Method for evaluating restoration effect of small river habitat

Abstract

The invention relates to a small river habitat restoration effect evaluation method, and aims at solving the problems of habitat damage, habitat fragmentation and the like caused by hydroelectric development to formulate restoration targets of restoring river connectivity, guaranteeing ecological base flow and constructing a stable river ecosystem. The method comprises the following steps: firstly, monitoring a river, then monitoring fish resources and an ecological environment, carrying out special investigation on ecological restoration measures, and finally, constructing an evaluation index system from the dimensions of river connectivity, habitat quality, biodiversity, ecological bearing capacity and the like based on monitoring data. Scientific quantitative evaluation is realized, support is provided for engineering optimization, and river ecological protection and restoration technology development can be promoted.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of ecological restoration, in particular to a small river habitat restoration effect evaluation method. BACKGROUND

[0002] Small rivers play an important role in regional ecosystems, providing habitat for numerous species and maintaining ecological balance. However, human activities such as water conservancy construction, overfishing, and pollution discharge have caused serious damage to small river habitats, leading to the interruption of river connectivity, changes in flow rate and water temperature rhythm, and the shrinking of spawning grounds for unique fish species, resulting in a decrease in plankton diversity. Habitat fragmentation caused by water conservancy projects further exacerbates ecological degradation. The traditional "engineering restoration first, evaluation lagging" model can lead to ineffective restoration projects due to the lack of scientific evaluation, and there is an urgent need to establish a "monitoring-evaluation-optimization" whole-process technical system.

[0003] To restore the ecological function of small rivers, habitat restoration projects have been widely implemented. However, there is currently a lack of scientific and systematic evaluation methods for the effectiveness of these projects, making it difficult to accurately assess their success and optimize subsequent restoration strategies. Existing methods focus mainly on single indicator monitoring and lack a comprehensive evaluation system covering hydrology, biology, and habitat. Additionally, there is a lack of dynamic feedback mechanisms for restoration measures. Early evaluation relies on single indicators such as water quality compliance rates and fish species numbers, which cannot capture the complexity of the ecological system. Traditional manual sampling is time-consuming and labor-intensive, and the data is often delayed. Existing methods focus on microscopic organisms or local river sections, lacking a watershed-scale ecological system health evaluation.

[0004] As can be seen, although some small river habitat restoration has been evaluated, there is a lack of evaluation standards and systematic evaluation methods. Therefore, developing a comprehensive and effective small river habitat restoration effect evaluation method is a key breakthrough in quantifying the effectiveness of current ecological restoration and is a necessary requirement for promoting the standardization and scientific development of river ecological protection and restoration technology. SUMMARY

[0005] To overcome the existing technical defects, the present application provides a small river habitat restoration effect evaluation method. The systematic tracking and monitoring of fish habitat ecological restoration and effect evaluation, through multi-source data fusion and dynamic model construction, realizes the scientific and quantitative evaluation of small river ecological restoration projects, and provides technical support for subsequent engineering optimization.

[0006] To achieve the above purpose, the present application provides the following technical solutions:

[0007] A small river habitat restoration effect evaluation method, comprising the following steps:

[0008] S1. Set up corresponding monitoring sections in the target water area and arrange monitoring points;

[0009] S2. Fish resource monitoring: periodically investigate the fish population and breeding ecology in the monitoring sections to obtain data such as species composition, resource quantity, age structure, and spatio-temporal distribution of reproduction, focusing on endemic fish and protected species;

[0010] S3. Ecological environment monitoring: simultaneously monitor water habitat parameters (water depth, flow rate, bottom substrate composition, etc.) and the species, density, and biomass of aquatic organisms (zooplankton, benthic organisms, etc.);

[0011] S4. Special investigation of ecological restoration measures: track and monitor the recapture rate of released fry, changes in early-stage resources, and habitat structure stability in the restoration area for measures such as fry release and habitat restoration;

[0012] S5. Effect evaluation and analysis: based on the monitoring data, construct an evaluation index system from dimensions such as river connectivity, habitat quality, biodiversity, and ecological carrying capacity, comprehensively evaluate the restoration effect, and propose optimization suggestions.

[0013] The target water area is a small river habitat with habitat destruction and habitat fragmentation caused by hydropower development, characteristics of blocked river connectivity and fragmented fish habitat, and ongoing restoration engineering.

