Method and system for determining ecological water level of groundwater based on ecological response of vegetation

Abstract

The present application relates to the technical field of groundwater ecological water level determination, in particular to a method and system for determining groundwater ecological water level based on ecological response of vegetation. The method comprises the following steps: continuously observing groundwater depth; layering to measure air gap salt concentration and observing vegetation growth state, obtaining air gap salt concentration profile, vegetation growth state observation data and distribution density of vegetation root along depth direction; converting the salt concentration profile into osmotic pressure profile, multiplying the osmotic pressure profile with the root distribution density point by point to identify peak value, and obtaining root osmotic stress level time series; sorting the root osmotic stress level time series, statistically calculating the inhibited proportion in each interval, and taking the point where the growth rate changes from increasing to decreasing as the osmotic stress threshold; outputting the groundwater depth when the osmotic stress threshold is reached as the groundwater ecological water level. The present application realizes accurate characterization of the corresponding relationship between groundwater depth and actual osmotic stress level of vegetation root, and makes the groundwater ecological water level effectively reflect the tolerance state of vegetation root.

Description

Technical Field

[0001] This invention relates to the field of groundwater ecological water level determination technology, specifically to a method and system for determining groundwater ecological water level based on vegetation ecological response. Background Technology

[0002] The ecological groundwater level refers to the critical groundwater depth threshold that can maintain the normal growth of natural vegetation in a region and ensure the stability of the ecosystem. Its accurate determination is of great significance for the ecological protection, rational development and regulation of groundwater resources in arid and semi-arid regions and inland salinized areas.

[0003] However, groundwater typically contains various salt components with varying solubility, resulting in an uneven distribution of salinity along the depth direction in the vadose zone. This distribution pattern dynamically changes with groundwater depth. Simultaneously, the root density of vegetation also varies along the depth direction. Groundwater depth reflects only an external indicator of the overall water and salinity status of the vadose zone. The actual degree of growth stress experienced by vegetation roots depends on the coupling effect between the salinity concentration at that depth and the root density at that depth, and this coupling relationship constantly changes with groundwater depth. Therefore, the degree of root growth stress corresponding to the same groundwater depth is not fixed, making it difficult to accurately characterize the correlation between groundwater depth and the actual level of growth stress experienced by vegetation roots. Consequently, the determined groundwater ecological water level threshold cannot truly reflect the tolerance status of vegetation roots. Summary of the Invention

[0004] (1) Technical problems to be solved The purpose of this invention is to provide a method and system for determining groundwater ecological water level based on vegetation ecological response, in order to solve the problem that various salts in groundwater are unevenly distributed along the profile due to differences in solubility, and this distribution changes with the groundwater depth, making it difficult to accurately characterize the correspondence between groundwater depth and the actual level of seepage stress borne by vegetation roots, resulting in the determined groundwater ecological water level threshold failing to reflect the actual tolerance state of vegetation roots.

[0005] (2) Technical solution To achieve the above objectives, on the one hand, the present invention provides a method for determining groundwater ecological water level based on vegetation ecological response, the method comprising: During the observation period in the target area, groundwater depth was collected at each observation time. At each observation time, soil samples were collected from the vadose zone and the salinity was measured. The vegetation growth status was observed simultaneously to obtain the vadose zone salinity profile and vegetation growth status observation data corresponding to each groundwater depth. The distribution density of vegetation roots along the depth direction was obtained.

[0006] The salinity profiles of the vadose zone corresponding to each groundwater depth were converted into osmotic pressure profiles. The osmotic pressure profiles were multiplied point by point along the depth direction by the distribution density of the vegetation roots at the same depth to obtain root stress intensity profiles corresponding to each groundwater depth. The peak values ​​in the root stress intensity profiles were identified. The peak values ​​were determined as the root osmotic stress levels at the corresponding groundwater depths to obtain the root osmotic stress level time series corresponding to the observation time.

[0007] The time series of root osmotic stress levels was divided into several intervals according to the numerical values ​​from small to large. The proportion of the inhibited state in the corresponding vegetation growth status observation data of each interval was counted to obtain the inhibited proportion sequence. The position where the proportion growth rate of the inhibited proportion sequence changed from increasing to decreasing was identified, and the root osmotic stress level corresponding to the position was determined as the osmotic stress threshold.

[0008] The groundwater ecological water level is output as the groundwater depth at which the root infiltration stress level reaches the infiltration stress threshold, corresponding to the groundwater depth at each observation time.

[0009] Furthermore, the method for collecting soil samples from the vadose zone at different observation times and measuring the salinity concentration, while simultaneously observing vegetation growth, to obtain vadose zone salinity profiles and vegetation growth status observation data corresponding to each groundwater depth includes: Preliminary salt concentration measurements were performed along the depth direction in the vadose zone to obtain a preliminary salt concentration distribution.

