A method for determining the suitable ecological water level range of flood-type lakes

Abstract

The present invention belongs to the technical field of lake water resource management and ecological protection and restoration, and relates to a method for determining a suitable ecological water level interval for a flooded lake, including: 1) determining the natural element index of the lake based on historical measured water level and terrain data; 2) establishing a remote sensing inversion model based on remote sensing satellite band parameters to calculate the physical and chemical indexes of the lake water body; 3) using the natural element index of the lake obtained in step 1) as a reference, combined with the physical and chemical indexes of the lake water body obtained in step 2) to determine the suitable ecological water level interval for the flooded lake. The present invention provides a method for determining the suitable ecological water level interval for a flooded lake that is simple and easy to implement, can dynamically characterize the suitable ecological water level of the lake, and can provide reliable technical support for lake ecological water level regulation and lake water resource management.

Description

Technical Field

[0001] The invention belongs to the technical field of lake water resource management and ecological protection and restoration, and relates to a method for determining an ecological water level, and in particular to a method for determining a suitable ecological water level interval for a flood-type lake. Background Art

[0002] The ecological water level of lakes is a key factor in the health of lake ecosystems, and has a direct or indirect impact on the amount of lake water, water quality, and the quality of the ecological environment in the watershed. However, with the development of human activities, the amount of water used for social economy is increasing, the water resources are in short supply, the lake water level continues to drop, the water quality deteriorates, and the lake ecosystem declines. For water-transmitting lakes, determining the appropriate ecological water level of the lake is of great significance for water resources management and solving the problem of lake ecological degradation.

[0003] At present, some scholars have studied the technology of determining the ecological water level of lakes. For example, the frequency analysis method based on the long series of measured water level data of lakes, the bio-space method to maintain the function of biological habitats, and the lake morphology method to maintain the function of lake morphology. However, the above methods have relatively single determination factors and are difficult to adjust dynamically. In particular, they do not fully consider the interactive relationship between water quality factors that have an important impact on lake ecosystems and lake water levels (volumes), and cannot provide a reference for the refined protection and restoration of lake ecosystems. Summary of the invention

[0004] In order to solve the above-mentioned technical problems existing in the background technology, the present invention provides a method for determining the suitable ecological water level interval of a flood-transit lake, which is simple and easy to implement, can dynamically characterize the suitable ecological water level of a lake, and can provide reliable technical support for lake ecological water level regulation and lake water resources management.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] A method for determining an appropriate ecological water level interval for a flood-type lake, characterized in that the method for determining an appropriate ecological water level interval for a flood-type lake comprises the following steps:

[0007] 1) Determine the natural element indicators of the lake based on historical measured water level and topographic data;

[0008] 2) Establish a remote sensing inversion model based on remote sensing satellite band parameters to calculate the physical and chemical indicators of lake water bodies;

[0009] 3) Using the lake natural element indicators obtained in step 1) as a reference and combining them with the lake water body physical and chemical indicators obtained in step 2) to determine the suitable ecological water level range for the flood-type lake.

[0010] Preferably, the natural element indicators of the lake in step 1) adopted in the present invention include the lowest ecological water level of the lake and the critical water level of volume change.

[0011] Preferably, the lake natural element index used in the present invention is determined by:

[0012] The minimum ecological water level of the lake is the water level with an empirical frequency of 90%;

[0013] The critical water level for volume change is the water level corresponding to the maximum volume change rate calculated from the relationship between the water level and the volume.

[0014] Preferably, the specific implementation of step 2) adopted in the present invention is:

[0015] 2.1) Determine the remote sensing satellite band parameters;

[0016] 2.2) Obtain lake satellite image data based on remote sensing satellite band parameters;

[0017] 2.3) Perform multiple linear regression on the results of step 2.2) to calculate the physical and chemical indicators of lake water.

[0018] Preferably, the remote sensing satellite band parameters in step 2) adopted in the present invention include blue light band blue, green light band green, red light band red, near infrared band nir, shortwave infrared band swir1 and shortwave infrared band swir2; the physical and chemical indicators of lake water include lake water transparency, lake water total nitrogen and lake water total phosphorus.

