Lake ecological restoration method based on mixed layer dynamic and nitrogen and phosphorus limitation coupling

Abstract

The invention discloses a lake ecological restoration method based on mixed layer dynamic and nitrogen and phosphorus limitation coupling. The lake ecological restoration method comprises the following steps: acquiring lake area, lake underwater topographic relief, lake water depth, lake water nutritive salt, lake latitude and wind speed data; constructing a multi-parameter coupling model for calculating the depth of the mixed layer, and judging the lake water depth type; constructing a mixed layer-water depth coupled nitrogen-phosphorus ratio dynamic model according to the lake water depth type; determining a lake nitrogen-phosphorus limitation dynamic threshold according to a nitrogen-phosphorus ratio dynamic model, and judging a lake nitrogen-phosphorus limitation type; forming a lake ecological restoration type matrix; and formulating a lake ecological restoration strategy. The method has the beneficial effects that the lake water depth type and the nitrogen and phosphorus limitation condition can be quickly determined, the defect that lake water mixing characteristics and eutrophication control elements are unknown before lake ecological environment restoration is made up, a lake ecological restoration scheme is put forward in a targeted mode, and the problem that the lake eutrophication treatment effect is poor is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of lake ecological environment restoration. Specifically, it relates to a lake ecological restoration method based on the coupling of mixed layer dynamics and nitrogen and phosphorus limitation. Background Art

[0002] Lake ecological restoration is crucial for improving water quality and controlling eutrophication. By restoring aquatic vegetation and regulating nutrients, the ecosystem function can be enhanced to ensure water resource security. Ecological restoration also helps to maintain biodiversity and improve the lake landscape. For different lakes, taking appropriate restoration measures is the key. However, the traditional classification methods based on lake basin origin (tectonic lakes, barrier lakes, etc.) or salinity (freshwater lakes, saltwater lakes) lack guiding significance for ecological restoration. Research has found that water depth affects the nutritional status of lakes. In shallow lakes, the lake water body is in a mixed state, nitrogen loss (denitrification) is enhanced, phosphorus loss (sedimentation) is weakened, and hydrodynamic disturbance promotes the release of phosphorus from sediments, ultimately leading to a decrease in the nitrogen-phosphorus mass ratio, making shallow lakes often show nitrogen limitation. However, in deep lakes, generally only the mixed layer of the lake is active, nitrogen loss is reduced, and the phosphorus sedimentation removal efficiency is improved, resulting in an increase in the nitrogen-phosphorus ratio, and the lake mainly shows phosphorus limitation. With the improvement of the lake nutritional level, the possibility of nitrogen limitation increases, while phosphorus limitation decreases, and in eutrophic lakes, it mainly shows nitrogen-phosphorus double limitation. Before carrying out ecological environment restoration of lakes, it is helpful to determine whether the lake belongs to a shallow, deep or transitional lake, and whether it is phosphorus limitation, nitrogen limitation or nitrogen-phosphorus double limitation, so as to formulate a targeted lake ecological environment restoration plan and provide theoretical guidance for precise lake governance.

[0003] At present, before carrying out ecological environment restoration of lakes, only the indicators such as total phosphorus and total nitrogen are used to divide poor / eutrophic lakes, without considering the coupling mechanism of hydrodynamic characteristics (such as the depth of the mixed layer) and nitrogen and phosphorus limitation, and ignoring the impact of seasonal changes in the mixed layer on the endogenous release of nitrogen and phosphorus. As a result, the formulated lake ecological restoration plan lacks pertinence, and blue-green algae blooms still occur in some restored lakes. Summary of the Invention

[0004] The purpose of the present invention is to provide a lake ecological restoration method based on the coupling of mixed layer dynamics and nitrogen and phosphorus limitation, which can quickly determine the water depth type and nitrogen and phosphorus limitation situation of the lake, and make up for the defects of unclear water body mixing characteristics and eutrophication control elements before lake ecological environment restoration.