[0010] The thickness of the sampling layer is determined based on the preliminary salt concentration distribution.

[0011] The vadose zone was divided into sampling layers according to the thickness of the sampling layer. Soil samples were collected layer by layer and the salt concentration was measured to obtain the vadose zone salt concentration profile corresponding to each groundwater burial depth.

[0012] At the same observation time when soil samples were collected, the transpiration rate of vegetation was measured to obtain observation data on vegetation growth status corresponding to each groundwater depth.

[0013] Furthermore, the method for determining the sampling layer thickness based on the preliminary salt concentration distribution includes: The concentration difference at each depth sampling point is obtained by subtracting the solubility of each salt group in the groundwater from the salt concentration at each depth sampling point in the preliminary salt concentration distribution.

[0014] The depth corresponding to the depth sampling point with the smallest concentration difference is determined as the encryption depth.

[0015] Using the encryption depth as the center, the thickness of the sampling layer is determined by a geometric progression towards both the groundwater surface and the surface.

[0016] Furthermore, the method of subtracting the solubility of each salt group in the groundwater from the salt concentration at each depth sampling point in the preliminary salt concentration distribution to obtain the concentration difference value at each depth sampling point includes: Obtain the solubility of each salt group in the groundwater.

[0017] The solubility of each salt group is subtracted from the salt concentration at each depth sampling point in the preliminary salt concentration distribution to obtain the concentration difference value of each salt group at each depth sampling point.

[0018] The minimum value among the concentration differences of each salt group at each depth sampling point is determined as the concentration difference at the corresponding depth sampling point.

[0019] Furthermore, the method of determining the sampling layer thickness by using the encryption depth as the center and proceeding towards the groundwater surface and the surface side according to a geometric progression includes: The difference between the maximum and minimum values ​​of the root distribution density of vegetation within the depth range adjacent to the encryption depth is obtained to obtain the variation range of root distribution density.

[0020] The ratio of the variation range of root distribution density to the preset baseline value of variation range is determined as the common ratio of the geometric sequence.

[0021] By multiplying the preset initial sampling layer thickness by the common ratio layer by layer, the sampling layer thicknesses extending towards the groundwater surface and the surface are obtained respectively.

[0022] Furthermore, the method for determining the preset change range benchmark value includes: Along the depth direction, the depth corresponding to the depth sampling point where the change amplitude first falls below the preset concentration change threshold is determined as the starting depth at which the salt concentration no longer changes with depth.

[0023] The depth range between the starting depth and the bottom of the vadose zone is defined as the reference depth range.

[0024] Obtain the difference between the maximum and minimum values ​​of the vegetation root distribution density within the reference depth range, and determine the difference as a preset variation range benchmark value.

[0025] Furthermore, the method for measuring the transpiration rate of vegetation at the same observation time when collecting soil samples to obtain vegetation growth status observation data corresponding to each groundwater depth includes: Obtain meteorological data corresponding to the same observation time as the transpiration rate measurement; calculate the potential transpiration rate based on the meteorological data; divide the transpiration rate by the potential transpiration rate to obtain the transpiration rate ratio.

[0026] The observation time when the transpiration rate ratio is lower than the preset transpiration rate ratio is defined as the suppressed state, and the observation time when the transpiration rate ratio is not lower than the preset transpiration rate ratio is defined as the normal state, so as to obtain the vegetation growth status observation data corresponding to each groundwater depth.

[0027] Furthermore, the method for converting the vadose zone salinity profile corresponding to each groundwater depth into an osmotic pressure profile includes: Obtain the water content profile of the vadose zone along the depth direction, the solubility of each salt component in the groundwater, and the initial concentration percentage of each salt component in the groundwater.

[0028] Based on the salt concentration profile and water content profile of the vadose zone, the salt concentration is converted into pore water salt concentration at each depth.

[0029] Based on the initial concentration ratio of each salt group in the groundwater, the salt concentration in the pore water is allocated to the corresponding concentration of each salt group.

[0030] The smaller value between the allocated concentration of each salt component and the solubility of the corresponding salt component is determined as the dissolved concentration of the corresponding salt component.

[0031] Divide the dissolved concentration and solubility of each salt component by its corresponding molar mass to obtain the molar concentration of each salt component. Calculate the osmotic pressure of each salt component at each depth and sum them to obtain the osmotic pressure profile. The formula for calculating the osmotic pressure of each salt component is as follows: .

[0032] in, For the first Each salt group corresponds to a specific osmotic pressure; For the first The van der Hoff coefficients corresponding to each salt group; For the first The molar concentration of the dissolved state corresponding to each salt group; It is the gas constant; This is the thermodynamic temperature corresponding to the water temperature; For the first The molar concentration of the solubility corresponding to each salt group; This is the preset concentration correction factor.

