Medium and small river health evaluation method based on ecological niche suitability analysis

Abstract

The invention provides a small and medium river health evaluation method based on ecological niche suitability analysis, and the method comprises the steps: screening a small and medium river index species set, constructing a small and medium river initial environment element set, extracting important ecological niche dimensions through a data dimension reduction technology, and constructing an ecological niche suitability curve of each dimension. The hyper-volume of the optimal ecological niche multi-dimensional hyper-rectangle in the ideal state is solved, an ecological niche suitability evaluation method based on the fitting degree of the actual and optimal ecological niche hyper-volume is provided, and a new medium and small river health evaluation system based on the indicator species ecological niche suitability is constructed; through the concept of quantifying the ecological niche, the new method for evaluating the health of the small and medium-sized rivers is provided from the perspective of ecology, and technical support is provided for better achieving the river and lake ecological environment recovery target.

Description

Technical Field

[0001] The present invention relates to the field of water ecological environment evaluation, and particularly to a health evaluation method for small and medium-sized rivers based on niche suitability analysis. Background Art

[0002] With the rapid development of modern social economy and technology, the explosive growth of population and the continuous improvement of material needs have caused the plundering development and utilization of water resources by humans. The over-exploitation, waste, and water pollution of water resources have damaged the "immune system" of river and lake ecosystems, making it impossible for river and lake ecosystems to restore water ecological health through self-regulation, resulting in problems such as water pollution, deterioration of hydrological conditions, damage to morphological structures, damage to species diversity, and degradation of river and lake functions.

[0003] At present, most river and lake health evaluation methods adopt multi-level and multi-index evaluation methods. The evaluation indicators involve multiple fields such as hydrology and water resources, river physical structure, water quality, and aquatic biological characteristics, and can comprehensively reflect the health status of rivers. However, when evaluating the health of small and medium-sized rivers, there are two problems: one is that the above methods require a large variety and quantity of data, while small and medium-sized rivers usually have relatively scarce data and may face the problem of insufficient data in actual operation; the other is that due to the small spatial scale of small and medium-sized rivers, there is a strong mutual feedback characteristic between the biological community and the environment in their ecosystems, and the current river health evaluation methods are relatively macroscopic and difficult to highlight the unique structure and connection characteristics of small and medium-sized river ecosystems.

[0004] Niche is a very important concept in modern ecology, which aims to characterize the needs of species for the external environment and reflects the interaction and mutual influence between species and the environment. The research and application of niche are one of the core contents of modern ecology. Historically, many scholars have tried to define niche, but due to the rich and diverse concept cores, it is difficult to apply in practice.

[0005] The present invention evaluates the niche suitability of species by quantifying the niche distribution in each dimension, solving the ideal niche hypervolume, and comparing the fitting degree of the actual niche hypervolume, and then evaluates the health status of small and medium-sized rivers. Summary of the Invention

[0006] The purpose of the present invention is to provide a health evaluation method for small and medium-sized rivers based on niche suitability analysis to evaluate the health status of small and medium-sized rivers in view of the deficiencies of the above-mentioned prior art.

[0007] To achieve the above object, the present invention adopts the following technical solutions: The present invention provides a health evaluation method for small and medium-sized rivers based on niche suitability analysis, including the following steps: S1. Screen the indicator species set of small and medium-sized rivers ; S2. Construct the initial environmental element set of small and medium-sized rivers ; S3. Extract the niche dimensions by data dimensionality reduction method; S4. Derive the niche suitability curves for each dimension; S5. Solve the hypervolume of the hyper-rectangle in the ideal state that is in the optimal niche ; S6. Analyze the fitting degree of the hypervolume of the niche in the actual and ideal situations, and evaluate the actual niche suitability; ; S7. Evaluate the health status of small and medium-sized rivers based on the niche suitability of each indicator species.

[0008] Furthermore, the specific content of S1 is as follows: According to the geographical location, climate conditions, species distribution, and composition of small and medium-sized rivers, select the indicator species that reflect the characteristics of small and medium-sized rivers , so as to form the indicator species set of small and medium-sized rivers for river health assessment : ; Among them, is the serial number of the indicator species; is the total number of indicator species for river health assessment.