[0005] In order to achieve the above purpose, the technical solution adopted by the present invention is: a lake ecological restoration method based on the coupling of mixed layer dynamics and nitrogen and phosphorus limitation, including the following steps: Step S1: Obtain data on lake area, underwater terrain undulation of the lake, lake water depth, nutrient salts in the lake water body, lake latitude, and wind speed; Step S2: Based on the lake area, lake underwater terrain undulation, lake water depth, lake latitude, and wind speed data obtained in Step S1, construct a multi-parameter coupling model for calculating the mixed layer depth, and determine the type of lake water depth; Step S3: Based on the lake water body nutrient data in Step S1 and the lake water depth type in Step S2, construct a dynamic model of nitrogen-phosphorus ratio coupling the mixed layer and water depth; Step S4: Based on the dynamic model of nitrogen-phosphorus ratio coupling the mixed layer and water depth constructed in Step S3, determine the dynamic threshold of lake nitrogen and phosphorus limitation, and determine the type of lake nitrogen and phosphorus limitation based on the dynamic threshold of lake nitrogen and phosphorus limitation; Step S5: Based on the coupling of the lake water depth type in Step S2 and the lake nitrogen and phosphorus limitation type in Step S4, form a lake ecological restoration type matrix; Step S6: Based on the lake ecological restoration type matrix formed in Step S5, formulate corresponding lake ecological restoration strategies.

[0006] Further, in Step S1, to obtain the lake area, lake underwater terrain undulation, lake water depth, lake water body nutrients, lake latitude, and wind speed data, specifically: Step S11, for the lake area, obtain high-resolution remote sensing images through the multi-spectral imager MSI, and automatically extract the lake water body contour using the improved normalized difference water index, as shown in formula (1): (1); Where MNDWI is the improved normalized difference water index, Green is the green light band, and MIR is the mid-infrared band; Extract the water body in the improved normalized difference water index MNDWI image, extract the pixels with the pixel value critical point in the improved normalized difference water index MNDWI image greater than the threshold 0, obtain the water body extraction result map, and automatically calculate the lake area through the geographic information system GIS platform; Step S12, for the lake underwater terrain undulation, generate a 1m resolution digital elevation model DEM of the lake bottom through the multi-beam sounding system combined with machine learning noise filtering for blind area filling of the autonomous underwater vehicle AUV, and calculate the lake underwater terrain undulation, as shown in formula (2): (2); Where R is the lake underwater terrain undulation, ΔH max is the maximum elevation difference at the lake bottom, in meters, and A is the lake area, in square meters; Step S13, obtain the maximum lake water depth through the multi-beam sounding system, and obtain the average lake water depth using the area-weighted method corrected by the terrain slope, as shown in formula (3): (3); Among them, Z avg is the average water depth of the lake, in meters; n is the total number of grid cells into which the underwater terrain of the lake is divided; Z i is the water depth value of the i-th grid cell into which the underwater terrain of the lake is divided, in meters; is the surface area of the i-th grid cell into which the underwater terrain of the lake is divided after slope correction, in square meters; Step S14, the lake water body nutrient data includes total phosphorus and total nitrogen; Step S15, the lake latitude data is obtained by calculating the geometric center coordinates of the lake polygon extracted from the remote sensing image; Step S16, the wind speed data is obtained by setting anemometers in different areas of the lake and regularly recording the wind speed data; adding up the regularly recorded wind speed data and dividing by the number of wind speed data to obtain the average wind speed within the period.

[0007] Furthermore, in step S2, a multi-parameter coupling model for calculating the mixed layer depth is constructed to judge the lake water depth type; specifically: Step S21, the lake water depth type refers to classifying the lake into a shallow lake (i.e., the mixed layer depth > the maximum water depth of the lake), a deep lake (i.e., the mixed layer depth < the average water depth of the lake), and a transitional lake (i.e., the average water depth of the lake ≤ the mixed layer depth ≤ the maximum water depth of the lake) by comparing the relationship between the mixed layer depth and the maximum water depth of the lake; Step S22, the lake mixed layer depth is estimated by coupling parameters such as the lake area, the undulation degree of the lake underwater terrain, the lake latitude, and the average wind speed, as shown in formula (4): (4); Among them, EPI represents the lake mixed layer depth, k1 is the dimensionless proportional coefficient between the lake mixed layer depth and the lake area, and k2 is the dimensionless proportional coefficient between the lake latitude and the lake mixed layer depth; A represents the lake area, represents the lake latitude, W represents the average wind speed, and R represents the undulation degree of the lake underwater terrain.