[0014] Preferably, step S1 comprises:

[0015] First, select key monitoring sections, set up corresponding monitoring sections in the main stream and tributaries according to the location of river restoration engineering and ecological function zones, with no less than 16 monitoring sections in the main stream and no less than 2 monitoring sections in the tributaries;

[0016] Second, select monitoring points according to the fish and bait resource abundance in each functional zone, key nodes of river connectivity, and representative habitats in backwater areas, and divide key monitoring points and non-key monitoring points.

[0017] Preferably, step S2 comprises the following contents:

[0018] The fish population monitoring frequency is once a year in spring and autumn, each investigation lasting 10 days, and the breeding ecology monitoring is carried out in the breeding season, among which the fixed section of drifting egg fish spawning ground, the 2km x 2km sample frame, and the 1m x 1m sample square in each sample frame are used for the flow investigation method, and the total runoff of eggs and larvae in one day and night is calculated.

[0019] The obtained indicators are: number of fish species, fish diversity index, proportion of deformed individuals, proportion of benthic feeding fish, proportion of omnivorous fish, and proportion of carnivorous fish.

[0020] Preferably, step S3 comprises the following:

[0021] The ecological environment monitoring indexes include: river shape, water depth, riverbed substrate composition, habitat continuity, plankton diversity index, benthic organism density and biomass, and the monitoring frequency is synchronized with fish resource monitoring.

[0022] The ecological flow maintenance degree, riverbed stability, river connectivity, riverbank stability, vegetation coverage, bank slope natural form rate, plankton diversity index, zooplankton diversity index, benthic animal diversity index and influence of alien species are obtained.

[0023] Preferably, step S4 comprises the following:

[0024] The proliferation release special investigation includes: the main release point selects a river section with wide river surface and various flow conditions, and the secondary release point selects an area with rich bait and good connectivity;

[0025] The habitat restoration special investigation targets the restoration river section, and the monitoring indexes include the density of juvenile fish, the distribution of breeding population and the habitat structure stability, and the monitoring frequency is synchronized with fish population monitoring.

[0026] Step S5 comprises the following: through biological integrity index (IBI) calculation, 16 indexes such as the number of fish species, the proportion of endemic species and the proportion of omnivorous fish are used.

[0027] The effect evaluation index system includes:

[0028] River connectivity: the effectiveness of dam removal and fishway is evaluated through the difference of fish population between dam and dam, and the distribution of fish in trunk and branch;

[0029] Habitat quality: based on biological integrity index (IBI), diversity index (Shannon-Wiener) and habitat parameter change;

[0030] Ecological carrying capacity: the fish carrying capacity is estimated by combining bait biomass, fish trophic level and energy flow model (such as Ecopath);

[0031] Proliferation release effect: the effect is evaluated by the recapture rate of marked fish and the contribution rate of released population to natural population.

[0032] The biological integrity index (IBI) calculation is based on 16 indexes such as the number of fish species, the proportion of endemic species and the proportion of omnivorous fish, and the comprehensive evaluation is carried out by using the assignment method.

[0033] The monitoring data collection method includes:

[0034] Fish resources: combined with active fishing, hydroacoustic investigation and environmental DNA high-throughput sequencing;

[0035] Habitat parameters: hydrological and geomorphological data were obtained using flow meters, dissolved oxygen meters and remote sensing technology;

[0036] Biological samples: benthic animals and plankton were collected by Petersen bottom sampler and plankton net and fixed and preserved using formaldehyde solution.

[0037] Based on the above indexes, a river ecological restoration effect evaluation index system (Table 1) was established; it was determined that the comprehensive evaluation index greater than 50 was good, 40-50 was better, 30-40 was relatively poor, and less than 30 was extremely poor.

[0038] The effect evaluation results are fed back to the repair engineering optimization, for example, adjusting the stocking point according to the fish resource distribution, and adjusting the river channel connection engineering design based on habitat continuity.

