Fish habitat suitability evaluation method

Abstract

The invention provides a fish habitat suitability evaluation method. The fish habitat suitability evaluation method comprises the following steps: acquiring a hydrodynamic index and a water environment index of a river to be detected; substituting the hydrodynamic index and the water environment index of the river to be detected into the suitability function of the target fish to obtain a comprehensive habitat suitability; and calculating corresponding weighted available areas under different flow conditions based on the comprehensive habitat suitability, and selecting a suitable ecological flow in combination with a Tennant method and a guarantee target. According to the method, the hydrodynamic indexes and the water environment indexes are obtained, the hydrodynamic indexes and the water environment indexes are combined with the target fish suitability degree function, the fish habitat suitability degree is comprehensively and accurately reflected, fish individual differences are fully considered, and evaluation one-sidedness is avoided. The weighted available area under different flows is calculated based on the comprehensive habitat suitability, and then the Tennant method and the guarantee target are fused, so that the ecological flow determination is more reliable and reasonable.

Description

Technical Field

[0001] The invention relates to the technical field of fish habitat evaluation, and specifically provides a method for evaluating the suitability of fish habitat. Background Art

[0002] With the development and utilization of natural resources by humans, the construction of water conservancy projects such as dams, pumping stations, reservoirs, and channels has not only changed the shape of rivers and riverbed landforms, but also affected the hydrological situation downstream, causing hydrological sequence jumps and variations. At the same time, some important water conservancy projects will change the water resource allocation pattern of the entire basin, affect or destroy the integrity of the ecosystem, and put the river's ecological environment under stress. Fish are the most important part of the river ecosystem and play an important role in material circulation and energy flow. Therefore, it is very important to conduct fish habitat suitability assessments and determine ecological flow thresholds.

[0003] Therefore, a new fish habitat suitability assessment scheme is needed in this field to solve the above problems. Summary of the invention

[0004] In order to overcome the above-mentioned defects, the present invention is proposed to provide a solution or at least partially solve the problem of being unable to accurately evaluate fish habitats.

[0005] The present invention provides a method for evaluating the suitability of fish habitats, comprising: obtaining hydrodynamic indicators and water environment indicators of a river to be tested; substituting the hydrodynamic indicators and water environment indicators of the river to be tested into a suitability function of target fish to obtain a comprehensive habitat suitability; calculating the corresponding weighted available area under different flow conditions based on the comprehensive habitat suitability, and selecting a suitable ecological flow in combination with the Tennant method and a guarantee target.

[0006] In one technical solution of the above-mentioned fish habitat suitability assessment method, the process of obtaining the hydrodynamic indicators and water environment indicators of the river to be tested includes: selecting representative years and representative water environment scenarios; simulating the distribution of hydrodynamic indicators and water environment indicators of the river to be tested in the representative years to obtain simulation results; and using the simulation results as the hydrodynamic indicators and water environment indicators of the river to be tested.

[0007] In a technical solution of the above-mentioned fish habitat suitability evaluation method, the process of selecting representative years and representative water environment scenarios at least includes: checking whether there is any variation in the selected flow sequence to be tested; if there is any variation, using the frequency curve method to select normal water years of different periods, and calculating the average water environment suitability of normal water years of different periods, and then selecting years with a similar average water environment suitability from the normal water years of different periods as representative water environment scenarios.

[0008] In a technical solution of the above-mentioned fish habitat suitability evaluation method, the process of selecting a representative year and a representative water environment scenario also includes: if there is no variation, the entire time period is taken as a whole to select a normal water year as a representative year and a representative water environment scenario.

[0009] In a technical solution of the above-mentioned fish habitat suitability evaluation method, the process of checking whether the selected flow sequence to be tested has variation includes: using MK jump variation diagnosis to check whether the selected flow sequence has variation.

[0010] In a technical solution of the above-mentioned fish habitat suitability evaluation method, the hydrodynamic indicators and water environment indicators of the river to be tested are substituted into the fitness function of the target fish to obtain the comprehensive habitat suitability process, including: gridding the river to be tested; determining the fitness function of each data in the hydrodynamic indicators and water environment indicators; calculating the suitability of each grid based on the fitness function corresponding to the hydrodynamic indicators and water environment indicators of the river to be tested; calculating the weight of each data in the hydrodynamic indicators and water environment indicators of the river to be tested; and calculating the comprehensive habitat suitability by weight addition method based on the weight of each data.