[0008] Furthermore, in step S3, based on the lake water body nutrient data in step S1 and the lake water depth type in step S2, a dynamic model of the nitrogen-phosphorus ratio coupling the mixed layer and water depth is constructed; specifically: Step S31, a dynamic model of the nitrogen-phosphorus ratio coupling the mixed layer and water depth is constructed through the total phosphorus and total nitrogen in the lake water body, the lake mixed layer depth, the maximum water depth of the lake, and the average water depth of the lake, as shown in formula (5): (5); Among them, N:P 动态It represents the mass ratio of total nitrogen and total phosphorus after correction. ρ(TN) and ρ(TP) respectively represent the concentrations of total nitrogen and total phosphorus in the lake water body. It represents the mixing layer - water depth coupling correction factor. α represents the shallow water amplification coefficient, and α is 1.2. β represents the deep water inhibition coefficient, and β is 0.05. Z max represents the maximum water depth of the lake, Z avg represents the average water depth of the lake. exp represents the exponential function with the natural constant e as the base; Step S32, for shallow lakes, that is, EPI > Z max , > 1, the exponential term = 0.999, the mixing layer - water depth coupling correction factor = > 1, amplifying the mass ratio of total nitrogen and total phosphorus after correction N:P 动态 ; Step S33, for deep lakes, that is, EPI < Z avg , < 1, the exponential term attenuates, the mixing layer - water depth coupling correction factor is equal to itself, and the value is 0.001, compressing the mass ratio of total phosphorus after correction N:P 动态 ; Step S34, for transitional lakes, that is, Z avg ≤ EPI ≤ Z max , the mixing layer - water depth coupling correction factor = 1, retaining the reference threshold; Among them, the reference threshold is the mixing layer - water depth coupling correction factor .

[0009] Furthermore, in step S4, based on the mixing layer - water depth coupling nitrogen - phosphorus ratio dynamic model constructed in step S3, determine the dynamic threshold of lake nitrogen - phosphorus limitation, and determine the type of lake nitrogen - phosphorus limitation based on the dynamic threshold of lake nitrogen - phosphorus limitation; specifically: Step S41, determine the dynamic threshold of lake nitrogen - phosphorus limitation based on the mixing layer - water depth coupling nitrogen - phosphorus ratio dynamic model constructed in step S3 and the phytoplankton stoichiometry theory, as shown in formula (6): (6); Step S42, jointly determine the type of lake nitrogen - phosphorus limitation based on formula (5) in step S31 and formula (6) in step S41, as shown in formula (7), and the specific formula is: (7).

[0010] Further, in step S5, a lake ecological restoration type matrix is formed based on the coupling of the lake water depth type in step S2 and the lake nitrogen and phosphorus limitation type in step S4; specifically: Based on the cross-combination of the lake water depth type in step S2 and the lake nitrogen and phosphorus limitation type in step S4, a 9-category lake ecological restoration type matrix is formed, specifically: Nitrogen-limited shallow lakes: N:P 动态 <nitrogen limitation threshold and EPI>Z max ; Double-limited shallow lakes: nitrogen limitation threshold ≤ N:P 动态 <phosphorus limitation threshold and EPI>Z max ; Phosphorus-limited shallow lakes: N:P 动态 ≥ phosphorus limitation threshold and EPI>Z max ; Nitrogen-limited transitional lakes: N:P 动态 <nitrogen limitation threshold and Z avg ≤ EPI<Z max ; Double-limited transitional lakes: nitrogen limitation threshold ≤ N:P 动态 <phosphorus limitation threshold and Z avg ≤ EPI<Z max ; Phosphorus-limited transitional lakes: N:P 动态 ≥ phosphorus limitation threshold and Z avg ≤ EPI<Z max ; Nitrogen-limited deep lakes: N:P 动态 <nitrogen limitation threshold and EPI<Z avg ; Double-limited deep lakes: nitrogen limitation threshold ≤ N:P 动态 <phosphorus limitation threshold and EPI<Z avg ; Phosphorus-limited deep lakes: N:P 动态 ≥ phosphorus limitation threshold and EPI<Z avg 。

[0011] The beneficial effects of the present invention are: (1) It can quickly and accurately determine the lake water depth type and the nitrogen and phosphorus limitation situation, make up for the deficiencies in the lake water body mixing characteristics and eutrophication control elements before lake ecological environment restoration, and specifically propose lake ecological restoration plans, which helps to solve the problem of poor lake eutrophication treatment effect, improve the accuracy and objectivity of lake ecological environment restoration plans, and provide theoretical guidance for precise lake governance.