[0009] Furthermore, the specific content of S2 is as follows: According to the characteristics of small and medium-sized rivers and the composition of the indicator species set, determine the environmental elements that affect the indicator species, and form the initial environmental element set of small and medium-sized rivers : ; ; ; ; ; Among them, is the initial physical element set; is the initial chemical element set; is the initial spatio-temporal distribution element set; is the initial water flow element set; is the substrate of small and medium-sized rivers; is the light; is the water temperature; is the small and medium-sized river value; is the dissolved oxygen content in water; is the total phosphorus in water is the river length position; is the water depth; is the time period; is the flow rate; is the flow velocity; is the water level fluctuation.

[0010] Furthermore, the specific content of S3 is as follows: Since the initial environmental factor set of small and medium-sized rivers contains a relatively large number of dimensions, some linearly correlated dimensions and dimensions with little impact on the indicator species set of small and medium-sized rivers need to be removed during actual calculations, so as to reduce the data occupancy space, improve the calculation speed, and reduce the spatial and temporal complexity of the algorithm. The initial environmental factor set of small and medium-sized rivers

[0011] is regarded as a matrix with rows and columns: ; Among them, is the number of environmental factor types, that is, the dimension; is the number of samples, and there are the number of environmental factor types ; is the vector composed of the th environmental factor sample.

[0012] Theoretically, the column vectors of each environmental factor in the matrix should be linearly independent, that is, the rank of the matrix is . However, during actual analysis, there is a correlation between some environmental factors, that is, the environmental column vectors can be represented by each other. Therefore, methods such as correlation analysis, principal component analysis, and eigenanalysis need to be used to remove redundant factors. Assuming that the remaining number of environmental factor types after removing linearly correlated factors is , then the environmental factor matrix after dimension reduction becomes , which is abbreviated as , where ; In addition, the influence degrees of the environmental factors in the environmental factor matrix after dimension reduction on the characteristics of the indicator species also vary. During calculation, environmental factors with a large influence degree should be retained, while environmental factors with a small influence degree should be removed. By using methods such as canonical correspondence analysis or redundancy analysis, the number of environmental factors is further reduced to dimensions, and finally a matrix that has a greater impact on each indicator species is extracted., abbreviated as , where . That is, after data dimensionality reduction, it is the number of dimensions used for niche analysis.

[0013] Furthermore, the specific content of S4 is as follows: Since each dimension in the matrix that has a greater impact on each indicator species after data dimensionality reduction is linearly independent, sample data can be used to deduce the niche suitability function of each dimension in the matrix that has a greater impact on each indicator species , and draw the niche suitability curve of each dimension. Polynomial fitting, generalized additive algorithm, and machine learning algorithm are used for calculation.

[0014] Furthermore, the specific content of S5 is as follows: Solve the optimal niche corresponding to the niche suitability function , the optimal niche is the theoretical solution value. In actual work, there is no unique optimal solution for the optimal niche , and from the data format requirements of subsequent similarity evaluation, the optimal niche is required to have a certain spatial extensibility in the dimensional Euclidean space, that is, the value range of the optimal niche of each dimension needs to be obtained. According to the actual work requirements, the corresponding allowable error value needs to be set, and combined with the niche suitability function and the optimal niche , solve the neighborhood value , and the calculation formula is: ; Due to the distribution form of the niche suitability function , the neighborhood value has two solutions, which are respectively denoted as the front neighborhood value and the back neighborhood value , and there is , then the value range of the optimal niche of each dimension is expressed as , and then the value range of the dimensional optimal niche is transformed into a dimensional hyper-rectangle in the Euclidean space, specifically: ; Then the dimensional hyper-volume calculation formula is: .

[0015] Further, S6 is specifically as follows: According to the actual environmental factor set , for the indicator species set in indicator species, the following method is used for calculation: That is: using the data dimensionality reduction method in S3, extract the actual important environmental factor matrix , and use the method in S5 to calculate the actual dimensional hyper-rectangle , then: ; Among them, is the value range of the th dimension of the actual niche, the lower boundary is represented by , and the upper boundary is represented by ; According to the calculation method in S5, deduce the dimensional hyper-volume of the actual niche as: .