[0011] In a technical solution of the above-mentioned fish habitat suitability evaluation method, the corresponding weighted available area under different flow conditions is calculated based on the comprehensive habitat suitability, and the process of selecting a suitable ecological flow in combination with the Tennant method and the protection target at least includes: calculating the weighted available habitat area based on the suitability and grid area of ​​each grid; calculating the corresponding weighted available area under different flow conditions, and plotting the flow and the corresponding weighted available area into a curve; combining the Tennant method and the protection target analysis curve to evaluate the changes in the habitat under different flow conditions and obtain a suitable ecological flow.

[0012] In a technical solution of the above-mentioned fish habitat suitability evaluation method, the process of calculating the weight of each data in the hydrodynamic indicators and water environment indicators of the river to be tested includes: standardizing each data in the hydrodynamic indicators and water environment indicators of the river to be tested; and obtaining the weight of each indicator through the principal component analysis method for the standardized data.

[0013] In the technical scheme for implementing the present invention, the present invention provides a method for evaluating the suitability of fish habitats, including: obtaining the hydrodynamic index and water environment index of the river to be tested; substituting the hydrodynamic index and water environment index of the river to be tested into the suitability function of the target fish to obtain the comprehensive habitat suitability; calculating the corresponding weighted available area under different flow conditions based on the comprehensive habitat suitability, combining the Tennant method and the security target, and selecting a suitable ecological flow. Compared with the prior art, the beneficial effect of the fish habitat suitability evaluation method provided by the present invention is: this method obtains hydrodynamic indicators and water environment indicators, and the hydrodynamic indicators and water environment indicators are combined with the target fish suitability function to comprehensively and accurately reflect the suitability of fish habitats, fully consider individual differences of fish, and avoid one-sided evaluation. Based on the comprehensive habitat suitability, the weighted available area under different flow conditions is calculated, and then the Tennant method and the security target are integrated to make the determination of ecological flow more reliable and reasonable. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The disclosure of the present invention will become more easily understood with reference to the accompanying drawings. It is easy for those skilled in the art to understand that these drawings are only for illustrative purposes and are not intended to limit the scope of protection of the present invention. In addition, similar numbers in the figures are used to represent similar components, among which:

[0015] Figure 1 is a schematic flow chart of the main steps of a method for evaluating the suitability of fish habitats according to an embodiment of the present invention;

[0016] Figure 2 It is a flowchart of a process of obtaining the hydrodynamic index and the water environment index of a river to be measured according to an embodiment of the present invention;

[0017] Figure 3 The flow rate and the corresponding weighted available area are plotted as a curve according to an embodiment of the present invention;

[0018] Figure 4 Schematic diagram of a fitness function according to an embodiment of the present invention. DETAILED DESCRIPTION

[0019] Some embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the protection scope of the present invention.

[0020] Embodiment 1

[0021] See attached Figure 1 , Figure 1 FIG. 1 is a flow chart showing the main steps of a method for evaluating the suitability of fish habitat according to an embodiment of the present invention. Figure 1As shown, the fish habitat suitability evaluation method in the embodiment of the present invention mainly includes the following steps S1 to S3.

[0022] Step S1, obtaining the hydrodynamic index and water environment index of the river to be tested.