[0012] (2)Based on the dynamic coupling mechanism of lake mixed layer depth and nitrogen-phosphorus ratio, a non-equal-weight similarity measurement model is constructed to quantitatively analyze the impact of lake hydrodynamic characteristics on the type of nutrient limitation. For the matrix of 9 types of lake ecological types, a differentiated restoration technology chain is constructed to break the limitations of existing technology applications, improve the accuracy and objectivity of evaluation results, and provide a standardized and intelligent solution for lake eutrophication control, which has significant social, ecological and economic benefits. Brief Description of the Drawings

[0013] Figure 1 It is a schematic structural diagram of the present invention. Detailed Embodiments

[0014] The technical solution adopted by the present invention is: a lake ecological restoration method based on the coupling of mixed layer dynamics and nitrogen-phosphorus limitation, including the following steps: Step S1: Obtain data on lake area, underwater terrain undulation of the lake, lake water depth, lake water body nutrients, lake latitude and wind speed; Step S2: Based on the lake area, underwater terrain undulation of the lake, lake water depth, lake latitude and wind speed data obtained in step S1, construct a multi-parameter coupling model for calculating the mixed layer depth, and judge the type of lake water depth; Step S3: Based on the lake water body nutrient data in step S1 and the lake water depth type in step S2, construct a dynamic model of nitrogen-phosphorus ratio coupling of the mixed layer-water depth; Step S4: Based on the dynamic model of nitrogen-phosphorus ratio coupling of the mixed layer-water depth constructed in step S3, determine the dynamic threshold of lake nitrogen-phosphorus limitation, and judge the type of lake nitrogen-phosphorus limitation based on the dynamic threshold of lake nitrogen-phosphorus limitation; Step S5: Based on the coupling of the lake water depth type in step S2 and the lake nitrogen-phosphorus limitation type in step S4, form a matrix of lake ecological restoration types; Step S6: Based on the matrix of lake ecological restoration types formed in step S5, formulate corresponding lake ecological restoration strategies.

[0015] Further, in step S1, obtaining data on lake area, underwater terrain undulation of the lake, lake water depth, lake water body nutrients, lake latitude and wind speed is specifically as follows: Step S11, for the lake area, high-resolution remote sensing images are obtained by a multi-spectral imager MSI, and the lake water body contour is automatically extracted by using an improved normalized difference water index, as shown in formula (1): (1); Among them, MNDWI is the improved normalized difference water index, Green is the green light band, and MIR is the mid-infrared band; Extract the water bodies in the improved Normalized Difference Water Index (MNDWI) image. Extract the pixels in the improved MNDWI image whose pixel values at the critical point are greater than the threshold of 0 to obtain the water body extraction result map, and automatically calculate the lake area through the Geographic Information System (GIS) platform; Step S12: For the undulation degree of the underwater terrain of the lake, combine the multi-beam sounding system with the machine learning noise filtering for filling the blind area of the Autonomous Underwater Vehicle (AUV) to generate a digital elevation model (DEM) with a resolution of 1 m at the bottom of the lake, and calculate the undulation degree of the underwater terrain of the lake as shown in formula (2): (2); where R is the undulation degree of the underwater terrain of the lake, and ΔH max is the maximum elevation difference at the bottom of the lake, in meters, and A is the lake area, in square meters; Step S13: The maximum water depth of the lake is obtained through the multi-beam sounding system, and the average water depth of the lake is obtained by the area-weighted method corrected by the terrain slope, as shown in formula (3): (3); where Z avg is the average water depth of the lake, in meters, n is the total number of grid cells into which the underwater terrain of the lake is divided, Z i is the water depth value of the i-th grid cell into which the underwater terrain of the lake is divided, in meters, and is the surface area corrected by the slope of the i-th grid cell into which the underwater terrain of the lake is divided, in square meters; Step S14: The lake water body nutrient data includes total phosphorus and total nitrogen; Step S15: The lake latitude data is obtained by calculating the geometric center coordinates of the lake polygon extracted from the remote sensing image; Step S16: For the wind speed data, set anemometers in different areas of the lake and regularly record the wind speed data; add up the regularly recorded wind speed data and divide by the number of wind speed data to obtain the average wind speed during the period.

[0016] Furthermore, in step S2, construct a multi-parameter coupling model for calculating the mixed layer depth to determine the lake water depth type; specifically: Step S21: The lake water depth type refers to classifying the lake into a shallow lake type (i.e., the mixed layer depth > the maximum water depth of the lake), a deep lake type (i.e., the mixed layer depth < the average water depth of the lake), and a transitional lake type (i.e., the average water depth of the lake ≤ the mixed layer depth ≤ the maximum water depth of the lake) by comparing the relationship between the mixed layer depth and the maximum water depth of the lake; Step S22: The lake mixed layer depth is estimated based on the coupling of parameters such as the lake area, the undulation degree of the underwater terrain of the lake, the lake latitude, and the average wind speed, as shown in formula (4): (4); Among them, EPI represents the depth of the lake mixed layer, k1 is a dimensionless proportionality coefficient between the depth of the mixed layer and the lake area, and k2 is a dimensionless proportionality coefficient between the lake latitude and the depth of the mixed layer; A represents the lake area, represents the lake latitude, W represents the average wind speed, and R represents the undulation degree of the underwater terrain of the lake.

