A method for determining a riverbed stability threshold based on benthic diversity

Abstract

The application discloses a riverbed stability threshold determination method based on benthic animal diversity, and belongs to the cross field of river ecological restoration and hydrological monitoring. The method first screens representative sections of four types of riverbed stability, measures the morphological data of each section at the starting and ending moments of the monitoring period, determines the riverbed erosion area and deposition area according to the morphological data, and calculates the riverbed stability index in combination with the riverbed width and the length of the monitoring period. After the wet season, benthic animal samples are collected, the species abundance S and the Shannon-Wiener diversity index are calculated, a S- nonlinear regression correlation model is constructed, and the critical value of the riverbed stability index corresponding to the mutation of the benthic animal diversity is determined through inflection point detection, that is, the riverbed stability threshold. The application quantitatively couples the physical erosion and deposition changes of the riverbed and the ecological response of the benthic animals, can provide quantitative basis for riverway restoration projects such as stepped deep pools and sand retaining dams, and is convenient to popularize and apply.

Description

Technical Field

[0001] This invention belongs to the field of river ecological restoration and hydrological monitoring technology, specifically relating to a method for determining riverbed stability thresholds based on benthic animal diversity. Background Technology

[0002] Rivers are the most active channels for the transport of matter and energy in terrestrial ecosystems, and the integrity of their physical structure is fundamental to maintaining aquatic biodiversity. However, under the dual impacts of climate change and intensive human activities, the degradation of river habitats is becoming increasingly prominent globally, and declining riverbed stability has become one of the important factors threatening the ecological health of rivers.

[0003] Influenced by the uplift of the Qinghai-Tibet Plateau, the mountainous areas of southwestern my country experience steep river gradients and severe riverbed erosion, leading to frequent geological disasters such as landslides and debris flows. The loose composition and weak erosion resistance of riverbed materials result in extremely poor riverbed stability in most rivers within the region. Rapid changes in riverbed erosion and deposition not only seriously threaten the lives and property of residents along the riverbanks but also destroy the habitats of benthic animals, leading to imbalances in the river ecosystem structure and a decline in biodiversity. Benthic animals, as a core component of the river ecosystem, directly reflect the ecological health of the river through their community structure and diversity, and are closely coupled with riverbed stability. Studies show that a stable riverbed provides benthic animals with relatively stable living space and sufficient food sources, while frequent erosion and deposition directly lead to benthic animal mortality, habitat destruction, and food shortages, thus restricting their population reproduction and maintenance.

[0004] Currently, riverbed stability assessment faces three main technical bottlenecks. First, assessment indicators are disconnected from ecological responses. Existing assessment methods largely rely on hydrodynamic parameters (such as flow velocity and gradient) or sediment parameters (such as median particle size). While these physical indicators reflect the mechanical properties of the riverbed against water flow, they do not fully consider the response characteristics of the ecosystem, making it difficult to accurately assess the actual ecological effects of changes in riverbed stability on the river ecosystem. Second, physical monitoring and ecological evaluation systems are fragmented. Riverbed scouring and deposition dynamic monitoring falls under the category of river dynamics, while benthic animal community surveys fall under the category of ecology. These two systems have long operated independently, lacking quantitative coupling techniques, leading to a widespread tendency in engineering projects to prioritize physical stability over ecological restoration. Third, there is a lack of standardized methods for determining ecological thresholds. Existing river management projects, lacking scientific guidance on stability thresholds, generally suffer from poor management effectiveness and low ecological restoration efficiency.

[0005] Therefore, it is urgent to establish a method for determining the riverbed stability threshold based on benthic animal diversity, which quantitatively couples ecological response with riverbed stability, thereby providing a scientific basis for river management in the mountainous areas of Southwest China, and has important theoretical and practical significance. Summary of the Invention

