entry);

[0070] 3) Steep slope + ecological concrete slope protection: medium rain correction factor 0.8 (look up the medium rain factor in the table “bank slope type - steep slope - ecological concrete slope protection”), medium water level correction factor 0.8 (same as the water level factor in the entry).

[0071] Final reduction ratio calculation (based on baseline value × rainfall coefficient × water level coefficient):

[0072] 1) Gentle slope + multi-layered trees, shrubs and grasses: TN≥30%×0.8×0.9=21.6%, TP≥25%×0.8×0.9=18%;

[0073] 2) Medium-slope + single herb (Cynodon dactylon): TN (15%×0.75×0.85) ~ (20%×0.75×0.85) = 9.56%~12.75%, TP (12%×0.75×0.85) ~ (18%×0.75×0.85) = 7.65%~11.48%;

[0074] 3) Steep slope + ecological concrete slope protection: TN (35%×0.8×0.8)~(40%×0.8×0.8)=22.4%~25.6%, TP (55%×0.8×0.8)~(60%×0.8×0.8)=35.2%~38.4%.

[0075] It should be noted that in this embodiment, the calculation logic for the regional average reduction ratio is as follows: a weighted average based on the area of ​​each region, and the specific calculation formula is as follows:

[0076] (Area of ​​gentle slopes × average reduction rate of gentle slopes + area of ​​medium slopes × average reduction rate of medium slopes + area of ​​steep slopes × average reduction rate of steep slopes) / total area;

[0077] The average reduction rate is taken as the median of the baseline value range for each region (e.g., the TN baseline value for medium slope is 15%~20%, and the median is 17.5%). The calculation process is as follows:

[0078] Average TN percentage: (2.3×21.6%+1.8×11.16%+0.9×24%) / 5≈18.9%;

[0079] Average TP percentage: (2.3×18%+1.8×9.57%+0.9×36.8%) / 5≈21.7%.

[0080] The summary table of modifications to this embodiment is shown in Table 2 below.

[0081] Table 2: Summary Table of Revision Notes

[0082]

[0083] The correction coefficient rules for this embodiment are as follows:

[0084] Rainfall intensity is classified as "low (≤20mm / h), medium (20~50mm / h), high (≥50mm / h)", with a smaller correction coefficient for higher intensity; water level fluctuation is classified as "small (≤0.5m), medium (0.5~1.5m), large (≥1.5m)", with a smaller correction coefficient for larger fluctuation.

[0085] Step 4: Output of Evaluation Results

[0086] Finally, the nitrogen and phosphorus reduction ratios were spatially visualized using geographic information software to generate a spatial distribution map of the nitrogen and phosphorus reduction effects in the target coastal zone.

[0087] In this embodiment, a graded coloring method is adopted, which divides the reduction into four levels according to the reduction ratio: excellent (≥30%), good (20%~30%), medium (10%~20%), and poor (<10%). Statistical reports are output simultaneously to clarify the differences in reduction effect and key influencing factors in different areas. For example, the reduction effect in single herbaceous areas on medium slopes is poor, mainly due to the large slope and weak herbaceous interception capacity.

[0088] In this embodiment of the invention, an electronic device is also provided, comprising: one or more processors; a storage device storing one or more programs thereon; when the one or more programs are executed by the one or more processors, the one or more processors implement the method for evaluating the nitrogen and phosphorus reduction effect in the coastal zone described in the above embodiments.

[0089] In this embodiment of the invention, a computer-readable storage medium is also provided, on which a computer program is stored. When the program is executed by a processor, it implements the steps in the method for evaluating the nitrogen and phosphorus reduction effect in the coastal zone described in the above embodiments.