[0019] Preferably, the multivariate linear regression equation in step 2.3) used in the present invention is:

[0020] Transparency=-8.36blue+77.89green-61.57red-7.86nir-1.24swir 1 +13.59swir 2 +0.33

[0021] TN=21.55blue+36.68green-56.37red-2.47nir-26.97swir 1 -20.50 swir 2 +0.80

[0022] TP=4.98blue+5.91green-9.39red+0.06nir-2.05swir 1 +6.26swir 2 -0.06

[0023] in:

[0024] Transparency is the transparency of lake water, the unit is m;

[0025] TN is the total nitrogen in lake water, in mg / L;

[0026] TP is the total phosphorus in lake water, in mg / L;

[0027] blue is the blue light band of remote sensing satellites;

[0028] Green is the green light band of remote sensing satellites;

[0029] red is the red light band of the remote sensing satellite;

[0030] NIR is the near-infrared band of remote sensing satellites;

[0031] swir1 is the shortwave infrared band 1 of the remote sensing satellite;

[0032] swir2 is the shortwave infrared band 2 of the remote sensing satellite.

[0033] Preferably, the specific implementation method of step 3) adopted by the present invention is:

[0034] 3.1) Calculating the comprehensive evaluation index of lake water quality according to the physical and chemical indicators of lake water calculated in step 2);

[0035] 3.2) grading the lake water quality comprehensive evaluation index calculated in step 3.1), and determining the lake water level interval based on the lake water quality comprehensive evaluation index according to the graded lake water quality comprehensive evaluation index;

[0036] 3.3) The lake water level range based on the comprehensive evaluation index of lake water quality obtained in step 3.2) is combined with the lake natural element index determined in step 1) to determine the suitable ecological water level range of the flood-type lake.

[0037] Preferably, the specific implementation method of step 3.1) adopted by the present invention is:

[0038] 3.1.1) normalizing the lake water body physical and chemical indicators calculated in step 2) to obtain normalized values;

[0039] 3.1.2) Calculate the comprehensive evaluation index of lake water quality according to the normalized value obtained in step 3.1.1); the expression of the comprehensive evaluation index of lake water quality is:

[0040]

[0041] in:

[0042] I is the comprehensive evaluation index of lake water quality;

[0043] i T is the normalized value of lake water transparency;

[0044] i TN is the normalized value of total nitrogen in lake water;

[0045] i TP is the normalized value of total phosphorus in lake water;

[0046] in:

[0047] i T 、i TN or TP The expression is:

[0048]

[0049] in:

[0050] i n is the normalized value of the physical and chemical indicators of lake water;

[0051] i min It is the minimum value of the normalized value of the physical and chemical indicators of lake water;

[0052] i max It is the maximum value of the normalized values ​​of the physical and chemical indicators of lake water.

[0053] The specific implementation method of step 3.2) adopted by the present invention is:

[0054] 3.2.1) The comprehensive evaluation index of lake water quality is divided into five levels: excellent, good, medium, fair and poor;

[0055] 3.2.2) Use hydrological and remote sensing monitoring data to match the annual lake water quality comprehensive evaluation index with the lake water level;

[0056] 3.2.3) Analyze the corresponding relationship between the comprehensive evaluation index of lake water quality of different grades and the lake water level, and select the lake water level corresponding to the excellent grade corresponding to the comprehensive evaluation index as the lake water level range based on the comprehensive evaluation index of lake water quality.

[0057] Preferably, the specific implementation method of step 3.3) adopted by the present invention is:

[0058] The lowest ecological water level of the lake calculated in step 1) is used as the lake water level red line;

[0059] The suitable ecological water level interval of the lake is determined according to the key water level of volume change calculated in step 1) and the lake water level interval based on the comprehensive evaluation index of lake water quality calculated in step 3.2), and the specific implementation method of the determination is:

[0060] If the critical water level of volume change calculated in step 1) is within the lake water level interval based on the comprehensive evaluation index of lake water quality, then the suitable ecological water level interval of the lake is [the lake water level corresponding to the lower limit of the excellent comprehensive evaluation index of lake water quality, and the lake water level corresponding to the upper limit of the excellent comprehensive evaluation index of lake water quality];

[0061] If the critical water level of volume change calculated in step 1) is outside the lake water level interval based on the comprehensive evaluation index of lake water quality, then the suitable ecological water level interval of the lake is [the critical water level of volume change, the lake water level corresponding to the upper limit of the excellent comprehensive evaluation index of lake water quality], or the suitable ecological water level interval of the lake is [the lake water level corresponding to the lower limit of the excellent comprehensive evaluation index of lake water quality, the critical water level of volume change];

[0062] If the lower limit of the suitable ecological water level range of the lake obtained above is lower than the lake water level red line, then the lower limit of the suitable ecological water level range of the lake shall be the lake water level red line.