[0006] The purpose of this invention is to provide a method for determining the riverbed stability threshold based on benthic animal diversity. By constructing a correlation model between the riverbed stability index and benthic animal diversity, the method aims to accurately define the riverbed stability threshold for maintaining the ecological health of rivers, thereby providing a scientific and quantifiable decision-making basis for river stability assessment and ecological restoration projects.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for determining riverbed stability thresholds based on benthic animal diversity includes the following steps: S1. Select no fewer than four river sections within the target watershed that cover four types of riverbed stability: stable, relatively stable, relatively unstable, and unstable, and set a monitoring cycle of no less than one complete hydrological cycle. S2. Using a total station, at the beginning and end of the monitoring period, measure the horizontal distance and elevation data of each river section, and simultaneously collect basic hydrological parameters such as riverbed width, water depth, and flow rate to obtain information on changes in cross-sectional morphology. S3. Based on the cross-sectional morphological change information, determine the riverbed incision area and siltation area of ​​each river cross-section during the monitoring period; S4. Calculate the riverbed stability index of each river section based on the incision area, siltation area, riverbed width, and monitoring period. S5. Collect benthic animal samples at various river sections, identify and statistically analyze the species abundance and Shannon-Wiener diversity index of benthic animals; S6. Construct nonlinear regression correlation models for species abundance, Shannon-Wiener diversity index and riverbed stability index respectively. Determine the critical value of riverbed stability index corresponding to the mutation of species abundance and Shannon-Wiener diversity index by inflection point detection. The critical value is the riverbed stability threshold.

[0008] Furthermore, the monitoring period described in step S1 covers the high-water season, the normal-water season, and the low-water season, and the monitoring period lasts for one year.

[0009] Furthermore, in step S1, when screening river sections, the consistency of the basin's geological background, vegetation coverage, and degree of human activity disturbance is taken into account, and the interference of non-bed stability factors on benthic animal diversity is excluded.

[0010] Furthermore, in step S2, when measuring with a total station, the measuring points are evenly distributed along the left bank to the right bank of the cross-section. The spacing between measuring points on a conventional cross-section is no more than 2m, and the measurement error of each measuring point does not exceed ±0.01m. The spacing between measuring points on a cross-section with complex riverbed topography is adjusted to 1~1.5m.

[0011] Furthermore, in step S3, based on the horizontal distance and elevation data of the cross sections at two time points, the initial profile and final profile of each river section are drawn, and the area of ​​the initial profile and final profile of each river section is calculated respectively. By comparison, the incision area and siltation area within the monitoring period are determined.

[0012] Furthermore, the riverbed stability index mentioned in step S4 The calculation formula is:

[0013] in, The width of the riverbed, For the duration of the monitoring period, To monitor the riverbed incision area during the monitoring period, The area of ​​riverbed siltation during the monitoring period.

[0014] Furthermore, the riverbed stability index The dimension is year / meter, which represents the average time required for a unit area of ​​scour and deposition to occur in the cross-section of the riverbed under the condition of unit river width; The higher the value, the stronger the riverbed's ability to resist erosion and deposition, and the higher the physical stability of benthic animal habitats.

[0015] Furthermore, in step S5, benthic animal samples are collected 1-2 weeks after the end of the high-water season. Three to five sampling points are evenly distributed across each river cross-section, and samples are collected using a Petersen sampler. The sampling area at each sampling point is 0.0625 square meters. The sampling depth was 0-20 cm from the surface of the riverbed; the Shannon-Wiener diversity index was mentioned. The calculation formula is:

[0016] in, For the first The number of individuals of a species This represents the total number of benthic animals at this sampling point. For species abundance.

[0017] Furthermore, the specific process for inflection point detection in step S6 is as follows: Loess smoothing is applied to the scattered data to eliminate local fluctuations; the second derivative of the smoothed curve is calculated, and a threshold for the sign of the second derivative is set. Screen candidate inflection points; divide the data into two segments using the candidate inflection points as the boundary and perform linear regression on each segment. When the determination coefficients of the two regression segments are both greater than 0.85 and the slopes of the two segments are significantly different after t-test, the point is confirmed as an effective inflection point.

[0018] Furthermore, the inflection points corresponding to the correlation models between species abundance and riverbed stability index were obtained respectively. The inflection point corresponding to the correlation model between the value, Shannon-Wiener diversity index and riverbed stability index The arithmetic mean of the two inflection point values ​​is taken as the threshold for riverbed stability; if the relative difference between the two inflection point values ​​exceeds 20%, the threshold corresponding to the Shannon-Wiener diversity index and the riverbed stability index correlation model is used. The inflection point value serves as the final threshold for riverbed stability.