[0039] Compared with the prior art, the present application has the following advantages and effects:

[0040] Through the construction of a systematic monitoring system, multi-dimensional index design and a scientific data processing model, the present application exhibits significant technical effects and advantages in ecological restoration effectiveness quantification, engineering optimization, policy support, etc. It covers four core dimensions of fish resources, aquatic habitat, aquatic organisms and restoration measures, avoiding the one-sidedness of traditional evaluation which only focuses on water quality or a single species. Advanced technologies such as water acoustics monitoring, environmental DNA high-throughput sequencing, stable isotope analysis and Ecopath ecological model are integrated, breaking through the monitoring limitations of traditional net sampling in deep water areas and rare species. Through the evaluation of the restoration effect of small river habitats, the present application guides river management and ecological restoration, which is conducive to realizing a virtuous cycle from scientific evaluation to precise management to long-term protection. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 The flowchart of the present application. DETAILED DESCRIPTION

[0042] The specific embodiments of the present application will be described in detail in combination with the drawings and specific circumstances.

[0043] Taking the ecological restoration of fish habitat in Heishui River as an example, the implementation example is described;

[0044] As a first-order tributary of the left bank of the Jinshajiang River, the Heishui River is affected by the impoundment of the Wudongde and Baihetan hydropower stations, and the river connectivity is blocked and the fish habitat is fragmented. The first stage of the restoration work has been completed, including the removal of the Laomuhe hydropower station, the construction of ecological base flow discharge facilities, and the habitat restoration of the river downstream of the Songxin Dam. The existing technical evaluation methods have the problems of single index, most of which only focus on the state at a certain time point, do not dynamically track the changes in the restoration process, lack of quantitative standards, lack of application of environmental DNA and hydroacoustic technology, and the like, and the specific restoration measures such as dam removal and stocking are not directly related to the changes of biological resources, so it is difficult to accurately evaluate the effectiveness of the measures. During this period, the ecological restoration effect is evaluated by using the method of the application, through setting up fish resources, ecological environment, and breeding ecology, and combining key monitoring points and sample frames, the hydrological, biological and habitat parameters of the whole basin are covered, the data comprehensiveness is realized, and the changes in spring and autumn are dynamically tracked. Sixteen quantitative indexes are proposed, and the assignment standards are clearly defined. The environmental DNA and hydroacoustic technology are introduced to make up for the limitations of traditional nets. For specific restoration measures such as dam removal and stocking, the contribution rate of the released population to the natural population is analyzed to verify the effectiveness of the measures.

[0045] S1. Set up corresponding monitoring sections in the relevant water area, and arrange monitoring points:

[0046] Firstly, the key monitoring sections are selected, and corresponding monitoring sections are set up in the main stream and tributaries according to the location of the river restoration project and the ecological function area;

[0047] The main stream monitoring sections are not less than 16, including the sections above the Sujiawan Dam, below the Gongdefang Dam, at the Laomuhe Dam site, the 825 backwater point and the Heishui River estuary;

[0048] The tributaries are not less than 2, including one section at the confluence of Zeku River and Xiluo River;

[0049] Then, the monitoring points are selected according to the fish and bait resource richness in each functional area, the key nodes of river connectivity, and the habitat representation of backwater area, including the section above the Sujiawan Dam (resource-rich area above the dam), the section below the Gongdefang Dam (connectivity area below the dam), the section 1km above the Laomuhe Dam (core area of dam removal), the 825 backwater point (drifting egg spawning site), and the Heishui River estuary (interflow habitat of main stream and tributaries);

[0050] Secondly, the special point (below the Songxin Dam) in the restoration area is selected, including the bottom improvement D1, the flow constriction submerged dike Q4, the flow constriction submerged dike Q5, the flow constriction submerged dike Q9 and the slot S9.

[0051] S2. The fish index is obtained by fish resource monitoring:

[0052] The fish population monitoring frequency is once a year in spring and autumn, and each investigation lasts for 10 days, including species composition, dominant species distribution, resource quantity, age structure and gonadal development characteristics.

[0053] The breeding ecological monitoring is carried out in the breeding season, wherein the fixed section is adopted for the spawning ground of the drifting egg fish, and the flow survey method of 2km*2km sample frame, 3 1m*1m sample squares in each sample frame is adopted for the sticky egg fish and the juvenile habitat. The total flow of the egg and fry in one day is calculated:

[0054] N m =∑M+∑M';

[0055] Wherein, N m is the total flow, ∑M is the collected amount (M=(Q / q)·m·C, Q is the section flow, q is the net flow, m is the collected egg and fry number, and C is the flow coefficient), and ∑M' is the non-collected time calculation amount (interpolation method calculation).

