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

Abstract

The present invention discloses a lake ecological restoration method based on the coupling of mixed layer dynamics and nitrogen and phosphorus restriction, comprising the following steps: obtaining lake area, lake underwater topography undulation, lake water depth, lake water nutrient salt, lake latitude, and wind speed data; constructing a multi-parameter coupling model for calculating the mixed layer depth to determine the lake water depth type; constructing a mixed layer-water depth coupled nitrogen-phosphorus ratio dynamic model based on the lake water depth type; determining the lake nitrogen and phosphorus restriction dynamic thresholds based on the nitrogen and phosphorus ratio dynamic model to determine the lake nitrogen and phosphorus restriction type; forming a lake ecological restoration type matrix; and formulating a lake ecological restoration strategy. The present invention has the beneficial effects of being able to quickly and efficiently determine the lake water depth type and nitrogen and phosphorus restriction conditions, making up for the defects of unclear lake water mixing characteristics and eutrophication control factors before lake ecological environment restoration, and proposing targeted lake ecological restoration plans, which helps to solve the problem of poor lake eutrophication control results.

Description

Technical Field

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

[0002] Lake ecological restoration is crucial for improving water quality and controlling eutrophication. By restoring aquatic vegetation and regulating nutrients, ecosystem function can be enhanced and water resource security can be guaranteed. Ecological restoration also helps maintain biodiversity and improve lake landscapes. Taking appropriate restoration measures tailored to the characteristics of different lakes is key. However, traditional classification methods based on basin origin (tectonic lakes, barrier lakes, etc.) or mineralization (freshwater lakes, saline lakes) lack guidance for ecological restoration. Studies have found that water depth influences lake nutrient status. In shallow lakes, the water is in a mixed state, which increases nitrogen loss (denitrification) and reduces phosphorus loss (sedimentation). Hydrodynamic disturbances promote the release of phosphorus from sediments, ultimately leading to a decrease in the nitrogen-to-phosphorus mass ratio, making shallow lakes often nitrogen-limited. However, in deep lakes, only the mixed layer is generally active, reducing nitrogen loss and improving the efficiency of phosphorus removal by sedimentation, resulting in an increase in the nitrogen-to-phosphorus ratio and a predominantly phosphorus-limited state. As lake nutrient levels rise, the likelihood of nitrogen limitation increases, while phosphorus limitation decreases. In eutrophic lakes, dual nitrogen and phosphorus limitation is the primary manifestation. Before restoring a lake's ecological environment, determining whether it is shallow, deep, or transitional, and whether it is phosphorus-limited, nitrogen-limited, or both, will help develop targeted lake ecological restoration plans and provide theoretical guidance for precise lake management policies.

[0003] Currently, lake restoration efforts are focused solely on indicators like total phosphorus and total nitrogen to classify them as either eutrophic or oligotrophic. This fails to integrate hydrodynamic characteristics (such as the depth of the mixed layer) with the coupling mechanisms of nitrogen and phosphorus limitation, and ignores the impact of seasonal mixed layer variations on endogenous nitrogen and phosphorus release. This results in poorly targeted lake restoration plans, leading to the continued occurrence of cyanobacterial blooms 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 restrictions, which can quickly determine the lake water depth type and nitrogen and phosphorus restriction conditions, and make up for the defects of unclear lake water mixing characteristics and eutrophication control factors before lake ecological environment restoration.

[0005] To achieve the above objectives, 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 restriction, comprising the following steps:

[0006] Step S1: obtaining lake area, lake underwater topography relief, lake depth, lake water nutrient salt, lake latitude and wind speed data;

[0007] Step S2: Based on the lake area, lake underwater topography, lake depth, lake latitude and wind speed data obtained in step S1, a multi-parameter coupling model for calculating the mixed layer depth is constructed to determine the lake depth type;

[0008] Step S3: Based on the lake water nutrient data of step S1 and the lake water depth type of step S2, a dynamic model of nitrogen and phosphorus ratio coupled with mixed layer and water depth is constructed;

[0009] Step S4: determining the dynamic thresholds of nitrogen and phosphorus limitation of the lake based on the mixed layer-water depth coupled nitrogen and phosphorus ratio dynamic model constructed in step S3, and determining the nitrogen and phosphorus limitation type of the lake based on the dynamic thresholds of nitrogen and phosphorus limitation of the lake;

[0010] Step S5: forming a lake ecological restoration type matrix based on the coupling of the lake water depth type in step S2 and the lake nitrogen and phosphorus limitation type in step S4;

[0011] Step S6: Based on the lake ecological restoration type matrix formed in step S5, formulate corresponding lake ecological restoration strategies.