[0016] Further, the optimal niche dimensional hyper-rectangle and the actual niche dimensional hyper-rectangle The positional relationship in space is divided into: separated, intersecting, optimal enclosing the actual, and actual enclosing the optimal. Then, the niche suitability index of each positional relationship is expressed as follows: ; Among them, is the total set of niche suitability indices in each positional relationship case; is the optimal niche dimensional hyper-rectangle and the actual niche dimensional hyper-rectangle When the spatial position is separated, the niche suitability index, referred to as the separated niche suitability index; is the optimal niche dimensional hyper-rectangle and the actual niche dimensional hyper-rectangle When the spatial position is intersecting, the niche suitability index, referred to as the intersecting niche suitability index; is the optimal niche dimensional hyper-rectangle completely enclosing the actual niche dimensional hyper-rectangle When, the niche suitability index, referred to as the opt-enclosing-act niche suitability index; For the actual niche d-dimensional hyper-rectangle completely contains the optimal niche d-dimensional hyper-rectangle when the niche suitability index, abbreviated as the actual-inclusive-optimal niche suitability index; If the optimal niche d-dimensional hyper-rectangle and the actual niche d-dimensional hyper-rectangle are spatially separated, that is, there is no intersection between the two, and the mathematical expression is , then the separated niche suitability index ; If the optimal niche d-dimensional hyper-rectangle and the actual niche d-dimensional hyper-rectangle are spatially intersecting, and the mathematical relationship expression is , then the niche suitability index is calculated by the ratio of the hyper-volume of the intersection part of the two hyper-rectangles to the hyper-volume of the union of the two hyper-rectangles, and the intersecting niche suitability index The calculation method is as follows: ; ; ; Among them, represents the posterior neighborhood value of the d-dimensional niche.

[0017] If the optimal niche d-dimensional hyper-rectangle contains the actual niche d-dimensional hyper-rectangle , that is, the optimal contains the actual, and the mathematical expression is , then the optimal-inclusive-actual niche suitability index ; If the actual niche d-dimensional hyper-rectangle completely contains the optimal niche d-dimensional hyper-rectangle , that is, the actual contains the optimal, and the mathematical expression is , then the actual-inclusive-optimal niche suitability index The calculation formula is: .

[0018] Furthermore, the specific content of S7 is: For the set of indicator species of small and medium-sized rivers in the For an indicator species, repeat S3 to S6, and calculate the niche suitability index of each indicator species respectively. The set thus formed is: ; According to the elements of the quantity, type, and rarity degree of each indicator species, use the algorithm averaging method, the analytic hierarchy process, and the entropy weight method to assign weights to each indicator species, and then calculate the comprehensive niche suitability index of the indicator species in small and medium-sized rivers , and the calculation formula is: ; Among them, is the matrix composed of the weights of each indicator species.

[0019] According to the obtained comprehensive habitat suitability index , combined with setting a suitable threshold , the health status of small and medium-sized rivers can be evaluated and analyzed.

[0020] The beneficial effects of the present invention are as follows: Currently, conventional river health assessment methods all evaluate from a single perspective of water environment or aquatic species. This time, by introducing the concept of niche, a river health assessment method based on the ecological perspective and focusing on the relationship between species and habitat is realized; at the same time, adopting the idea of combining numbers and shapes, the niche matrix is transformed into a hyper-rectangle in Euclidean space, converting complex algebraic problems into more intuitive geometric problems, and a similarity calculation method based on hyper-rectangle fitting degree is proposed, quantitatively analyzing the niche suitability method. It provides a new method for more accurately evaluating the health of rivers, and thus promotes the healthy recovery of rivers and lakes.

[0021] The beneficial effects of the present invention are as follows: Currently, conventional river health assessment methods all evaluate from a single perspective of water environment or aquatic species. This time, by introducing the concept of niche, a river health assessment method based on the ecological perspective and focusing on the relationship between species and habitat is realized; at the same time, adopting the idea of combining numbers and shapes, the niche matrix is transformed into a hyper-rectangle in Euclidean space, converting complex algebraic problems into more intuitive geometric problems, and a similarity calculation method based on hyper-rectangle fitting degree is proposed, quantitatively analyzing the niche suitability method. It provides a new method for more accurately evaluating the health of rivers, and thus promotes the healthy recovery of rivers and lakes. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a flowchart of a method for evaluating the health of small and medium-sized rivers based on niche suitability analysis; Figure 2 is an indicator species Regarding the environmental dimension niche fitness curve graph; Figure 3 is an indicator species Niche suitability curve for the water temperature of the environmental dimension; Figure 4 is an indicator species For the environmental dimension niche suitability curve; Figure 5 is an indicator species Niche suitability curve for the water temperature of the environmental dimension; Figure 6 is an indicator species of two-dimensional optimal and actual niche hyper-rectangle spatial position relationship diagram of water temperature; Figure 7 is an indicator species of two-dimensional optimal and actual niche hyper-rectangle spatial position relationship diagram of water temperature. Specific implementation manner