[0090] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for evaluating nitrogen and phosphorus reduction effect in a coastal zone, characterized by, Includes the following steps: Step 1, Data Acquisition: Use a low-altitude multispectral UAV to acquire multispectral image data and digital surface model of the target coastal zone; conduct ground measurements, sampling and surveys to obtain the actual slope, elevation and long-term hydrological dynamic data of the target coastal zone; Low-altitude multispectral UAV data acquisition was conducted on the target coastal zone to obtain image data and digital surface models including green, red, and near-infrared bands; Typical sampling points were set up in the target coastal zone to conduct ground field surveys and collect data, including soil samples, plant species and structures, and actual slope and elevation data of the sampling points. Simultaneously, long-term rainfall intensity data and water level fluctuation data in the region were recorded. Among them, rainfall intensity data were recorded continuously for at least one hydrological year, and water level fluctuation data covered the wet, normal, and dry seasons. Step 2, Core Parameter Extraction: Establish a lookup table for riparian zone type, slope, planting combination nitrogen and phosphorus reduction ratio, and hydrological correction coefficient; use ground-measured elevation data to correct the digital surface model, construct an accurate digital elevation model of the target riparian zone, determine the slope, divide the slope interval according to the lookup table, and combine multispectral image data, ground survey data, and digital surface model to identify the target riparian zone type and planting / slope protection combination structure; The table for finding nitrogen and phosphorus reduction ratios and hydrological correction coefficients for riparian zone type, slope, and planting combination is based on the existing WOS core collection and CNKI database. Through bibliometric analysis, it systematically sorts out the technical rules for nitrogen and phosphorus interception in riparian zones. It is used to determine the corresponding slope level, planting / slope protection combination type, total nitrogen reduction ratio, total phosphorus reduction ratio, rainfall intensity correction coefficient, and water level fluctuation correction coefficient according to the riparian zone type. The types of coastal zones include: slope type and nearshore water type; The slope grades include: gentle slope, medium slope, steep slope and gentle water area; In riparian zones, planting / slope protection combinations for gentle slopes include: plant slope protection, gabion slope protection, eco-bag slope protection, and eco-concrete slope protection; planting / slope protection combinations for medium slopes include: plant slope protection and geocell slope protection; and planting / slope protection combinations for steep slopes include: eco-concrete slope protection and gabion slope protection. In nearshore waters, planting / slope protection combinations in gentle water areas include: submerged plants and ecological floating islands; The extraction of the core parameters includes the following sub-steps: Step 2.1, Digital Elevation Model Construction: The digital surface model obtained by the UAV is corrected using ground-measured elevation data, and the interference of vegetation canopy is eliminated. For areas with multiple layers of trees, shrubs and grasses, the vegetation height is measured in the field to assist in the correction, so as to obtain an accurate digital elevation model of the target coastal zone. Step 2.2, Determination of slope and slope intervals: Based on the digital elevation model, geographic information software is used to obtain the slope distribution data of the target coastal zone, and slope intervals are divided in combination with the slope classification standard; Step 2.3, Identification of Coastal Zone Type and Plant Structure: Combining UAV multispectral imagery, ground survey photos, and digital surface models, the Normalized Difference Vegetation Index (NDVI) is used to help identify plant-covered areas. Combined with field survey records, the target coastal zone type and planting / slope protection combination structure are determined. Step 3, Calculation of nitrogen and phosphorus reduction ratio: Based on the core parameters, find the lookup table described in Step 2 to obtain the nitrogen and phosphorus reduction baseline values. Combine the hydrological dynamic data to extract the rainfall intensity correction coefficient and water level fluctuation correction coefficient, and calculate the final nitrogen and phosphorus reduction ratio. Step 4: Output of evaluation results: Visualize the nitrogen and phosphorus reduction ratio spatially, generate a spatial distribution map of the nitrogen and phosphorus reduction effect of the target coastal zone, and output a statistical report.

2. The method for evaluating the nitrogen and phosphorus reduction effect of the coastal zone according to claim 1, characterized in that, The slope level described in step 2: Gentle slope: The ratio between the vertical height and horizontal width of the slope is ≤1:2; Medium slope: The ratio between the vertical height and horizontal width of the slope is 1:1.5 to 1:2; Steep slopes: The ratio between the vertical height and horizontal width of the slope is ≥1:1.5; Calm waters: No obvious slope.

3. The method for evaluating the nitrogen and phosphorus reduction effect of the coastal zone according to claim 1, characterized in that, The Normalized Difference Vegetation Index (NDVI) mentioned in step 2.3 is calculated as follows: NDVI = (Near-infrared band - Red band) / (Near-infrared band + Red band); When NDVI ≥ 0.3, it is considered as effective vegetation cover.

4. The method for evaluating the nitrogen and phosphorus reduction effect of the coastal zone according to claim 1, characterized in that, Step 3, the calculation of the nitrogen and phosphorus reduction ratio, includes the following sub-steps: Step 3.1, Benchmark Value Lookup: Based on the target riparian zone type, slope range, and planting / slope protection combination structure extracted in Step 2, obtain the benchmark values ​​for total nitrogen reduction ratio and total phosphorus reduction ratio from the lookup table; Step 3.2, Hydrological Correction: Based on the rainfall intensity level and water level fluctuation level of the target riparian zone, extract the corresponding rainfall intensity correction coefficient and water level fluctuation correction coefficient from the lookup table, and calculate the final nitrogen and phosphorus reduction ratio, as shown in the following formula: Final reduction ratio = baseline value × rainfall intensity correction factor × water level fluctuation correction factor.

5. The method for evaluating the nitrogen and phosphorus reduction effect of the coastal zone according to claim 4, characterized in that, In step 3.2, if there are spatial differences in rainfall or water level within the target coastal zone, correction coefficients are extracted for each sub-region for hydrological correction.

6. The method for evaluating the nitrogen and phosphorus reduction effect in coastal zones according to claim 5, characterized in that, The spatial distribution map of nitrogen and phosphorus reduction effect described in step 4 uses a graded color scheme to classify the reduction effect into four levels: excellent, good, medium, and poor, according to the reduction ratio; the statistical report clarifies the differences in reduction effect and key influencing factors.

7. An electronic device, characterized in that, include: One or more processors; A storage device on which one or more programs are stored; When the one or more programs are executed by the one or more processors, the one or more processors implement the method for evaluating the nitrogen and phosphorus reduction effect in the coastal zone as described in any one of claims 1 to 6.

8. A computer-readable storage medium, characterized in that, It stores a computer program that, when executed by a processor, implements the steps in the method for evaluating the nitrogen and phosphorus reduction effect in the coastal zone as described in any one of claims 1 to 6.

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