[0012] Furthermore, in step S1, lake area, lake underwater topography relief, lake depth, lake water nutrient salt, lake latitude and wind speed data are obtained, specifically:

[0013] In step S11, the lake area is imaged using a multispectral imager (MSI) to obtain a high-resolution remote sensing image. The improved normalized difference water index is used to automatically extract the lake surface water contour, as shown in formula (1):

[0014] (1);

[0015] Among them, MNDWI is the modified normalized difference water index, Green is the green band, and MIR is the mid-infrared band;

[0016] Water bodies are extracted from the modified normalized difference water index (MNDWI) image. Pixels whose critical points are greater than a threshold of 0 are extracted from the modified normalized difference water index (MNDWI) image. A water body extraction result map is obtained, and the lake area is automatically calculated using a geographic information system (GIS) platform.

[0017] In step S12, the lake underwater terrain relief is calculated by using a multi-beam bathymetry system combined with an autonomous underwater vehicle (AUV) to fill in blind spots and perform machine learning noise filtering to generate a 1m resolution digital elevation model (DEM) of the lake bottom, as shown in formula (2):

[0018] (2);

[0019] Where R is the lake underwater topography, ΔH max is the maximum height difference of the lake bottom, in meters, and A is the lake area, in square meters;

[0020] In step S13, the maximum water depth of the lake is obtained by the multi-beam bathymetry 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):

[0021] (3);

[0022] 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 lake's underwater terrain is divided, and Z i is the water depth value of the grid cell into which the underwater terrain of the i-th lake is divided, in meters, is the slope-corrected surface area of ​​the grid cells into which the underwater terrain of the i-th lake is divided, in square meters;

[0023] Step S14: lake water nutrient data including total phosphorus and total nitrogen;

[0024] Step S15, lake latitude data is obtained by calculating the geometric center coordinates of lake polygons extracted from remote sensing images;

[0025] Step S16, wind speed data, by setting anemometers in different areas of the lake, regularly recording wind speed data; adding up the regularly recorded wind speed data and dividing it by the number of wind speed data to obtain the average wind speed in the period.

[0026] Furthermore, in step S2, a multi-parameter coupling model is constructed to calculate the depth of the mixed layer and determine the lake water depth type; specifically:

[0027] Step S21, lake depth type refers to classifying lakes into shallow lakes (i.e., mixed layer depth > maximum lake depth), deep lakes (i.e., mixed layer depth < average lake depth), and transitional lakes (i.e., average lake depth ≤ mixed layer depth ≤ maximum lake depth) by comparing the relationship between the mixed layer depth and the maximum lake depth.

[0028] In step S22, the depth of the lake mixed layer is estimated based on the coupled parameters of the lake area, the lake underwater topography, the lake latitude, and the average wind speed, as shown in formula (4):

[0029] (4);

[0030] Among them, EPI represents the depth of the lake mixed layer, k1 is the dimensionless proportional coefficient between the depth of the lake mixed layer and the lake area, k2 is the dimensionless proportional coefficient between the lake latitude and the depth of the lake mixed layer; A represents the lake area, represents the latitude of the lake, W represents the average wind speed, and R represents the undulation of the underwater terrain of the lake.