[0019] The beneficial effects of the above technical solution are as follows: First, this invention proposes a new riverbed stability evaluation index. The index. This index uses the average time required for a unit area of ​​scour and deposition to occur per unit width of riverbed as a stability measure, and has a clear physical meaning. Compared to traditional assessment methods that rely on single parameters such as flow velocity, gradient, or median grain size, The index comprehensively reflects the total intensity of scouring and sedimentation of the riverbed during the monitoring period, providing a more complete characterization of the dynamic changes in the riverbed. Linking this index with benthic animal diversity represents a technological breakthrough in evaluating riverbed stability from an ecological perspective, overcoming the shortcomings of existing assessment methods that lack ecological response.

[0020] Second, this invention determines the critical threshold by which riverbed stability affects benthic animal diversity. This is achieved by constructing... A nonlinear regression correlation model between the index and species abundance S and the Shannon-Wiener diversity index H', combined with second derivative inflection point detection and piecewise linear regression significance testing, can accurately identify mutations in benthic animal diversity. Critical value. Implementation examples demonstrate that S- Model and - The model's coefficients of determination reached 0.92 and 0.90, respectively, indicating a good fit. The determined thresholds can effectively distinguish whether the benthic animal community is in a suitable or degenerate state.

[0021] Third, this invention provides clear quantitative targets for river management projects in the mountainous areas of Southwest China. The management projects can... Raising the index above a certain threshold serves as a design basis and acceptance standard, addressing the lack of scientific guidance in previous projects. After applying this threshold to guide the construction of a stepped deep-pool system in unstable river sections, subsequent monitoring showed a significant increase in benthic animal diversity, validating the practical engineering guidance value of the riverbed stability threshold determined by this method.

[0022] Fourth, the method of this invention is highly standardized and easy to operate. The entire operation process covers aspects such as cross-section screening and monitoring, high-precision measurement with a total station, cross-section drawing, stability index calculation, and determination of inflection point detection thresholds. Each step uses mature measurement and drawing tools, and the operation steps are clear and easy to understand, facilitating widespread application within the industry. This method helps improve the scientific rigor and relevance of river management projects, improves the river's ecological environment, and safeguards regional life, property, and ecological security, thus possessing significant engineering application value. Attached Figure Description

[0023] Figure 1 A conceptual diagram of the riverbed cross-section; Figure 2 This is a comparison chart of the changes of a representative cross section of a river within a one-year monitoring period in an embodiment of the present invention; Figure 3 This is a diagram showing the coupling relationship between benthic animal diversity and the riverbed stability index Bs in this invention. Detailed Implementation

[0024] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0025] It should be noted that, unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0026] This invention provides a method for determining riverbed stability thresholds based on benthic animal diversity, comprising the following steps: river cross-section screening and monitoring cycle determination, riverbed cross-section data collection, riverbed cross-section profile drawing and area determination, riverbed stability definition and calculation, benthic animal sampling and diversity index calculation, and threshold determination. The following detailed description of each step is provided in conjunction with the specific implementation process.

[0027] Step S1: River section selection and monitoring cycle determination River cross-section selection: Within the target watershed, taking into account key factors such as riverbed sediment, slope, and historical scouring and deposition, select no fewer than four representative river cross-sections to ensure that the selected river cross-sections fully cover the four types of riverbed stability: stable, relatively stable, relatively unstable, and unstable.

[0028] When selecting river sections, it is necessary to take into account the consistency of the basin's geological background, vegetation cover, and degree of human disturbance in order to eliminate significant interference from non-bed stability factors on benthic animal diversity.

[0029] Monitoring cycle determination: The monitoring cycle is set to be no less than one complete hydrological cycle. This hydrological cycle must cover the high-water season, normal-water season, and low-water season to ensure complete coverage of the entire process of river scouring and deposition changes throughout the year, thereby comprehensively capturing the scouring and deposition dynamics of the river under different hydrological conditions. As a preferred option, the monitoring cycle length is 1 year.