[0023] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0024] Please refer to Figure 1 , a method for evaluating the health of small and medium-sized rivers based on niche suitability analysis, comprising the following steps: S1. Screening the indicator species set of small and medium-sized rivers ; Select a certain small and medium-sized river as the research area for this embodiment. According to the geographical location, climate conditions, species distribution, and composition of the small and medium-sized river , two indicator species and reflecting the characteristics of the small and medium-sized river are screened out and , denoted as : ; S2. Constructing the initial environmental element set of small and medium-sized rivers ; S3. Extracting the niche dimensions by data dimensionality reduction method; S4. Deriving the niche suitability curves of each dimension; S5. Solving the hyper-volume of the dimensional hyper-rectangle in the optimal niche in the ideal state; S6. Analyzing the niches in the actual and ideal situations Dimensional super volume fit, to evaluate actual niche suitability; S7. Evaluate the health status of small and medium-sized rivers based on the niche suitability of each indicator species.

[0025] S2. Constructing the initial environmental element set of small and medium-sized rivers : According to small and medium rivers Characteristic and indicator species set composition, determine the indicator species and Environmental factors that have an impact, after analysis, affect indicator species and indicator species The main physical factors are light and water temperature The main chemical factors are and total nitrogen , the temporal and spatial distribution elements are mainly water depth , the main flow factor is flow velocity , thus forming small and medium-sized rivers Initial environment feature set .

[0026] S3. Extracting ecological niche dimensions using data dimensionality reduction method: First, small and medium rivers Initial environment feature set Treated as a 6-row matrix , according to the calculation, the rank of the matrix , which shows that the matrix The rank is not full, so the correlation analysis method is used to eliminate the linearly related environmental factors to ensure that the remaining environmental factors are linearly independent and mutually independent vectors. and water temperature , water depth and light , the correlation is high.

[0027] Therefore, water depth is excluded and light After removing the relevant factors, four linearly independent environmental factors are retained, which is consistent with the matrix analysis. The conclusion is consistent.

[0028] This example uses the canonical correspondence method to analyze the effects of various environmental factors on indicator species. and indicator species The results show that for indicator species and indicator species For example, total nitrogen and flow rate Both have relatively low influence degrees on niche characteristics. For the convenience of calculation, total nitrogen and flow velocity are excluded as two environmental factors, and only water temperature and are retained for subsequent niche analysis.

[0029] S4. Derive the niche suitability curves for each dimension: Use the generalized additive algorithm to derive the indicator species and the indicator species in the niche suitability functions for the two dimensions of water temperature and , and draw the corresponding niche suitability curves. Please refer to Figure 2 and Figure 3 ; S5. Solve the hypervolume of the hyper-rectangle in the optimal niche in the ideal state: From , the upper and lower neighborhood values of the two dimensions of the indicator species Figures 3 to 7 and the indicator species can be obtained, and based on this, the two-dimensional hyper-rectangle of the indicator species and the two-dimensional hyper-rectangle of the indicator species are obtained. Specifically: ; ; ; According to the hypervolume expression, calculate the two-dimensional hypervolume of the two-dimensional hyper-rectangle of the indicator species and the two-dimensional hyper-rectangle of the indicator species . Specifically in this embodiment, the hypervolume of the two-dimensional hyper-rectangle is the projection of the hyper-rectangle on the two-dimensional plane, that is, the area of the rectangle. The calculation formula is: ; ; S6. Analyze the dimensional hypervolume fitting degree of the niche in the actual and ideal situations, and evaluate the actual niche suitability; According to the actual environmental factor set , use the data dimensionality reduction method in S3 to extract the actual important environmental factor matrix , and use the method in S5 to calculate the actual niche of the indicator species dimensional hyper-rectangle and the actual niche of the indicator species dimensional hyper-rectangle , the expression is: ; ; Among them, is the indicator species the value range of the first dimension of the actual niche is [7.8, 8.3]; is the indicator species the water temperature of the second dimension of the actual niche the value range is [20.1, 22.5]; is the indicator species the first dimension of the actual niche the value range is [8.0, 8.4]; is the indicator species the water temperature of the second dimension of the actual niche the value range is [20.0, 23.6].