[0031] Furthermore, in step S3, a dynamic model of nitrogen-phosphorus ratio coupled with mixed layer and water depth is constructed based on the lake water nutrient data of step S1 and the lake water depth type of step S2; specifically:

[0032] In step S31, a dynamic model of nitrogen-phosphorus ratio coupled with mixed layer and water depth is constructed by combining the total phosphorus and total nitrogen in the lake water, the depth of the mixed layer, the maximum water depth of the lake, and the average water depth of the lake, as shown in formula (5):

[0033] (5);

[0034] Among them, N:P 动态 represents the mass ratio of total nitrogen and total phosphorus correction, ρ(TN) and ρ(TP) represent the concentrations of total nitrogen and total phosphorus in lake water, respectively. represents the mixed layer-water depth coupling correction factor, α represents the shallow water amplification factor, α is 1.2, β represents the deep water suppression factor, β is 0.05, Z max Indicates the maximum 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;

[0035] Step S32, shallow lake, that is, EPI>Z max , >1, exponential term =0.999, mixed layer-water depth coupling correction factor = >1, amplify the total nitrogen and total phosphorus correction mass ratio N:P 动态 ;

[0036] Step S33, deep water lake, namely EPI <Z avg , <1, exponential term Attenuation, mixed layer-water depth coupling correction factor Equal to itself, the value is equal to 0.001, the mass ratio of total phosphorus correction N:P 动态 ;

[0037] Step S34, transitional lake Z avg ≤ EPI ≤ Z max , mixed layer-water depth coupling correction factor =1, retain the baseline threshold;

[0038] Among them, the benchmark threshold is the mixed layer-water depth coupling correction factor .

[0039] Furthermore, in step S4, based on the dynamic model of nitrogen-phosphorus ratio coupled with mixed layer and water depth constructed in step S3, the dynamic threshold of nitrogen and phosphorus limitation of the lake is determined, and the nitrogen and phosphorus limitation type of the lake is determined based on the dynamic threshold of nitrogen and phosphorus limitation of the lake; specifically:

[0040] In step S41, the dynamic threshold of nitrogen and phosphorus limitation in the lake is determined based on the mixed layer-water depth coupled nitrogen and phosphorus ratio dynamic model constructed in step S3 and the phytoplankton stoichiometry theory, as shown in formula (6):

[0041] (6);

[0042] In step S42, the nitrogen and phosphorus limitation type of the lake is determined based on formula (5) in step S31 and formula (6) in step S41, as shown in formula (7). The specific formula is:

[0043] (7).

[0044] Furthermore, 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 restriction type in step S4; specifically:

[0045] Based on the cross-combination of lake depth type in step S2 and lake nitrogen and phosphorus restriction type in step S4, a matrix of nine lake ecological restoration types is formed, specifically:

[0046] Nitrogen-limited shallow lakes: N:P 动态 <Nitrogen limiting threshold and EPI>Z max ;

[0047] Double-limited shallow lakes: nitrogen limitation threshold ≤ N:P 动态 Z max ;

[0048] Phosphorus-limited shallow lakes: N:P 动态 ≥P limit threshold and EPI>Z max ;

[0049] Nitrogen-limited transitional lakes: N:P 动态 < nitrogen limiting threshold and Z avg ≤EPI <Z max ;

[0050] Double-limit transition lake: nitrogen limitation threshold ≤ N:P 动态 <P limit threshold and Z avg≤EPI <Z max ;

[0051] Phosphorus-limited transitional lakes: N:P 动态 ≥P limit threshold and Z avg ≤EPI <Z max ;

[0052] Nitrogen-limited deep lakes: N:P 动态 < nitrogen limiting threshold and EPI <Z avg ;

[0053] Double-limited deepwater lakes: nitrogen limitation threshold ≤ N:P 动态 <P limit threshold and EPI <Z avg ;

[0054] Phosphorus-limited deep lakes: N:P 动态 ≥P limit threshold and EPI <Z avg .

[0055] The beneficial effects of the present invention are: (1) it can quickly and efficiently determine the lake water depth type and nitrogen and phosphorus limitation conditions, make up for the defects of unclear lake water mixing characteristics and eutrophication control factors before lake ecological environment restoration, and propose targeted lake ecological restoration plans, which helps to solve the problem of poor lake eutrophication control effects, improve the accuracy and objectivity of lake ecological environment restoration plans, and provide theoretical guidance for precise lake management policies.