[0030] Step S2: Riverbed cross-section data acquisition High-precision measurements were conducted using a total station, with full-section measurements performed on each selected cross-section at both the start and end of monitoring. Measurement points were evenly distributed along the left and right banks of the cross-section, with a spacing of no more than 2 meters between points on conventional cross-sections, and an overall measurement error not exceeding ±0.01 meters. For cross-sections with complex riverbed topography, the spacing between measurement points was adjusted to 1–1.5 meters. During the measurement process, the horizontal distance from the left bank and the corresponding elevation data of each measurement point were recorded simultaneously. Basic hydrological parameters such as riverbed width, water depth, flow velocity, and current discharge were also collected.

[0031] Step S3: Drawing the cross-sectional view of the riverbed and determining its area like Figure 1 As shown, by comparing the initial cross-section at the start of the monitoring period with the final cross-section at the end, the areas of change in riverbed morphology can be visually identified. The area where the final cross-section is lower than the initial cross-section and concave downwards represents the riverbed incision area. The area where the final cross-section is higher than the initial cross-section and bulges upward represents the riverbed siltation area. .

[0032] Based on the horizontal distance and elevation data of the cross-sections collected in step S2 at two different times, initial and final profiles of each river section are drawn using professional drawing software. During the drawing process, it is essential to ensure consistent coordinate scales, with the horizontal direction representing distance from the left bank and the vertical direction representing elevation. Key feature points of the cross-sections, such as the maximum water depth point, scour extreme point, and sedimentation extreme point, must be clearly marked. AutoCAD or ArcGIS can be used as the drawing software.

[0033] After the profile maps were drawn, the areas of the initial and final profile maps of each river section were calculated, and the riverbed incision area during the monitoring period was determined by comparison. and siltation area Among them, the undercut area This refers to the area of ​​the riverbed cross-section that has been eroded downwards by the water flow during the monitoring period, and the area of ​​sediment deposition. This refers to the area of ​​the riverbed cross-section that has been raised due to sediment deposition during the monitoring period. The accuracy of the incised area and siltation area can be verified by calculating the areas of the initial and final cross-sections using cross-sectional area calculation tools.

[0034] Step S4: Definition and Calculation of Riverbed Stability Define the riverbed stability index This refers to the time required for a unit area of ​​the riverbed cross-section to change per unit width, used to quantify the stability of the riverbed against erosion and deposition. The more stable the riverbed, the better. The larger the value, the longer it takes for a unit area of ​​riverbed to undergo changes in scouring and deposition per unit width; conversely, the smaller the value, the more unstable the riverbed. The smaller the value, the shorter the time required for the same area change to occur. The dimension of this index is years per meter, and its physical meaning is the average time required for a unit area of ​​scour and deposition to occur in the cross-section of the riverbed under the condition of unit river width.

[0035] The specific calculation process is as follows: First, calculate the water flow force for bed transfer. The expression is:

[0036] in, The incision area of ​​sediment on the cross-section of the riverbed within the monitoring period T is expressed in units of... ; The sediment deposition area on the riverbed cross section within monitoring period T is expressed in units of... T represents the monitoring cycle duration, in years.

[0037] Then calculate the bed force per unit river width. The expression is:

[0038] Where B is the width of the riverbed, in meters. It represents the rate of change of riverbed area per unit time over a unit river width, eliminating the influence of differences in river width and facilitating comparisons between rivers of different widths.

[0039] Finally, the riverbed stability index was calculated. The reciprocal of the bed-moving force per unit river width is used to characterize it, and the expression is:

[0040] The riverbed stability index of each river section is calculated using the above formula. . The higher the value, the stronger the riverbed's ability to resist erosion and deposition, and the higher the physical stability of benthic animal habitats.

[0041] Step S5: Benthic animal sampling and diversity index calculation Benthic animal sampling: Sampling is conducted 1-2 weeks after the end of the high-water season within the monitoring period. At this time, the benthic animal community has stabilized due to erosion and sedimentation, objectively reflecting the community status after the end of the annual hydrological cycle. During sampling, 3-5 sampling sub-points are evenly distributed within each river cross-section. A Petersen sediment sampler is used for benthic animal collection, with each sub-point covering an area of ​​0.0625 square meters. The samples were collected at a depth of 0-20 cm from the surface of the riverbed. The collected samples were brought back to the laboratory, sorted, classified, and identified, and the number of benthic animal species at each sampling point was counted.