[0023] In this embodiment, the hydrodynamic index reflects the movement characteristics of the water flow in the river and the related physical conditions. For example, the water flow velocity is crucial to the survival of fish. Different fish have different adaptation ranges to the water flow velocity at different growth stages. Some fish like to move in places with turbulent water flow, while others prefer areas with gentle water flow. There is also water depth. Deeper or shallower waters will provide different habitats for fish with different habits. For example, some large fish often need deeper waters to hide and move. In addition, the amplitude of water level change is also one of the important indicators. Frequent and large changes in water level may affect the reproduction, foraging and habitat stability of fish. Water environment indicators mainly reflect the water quality and related chemical and biological characteristics of the river. Common ones include water temperature. Fish are cold-blooded animals, and water temperature directly affects their metabolic rate, reproductive cycle, etc. Each fish has a suitable water temperature range for survival; dissolved oxygen content is also critical. Sufficient dissolved oxygen in the water is necessary for fish to breathe. Too low dissolved oxygen will cause fish to be hypoxic or even die; there is also pH value. Different fish have different tolerance to water pH. Exceeding the appropriate range will have adverse effects on the physiological functions of fish; in addition, the concentration of pollutants in the water, such as chemical oxygen demand (COD) and ammonia nitrogen content, etc. These indicators reflect the degree of water pollution. A clean and good water quality environment is more suitable for fish to live and survive. By collecting data on these water environment indicators through professional water quality testing and other methods, we can know the water environment status of the river.

[0024] Step S2: Substitute the hydrodynamic index and water environment index of the river to be tested into the suitability function of the target fish to obtain the comprehensive habitat suitability.

[0025] In this embodiment, the input hydrodynamic index and water environment index are calculated according to certain weights and calculation rules.

[0026] Step S3: Calculate the weighted available area corresponding to different flow conditions based on the comprehensive habitat suitability, and select the appropriate ecological flow by combining the Tennant method and the protection target.

[0027] In this embodiment, the weighted available area is calculated based on the obtained comprehensive habitat suitability and combined with different flow conditions. It can be imagined that under different flow conditions, the corresponding habitat space available for fish to actually use is different, and because the comprehensive habitat suitability is high or low, the weighted processing should be performed according to the suitability when calculating the available area. For example, when the flow of a certain section of the river is large, some areas are large but the comprehensive habitat suitability is low, so the weight of this part of the area in the weighted calculation is relatively small; while under other flows, there may be areas with small areas but high suitability, and their weights will be larger. In this way, the weighted available area corresponding to different flows is accurately calculated to reflect the impact of different flows on the actual utilization of fish habitats. The protection target is considered from a more macro and multi-faceted perspective, such as ensuring the overall stability of biodiversity in the area where the river is located and meeting the needs of local fishery sustainable development. It is a goal set in combination with actual ecological protection, social economy and other demands. The fish habitat conditions under different flow rates obtained through weighted available area analysis are combined with the flow reference given by the Tennant method and the requirements of the security objectives, and a trade-off and analysis are made to select appropriate ecological flow values ​​that can meet the fish's requirements for habitat suitability and meet the overall ecology and related security needs. In this way, the ecological flow that the river should maintain can be determined scientifically and rationally to ensure the health and stability of fish and the entire river ecosystem.

[0028] In one embodiment, Figure 2 As shown, step S1, the process of obtaining the hydrodynamic index and water environment index of the river to be tested includes:

[0029] Step S11, select representative years and representative water environment scenarios. In this embodiment, the selection of representative years is to be able to examine the condition of the river in a relatively typical and representative time period. Usually, the selection is based on the hydrological, meteorological and other data of the river over many years. For example, select years with similar multi-year average flow, or years that cover the common flood season and dry season characteristics of the river more completely, etc. The purpose is to allow the selected year to reflect the normal performance of the river under different flow conditions, seasonal changes, etc. to a certain extent, and avoid the selection of special, extreme and non-universal years, which will cause the subsequent indicators to fail to accurately reflect the true characteristics of the river. Selecting representative water environment scenarios means selecting scenarios that are more common in the river area and can reflect its general water environment characteristics.