[0017] Furthermore, in step S3, based on the lake water body nutrient data in step S1 and the lake water depth type in step S2, a dynamic model of the nitrogen-phosphorus ratio coupling the mixed layer and water depth is constructed; specifically: Step S31, a dynamic model of the nitrogen-phosphorus ratio coupling the mixed layer and water depth is constructed through the total phosphorus and total nitrogen in the lake water body, the depth of the lake mixed layer, the maximum depth of the lake, and the average depth of the lake, as shown in formula (5): (5); Among them, N:P 动态 represents the corrected mass ratio of total nitrogen to total phosphorus, ρ(TN) and ρ(TP) respectively represent the concentrations of total nitrogen and total phosphorus in the lake water body, represents the coupling correction factor of the mixed layer-water depth, α represents the shallow water amplification coefficient, α is 1.2, β represents the deep water inhibition coefficient, β is 0.05, Z max represents the maximum depth of the lake, Z avg represents the average depth of the lake, and exp represents the exponential function with the natural constant e as the base; Step S32, for shallow lakes, that is, EPI > Z max , > 1, the exponential term , the coupling correction factor of the mixed layer-water depth = > 1, amplifying the corrected mass ratio of total nitrogen to total phosphorus N:P 动态 ; Step S33, for deep lakes, that is, EPI < Z avg , < 1, the exponential term decays, and the coupling correction factor of the mixed layer-water depth is equal to itself, with a value of 0.001, compressing the corrected mass ratio of total phosphorus N:P 动态 ; Step S34, for transitional lakes, that is, Z avg ≤ EPI ≤ Z max , the coupling correction factor of the mixed layer-water depth , retaining the reference threshold; Among them, the reference threshold is the coupling correction factor of the mixed layer-water depth .

[0018] Further, in step S4, based on the dynamic model of the nitrogen-phosphorus ratio coupling the mixed layer and water depth constructed in step S3, determine the dynamic threshold of lake nitrogen and phosphorus limitation, and determine the type of lake nitrogen and phosphorus limitation based on the dynamic threshold of lake nitrogen and phosphorus limitation; specifically: Step S41, determine the dynamic threshold of lake nitrogen and phosphorus limitation based on the dynamic model of the nitrogen-phosphorus ratio coupling the mixed layer and water depth constructed in step S3 and the phytoplankton stoichiometry theory, as shown in formula (6): (6); Step S42, jointly determine the type of lake nitrogen and phosphorus limitation based on formula (5) in step S31 and formula (6) in step S41, as shown in formula (7), and the specific formula is: (7).

[0019] Further, in step S5, based on the coupling of the lake water depth type in step S2 and the lake nitrogen and phosphorus limitation type in step S4, form a matrix of lake ecological restoration types; specifically: Based on the cross-combination of the lake water depth type in step S2 and the lake nitrogen and phosphorus limitation type in step S4, form a matrix of 9 types of lake ecological restoration types, specifically: Nitrogen-limited shallow lakes: N:P 动态 <nitrogen limitation threshold and EPI>Z max , showing insufficient exogenous nitrogen input and inhibited endogenous phosphorus release; Double-limited shallow lakes: nitrogen limitation threshold ≤ N:P 动态 <phosphorus limitation threshold and EPI>Z max , showing the coexistence of nitrogen loss and phosphorus release caused by strong mixing; Phosphorus-limited shallow lakes: N:P 动态 ≥ phosphorus limitation threshold and EPI>Z max , showing that exogenous phosphorus input is dominant; Nitrogen-limited transitional lakes: N:P 动态 <nitrogen limitation threshold and Z avg ≤ EPI<Z max , showing that seasonal denitrification is dominant; Double-limited transitional lakes: nitrogen limitation threshold ≤ N:P 动态 <phosphorus limitation threshold and Z avg ≤ EPI<Z max , showing the alternation of mixing and stratification; Phosphorus-limited transitional lakes: N:P 动态 ≥ phosphorus limitation threshold and Z avg ≤ EPI<Z max , showing a short-term surge in sediment phosphorus flux; Nitrogen-limited deep lakes: N:P动态 <Nitrogen limitation threshold and EPI < Z avg , which is manifested as layered inhibition of endogenous release and insufficient exogenous nitrogen; Doubly limited deep lakes: Nitrogen limitation threshold ≤ N:P 动态 <Phosphorus limitation threshold and EPI < Z avg , which is manifested as deep phosphorus accumulation and upwelling; Phosphorus-limited deep lakes: N:P 动态 ≥ Phosphorus limitation threshold and EPI < Z avg , which is manifested as continuous exogenous phosphorus input.