[0042] Based on the standard benthic animal collection procedure, this invention employs the kick-net sampling method: three samples are selected from each river section sampling point and mixed into a composite sample, which is then initially sieved through a 420μm aperture sieve (40 mesh) to remove matrix impurities. The samples are then sealed on-site with time, location, and environmental parameters labeled before being brought back to the laboratory for classification. Laboratory processing includes a sample pretreatment stage, where organisms and sediment are separated by flotation-sedimentation on the day of sampling; and a biological sorting stage, where live organism sorting is performed using a white porcelain dish inspection method combined with micromanipulation instruments (dissecting forceps, pipettes, and brushes). The screened samples are preserved using the ethanol method, fixed with 75% ethanol solution and double-labeled with both bottle and bag labels.

[0043] Biological sample identification: Structural characteristics of benthic animals were observed using an optical microscope and accompanying imaging system to identify and count biological species. Sample identification was performed with the greatest possible precision down to the smallest taxonomic unit. If a species could not be identified due to damage or missing data, it was identified as a known reference species or a lower reference species to minimize experimental errors. Species in each sample area were weighed on an electronic balance with relatively high precision (0.0001 g), and then converted to unit density (ind. / ) based on the quadrat determined by the actual sample survey. ) and unit biomass (g / ).

[0044] Biotic richness, also known as species abundance, refers to the total number of benthic animal species recorded within a unit sampling area; biomass density refers to the number of biological species per square meter, measured in individuals / square meter. .

[0045] After completing the conversion of species abundance and biomass density indices, in order to further verify the ability of the riverbed stability index to characterize the overall ecological function of the benthic community, this embodiment uses the community-weighted mean trait value (CWM) to characterize the functional trait combination characteristics of benthic animals. Based on the coupled operation of the sample point-species matrix and the species-trait matrix, the CWM calculation is performed through the built-in dbFD algorithm of the R language package FD, and the Euclidean distance matrix is ​​constructed to analyze the functional space structure.

[0046] CWM calculation formula:

[0047] in, For the first The relative abundance of each species, For the first Functional characteristic values ​​of each species.

[0048] The species abundance S at each sampling point was obtained statistically, and the Shannon-Wiener diversity index was calculated based on the number of species and the number of individuals of each species. The calculation formula is:

[0049] in, For the first The number of individuals of each species, where N is the total number of benthic animals at that sampling point.

[0050] Species abundance S and Shannon-Wiener diversity index were collected from various sampling points along the same river cross section. The average value is used as the indicator of benthic animal diversity at this section. Benthic animal identification must strictly follow the "Classification and Retrieval of Aquatic Insects in China" and the "Technical Specifications for Benthic Animal Monitoring in Inland Water Bodies". Annelids and mollusks should be identified to the genus level or above, and arthropods should be identified to the family level or above. For species that are difficult to identify, they should be marked as unidentified groups, and their numbers should be counted separately but not included in the calculation of species abundance S.

[0051] Step S6: Threshold Determination The riverbed stability index of each river section calculated in step S4 The x-axis represents the species abundance S obtained in step S5, and the y-axis represents the species abundance S and the Shannon-Wiener diversity index, respectively. Using Origin or SPSS software as the ordinate, correlation models were fitted, and corresponding models were constructed. - , - A nonlinear regression correlation model. The determination coefficient R0 is used. 2 To test the goodness of fit of the model, R0 2 It needs to be greater than 0.85.

[0052] The inflection point detection method was used to determine the mutation points of benthic animal diversity indicators, combined with ecological threshold theory, to screen out the corresponding riverbed stability indices. This serves as the final threshold. The specific inflection point detection process is as follows: (1) Data preprocessing: Loess smoothing is performed on the scattered data with a span parameter of 0.75 to eliminate local fluctuations caused by sampling errors.

[0053] (2) Calculation of the second derivative: Calculate the numerical second derivative of the smoothed curve using the following formula: Where the step size h is taken as The median of the data interval.