[0056] (2) Based on the dynamic coupling mechanism of lake mixed layer depth and nitrogen-phosphorus ratio, a non-equal similarity measurement model is constructed to quantitatively analyze the impact of lake hydrodynamic characteristics on nutrient limitation types; for the matrix of nine 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

[0057] Figure 1 It is a structural schematic diagram of the present invention. DETAILED DESCRIPTION

[0058] 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 restriction, comprising the following steps:

[0059] Step S1: obtaining lake area, lake underwater topography relief, lake depth, lake water nutrient salt, lake latitude and wind speed data;

[0060] Step S2: Based on the lake area, lake underwater topography, lake depth, lake latitude and wind speed data obtained in step S1, a multi-parameter coupling model for calculating the mixed layer depth is constructed to determine the lake depth type;

[0061] Step S3: Based on the lake water nutrient data of step S1 and the lake water depth type of step S2, a dynamic model of nitrogen and phosphorus ratio coupled with mixed layer and water depth is constructed;

[0062] Step S4: determining the dynamic thresholds of nitrogen and phosphorus limitation of the lake based on the mixed layer-water depth coupled nitrogen and phosphorus ratio dynamic model constructed in step S3, and determining the nitrogen and phosphorus limitation type of the lake based on the dynamic thresholds of nitrogen and phosphorus limitation of the lake;

[0063] Step S5: forming a lake ecological restoration type matrix based on the coupling of the lake water depth type in step S2 and the lake nitrogen and phosphorus limitation type in step S4;

[0064] Step S6: Based on the lake ecological restoration type matrix formed in step S5, formulate corresponding lake ecological restoration strategies.

[0065] Furthermore, in step S1, lake area, lake underwater topography relief, lake depth, lake water nutrient salt, lake latitude and wind speed data are obtained, specifically:

[0066] In step S11, the lake area is imaged using a multispectral imager (MSI) to obtain a high-resolution remote sensing image. The improved normalized difference water index is used to automatically extract the lake surface water contour, as shown in formula (1):

[0067] (1);

[0068] Among them, MNDWI is the modified normalized difference water index, Green is the green band, and MIR is the mid-infrared band;

[0069] Water bodies are extracted from the modified normalized difference water index (MNDWI) image. Pixels whose critical points are greater than a threshold of 0 are extracted from the modified normalized difference water index (MNDWI) image. A water body extraction result map is obtained, and the lake area is automatically calculated using a geographic information system (GIS) platform.

[0070] In step S12, the lake underwater terrain relief is calculated by using a multi-beam bathymetry system combined with an autonomous underwater vehicle (AUV) to fill in blind spots and perform machine learning noise filtering to generate a 1m resolution digital elevation model (DEM) of the lake bottom, as shown in formula (2):

[0071] (2);

[0072] Where R is the lake underwater topography, ΔHmax is the maximum height difference of the lake bottom, in meters, and A is the lake area, in square meters;

[0073] In step S13, the maximum water depth of the lake is obtained by the multi-beam bathymetry 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):

[0074] (3);

[0075] 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 lake's underwater terrain is divided, and Z i is the water depth value of the grid cell into which the underwater terrain of the i-th lake is divided, in meters, is the slope-corrected surface area of ​​the grid cells into which the underwater terrain of the i-th lake is divided, in square meters;

[0076] Step S14: lake water nutrient data including total phosphorus and total nitrogen;

[0077] Step S15, lake latitude data is obtained by calculating the geometric center coordinates of lake polygons extracted from remote sensing images;

[0078] Step S16, wind speed data, by setting anemometers in different areas of the lake, regularly recording wind speed data; adding up the regularly recorded wind speed data and dividing it by the number of wind speed data to obtain the average wind speed in the period.

[0079] Furthermore, in step S2, a multi-parameter coupling model is constructed to calculate the depth of the mixed layer and determine the lake water depth type; specifically:

[0080] Step S21, lake depth type refers to classifying lakes into shallow lakes (i.e., mixed layer depth > maximum lake depth), deep lakes (i.e., mixed layer depth < average lake depth), and transitional lakes (i.e., average lake depth ≤ mixed layer depth ≤ maximum lake depth) by comparing the relationship between the mixed layer depth and the maximum lake depth.