[0030] S5. According to the calculation method in S5, deduce the 2D hypervolume of the actual niche of the indicator species and the 2D hypervolume of the actual niche of the indicator species and the indicator species the 2D hypervolume of the actual niche is: ; ; From Figure 7 it can be seen that the hyperrectangles of the two-dimensional optimal and actual niches of the indicator species and the indicator species both show intersection and non-inclusion in spatial position, that is, it meets the discrimination condition. Therefore, the niche suitability of the indicator species and the indicator species is calculated as: ; ; S7. Evaluate the health status of small and medium-sized rivers based on the niche suitability of each indicator species; According to the two indicator species in the indicator species set of small and medium-sized rivers and the indicator species and the indicator species , construct a niche suitability set as: ; Use the arithmetic mean method to calculate the comprehensive habitat suitability index of the indicator species of small and medium-sized rivers ​, the calculation formula is: ; Set the health assessment threshold for small and medium-sized rivers as , which are 0 - 0.25, 0.25 - 0.5, 0.5 - 0.7, >0.75 respectively. The health conditions of the rivers are characterized as unhealthy, sub-healthy, healthy, and strongly healthy in turn. Based on this, the small and medium-sized rivers in this embodiment are unhealthy rivers.

[0031] The above embodiments only express the implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the invention patent of the present invention should be based on the appended claims.

Claims

1. A health assessment method for small and medium-sized rivers based on niche suitability analysis, characterized in that Including the following steps: S1. Screen the indicator species set of small and medium-sized rivers ; S2. Construct the initial environmental element set of small and medium-sized rivers ; S3. Extract the niche dimensions by the data reduction method; S4. Derive the niche suitability curves for each dimension; S5. Solve the hypervolume of the dimensional hyperrectangle in the optimal ecological niche; S6. Analyze the hypervolume fitness of the realized and ideal niches to evaluate the suitability of the realized niche; S7. Evaluate the health status of small and medium-sized rivers based on the niche suitability of each indicator species.

2. The health assessment method for small and medium-sized rivers based on niche suitability analysis according to claim 1, wherein, Specifically, S1 is as follows: According to the geographical location, climatic conditions, species distribution, and composition of small and medium-sized rivers, indicator species reflecting the characteristics of small and medium-sized rivers are selected , thus forming an indicator species set for small and medium-sized rivers used in river health assessment : ； Among them, is the serial number of the indicator species; is the total number of indicator species for river health assessment.

3. The health assessment method for small and medium-sized rivers based on niche suitability analysis according to claim 2, wherein, Specifically, S2 is as follows: According to the characteristics of small and medium-sized rivers and the composition of the indicator species set, determine the environmental elements that affect the indicator species, and constitute the initial environmental element set of small and medium-sized rivers : ； ； ； ； ； Among them, is the initial set of physical elements; is the initial set of chemical elements; is the initial set of spatio-temporal distribution elements; is the initial set of water flow elements; is the sediment of small and medium-sized rivers; is the light; is the water temperature; is the small and medium-sized river value; is the dissolved oxygen content in the water body; is the total phosphorus in the water body; is the river length position; is the water depth; is the time period; is the flow rate; is the flow velocity; is the water level fluctuation.

4. The health assessment method for small and medium-sized rivers based on niche suitability analysis according to claim 3, wherein, Specifically, S3 is as follows: The initial environmental element set of small and medium-sized rivers is regarded as a row column matrix : ； Among them, is the number of environmental factor types, i.e., the dimension; is the number of samples, and there are the number of environmental factor types ; is the vector composed of the th environmental factor sample.