[0054] (3) Inflection point candidate screening: Set the threshold for the sign change of the second derivative. ,when From positive to negative and When the inflection point is reached, mark that point as a candidate inflection point.

[0055] (4) Significance test: Using the candidate inflection point as the boundary, the data is divided into two segments and linear regression is performed on each segment. The determination coefficients of the two regression segments are calculated. and ,like >0.85 and If the slope is greater than 0.85 and the difference between the two slopes is significant (t-test p < 0.05), then the point is confirmed as a valid inflection point.

[0056] (5) Threshold determination: Obtain the threshold values ​​respectively. - The inflection point of the correlation model corresponds to value, - The inflection point of the correlation model corresponds to The arithmetic mean of the two inflection point values ​​is taken as the riverbed stability threshold. If the relative difference between the two inflection point values ​​exceeds 20%, then... - Correlation model The inflection point value is used as the final threshold for riverbed stability because the Shannon index is more sensitive to changes in community structure.

[0057] When the riverbed stability index When the riverbed stability index is greater than or equal to this threshold, benthic animal diversity remains at an appropriate level, and the river ecosystem is stable; when the riverbed stability index is greater than or equal to this threshold, the riverbed diversity remains at an appropriate level, and the river ecosystem is stable. When the value is below this threshold, benthic animal diversity decreases significantly, and river ecosystems degrade.

[0058] Example This embodiment takes the Xiaojiang River basin in the southwestern mountainous area as an example and uses the method of the present invention to determine the riverbed stability threshold.

[0059] I. Section Screening and Monitoring Cycle Determination Within the Xiaojiang River basin, considering factors such as riverbed sediment, slope, and historical erosion and deposition, four representative river sections—Shengou, Diaogahe, Jiangjiagou, and Dabainigou—were selected. The monitoring period was set at one year, from April 2009 to April 2010, fully covering a hydrological cycle including the high-water season, normal-water season, and low-water season.

[0060] II. Riverbed Cross-Section Data Collection A Leica TS06 total station was used to conduct high-precision topographic surveys of the riverbed cross-section. In this embodiment, the measured data for calculating the riverbed stability index were collected in April 2009, October 2009, and April 2010. Full-section remeasurement was carried out on four representative cross-sections. Measurement points were evenly distributed from the left bank to the right bank of each cross-section, with a spacing of 1.5m between the measurement points. Two sets of basic data were collected simultaneously: the horizontal distance of each measurement point from the left bank and the riverbed elevation.

[0061] Figure 2 This is a schematic diagram of the elevation changes of the cross section over multiple periods. Figure 2 (a) The three-phase historical measurement data of the Diaoga River show the changes in riverbed erosion and deposition. Figure 2 (b) shows the measured cross-sectional curves of this embodiment from 2009 to 2010; different line types in the figure correspond to the measurement time, and the areas marked by dashed boxes are areas with significant changes in riverbed scouring and deposition.

[0062] Meanwhile, the width of the riverbed at each cross-section was measured: 0.99m for Shenggou, 19.48m for Diaoga River, 27.6m, 32.4m and 33.69m for Jiangjiagou in April 2009, October 2009 and April 2010 respectively, and 49.2m, 48.28m and 50.6m for Dabainigou in April 2009, October 2009 and April 2010 respectively.

[0063] III. Drawing of Riverbed Cross-Section Diagram and Determination of Area Using AutoCAD software, initial and final cross-sectional views of four sections were drawn based on the horizontal distance and elevation data from two measurements. The scour points, siltation points, and maximum water depth points of each section were accurately marked. The area of ​​the initial and final cross-sections was calculated and compared using the software's area calculation tool to obtain the incision area and siltation area of ​​each section: deep ditch =0.0084 , =0.0098 Diaoga River =3.4335 , =2.8316 Jiangjiagou =1.7893 , =18.7191 Dabai Nigou =15.6488 , =61.1307 .