[0030] Step S12, simulate the distribution of hydrodynamic indexes and water environment indexes of the river to be tested in the representative year, and obtain simulation results; the simulation results are used as the hydrodynamic indexes and water environment indexes of the river to be tested. In this embodiment, for the simulation of the distribution of hydrodynamic indexes, parameters such as the topographic data of the river (such as riverbed slope, changes in river width, etc.), flow data representing the year, boundary conditions (upstream and downstream water levels, etc.) are input into the hydrodynamic model. The model calculates the specific distribution of hydrodynamic indexes such as water flow velocity, water depth, and water level changes at different locations and different periods of the river based on hydraulic principles and related mathematical algorithms. The meteorological data representing the year (data such as temperature and precipitation that affect evaporation and dilution of water bodies), emission data of surrounding pollution sources (types of pollutants, emission amounts, emission rules, etc.), and the hydrodynamic conditions of the river itself are input as input parameters into the water environment model. The model simulates the distribution of water environment indicators such as dissolved oxygen, water temperature, pH, and concentrations of various pollutants in water in different regions and seasons of the river based on the principles of water quality migration and transformation and material balance. Finally, the distribution results of the hydrodynamic and water environment indicators obtained through these simulations are used as the actual hydrodynamic and water environment indicators of the river to be tested. Because it is often very costly and difficult to conduct accurate field measurements of the entire river section and the entire time period, through reasonable simulation, as long as the model is reliable and the input parameters are accurate, various indicators that can reflect the true state of the river can be obtained relatively efficiently and accurately, and then the relevant steps of subsequent fish habitat suitability evaluation can be carried out based on these indicators.

[0031] In one embodiment, the process of step S11, selecting a representative year and a representative water environment scenario, at least includes:

[0032] Step S1111, checking whether the selected flow sequence to be tested has any variation;

[0033] Step S112: If there is variation, the frequency curve method is used to select normal water years of different periods, and the average water environment suitability of normal water years of different periods is calculated. Then, the year with a similar average water environment suitability is selected from the normal water years of different periods as the representative water environment scenario.

[0034] In this embodiment, the flow sequence is a data set that reflects the change of river flow over time. The frequency curve is drawn based on the historical data of river flow, which shows the frequency of occurrence of different flows. A normal water year refers to a year in which the flow is close to the multi-year average flow. Through the frequency curve, the years in which the flow is close to the average level in different periods (such as different ten-year stages in the past few decades) can be found. For each selected normal water year, its average water environment suitability needs to be calculated. First, for each water environment indicator, its suitable range for the target fish is determined. For example, the suitable water temperature range for a certain fish may be 15-25°C. Then, according to the data of these indicators in the normal water year obtained by actual measurement or simulation, the water environment suitability of each normal water year is calculated according to a certain weight (the weight can be determined according to the sensitivity of the fish to each indicator). Finally, the water environment suitability of normal water years in different periods is averaged. After obtaining the average water environment suitability of normal water years in different periods, the year close to the average water environment suitability should be selected from these normal water years as a representative water environment scenario. The purpose of this is to find a year in which the water environment conditions can also represent the average level of the period when the flow is relatively stable (normal water year). The water environment scenario of this representative year can be used as a typical case for the subsequent steps of fish habitat suitability assessment, because it can better reflect the water environment conditions that fish may face under relatively normal (normal water year) flow conditions.

[0035] In one embodiment, the process of step S11, selecting a representative year and a representative water environment scenario, further includes: step S113, if there is no variation, taking the entire time period as a whole and selecting a normal water year as the representative year and the representative water environment scenario.

[0036] In this embodiment, when it is determined that the selected flow sequence to be measured does not have variation, it means that the flow of the river is relatively stable over a long period of time, and there is no obvious trend change or large discrete fluctuation. Under this relatively stable flow state, a normal water year (that is, a year with a flow close to the multi-year average flow) can well represent the conventional and typical hydrological characteristics of this river.

[0037] In one embodiment, the process of checking whether the selected traffic sequence to be tested has a variation includes: using an MK jump variation diagnosis method to check whether the selected traffic sequence has a variation.

[0038] Alternatively, in an alternative approach, statistical methods are used to test the variation of the traffic sequence. For example, the Mann-Kendall nonparametric test method can be used, which can detect whether there is a monotonic trend (increasing or decreasing) in the traffic sequence. The coefficient of variation (CV) can also be used to measure the degree of dispersion of the traffic sequence, and the stability of the traffic can be determined by comparing the mean and standard deviation of the traffic in different time periods. If the coefficient of variation is large, it means that the degree of dispersion of the traffic sequence is high and there is a greater possibility of variation. In either case, the variation of the traffic sequence can be tested.