5. The health assessment method for small and medium-sized rivers based on niche suitability analysis according to claim 4, characterized in that, Specifically, S5 is as follows: Solve the niche suitability function for each dimension The corresponding optimal niche , and calculate the neighborhood value according to the set allowable error value , and the calculation formula is: The calculation formula is: ； Due to the distribution form of the niche suitability function , the neighborhood value has two solutions, which are respectively denoted as the front neighborhood value and the back neighborhood value . And there is , then the value range of the optimal niche in each dimension is expressed as . Furthermore, the value range of the -dimensional optimal niche is transformed into an -dimensional hyper-rectangle in the Euclidean space, specifically as follows: ； Then Hypervolume The calculation formula is as follows: 。 6. The health assessment method for small and medium-sized rivers based on niche suitability analysis according to claim 5, characterized in that, Specifically, S6 is as follows: According to the actual environmental factor set , using the data dimensionality reduction method in S3, extract the actual important environmental factor matrix , and use the method in S5 to calculate the actual dimensional hyper-rectangle , then: ； Among them, is the value range of the dimension of the actual niche. The lower boundary is represented by , and the upper boundary is represented by . According to the calculation method in S5, deduce the hypervolume of the n-dimensional realized niche as follows: 。 7. A health assessment method for small and medium-sized rivers based on niche suitability analysis according to claim 6, characterized in that Optimal niche D-dimensional hyper-rectangle and the actual niche D-dimensional hyper-rectangle The positional relationships in space are divided into: separated, intersecting, the optimal niche enclosing the actual niche, and the actual niche enclosing the optimal niche. The niche suitability indices for each positional relationship are expressed as follows: ； Among them, is the total set of niche suitability indices in various positional relationships; is the optimal niche d-dimensional hyper-rectangle and the actual niche d-dimensional hyper-rectangle The niche suitability index when the spatial positions are separated, abbreviated as the separated niche suitability index; is the optimal niche d-dimensional hyper-rectangle and the actual niche d-dimensional hyper-rectangle The niche suitability index when the spatial positions intersect, abbreviated as the intersecting niche suitability index; is the optimal niche d-dimensional hyper-rectangle completely contains the actual niche d-dimensional hyper-rectangle The niche suitability index at this time, abbreviated as the optimal containing actual niche suitability index; is the actual niche d-dimensional hyper-rectangle completely contains the optimal niche d-dimensional hyper-rectangle The niche suitability index at this time, abbreviated as the actual containing optimal niche suitability index; If the optimal niche d-dimensional hyper-rectangle and the actual niche d-dimensional hyper-rectangle are spatially separated, that is, there is no intersection between the two, and the mathematical expression is , then the fitness index of the separated niche ; If the optimal niche d-dimensional hyper-rectangle and the actual niche d'-dimensional hyper-rectangle intersect in space, the mathematical expression is ; then the niche suitability index is calculated by the ratio of the hyper-volume of the intersection of the two hyper-rectangles to the hyper-volume of the union of the two hyper-rectangles, and the intersection niche suitability index The calculation method is as follows: ； ； ； ； Among them, represents the posterior neighborhood value of the dimensional niche; If the optimal niche d-dimensional hyper-rectangle contains the actual niche d'-dimensional hyper-rectangle , that is, the optimal contains the actual. The mathematical expression is , then the suitability index of the optimal-covering-actual niche ; If the realized niche d-dimensional hyper-rectangle completely contains the optimal niche d-dimensional hyper-rectangle , that is, the realized niche contains the optimal niche, and the mathematical expression is , then the realized niche suitability index The calculation formula is: 。 8. The health assessment method for small and medium-sized rivers based on niche suitability analysis according to claim 7, characterized in that, Specifically, S7 is as follows: Indicator species set for small and medium-sized rivers in the species of indicator species, repeat S3 to S6, and calculate the niche suitability index of each indicator species respectively. The set thus formed is as follows: ； According to the elements of the quantity, species, and rarity of each indicator species, the algorithm averaging method, the analytic hierarchy process, and the entropy weight method are used to assign weights to each indicator species, and then the comprehensive niche suitability index of the indicator species in small and medium-sized rivers is calculated. , and the calculation formula is: ； Among them, is a matrix composed of the weights of each indicator species.

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