[0063] The advantages of the present invention are:

[0064] The method for determining the suitable ecological water level interval of a flood-type lake provided by the present invention includes: 1) determining the natural element index of the lake based on the historical measured water level and terrain data; 2) establishing a remote sensing inversion model based on the remote sensing satellite band parameters to calculate the physical and chemical indexes of the lake water body; 3) using the obtained natural element index of the lake as a reference, combined with the physical and chemical indexes of the lake water body, to determine the suitable ecological water level interval of the flood-type lake. The method for determining the suitable ecological water level interval of a flood-type lake provided by the present invention proposes a comprehensive evaluation index of lake water quality based on the water quality of the water body, and realizes the determination of the suitable ecological water level interval of the lake by combining the hydrological and topographic information of the lake; at the same time, the present invention uses remote sensing technology to analyze the water quality of the lake water body. Compared with traditional ecological surveys and water quality monitoring methods, remote sensing technology can provide a large amount of spatiotemporal data information, has strong continuity and real-time performance, and can predict the changes in the suitable ecological water level at low cost and adjust the strategy in time. The present invention integrates the natural elements of the lake and the physical and chemical properties of the water body as the basis for determining the ecological water level, and obtains the dynamic ecological water level interval of the lake taking into account the dual elements of water quantity and water quality. This reflects the demand of the lake ecosystem for water bodies and water areas, and also reflects the requirements for water quality, and can provide technical support for lake water resources management and ecological scheduling. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 It is the water level experience frequency curve diagram of Wuliangsuhai in the embodiment;

[0066] Figure 2 is a curve diagram of the lake volume change rate of Wuliangsuhai in the embodiment;

[0067] Figure 3 : is a lake water level-area relationship diagram of Wuliangsuhai Lake in the embodiment;

[0068] Figure 4 It is the remote sensing inversion of ecological indicators such as lake transparency, total nitrogen and total phosphorus of Wuliangsuhai Lake;

[0069] Figure 5 1 is a water quality evaluation index-water level relationship diagram of Wuliangsuhai Lake in the embodiment. DETAILED DESCRIPTION

[0070] The natural elements of lakes and the physical and chemical properties of lake waters are important factors affecting the ecological functions of lakes. Therefore, it is very necessary to jointly determine the suitable ecological water level range of lakes using the natural element indicators of lakes and the comprehensive water quality evaluation index based on the physical and chemical indicators of lake waters.

[0071] The present invention provides a method for determining a suitable ecological water level interval of a flood-type lake, which is applicable to determining a suitable ecological water level of a lake, and includes the following contents:

[0072] Step 1: Determine the natural element index of the lake using the historical measured water level and topographic data of the lake;

[0073] Among them, the natural element indicators of lakes include the lowest ecological water level of lakes and the key water level of volume change, which respectively characterize the impact of basin meteorology and hydrology and lake topography on lake ecology. The specific calculation contents of the natural element indicators of lakes are as follows:

[0074] For the lowest ecological water level of the lake, a long series of measured water levels were used for empirical frequency analysis, and the water level with an empirical frequency of 90% was selected as the lowest ecological water level of the lake;

[0075] For the critical water level of volume change, the lake water level-volume change rate is calculated based on the "water level-volume relationship", and the water level corresponding to the maximum volume change rate is taken as the critical water level of volume change.

[0076] Step 2: Based on the remote sensing satellite band parameters, including blue, green, red, near infrared (NIR), and short-wave infrared (SWIR1 and SWIR2), multiple linear regression remote sensing inversion is performed on the lake transparency, total nitrogen, total phosphorus and other physical and chemical indicators; among them, SWIR1 is usually used to detect water content, soil type, mineral and rock type, etc. The water content is related to the radiation reflectivity of the SWIR1 band, so the water content can be inferred from the SWIR1 band. SWIR2 has a higher degree of discrimination for objects with different chemical characteristics, so it has important applications in geological research.