[0020] Furthermore, in step S6, according to the lake ecological restoration type matrix formed in step S5, corresponding lake ecological restoration strategies are formulated; specifically: Step S61, for shallow lakes, the ecological restoration strategy is specifically: When the nutrient limitation type is nitrogen limitation, the ecological restoration strategy adopts constructed wetland denitrification + exogenous nitrogen interception. The key technical parameters are that the wetland area ratio ≥ 15%, and the hydraulic load < 0.3 cubic meters per square meter per day. The scientific basis is to compensate for denitrification losses and block agricultural / sewage nitrogen input; When the nutrient limitation type is double limitation, the ecological restoration strategy adopts sediment passivation + submerged plant restoration. The key technical parameters are that the dosage of aluminum salt / lanthanum salt is 50 - 80 grams per square meter, and the coverage rate of submerged plants ≥ 40%. The scientific basis is to simultaneously inhibit endogenous phosphorus release and enhance nitrogen absorption capacity; When the nutrient limitation type is phosphorus limitation, the ecological restoration strategy adopts ecological dredging + chemical phosphorus locking. The key technical parameters are that the dredging depth is 0.2 - 0.4 meters, and the dosage of lanthanum-modified bentonite is 3 - 5 kilograms per square meter. The scientific basis is to remove phosphorus-rich bottom mud and stabilize sediment phosphorus in the long term.

[0021] Step S62, for transitional lakes, the ecological restoration strategy is specifically: When the nutrient limitation type is nitrogen limitation, the ecological restoration strategy adopts biofilm denitrification + water level regulation. The key technical parameters are that the filling rate of biofilm carriers ≥ 30%, and the water level fluctuation is ± 0.3 meters per month. The scientific basis is that biofilm enhances denitrification, and water level fluctuation inhibits sediment resuspension; When the nutrient limitation type is double limitation, the ecological restoration strategy adopts ecological floating beds + fish regulation. The key technical parameters are that the floating bed coverage rate ≥ 20%, and the density of silver carp and bighead carp is 40 - 60 kilograms per hectare. The scientific basis is that floating beds absorb nitrogen and phosphorus, and fish inhibit algal proliferation; When the nutrient limitation type is phosphorus limitation, the ecological restoration strategy adopts artificial surging + nano-oxygen bubble aeration. The key technical parameters are that the surging frequency is 4 - 6 times per week, and the DO of the oxygen bubble generator > 6 mg / L (DO is dissolved oxygen). The scientific basis is to enhance mixing and inhibit stratification, and oxidize the reduced phosphorus at the sediment interface.

[0022] Step S63. For deep lakes, the ecological restoration strategy is specifically as follows: When the nutrient limitation type is nitrogen limitation, the ecological restoration strategy is deep aeration + external nitrogen interception, and the key technical parameter is the aeration depth ( being the average water depth of the lake), the TN of the sewage treatment plant < 3 mg / L (TN is total nitrogen). The scientific basis is to destroy the stratification to promote nitrogen volatilization and block external input; When the nutrient limitation type is dual limitation, the ecological restoration strategy is ferric salt passivation + benthic biological restoration, and the key technical parameters are the dosage of ferrous sulfate 20 - 30 g / m² and the density of snails 5 - 8 individuals / m². The scientific basis is to fix sediment phosphorus and benthic organisms to promote nitrogen cycling; When the nutrient limitation type is phosphorus limitation, the ecological restoration strategy is water source isolation + ecological water replenishment, and the key technical parameters are the width of the isolation belt ≥ 100 m and the ratio of TN:TP in the replenished water > 40 (TN:TP represents the ratio of total nitrogen and total phosphorus). The scientific basis is to reduce external phosphorus input and dilute the phosphorus concentration.