[0039] In one embodiment, step S2, substituting the hydrodynamic index and water environment index of the river to be tested into the suitability function of the target fish to obtain the comprehensive habitat suitability includes:

[0040] Step S21, grid division is performed on the river to be measured. In this embodiment, the grid division can be performed according to certain rules based on factors such as the actual length and width of the river and the accuracy required for the study.

[0041] Step S22, determine the suitability function of each data in the hydrodynamic index and the water environment index. In this embodiment, it can be determined based on the relevant research results of fish biology and past practical experience. For example, for a certain fish species, after a lot of observations and experiments, it is known that the water flow velocity range suitable for its survival is 0.5-1.5 m / s, then a suitability function for the water flow velocity can be constructed. When the water flow velocity is within this range, the suitability function value is relatively high, and beyond this range, the suitability function value gradually decreases. A piecewise function or other suitable function form may be used to express the relationship between the degree of suitability and the change of the indicator value. For other indicators, such as water temperature, dissolved oxygen, etc., the corresponding suitability functions are also constructed according to the tolerance range and suitable interval of fish to them. Specifically, taking water depth, Froude number, water temperature, total phosphorus concentration, non-ionic ammonia concentration, and dissolved oxygen saturation as examples, Figure 4 is shown as its fitness function.

[0042] Step S23, based on the fitness function corresponding to the hydrodynamic index and water environment index of the river to be tested, calculate the fitness of each grid. In this embodiment, for each grid, there are specific data of the corresponding hydrodynamic index and water environment index. Substituting these data into the fitness function of the corresponding index, the fitness value of the index for the target fish in this grid can be obtained.

[0043] Step S24, calculate the weight of each data in the hydrodynamic index and water environment index of the river to be tested. In this embodiment, it can be determined comprehensively based on factors such as the sensitivity of fish to each index, the criticality of the index at different stages of the fish life history (such as breeding period, juvenile growth period, etc.), and the importance of each index on the impact of fish populations in previous studies. Professional data analysis methods such as hierarchical analysis method and principal component analysis can be used to finally calculate the weight value that each hydrodynamic index and water environment index should have by constructing a judgment matrix and analyzing the contribution rate of each index.

[0044] Step S25, based on the weight of each data, the weighted addition method is used to calculate the comprehensive habitat suitability. In this embodiment, for each grid, the suitability value of each indicator in the grid is multiplied by its corresponding weight, and then these products are added together, and the result obtained is the comprehensive habitat suitability corresponding to this grid. For example, the water flow velocity suitability value in a certain grid is 0.6, the weight is 0.3, the water temperature suitability value is 0.8, the weight is 0.5, and so on for other indicators, calculated according to the weighted addition method (such as 0.6×0.3+0.8×0.5+...), and finally the comprehensive habitat suitability of the grid is calculated.

[0045] In one embodiment, step S3, calculating the weighted available area corresponding to different flow conditions based on the comprehensive habitat suitability, combining the Tennant method and the protection target, and selecting the appropriate ecological flow process at least includes:

[0046] Step S31, based on the suitability and grid area of ​​each grid, calculate the weighted available habitat area. In this embodiment, for each grid, its contribution to the overall available habitat area depends not only on its actual area, but also on its suitability. The higher the suitability of the grid, the more suitable it is for fish as a habitat, and the greater its weight is when calculating the available area; conversely, the weight of the grid with low suitability is relatively small. Specifically, the area of ​​each grid can be multiplied by its corresponding comprehensive habitat suitability to obtain the weighted area of ​​the grid.

[0047] Step S32: Calculate the corresponding weighted available area under different flow conditions, and plot the flow and the corresponding weighted available area into a curve, such as Figure 3 In this embodiment, the flow of the river is constantly changing, and different flow rates will affect the hydrodynamics, water environment and other aspects of the river, thereby changing the actual situation of the fish habitat. Therefore, it is necessary to repeat the calculation process of the weighted available habitat area in step S31 for multiple different flow conditions.