[0077] Step 3, calculating the comprehensive evaluation index of lake water quality;

[0078] The physical and chemical indicators of lake water (transparency, total nitrogen, total phosphorus) were normalized and comprehensively rated to obtain the comprehensive evaluation index of lake water quality I as follows:

[0079]

[0080] Where i n ,i,i min and i max are the normalized value, initial value, minimum value and maximum value of a water quality indicator respectively; I is the comprehensive evaluation index of lake water quality, and the subscripts T, TN and TP refer to transparency, total nitrogen and total phosphorus respectively.

[0081] Step 4: Divide the comprehensive evaluation index into five levels: excellent (0.8-1.0), good (0.6-0.8), medium (0.4-0.6), general (0.2-0.4) and poor (0-0.2). Through hydrological and remote sensing monitoring data, the annual comprehensive evaluation index is matched with the lake water level one by one, and the corresponding relationship between the comprehensive evaluation index of lakes of different levels and the lake water level is analyzed. The excellent level corresponding to the comprehensive evaluation index, that is, the lake water level corresponding to the range of 0.8-1.0, is selected as the lake water level interval based on the comprehensive evaluation index of lake water quality.

[0082] Step 5, determine the suitable ecological water level range of the lake by combining the lowest ecological water level of the lake, the key water level of volume change and the lake water level range based on the comprehensive evaluation index of lake water quality. When the lake water level is lower than the lowest ecological water level of the lake for a long time, it often leads to the degradation of the lake ecosystem and even causes irreversible impacts. Therefore, the lowest ecological water level of the lake calculated in step 1 is used as the lake water level red line. The key water level of volume change is the abnormal mutation point of the lake volume, which is often accompanied by a series of important or urgent hydrological events. It is an important reference for whether the ecological water level range is reasonable. Therefore, if the critical water level for volume change calculated in step 1 is within the lake water level interval based on the comprehensive evaluation index of lake water quality, it means that the impact of the change of the critical water level on the change of water quality is within a reasonable range. The lake water level interval based on the comprehensive evaluation index of lake water quality is selected as the suitable ecological water level interval of the lake, that is, the ecological interval is [comprehensive evaluation index 0.8 corresponds to lake water level, comprehensive evaluation index 1.0 corresponds to lake water level]; if the critical water level for volume change calculated in step 1 is on the left (or right) side of the lake water level interval based on the comprehensive evaluation index of lake water quality, it means that the change of the critical water level may have an impact on the water quality of the lake. At this time, the impact of the critical water level on the suitable ecological water level interval of the lake should be considered. The suitable ecological water level interval of the lake is taken as [critical water level for volume change, lake water level corresponding to comprehensive evaluation index 1.0] (or [comprehensive evaluation index 0.8 corresponds to lake water level, critical water level for volume change]); if the lower limit of the above ecological interval is lower than the lake water level red line, the lower limit is the lake water level red line.

[0083] The technical solution provided by the present invention is described in detail below with reference to the accompanying drawings:

[0084] 1) Analysis of natural elements of lakes

[0085] This example analyzes the suitable ecological water level in the Wuliangsu Lake Basin based on the volume of the Wuliangsu Lake, water level changes, and ecological water replenishment process. Figure 1 ), the lake water level corresponding to the empirical frequency of 90% is taken as the lowest ecological water level, which is 1018.46m. At this time, the corresponding lake volume is 228 million m 3 Then, based on the water level-volume change rate analysis method, the volume of Wuliangsu Lake in the long time series was statistically analyzed, and the maximum value of the lake volume change rate was selected as the key water level of volume change ( Figure 2 ). Based on this method, it can be calculated that the critical water level of the volume change of Wuliangsu Lake is 1019.21m, and the corresponding suitable volume is 470 million m 3 , corresponding to a lake area of ​​312.05km 2 ( Figure 3 ).

[0086] 2) Remote sensing inversion of lake physical and chemical indicators

[0087] Based on Landsat satellite image data from 1990 to 2021, combined with water quality data from sampling points in the study area, six commonly used bands (red, green, blue, near infrared, shortwave infrared 1, and shortwave infrared 2) were used for multiple linear regression to estimate lake water transparency, total nitrogen, and total phosphorus. The regression equations corresponding to the three indicators were obtained as follows:

[0088] Transparency=-8.36blue+77.89green-61.57red-7.86nir-1.24swir 1 +13.59swir 2 +0.33(3)

[0089] TN=21.55blue+36.68green-56.37red-2.47nir-26.97swir 1 -20.50 swir 2 +0.80(4)

[0090] TP=4.98blue+5.91green-9.39red+0.06nir-2.05swir 1 +6.26swir 2 -0.06(5)

[0091] in:

[0092] Transparency is transparency, m;

[0093] TN is total nitrogen, mg / L;

[0094] TP is total phosphorus, mg / L.