[0023] The above are the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications that do not depart from the disclosure of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A lake ecological restoration method based on the coupling of mixed layer dynamics and nitrogen and phosphorus limitation, characterized in that: Including the following steps: Step S1: Obtain data on lake area, undulation degree of underwater terrain of the lake, lake water depth, lake water body nutrients, lake latitude, and wind speed; Step S2: Based on the data of lake area, undulation degree of underwater terrain of the lake, lake water depth, lake latitude, and wind speed obtained in Step S1, construct a multi-parameter coupling model for calculating the mixed layer depth, and judge the type of lake water depth; Step S3: Based on the lake water body nutrient data in Step S1 and the lake water depth type in Step S2, construct a dynamic model of nitrogen-phosphorus ratio coupling of the mixed layer-water depth; Step S4: Based on the dynamic model of nitrogen-phosphorus ratio coupling of the mixed layer-water depth constructed in Step S3, determine the dynamic threshold of lake nitrogen-phosphorus limitation, and judge the type of lake nitrogen-phosphorus limitation based on the dynamic threshold of lake nitrogen-phosphorus limitation; Step S5: Based on the coupling of the lake water depth type in Step S2 and the lake nitrogen-phosphorus limitation type in Step S4, form a matrix of lake ecological restoration types; Step S6: Based on the matrix of lake ecological restoration types formed in Step S5, formulate corresponding lake ecological restoration strategies.

2. The lake ecological restoration method based on the coupling of mixed layer dynamics and nitrogen and phosphorus limitation according to claim 1, characterized in that: In Step S1, to obtain data on lake area, undulation degree of underwater terrain of the lake, lake water depth, lake water body nutrients, lake latitude, and wind speed, specifically: Step S11, for the lake area, obtain high-resolution remote sensing images through the Multi-Spectral Imager (MSI), and automatically extract the water body contour of the lake surface using the improved Normalized Difference Water Index, as shown in formula (1): （1）； Among them, MNDWI is the improved Normalized Difference Water Index, Green is the green light band, and MIR is the mid-infrared band; Extract the water body in the improved Normalized Difference Water Index (MNDWI) image, extract the pixels with the pixel value critical point greater than the threshold 0 in the improved Normalized Difference Water Index (MNDWI) image to obtain the water body extraction result map, and automatically calculate the lake area through the Geographic Information System (GIS) platform; Step S12, for the undulation degree of underwater terrain of the lake, generate a digital elevation model (DEM) with a resolution of 1 m at the bottom of the lake through a multi-beam sounding system combined with machine learning noise filtering for filling the blind area of the Autonomous Underwater Vehicle (AUV), and calculate the undulation degree of underwater terrain of the lake, as shown in formula (2): （2）； Among them, R is the undulation degree of the underwater topography of the lake, and ΔH max is the maximum elevation difference of the lake bottom, with the unit of meter, and A is the area of the lake, with the unit of square meter; Step S13, obtain the maximum water depth of the lake through a multi-beam sounding system, and obtain the average water depth of the lake using the area-weighted method corrected by the terrain slope, as shown in formula (3): (3)； Among them, Z avg is the average water depth of the lake, in meters; n is the total number of grid cells into which the underwater topography of the lake is divided; Z i is the water depth value of the i-th grid cell into which the underwater topography of the lake is divided, in meters; is the surface area of the i-th grid cell into which the underwater topography of the lake is divided after slope correction, in square meters; Step S14, the lake water body nutrient data includes total phosphorus and total nitrogen; Step S15, obtain the lake latitude data by calculating the geometric center coordinates of the lake polygon extracted from the remote sensing image; Step S16, for the wind speed data, set anemometers in different areas of the lake and regularly record the wind speed data; add up the regularly recorded wind speed data and divide by the number of wind speed data to obtain the average wind speed within the period.

3. The lake ecological restoration method based on the coupling of the dynamics of the mixed layer and nitrogen and phosphorus limitation according to claim 2, wherein: In Step S2, construct a multi-parameter coupling model for calculating the mixed layer depth and judge the type of lake water depth; specifically: Step S21: The lake water depth type is determined by comparing the relationship between the lake mixed layer depth and the maximum water depth. Lakes are classified into shallow lakes (i.e., the mixed layer depth > the maximum water depth of the lake), deep lakes (i.e., the mixed layer depth < the average water depth of the lake), and transitional lakes (i.e., the average water depth of the lake ≤ the mixed layer depth ≤ the maximum water depth of the lake). Step S22: The lake mixed layer depth is estimated by coupling parameters such as lake area, underwater terrain undulation of the lake, lake latitude, and average wind speed, as shown in Equation (4): （4）； Among them, EPI represents the depth of the lake mixed layer, k1 is a dimensionless proportionality coefficient between the depth of the lake mixed layer and the lake area, and k2 is a dimensionless proportionality coefficient between the lake latitude and the depth of the lake mixed layer; A represents the lake area, represents the lake latitude, W represents the average wind speed, and R represents the undulation degree of the underwater topography of the lake.