[0081] In step S22, the depth of the lake mixed layer is estimated based on the coupled parameters of the lake area, the lake underwater topography, the lake latitude, and the average wind speed, as shown in formula (4):

[0082] (4);

[0083] Among them, EPI represents the depth of the mixed layer of the lake, k1 is the dimensionless proportional coefficient between the mixed layer depth and the lake area, k2 is the dimensionless proportional coefficient between the lake latitude and the mixed layer depth; A represents the lake area, represents the latitude of the lake, W represents the average wind speed, and R represents the undulation of the underwater terrain of the lake.

[0084] Furthermore, in step S3, a dynamic model of nitrogen-phosphorus ratio coupled with mixed layer and water depth is constructed based on the lake water nutrient data of step S1 and the lake water depth type of step S2; specifically:

[0085] In step S31, a dynamic model of nitrogen-phosphorus ratio coupled with mixed layer and water depth is constructed by combining the total phosphorus and total nitrogen in the lake water, the depth of the mixed layer, the maximum water depth of the lake, and the average water depth of the lake, as shown in formula (5):

[0086] (5);

[0087] Among them, N:P 动态 represents the mass ratio of total nitrogen and total phosphorus correction, ρ(TN) and ρ(TP) represent the concentrations of total nitrogen and total phosphorus in lake water, respectively. represents the mixed layer-water depth coupling correction factor, α represents the shallow water amplification factor, α is 1.2, β represents the deep water suppression factor, β is 0.05, Z max Indicates the maximum 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;

[0088] Step S32, shallow lake, that is, EPI>Z max , >1, exponential term , mixed layer-water depth coupling correction factor = >1, amplify the total nitrogen:total phosphorus correction mass ratio N:P 动态 ;

[0089] Step S33, deep water lake, namely EPI <Z avg , <1, exponential term Attenuation, mixed layer-water depth coupling correction factor Equal to itself, the value is equal to 0.001, the mass ratio of total phosphorus correction N:P 动态 ;

[0090] Step S34, transitional lake Z avg ≤ EPI ≤ Z max , mixed layer-water depth coupling correction factor , retain the baseline threshold;

[0091] Among them, the benchmark threshold is the mixed layer-water depth coupling correction factor .

[0092] Furthermore, in step S4, based on the dynamic model of nitrogen-phosphorus ratio coupled with mixed layer and water depth constructed in step S3, the dynamic threshold of nitrogen and phosphorus limitation of the lake is determined, and the nitrogen and phosphorus limitation type of the lake is determined based on the dynamic threshold of nitrogen and phosphorus limitation of the lake; specifically:

[0093] In step S41, the dynamic threshold of nitrogen and phosphorus limitation in the lake is determined based on the mixed layer-water depth coupled nitrogen and phosphorus ratio dynamic model constructed in step S3 and the phytoplankton stoichiometry theory, as shown in formula (6):

[0094] (6);

[0095] In step S42, the nitrogen and phosphorus limitation type of the lake is determined based on formula (5) in step S31 and formula (6) in step S41, as shown in formula (7). The specific formula is:

[0096] (7).

[0097] Furthermore, 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 restriction type in step S4; specifically:

[0098] Based on the cross-combination of lake depth type in step S2 and lake nitrogen and phosphorus restriction type in step S4, a matrix of nine lake ecological restoration types is formed, specifically:

[0099] Nitrogen-limited shallow lakes: N:P 动态 <Nitrogen limiting threshold and EPI>Z max , which is manifested by insufficient exogenous nitrogen input and suppressed endogenous phosphorus release;

[0100] Double-limited shallow lakes: nitrogen limitation threshold ≤ N:P 动态 Z max , which is manifested by strong mixing leading to nitrogen loss and phosphorus release coexisting;

[0101] Phosphorus-limited shallow lakes: N:P 动态 ≥P limit threshold and EPI>Z max , which is dominated by exogenous phosphorus input;

[0102] Nitrogen-limited transitional lakes: N:P 动态 < nitrogen limiting threshold and Z avg ≤EPI <Z max , showing seasonal denitrification dominance;

[0103] Double-limit transition lake: nitrogen limitation threshold ≤ N:P 动态 <P limit threshold and Z avg ≤EPI <Z max, which is characterized by alternation of mixing and stratification;