[0048] Step S33, combining the Tennant method and the security target analysis curve, evaluate the changes in habitat under different flow conditions and obtain the appropriate ecological flow. In this embodiment, each flow value is used as the horizontal coordinate, and its corresponding weighted available habitat area is used as the vertical coordinate. These data points are marked one by one in the plane rectangular coordinate system, and then these points are connected with a smooth curve to obtain the relationship curve between flow and weighted available area. This curve intuitively shows how the habitat area available to fish in the river changes accordingly with the change of flow, which can help us more clearly understand the impact of flow on fish habitat.

[0049] In one embodiment, the process of step S24, calculating the weight of each data in the hydrodynamic index and water environment index of the river to be tested, includes:

[0050] Step S241, standardizing the data of the hydrodynamic index and water environment index of the river to be tested;

[0051] Step S242: Obtain the weight of each indicator from the standardized data using principal component analysis.

[0052] In this embodiment, the Z-score method is used to standardize the data, and then the principal component analysis is performed. The coefficient of each indicator in each selected principal component is multiplied by the variance contribution rate of the principal component, and then these products are added up to obtain the comprehensive coefficient corresponding to each indicator. After obtaining the comprehensive coefficient of each indicator, in order to accurately represent the relative weight of each indicator in the entire evaluation system, normalization processing is required.

[0053] So far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the original technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present invention.

Claims

1. A method for evaluating the suitability of fish habitats, characterized in that: include: Obtain the hydrodynamic index and water environment index of the river to be tested; Substituting the hydrodynamic index and water environment index of the river to be tested into the suitability function of the target fish to obtain the comprehensive habitat suitability; Based on the comprehensive habitat suitability, the corresponding weighted available area under different flow conditions is calculated, and the appropriate ecological flow is selected in combination with the Tennant method and the protection target.

2. The method according to claim 1, characterized in that The process of obtaining the hydrodynamic index and water environment index of the river to be tested includes: Select representative years and representative water environment scenarios; The distribution of hydrodynamic indexes and water environment indexes of the river to be tested in a representative year is simulated to obtain simulation results; and the simulation results are used as the hydrodynamic indexes and water environment indexes of the river to be tested.

3. The method according to claim 2, characterized in that The process of selecting representative years and representative water environment scenarios shall at least include: Check whether the selected traffic sequence to be tested has any variation; If there is variation, the frequency curve method is used to select normal water years of different periods, and the average water environment suitability of normal water years of different periods is calculated. Then, among the normal water years of different periods, the years with a suitability close to the average water environment suitability are selected as representative water environment scenarios.

4. According to the method of claim 3, the process of selecting the representative year and the representative water environment scenario further comprises: If there is no variation, the entire time period is taken as a whole and the average water year is selected as the representative year and representative water environment scenario.

5. The method according to claim 3, characterized in that: The process of checking whether the selected traffic sequence to be tested has a variation includes: using an MK jump variation diagnosis method to check whether the selected traffic sequence has a variation.

6. The method according to claim 1, characterized in that Substituting the hydrodynamic index and water environment index of the river to be tested into the suitability function of the target fish to obtain the comprehensive habitat suitability process includes: Grid the river to be measured; Determine the suitability function of each data in hydrodynamic index and water environment index; Calculating the suitability of each grid based on the fitness function corresponding to the hydrodynamic index and water environment index of the river to be tested; Calculate the weight of each data in the hydrodynamic index and water environment index of the river to be tested; Based on the weight of each data, the comprehensive habitat suitability was calculated using the weighted addition method.

7. The method according to claim 6, characterized in that Based on the comprehensive habitat suitability, the weighted available area corresponding to different flow conditions is calculated. Combining the Tennant method and the protection target, the process of selecting the appropriate ecological flow includes at least: Based on the suitability and area of ​​each grid, the weighted available habitat area is calculated; Calculate the corresponding weighted available area under different flow conditions, and draw a curve between the flow and the corresponding weighted available area; The curves were analyzed by combining the Tennant method and the guarantee target to evaluate the changes in habitats under different flow conditions and obtain the appropriate ecological flow.

8. The method according to claim 5, characterized in that The process of calculating the weight of each data in the hydrodynamic index and water environment index of the river to be tested includes: Standardize the data of the hydrodynamic index and water environment index of the river to be tested; The weight of each indicator is obtained by principal component analysis of the standardized data.

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