[0095] R of transparency, total nitrogen and total phosphorus in the regression model 2 The values ​​are 0.886, 0.818, and 0.903, respectively, which have a certain degree of accuracy. Therefore, the model can be used for long-term water quality estimation. Figure 4The figure shows the spatiotemporal changes in lake transparency, total nitrogen and total phosphorus. As can be seen from the figure, from 1990 to 2005, the transparency of the lake water body decreased significantly, which is closely related to the increase in human activities. Since 2010, with the help of ecological water replenishment, the water quality of the lake has gradually improved, and the overall water quality has continued to improve. In addition, from 1990 to 2000, the transparency of the water body in the middle of the lake was significantly better than that in the north and south ends, but since 2010, the water quality in the middle and north of the lake has improved significantly, which may be due to the gradual increase in ecological water supply, further increase in water flow, and more frequent water changes. The overall total nitrogen concentration of the lake was relatively high around 2000, but it has dropped significantly by 2020. From the perspective of interannual spatial changes, total nitrogen tends to accumulate at the edge of the lake surface water area, especially at the inlet of several rivers on the west side of the lake, where the total nitrogen enrichment phenomenon is obvious. The changes in total phosphorus concentration in the lake are different from those in total nitrogen. From 2000 to 2015, the distribution of total phosphorus concentration showed an increasing trend, which may be related to the fertilization process of crops in the basin, but around 2020, the total phosphorus concentration in the lake began to gradually decline.

[0096] 3) Comprehensive evaluation of suitable ecological water level of lakes

[0097] Figure 5 In the data, the comprehensive evaluation index of lake water quality is graded and a corresponding relationship is established with the lake water level, reflecting the response between lake water quality and water level. As can be seen from the figure, the comprehensive evaluation index of lake water quality is positively correlated with the change of water level. As the lake water level rises, the water quality gradually improves. The years with a comprehensive evaluation index above 0.8 are 2013, 2016 and 2017, and the corresponding lake water level range based on the comprehensive evaluation index of lake water quality is 1019.16m-1019.23m. Combined with the lowest ecological water level (1018.46m) and the key water level of volume change (1019.21m) in the analysis results of the natural elements of the lake, it can be seen that the red line of the lake water level is 1018.46m, and the suitable ecological water level range of the lake is determined by the comprehensive evaluation index, which is 1019.16m-1019.23m.

Claims

1. A method for determining an appropriate ecological water level interval for a flood-type lake, characterized by: The method for determining the suitable ecological water level interval of the flood-type lake comprises the following steps: 1) Determine the natural element indicators of the lake based on historical measured water levels and topographic data; the natural element indicators of the lake include the lowest ecological water level of the lake and the key water level of volume change; The method for determining the natural element indicators of the lake is: The minimum ecological water level of the lake is the water level with an empirical frequency of 90%; The critical water level of volume change is the water level corresponding to the maximum volume change rate calculated from the relationship between water level and volume; 2) Establish a remote sensing inversion model based on remote sensing satellite band parameters to calculate the physical and chemical indicators of lake water bodies; The specific implementation method of step 2) is: 2.1) Determine the remote sensing satellite band parameters; 2.2) Obtain lake satellite image data based on remote sensing satellite band parameters; 2.3) Perform multiple linear regression on the results of step 2.2) to calculate the physical and chemical indicators of lake water; The physical and chemical indicators of lake water bodies include lake water transparency, lake water total nitrogen and lake water total phosphorus; 3) Using the natural element index of the lake obtained in step 1) as a reference and combining it with the physical and chemical index of the lake water body obtained in step 2) to determine the suitable ecological water level range of the flood-type lake; The specific implementation method of step 3) is: 3.1) Calculating the comprehensive evaluation index of lake water quality according to the physical and chemical indicators of lake water calculated in step 2); 3.2) grading the lake water quality comprehensive evaluation index calculated in step 3.1), and determining the lake water level interval based on the lake water quality comprehensive evaluation index according to the graded lake water quality comprehensive evaluation index; 3.3) The lake water level interval based on the comprehensive evaluation index of lake water quality obtained in step 3.2) is combined with the lake natural element index determined in step 1) to determine the suitable ecological water level interval of the overwater lake. Specifically, the lowest ecological water level of the lake calculated in step 1) is used as the lake water level red line; the suitable ecological water level interval of the lake is determined according to the key water level of volume change calculated in step 1) and the lake water level interval based on the comprehensive evaluation index of lake water quality calculated in step 3.2).