4. The lake ecological restoration method based on the coupling of the dynamics of the mixed layer and nitrogen and phosphorus limitation according to claim 3, characterized in that: In Step S3, based on the lake water body nutrient data in Step S1 and the lake water depth type in Step S2, a dynamic model of the nitrogen-phosphorus ratio coupled with the mixed layer and water depth is constructed. Specifically: Step S31: A dynamic model of the nitrogen-phosphorus ratio coupled with the mixed layer and water depth is constructed by using the total phosphorus and total nitrogen in the lake water body, the lake mixed layer depth, the maximum water depth of the lake, and the average water depth of the lake, as shown in Equation (5): （5）； Among them, N:P 动态 represents the corrected mass ratio of total nitrogen to total phosphorus. ρ(TN) and ρ(TP) respectively represent the concentrations of total nitrogen and total phosphorus in the lake water body. represents the mixing layer - water depth coupling correction factor. α represents the shallow water amplification coefficient, α is 1.2, β represents the deep water inhibition coefficient, β is 0.05, Z max represents the maximum water depth of the lake, Z avg represents the average water depth of the lake, and exp represents the exponential function with the natural constant e as the base. Step S32, shallow lakes, i.e., EPI > Z max , > 1, exponential term , mixing layer - water depth coupling correction factor = > 1, amplifying the mass ratio N:P of total nitrogen and total phosphorus correction 动态 ; Step S33, deep lakes where EPI < Z avg , < 1, exponential term Decay, mixing layer - water depth coupling correction factor Equals itself, with a value of 0.001, mass ratio N:P for total phosphorus correction 动态 ; Step S34, transitional lake Z avg ≤ EPI ≤ Z max , mixing layer - water depth coupling correction factor = 1, retain the reference threshold; Among them, the baseline threshold is the nitrogen-phosphorus ratio coupled with the mixed layer and water depth correction factor. 。 5. The lake ecological restoration method based on the coupling of the dynamics of the mixed layer and nitrogen and phosphorus limitation according to claim 4, characterized in that: In Step S4, based on the dynamic model of the nitrogen-phosphorus ratio coupled with the mixed layer and water depth constructed in Step S3, the dynamic threshold of lake nitrogen and phosphorus limitation is determined, and the lake nitrogen and phosphorus limitation type is judged based on the dynamic threshold of lake nitrogen and phosphorus limitation. Specifically: Step S41: The dynamic threshold of lake nitrogen and phosphorus limitation is determined based on the dynamic model of the nitrogen-phosphorus ratio coupled with the mixed layer and water depth constructed in Step S3 and the phytoplankton stoichiometry theory, as shown in Equation (6): （6）； Step S42: The lake nitrogen and phosphorus limitation type is jointly determined based on Equation (5) in Step S31 and Equation (6) in Step S41, as shown in Equation (7). The specific formula is: （7）。 6. The lake ecological restoration method based on the coupling of mixed layer dynamics and nitrogen and phosphorus limitation according to claim 5, characterized in that: In Step S5, based on the coupling of the lake water depth type in Step S2 and the lake nitrogen and phosphorus limitation type in Step S4, a matrix of lake ecological restoration types is formed. Specifically: Based on the cross-combination of the lake water depth type in Step S2 and the lake nitrogen and phosphorus limitation type in Step S4, a matrix of 9 types of lake ecological restoration types is formed. Specifically: Nitrogen-limited shallow lakes: N:P 动态 <Nitrogen limitation threshold and EPI>Z max ; Doubly limited shallow lakes: nitrogen limitation threshold ≤ N:P 动态 <phosphorus limitation threshold and EPI > Z max ; Phosphorus-limited shallow lakes: N:P 动态 ≥ phosphorus limitation threshold and EPI > Z max ; Nitrogen-limited transitional lakes: N:P 动态 <Nitrogen limitation threshold and Z avg ≤EPI < Z max ; Dual-limitation transitional lakes: nitrogen limitation threshold ≤ N:P 动态 <phosphorus limitation threshold and Z avg ≤ EPI < Z max ; Phosphorus-limited transitional lake: N:P 动态 ≥ Phosphorus limitation threshold and Z avg ≤ EPI < Z max ; Nitrogen-limited deep lakes: N:P 动态 <Nitrogen limitation threshold and EPI < Z avg ; Doubly restricted deep lakes: nitrogen restriction threshold ≤ N:P 动态 <phosphorus restriction threshold and EPI < Z avg ; Phosphorus-limited deep lakes: N:P 动态 ≥ Phosphorus limitation threshold and EPI < Z avg .

Images