[0104] Phosphorus-limited transitional lakes: N:P 动态 ≥P limit threshold and Z avg ≤EPI <Z max , manifested as a short-term surge in sediment phosphorus flux;

[0105] Nitrogen-limited deep lakes: N:P 动态 < nitrogen limiting threshold and EPI <Z avg , which is manifested by stratification inhibiting endogenous release and insufficient exogenous nitrogen;

[0106] Double-limited deepwater lakes: nitrogen limitation threshold ≤ N:P 动态 <P limit threshold and EPI <Z avg , manifested as upwelling of deep phosphorus accumulation;

[0107] Phosphorus-limited deep lakes: N:P 动态 ≥P limit threshold and EPI <Z avg , which is manifested by continuous input of exogenous phosphorus.

[0108] Furthermore, in step S6, a corresponding lake ecological restoration strategy is formulated based on the lake ecological restoration type matrix formed in step S5; specifically:

[0109] Step S61: For shallow lakes, the ecological restoration strategy is as follows:

[0110] The nutrient limitation type is nitrogen. The ecological restoration strategy uses constructed wetland denitrification plus exogenous nitrogen interception. The key technical parameters are a wetland area of ​​15% or more and a hydraulic load of less than 0.3 cubic meters per square meter per day. The scientific basis is to compensate for denitrification losses and block the input of agricultural / wastewater nitrogen.

[0111] The nutrient limitation type is dual limitation, and the ecological restoration strategy adopts sediment passivation + submerged plant restoration. The key technical parameters are aluminum salt / lanthanum salt dosage of 50-80 grams / square meter and submerged plant coverage rate ≥40%. The scientific basis is to simultaneously inhibit the release of endogenous phosphorus and enhance nitrogen absorption capacity;

[0112] The type of nutrient limitation is phosphorus limitation. The ecological restoration strategy adopts ecological dredging + chemical phosphorus locking. The key technical parameters are dredging depth of 0.2-0.4 meters and lanthanum-modified bentonite of 3-5 kg / square meter. The scientific basis is to remove phosphorus-rich sediment and stabilize sediment phosphorus in the long term.

[0113] Step S62: For transitional lakes, the ecological restoration strategy is as follows:

[0114] The nutrient limitation type is nitrogen, and the ecological restoration strategy uses biofilm denitrification plus water level regulation. The key technical parameters are a biofilm carrier filling rate ≥ 30% and a water level fluctuation of ±0.3 meters / month. The scientific basis is that biofilm enhances denitrification and water level fluctuations inhibit sediment resuspension.

[0115] The nutrient limitation type is dual limitation, and the ecological restoration strategy adopts ecological floating beds + fish regulation. The key technical parameters are floating bed coverage ≥ 20% and silver carp and bighead carp density 40-60 kg / hectare. The scientific basis is that floating beds absorb nitrogen and phosphorus, and fish inhibit algae proliferation.

[0116] The type of nutrient limitation is phosphorus limitation. The ecological restoration strategy adopts artificial surge + nano-oxygen bubble oxygenation. The key technical parameters are surge frequency of 4-6 times / week and oxygen bubble generator DO>6 mg / L (DO is dissolved oxygen). The scientific basis is to enhance mixing to inhibit stratification and oxidize the reduced phosphorus at the sediment interface.

[0117] Step S63: For deep-water lakes, the ecological restoration strategy is as follows:

[0118] The nutrient limitation type is nitrogen limitation. The ecological restoration strategy adopts deep aeration + exogenous nitrogen interception. The key technical parameter is aeration depth. ( is the average water depth of the lake), the sewage treatment plant TN < 3 mg / L (TN is total nitrogen), the scientific basis is to destroy stratification to promote nitrogen volatilization and block external input;

[0119] The nutrient limitation type is dual limitation, and the ecological restoration strategy uses iron salt passivation + benthic bioremediation. The key technical parameters are ferrous sulfate dosage of 20-30 grams per square meter and snail density of 5-8 individuals per square meter. The scientific basis is that it fixes sediment phosphorus and benthic organisms promote nitrogen cycling.