2. The method for determining the suitable ecological water level interval of a flood-type lake according to claim 1 is characterized by: The remote sensing satellite band parameters in step 2) include a blue light band blue, a green light band green, a red light band red, a near infrared band nir, a short wave infrared band swir1 and a short wave infrared band swir2.

3. The method for determining the suitable ecological water level interval of a flood-type lake according to claim 2 is characterized by: The multivariate linear regression equation in step 2.3) is: Transparency=-8.36blue+77.89green-61.57red-7.86nir-1.24swir1+13.59swir2+0.33 TN=21.55blue+36.68green-56.37red-2.47nir-26.97swir1-20.50swir2+0.80 TP=4.98blue+5.91green-9.39red+0.06nir-2.05swir1+6.26swir2-0.06 in: Transparency is the transparency of lake water, the unit is m; TN is the total nitrogen in lake water, in mg / L; TP is the total phosphorus in lake water, in mg / L; blue is the blue light band of remote sensing satellites; Green is the green light band of remote sensing satellites; red is the red light band of the remote sensing satellite; NIR is the near-infrared band of remote sensing satellites; swir1 is the shortwave infrared band 1 of the remote sensing satellite; swir2 is the shortwave infrared band 2 of the remote sensing satellite.

4. The method for determining the suitable ecological water level interval of a flood-type lake according to claim 3 is characterized by: The specific implementation method of step 3.1) is: 3.1.1) normalizing the lake water body physical and chemical indicators calculated in step 2) to obtain normalized values; 3.1.2) Calculate the comprehensive evaluation index of lake water quality according to the normalized value obtained in step 3.1.1); the expression of the comprehensive evaluation index of lake water quality is: in: I is the comprehensive evaluation index of lake water quality; i T is the normalized value of lake water transparency; i TN is the normalized value of total nitrogen in lake water; i TP is the normalized value of total phosphorus in lake water; in: i T 、i TN or TP The expression is: in: i n is the normalized value of the physical and chemical indicators of lake water; i min It is the minimum value of the normalized value of the physical and chemical indicators of lake water; i max It is the maximum value of the normalized values ​​of the physical and chemical indicators of lake water.

5. The method for determining the suitable ecological water level interval of a flood-type lake according to claim 4 is characterized in that: The specific implementation method of step 3.2) is: 3.2.1) The comprehensive evaluation index of lake water quality is divided into five levels: excellent, good, medium, fair and poor; 3.2.2) Use hydrological and remote sensing monitoring data to match the annual lake water quality comprehensive evaluation index with the lake water level; 3.2.3) Analyze the corresponding relationship between the comprehensive evaluation index of lake water quality of different grades and the lake water level, and select the lake water level corresponding to the excellent grade corresponding to the comprehensive evaluation index as the lake water level range based on the comprehensive evaluation index of lake water quality.

6. The method for determining the suitable ecological water level interval of a flood-type lake according to claim 5, characterized in that: In step 3.3) The specific implementation method is determined as follows: If the critical water level of volume change calculated in step 1) is within the lake water level interval based on the comprehensive evaluation index of lake water quality, then the suitable ecological water level interval of the lake is [the lake water level corresponding to the lower limit of the excellent comprehensive evaluation index of lake water quality, and the lake water level corresponding to the upper limit of the excellent comprehensive evaluation index of lake water quality]; If the critical water level of volume change calculated in step 1) is outside the lake water level interval based on the comprehensive evaluation index of lake water quality, then the suitable ecological water level interval of the lake is [the critical water level of volume change, the lake water level corresponding to the upper limit of the excellent comprehensive evaluation index of lake water quality], or the suitable ecological water level interval of the lake is [the lake water level corresponding to the lower limit of the excellent comprehensive evaluation index of lake water quality, the critical water level of volume change]; If the lower limit of the suitable ecological water level range of the above-mentioned lake is lower than the lake water level red line, the lower limit of the suitable ecological water level range of the lake shall be the lake water level red line.

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