[0056] The obtained indexes are: the number of fish species, fish diversity index, proportion of fish deformity, proportion of benthic feeding fish, proportion of omnivorous fish, and proportion of carnivorous fish.

[0057] S3. The ecological environment monitoring obtains the ecological environment indexes:

[0058] The water depth, flow rate (LS45A type flow rate meter), bottom composition (hard bottom / soft bottom classification), and habitat continuity (river connectivity index) are monitored synchronously with the fish monitoring, once in spring and autumn; and the ecological flow maintenance degree, river bed stability, river connectivity, river bank stability, vegetation coverage, and bank slope natural form rate are obtained.

[0059] The plankton, benthic animals, sessile algae, floating organisms, and river habitats are monitored; and the obtained indexes are: plankton diversity index, zooplankton diversity index, benthic animal diversity index, and influence of alien species.

[0060] S4. The special investigation of ecological restoration measures: aiming at the measures such as the stocking and releasing and habitat restoration engineering, the tracking monitoring of the recapture rate of the released fry, the change of the early stage resources of fish in the restoration area, and the stability of the habitat structure is carried out.

[0061] The special investigation of the stocking and releasing includes: the main releasing point is selected in the river section with wide river surface and various flow conditions, and the secondary releasing point is selected in the area with rich bait and good connectivity.

[0062] The special investigation of the habitat restoration is carried out for the restoration river section, and the monitoring indexes include the density of the fry, the distribution of the breeding population, and the stability of the habitat structure, and the monitoring frequency is synchronous with the fish population monitoring. The recapture rate of the stocking and releasing population is determined according to the proportional relationship between the number of the released individuals and the total number of the captured individuals:

[0063] S%=N0pR / N×100%

[0064] Where S% is the recapture rate of the released population; R is the proportion of the yearling individuals in the catch; N is the number of released individuals, and N0 is the total number of catches after release.

[0065] S5. Effect evaluation analysis: Based on 16 indicators such as the number of fish species, the proportion of endemic species, and the proportion of omnivorous fish, the comprehensive evaluation was carried out by using the assignment method through the calculation of the biological integrity index (IBI). From the two dimensions of river natural function and ecological environment function, i.e. for the specific needs of the restoration of Heishui River, the core of the restoration of hydropower engineering, i.e. the restoration of water connectivity after dam removal, the restoration degree of the physical structure of habitat, the influence of the bottom improvement project on fish spawning and habitat, the shelter effect of the restoration project on local key species through the number of species and the proportion of endemic species, and the proportion of fish of different feeding habits further reflecting the integrity of food web and the efficiency of energy flow were evaluated.

[0066] IBI calculation:

[0067] (1) The scores of each indicator were calculated by using weighted average, and each index score was standardized by percentage.

[0068] In the early stage of the evaluation system operation, the weights of each indicator were temporarily equal.

[0069] S' = 20 x∑IiWi

[0070] In the formula: S' is the score of each category; I is the score of the sub-indicator under the corresponding category; and W is the weight corresponding to the indicator.

[0071] (2) After the score was calculated, the key indicators were compared respectively, and the minimum value was taken to determine the final score of each condition index.

[0072] S = min(S', 20 x I')

[0073] In the formula, S is the final score of each condition, S' is the calculated score of each category condition, and I' is the score of the key indicator.

[0074] (5) The average values of the fish condition index, the important species condition index, and the habitat condition index were calculated as the final score of the aquatic organism integrity index of the evaluated water area.

[0075] (6) The comprehensive score calculation formula of Heishui River Basin is as follows:

[0076]

[0077] In the formula: is the comprehensive score of the aquatic organism integrity index of Heishui River Basin; Si is the score of the aquatic organism integrity index of each evaluated water area; and Mi is the length of each evaluated water area.

[0078] IBI was first proposed by Karr (1981) and widely used in river health assessment, but traditional IBI focuses on a single biological group. The present patent breaks through the limitation of traditional IBI relying only on biological data by scoring hydrology, habitat and biological community indicators together. At the same time, new evaluation indicators such as river connectivity are added according to the characteristics of hydropower engineering restoration.