[0120] The type of nutrient limitation is phosphorus limitation. The ecological restoration strategy adopts water source isolation + ecological water replenishment. The key technical parameters are isolation zone width ≥ 100 meters and water replenishment TN:TP>40 (TN:TP represents the ratio of total nitrogen and total phosphorus). The scientific basis is to reduce exogenous phosphorus input and dilute the phosphorus concentration.

[0121] The above description is a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications that do not depart from the disclosure of the present invention should be included in 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 restriction, characterized by: The following steps are involved: Step S1: obtaining lake area, lake underwater topography relief, lake depth, lake water nutrient salt, lake latitude and wind speed data; Step S2: Based on the lake area, lake underwater topography, lake depth, lake latitude and wind speed data obtained in step S1, a multi-parameter coupling model for calculating the mixed layer depth is constructed to determine the lake depth type; Step S3: Based on the lake water nutrient data from step S1 and the lake water depth type from step S2, a dynamic model of nitrogen-phosphorus ratio coupled with mixed layer and water depth is constructed; Step S4: determining the dynamic thresholds of nitrogen and phosphorus limitation of the lake based on the mixed layer-water depth coupled nitrogen and phosphorus ratio dynamic model constructed in step S3, and determining the nitrogen and phosphorus limitation type of the lake based on the dynamic thresholds of nitrogen and phosphorus limitation of the lake; Step S5: forming a lake ecological restoration type matrix based on the coupling of the lake water depth type in step S2 and the lake nitrogen and phosphorus limitation type in step S4; Step S6: formulating a corresponding lake ecological restoration strategy based on the lake ecological restoration type matrix formed in step S5; In step S2, a multi-parameter coupling model is constructed to calculate the depth of the mixed layer and determine the lake water depth type; specifically: Step S21, lake depth type refers to classifying lakes into shallow lakes (i.e., mixed layer depth > maximum lake depth), deep lakes (i.e., mixed layer depth < average lake depth), and transitional lakes (i.e., average lake depth ≤ mixed layer depth ≤ maximum lake depth) by comparing the relationship between the mixed layer depth and the maximum lake depth. In step S22, the depth of the lake mixed layer is estimated based on the coupled parameters of the lake area, the lake underwater topography, 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 the dimensionless proportional coefficient between the lake mixed layer depth and the lake area, k2 is the dimensionless proportional coefficient between the lake latitude and the lake mixed layer depth; A represents the lake area, represents the latitude of the lake, W represents the average wind speed, and R represents the undulation of the underwater topography of the lake; In step S3, a dynamic model of nitrogen-phosphorus ratio coupled with mixed layer and water depth is constructed based on the lake water nutrient data of step S1 and the lake water depth type of step S2. Specifically, In step S31, a dynamic model of nitrogen-phosphorus ratio coupled with mixed layer and water depth is constructed by combining the total phosphorus and total nitrogen in the lake water, the depth of the mixed layer, 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 represents the mass ratio of total nitrogen and total phosphorus correction, ρ(TN) and ρ(TP) represent the concentrations of total nitrogen and total phosphorus in lake water, respectively. represents the mixed layer-water depth coupling correction factor, α represents the shallow water amplification factor, α is 1.2, β represents the deep water suppression factor, β is 0.05, Z max Indicates the maximum 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 lake, that is, EPI>Z max , >1, exponential term , mixed layer-water depth coupling correction factor = >1, amplify the total nitrogen and total phosphorus correction mass ratio N:P 动态 ; Step S33, deep water lake, namely EPI <Z avg , <1, exponential term Attenuation, mixed layer-water depth coupling correction factor Equal to itself, the value is equal to 0.001, the mass ratio of total phosphorus correction N:P 动态 ; Step S34, transitional lake Z avg ≤ EPI ≤ Z max , mixed layer-water depth coupling correction factor =1, retain the baseline threshold; Among them, the benchmark threshold is the mixed layer-water depth coupling correction factor .