[0064] IV. Riverbed Stability Calculation Calculate the riverbed stability index at each cross-section Taking deep trenches as an example, =B×T / ( + =0.99×1 / (0.0084+0.0098)≈54.4 years / meter. Similarly, the calculation for Diaoga River yields... Approximately 3.11 years / meter, Jiangjiagou Approximately 1.62 years / meter, Dabainigou Approximately 0.64 years / meter. (Four cross-sections) The values ​​show a clear gradient distribution, ranging from 54.4 years / meter in Shengou to 0.64 years / meter in Dabainigou, corresponding to four riverbed stability levels: stable, relatively stable, relatively unstable, and unstable, respectively.

[0065] V. Benthic animal sampling and diversity index calculation In October 2010, one week after the end of the high-water season, standardized sampling of benthic animals was conducted at four cross-sections. Four sampling points were set up at each cross-section, and samples were collected using a Petersen sampler. The sampling area at each point was 0.0625 square meters, and the sampling depth was 0 to 20 centimeters from the surface of the riverbed. After the samples were brought back to the laboratory, they were classified and identified according to the "Classification and Retrieval of Aquatic Insects in China" and the "Technical Specifications for Monitoring Benthic Animals in Inland Water Bodies." Species abundance (S) was calculated as follows: Shenggou 56 species, Diaogahe 36 species, Jiangjiagou 18 species, and Dabainigou 0 species. The Shannon-Wiener diversity index was calculated using the formula... : Shengou 3.31, Diaogahe 1.97, Jiangjiagou 0.87, Dabainigou 0.

[0066] VI. Threshold Determination like Figure 3 As shown, Origin software was used to build... - and - Nonlinear regression association model Figure 3 (a) Corresponding - Fitted curve, Figure 3 (b) Corresponding - Fitted curve. - The expression for the association model is: Coefficient of determination R2 =0.92. - The expression for the association model is: Coefficient of determination R 2 =0.90. The goodness of fit of both models is greater than 0.85, indicating good model quality.

[0067] Inflection point detection was used to identify inflection points on the two fitted curves. The specific process was as follows: Loess smoothing was applied to the scattered data, with a span parameter of 0.75; the second derivative of the numerical values ​​was calculated, with a step size h. Median of data intervals; setting a threshold for the sign of the second derivative. Candidate inflection points were screened; piecewise linear regression was performed using these candidate points as boundaries. The determination coefficients of both regression segments were greater than 0.85, and the slopes of the two segments showed a significant difference after a t-test, confirming the existence of a valid inflection point. Figure 3 As shown, the inflection points of the two models are determined. The value is 10.0 years / meter. Therefore, the riverbed stability threshold for this watershed is determined to be 10.0 years / meter. When the value is ≥10.0 years / meter, benthic animal diversity is maintained at an appropriate level; when When the value is less than 10.0 years / meter, benthic animal diversity is significantly reduced.

[0068] This threshold was applied to guide river management projects in the Xiaojiang River basin, constructing a stepped deep-pool system in unstable river sections such as Jiangjiagou and Dabainigou, thereby raising riverbed stability above the threshold. Subsequent monitoring results showed a significant increase in benthic animal diversity, indicating that the management project achieved its expected results and validating the scientific validity and practicality of this method.

[0069] Finally, it should be noted that any parts of this invention not described in detail are prior art. Those skilled in the art will understand that the above descriptions are merely preferred embodiments of the invention and are not intended to limit the invention. Although the invention has been described in detail with reference to the foregoing examples, those skilled in the art can still modify the technical solutions described in the foregoing examples or make equivalent substitutions for some of the technical features. All modifications and equivalent substitutions made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A method for determining riverbed stability threshold based on benthic animal diversity, characterized in that, Includes the following steps: S1. Select no fewer than four river sections within the target watershed that cover four types of riverbed stability: stable, relatively stable, relatively unstable, and unstable, and set a monitoring cycle of no less than one complete hydrological cycle. S2. Using a total station, at the beginning and end of the monitoring period, measure the horizontal distance and elevation data of each river section, and simultaneously collect basic hydrological parameters such as riverbed width, water depth, and flow rate to obtain information on changes in cross-sectional morphology. S3. Based on the cross-sectional morphological change information, determine the riverbed incision area and siltation area of ​​each river cross-section during the monitoring period; S4. Calculate the riverbed stability index of each river section based on the incision area, siltation area, riverbed width, and monitoring period. S5. Collect benthic animal samples at various river sections, identify and statistically analyze the species abundance and Shannon-Wiener diversity index of benthic animals; S6. Construct nonlinear regression correlation models for species abundance, Shannon-Wiener diversity index and riverbed stability index respectively. Determine the critical value of riverbed stability index corresponding to the mutation of species abundance and Shannon-Wiener diversity index by inflection point detection. The critical value is the riverbed stability threshold.