[0079] The effect evaluation index system includes:

[0080] River connectivity: assess the effectiveness of dam removal and fishway by the difference of fish population between dam and non-dam, and the distribution of fish in trunk and branch streams;

[0081] Habitat quality: based on biological integrity index (IBI), diversity index (Shannon-Wiener) and habitat parameter changes;

[0082] Ecological carrying capacity: estimate fish carrying capacity by combining prey biomass, fish trophic level and energy flow model (such as Ecopath);

[0083] Effect of stocking and releasing: assess by the recapture rate of tagged fish and the contribution rate of released population to natural population.

[0084] The biological integrity index (IBI) calculation is based on 16 indicators such as the number of fish species, the proportion of endemic species and the proportion of omnivorous fish, and uses the valuation method for comprehensive evaluation.

[0085] The monitoring data collection method includes:

[0086] Fish resources: combined with active fishing, hydroacoustic investigation and environmental DNA high-throughput sequencing;

[0087] Habitat parameters: use current meter, dissolved oxygen meter and remote sensing technology to obtain hydrological and geomorphological data;

[0088] Biological samples: collect benthic animals and plankton by Petersen bottom sampler and plankton net, and use formaldehyde solution for fixation and preservation.

[0089] Based on the above 16 indicators, a river ecological restoration effect evaluation index system is established (Table 1); it is determined that the comprehensive evaluation index greater than 50 is good, 40-50 is better, 30-40 is relatively poor, and less than 30 is extremely poor.

[0090] Table 1: River ecological restoration effect evaluation index system

[0091]

[0092]

[0093] Table 2: The valuation results of each index in this example are:

[0094]

[0095] The final evaluation result of this embodiment is: the comprehensive evaluation index is 58, and the ecological restoration effect is good. Therefore, the optimization suggestions for the comprehensive evaluation of the restoration effect include:

[0096] (1) Hydrology and structure optimization

[0097] Further strengthen the flow regulation, through ecological water supplement or reservoir regulation to ensure the minimum ecological flow, priority to meet the needs of sensitive species. Consider adding fish channels within a reasonable range to enhance longitudinal and lateral connectivity.

[0098] (2) Riparian zone restoration

[0099] Ecological reconstruction of hardened bank slope, restore natural meandering shape, reduce artificial intervention, at the same time enhance the function of riparian zone to filter pollutants, avoid single species planting.

[0100] (3) Biodiversity improvement

[0101] Control water eutrophication, reduce agricultural non-point source pollution input. Add gravel, deadwood and other habitat substrates in slow-flowing areas to improve benthic environment. Moderate regulation of omnivorous fish population (such as releasing carnivorous fish natural enemies), avoid excessive competition leading to imbalance of nutrient structure.

[0102] (4) Long-term monitoring and risk prevention and control

[0103] Establish regular monitoring mechanism, actively guide the surrounding residents to participate in the protection of riparian zone, reduce human damage. Evaluate the restoration effect in time, dynamically adjust the measures.

Claims

1. A method for evaluating the effect of small river habitat restoration, characterized by, The method comprises the following steps: S1. Setting selected key monitoring sections in the target water area and arranging monitoring points; S2. Fish resource monitoring: periodically investigating fish populations and breeding ecology in the key monitoring sections selected in S1 to obtain data of species composition, resource quantity, age structure, and spatiotemporal distribution of reproduction, and focusing on special fish and protected species; S3. Ecological environment monitoring: monitoring water habitat parameters and the species, density and biomass of aquatic biological resources at the monitoring points in S1; S4. Special investigation of ecological restoration measures: tracking and monitoring the recapture rate of released fry, the change of early-stage fish resources and the stability of habitat structure in the restoration area for the release and habitat restoration projects; The special investigation of release includes: selecting a river section with wide river surface and various water flow conditions as the main release point, and selecting an area with rich bait and good connectivity as the secondary release point; The special investigation of habitat restoration includes monitoring the density of juvenile fish, the distribution of breeding groups and the stability of habitat structure in the restoration river section, and the monitoring frequency is synchronized with the fish population monitoring; S5. Effect evaluation and analysis: based on the monitoring data, an evaluation index system is constructed from the dimensions of river connectivity, habitat quality, biodiversity and ecological carrying capacity, the restoration effect is comprehensively evaluated, and optimization suggestions are put forward; The target water area is a small river habitat with habitat destruction and habitat fragmentation caused by hydropower development, characteristics of blocked river connectivity and fragmented fish habitat, and ongoing restoration projects; The water habitat parameters include water depth, flow rate and bottom composition; the aquatic biological resources include planktonic animals and plants and benthic organisms.