2. The lake ecological restoration method based on the coupling of mixed layer dynamics and nitrogen and phosphorus restriction according to claim 1 is characterized in that: In step S1, lake area, lake underwater topography relief, lake depth, lake water nutrient salt, lake latitude and wind speed data are obtained, specifically: In step S11, the lake area is imaged using a multispectral imager (MSI) to obtain a high-resolution remote sensing image. The improved normalized difference water index is used to automatically extract the lake surface water contour, as shown in formula (1): （1）； Among them, MNDWI is the modified normalized difference water index, Green is the green band, and MIR is the mid-infrared band; Water bodies are extracted from the modified normalized difference water index (MNDWI) image. Pixels whose critical points are greater than a threshold of 0 are extracted from the modified normalized difference water index (MNDWI) image. A water body extraction result map is obtained, and the lake area is automatically calculated using a geographic information system (GIS) platform. In step S12, the lake underwater terrain relief is calculated by using a multi-beam bathymetry system combined with an autonomous underwater vehicle (AUV) to fill in blind spots and perform machine learning noise filtering to generate a 1m resolution digital elevation model (DEM) of the lake bottom, as shown in formula (2): （2）； Where R is the lake underwater topography, ΔH max is the maximum height difference of the lake bottom, in meters, and A is the lake area, in square meters; In step S13, the maximum water depth of the lake is obtained by the multi-beam bathymetry 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)； 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 lake's underwater terrain is divided, and Z i is the water depth value of the grid cell into which the underwater terrain of the i-th lake is divided, in meters, is the slope-corrected surface area of ​​the grid cells into which the underwater terrain of the i-th lake is divided, in square meters; Step S14: lake water nutrient data including total phosphorus and total nitrogen; Step S15, lake latitude data is obtained by calculating the geometric center coordinates of lake polygons extracted from remote sensing images; Step S16, wind speed data, by setting anemometers in different areas of the lake, regularly recording wind speed data; adding up the regularly recorded wind speed data and dividing it by the number of wind speed data to obtain the average wind speed in the period.

3. The lake ecological restoration method based on the coupling of mixed layer dynamics and nitrogen and phosphorus restriction according to claim 2 is characterized in that: In step S4, the dynamic nitrogen and phosphorus ratio model of the mixed layer-water depth coupling constructed in step S3 is used to determine the dynamic threshold of nitrogen and phosphorus limitation in the lake, and the nitrogen and phosphorus limitation type of the lake is determined based on the dynamic threshold of nitrogen and phosphorus limitation in the lake; specifically, In step S41, the dynamic threshold of nitrogen and phosphorus limitation in the lake is determined based on the mixed layer-water depth coupled nitrogen and phosphorus ratio dynamic model constructed in step S3 and the phytoplankton stoichiometry theory, as shown in formula (6): （6）； In step S42, the nitrogen and phosphorus limitation type of the lake is determined based on formula (5) in step S31 and formula (6) in step S41, as shown in formula (7). The specific formula is: （7）。 4. The lake ecological restoration method based on the coupling of mixed layer dynamics and nitrogen and phosphorus restriction according to claim 3 is characterized in that: 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 restriction type in step S4; specifically: Based on the cross-combination of lake depth type in step S2 and lake nitrogen and phosphorus restriction type in step S4, a matrix of nine lake ecological restoration types is formed, specifically: Nitrogen-limited shallow lakes: N:P 动态 <Nitrogen limiting threshold and EPI>Z max ; Double-limited shallow lakes: nitrogen limitation threshold ≤ N:P 动态 Z max ; Phosphorus-limited shallow lakes: N:P 动态 ≥P limit threshold and EPI>Z max ; Nitrogen-limited transitional lakes: N:P 动态 < nitrogen limiting threshold and Z avg ≤EPI <Z max ; Double-limit transition lake: nitrogen limitation threshold ≤ N:P 动态 <P limit threshold and Z avg ≤EPI <Z max ; Phosphorus-limited transitional lakes: N:P 动态 ≥P limit threshold and Z avg ≤EPI <Z max ; Nitrogen-limited deep lakes: N:P 动态 < nitrogen limitation threshold and EPI <Z avg ; Double-limited deepwater lakes: nitrogen limitation threshold ≤ N:P 动态 <P limit threshold and EPI <Z avg ; Phosphorus-limited deep lakes: N:P 动态 ≥P limit threshold and EPI <Z avg .

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