2. The method for determining the riverbed stability threshold based on benthic animal diversity according to claim 1, characterized in that, The monitoring period mentioned in step S1 covers the high water period, normal water period and low water period, and the monitoring period lasts for 1 year.

3. The method for determining the riverbed stability threshold based on benthic animal diversity according to claim 1, characterized in that, When screening river sections in step S1, the consistency of the basin's geological background, vegetation coverage, and degree of human activity disturbance should be taken into account, and the interference of non-bed stability factors on benthic animal diversity should be excluded.

4. The method for determining the riverbed stability threshold based on benthic animal diversity according to claim 1, characterized in that, In step S2, when measuring with a total station, the measuring points are evenly distributed along the left bank to the right bank of the cross-section. The spacing between measuring points on a conventional cross-section is no more than 2m, and the measurement error of each measuring point does not exceed ±0.01m. The spacing between measuring points on a cross-section with complex riverbed topography is adjusted to 1~1.5m.

5. The method for determining the riverbed stability threshold based on benthic animal diversity according to claim 1, characterized in that, In step S3, based on the cross-sectional horizontal distance and elevation data at two time points, the initial profile and final profile of each river section are drawn, and the area of ​​the initial profile and final profile of each river section is calculated respectively. By comparison, the incision area and siltation area within the monitoring period are determined.

6. The method for determining the riverbed stability threshold based on benthic animal diversity according to claim 1, characterized in that, The riverbed stability index mentioned in step S4 The calculation formula is: in, The width of the riverbed, For the duration of the monitoring period, To monitor the riverbed incision area during the monitoring period, The area of ​​riverbed siltation during the monitoring period.

7. The method for determining the riverbed stability threshold based on benthic animal diversity according to claim 6, characterized in that, The riverbed stability index The dimension is year / meter, which represents the average time required for a unit area of ​​scour and deposition to occur in the cross-section of the riverbed under the condition of unit river width; The higher the value, the stronger the riverbed's ability to resist erosion and deposition, and the higher the physical stability of benthic animal habitats.

8. The method for determining the riverbed stability threshold based on benthic animal diversity according to claim 1, characterized in that, In step S5, benthic animal samples are collected 1-2 weeks after the end of the high-water season. Three to five sampling points are evenly distributed across each river cross-section, and samples are collected using a Petersen sampler. The sampling area at each point is 0.0625 square meters. The sampling depth was 0-20 cm from the surface of the riverbed; the Shannon-Wiener diversity index was mentioned. The calculation formula is: in, For the first The number of individuals of a species This represents the total number of benthic animals at this sampling point. For species abundance.

9. The method for determining the riverbed stability threshold based on benthic animal diversity according to claim 1, characterized in that, The specific process for inflection point detection in step S6 is as follows: Loess smoothing is applied to the scattered data to eliminate local fluctuations; the second derivative of the smoothed curve is calculated, and a threshold for the sign of the second derivative is set. Filtering inflection point candidates; The data is divided into two segments by the candidate inflection point, and linear regression is performed on each segment separately. When the determination coefficients of the two regressions are both greater than 0.85 and the slopes of the two segments are significantly different after t-test, the point is confirmed as an effective inflection point.

10. The method for determining the riverbed stability threshold based on benthic animal diversity according to claim 1, characterized in that, Obtain the inflection points corresponding to the correlation models between species abundance and riverbed stability index. The inflection point corresponding to the correlation model between the value, Shannon-Wiener diversity index and riverbed stability index The arithmetic mean of the two inflection point values ​​is taken as the threshold for riverbed stability; if the relative difference between the two inflection point values ​​exceeds 20%, the threshold corresponding to the Shannon-Wiener diversity index and the riverbed stability index correlation model is used. The inflection point value serves as the final threshold for riverbed stability.

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