2. The method for evaluating the effect of small river habitat restoration according to claim 1, wherein Step S1 is: Selecting key monitoring sections: setting corresponding monitoring sections in the main stream and tributaries according to the location of the river restoration project and the ecological function area, with no less than 16 monitoring sections in the main stream and no less than 2 monitoring sections in the tributaries; Secondly, monitoring points are selected according to the richness of fish and bait resources in each functional area, key nodes of river connectivity and representative habitats in backwater areas, and are divided into key monitoring points and non-key monitoring points.

3. The method for evaluating the effect of small river habitat restoration according to claim 1 or 2, wherein The step S2 is specifically: The fish population monitoring frequency is once a year in spring and autumn, each investigation lasting 10 days, including species composition, dominant species distribution, resource quantity, age structure and gonadal development characteristics; The breeding ecology monitoring is carried out in the breeding season, in which one section is fixed for the spawning ground of fish with drifting eggs, and a 2km×2km sample frame is used for the flow investigation method of 3 1m×1m sample squares in each sample frame for fish with sticky eggs and juvenile habitats; the total runoff of eggs and larvae in one day is calculated.

4. The evaluation method according to claim 3, characterized in that The specific evaluation indexes obtained in the step S2 include: the number of fish species, fish diversity index, proportion of fish with deformities, proportion of benthic fish, proportion of omnivorous fish, and proportion of carnivorous fish.

5. The evaluation method according to claim 1, characterized in that The step S3 is specifically: monitoring water depth, flow rate, bottom composition and habitat continuity, which is synchronized with fish monitoring, once in spring and autumn; the ecological flow maintenance degree, riverbed stability, river connectivity, riverbank stability, vegetation coverage and natural form rate of bank slope are obtained; Monitoring plankton, benthic animals, sessile algae, floating organisms, river habitats. The obtained indicators are: plankton diversity index, zooplankton diversity index, benthic animal diversity index, and the influence of alien species.

6. The evaluation method according to claim 1, characterized in that The step S4 is specifically: tracking and monitoring the recapture rate of released fry, changes in early-stage fish resources in the restoration area, and habitat structure stability for measures such as propagation release and habitat restoration engineering. The recapture rate of the propagation release group is determined according to the proportional relationship between the number of released individuals and the total number of catches: S% = N0pR / N x 100% Where S% is the recapture rate of the propagation release group; R is the proportion of individuals of the current year in the total catch; N is the number of released individuals, and N0 is the total number of catches after release.

7. The evaluation method according to claim 1, characterized in that The step S5 is specifically: through the calculation of the biological integrity index IBI, based on the combination of the indicators of claim 4, claim 5 and claim 6, using the valuation method for comprehensive evaluation, for the specific needs of Heishui River restoration, the core of the restoration of the water conservancy project is the restoration of water connectivity after dam removal, the restoration degree of the physical structure of the habitat, the influence of the bottom improvement project on fish spawning and habitat, the evaluation of the shelter effect of the restoration project on local key species through the number of species and the proportion of endemic species, and the proportion of fish of different feeding habits further reflecting the integrity of the food web and the efficiency of energy flow.

8. The evaluation method according to claim 1, characterized in that The IBI calculation method of step S5 includes: (1) Calculate the score of each indicator by weighted average, and standardize each index score to percentage. In the initial stage of the evaluation system, the weights of each indicator are temporarily equal; S' = 20 x ∑IiWi Where S' is the score of each category, I is the score of the corresponding sub-indicator, and W is the weight of the indicator; (2) After calculating the score, compare the key indicators respectively, and take the minimum value to determine the final score of each condition index S = min(S', 20 x I') Where S is the final score of each condition, S' is the calculated score of each category, and I' is the score of the key indicator; (3) Calculate the average of the fish condition index, the important species condition index and the habitat condition index as the final score of the aquatic organism integrity index of the evaluated water area; (4) The comprehensive score calculation formula of Heishui River Basin is as follows: In the formula: is the comprehensive score of the aquatic organism integrity index of the Heishui River Basin; Si is the score of the aquatic organism integrity index of each evaluation water area; and Mi is the length of each evaluation water area.

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