[0033] Furthermore, the method for identifying peak values ​​in the root stress intensity profile includes: Linear interpolation of the osmotic pressure profile yields the interpolated osmotic pressure profile.

[0034] The distribution density of vegetation roots along the depth direction is interpolated using cubic splines to obtain the interpolated root distribution density profile.

[0035] The interpolated osmotic pressure profile and the interpolated root distribution density profile are multiplied point by point at the same depth to obtain the interpolated root stress intensity profile.

[0036] Identify peak values ​​in the interpolated root stress intensity profile.

[0037] Based on the same inventive concept, this invention also provides a groundwater ecological water level determination system based on vegetation ecological response, the system comprising: The multi-source observation data acquisition module is used to collect groundwater depth at each observation time during the observation period in the target area; at each observation time, soil samples are collected in layers of the vadose zone and the salt concentration is measured, and the vegetation growth status is observed simultaneously to obtain the vadose zone salt concentration profile and vegetation growth status observation data corresponding to each groundwater depth; and the distribution density of vegetation roots along the depth direction is obtained.

[0038] The permeability stress level calculation module is used to convert the vadose zone salinity concentration profile corresponding to each groundwater depth into an osmotic pressure profile; multiply the osmotic pressure profile by the root distribution density along the depth direction at the same depth point by point to obtain the root stress intensity profile corresponding to each groundwater depth; identify the peak value in the root stress intensity profile; determine the peak value as the root permeability stress level at the corresponding groundwater depth, and obtain the root permeability stress level time series corresponding to the observation time.

[0039] The osmotic stress threshold identification module is used to divide the root osmotic stress level time series into several intervals according to the numerical values ​​from small to large, and to count the proportion of the inhibited state in the corresponding vegetation growth status observation data in each interval to obtain the inhibited proportion sequence; to identify the position in the inhibited proportion sequence where the proportion growth rate changes from increasing to decreasing, and to determine the root osmotic stress level corresponding to the position as the osmotic stress threshold.

[0040] The ecological water level determination and output module is used to output the groundwater ecological water level when the root seepage stress level reaches the seepage stress threshold at each observation time.

[0041] (3) Beneficial effects Compared with the prior art, the beneficial effects of the present invention are: 1. By converting the salinity profile of the vadose zone into an osmotic pressure profile and multiplying it point by point with the distribution density of vegetation roots along the depth direction to identify the peak value, the root osmotic stress level is obtained. Combined with the inflection point of the inhibited proportion growth rate, the osmotic stress threshold is determined. This achieves an accurate characterization of the correspondence between groundwater depth and the actual osmotic stress level of vegetation roots, so that the determined groundwater ecological water level can truly reflect the tolerance state of vegetation roots.

[0042] 2. The depth of sampling is determined by preliminary salt concentration measurement, and the thickness of the sampling layer is expanded by a geometric series based on the common ratio determined by the variation of root distribution density. This achieves dense sampling in key areas and sparse sampling in other areas, which reduces the sampling workload while ensuring the accuracy of salt concentration measurement at key depths, and further improves the accuracy of groundwater ecological water level determination results. Attached Figure Description

[0043] Figure 1 This is a flowchart of the groundwater ecological water level determination method based on vegetation ecological response according to Embodiment 1 of the present invention. Figure 2 This is a schematic diagram of the module composition of the groundwater ecological water level determination system based on vegetation ecological response in Embodiment 2 of the present invention. Detailed Implementation

[0044] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] Before providing examples, it is necessary to describe the application scenarios of this invention. This invention is applicable to arid and semi-arid regions, inland salinized areas, and other areas where groundwater depth is shallow, vadose zone salinity fluctuates dynamically with groundwater depth, and natural vegetation roots directly rely on groundwater or capillary water for growth. It can be used for on-site monitoring and determination of groundwater ecological water levels in scenarios such as groundwater development and utilization planning, dynamic regulation of groundwater levels, and delineation of ecological protection red lines, providing a basis for the rational allocation of water resources and the ecological protection of natural vegetation in relevant areas.

[0046] Example 1: As Figure 1 As shown in the figure, this embodiment provides a method for determining groundwater ecological water level based on vegetation ecological response, the method including: S1. During the observation period in the target area, collect groundwater depth at each observation time; at each observation time, collect soil samples from the vadose zone and measure the salt concentration, and simultaneously observe the vegetation growth status to obtain vadose zone salt concentration profiles and vegetation growth status observation data corresponding to each groundwater depth.

[0047] The method for collecting soil samples from the vadose zone at different observation times, measuring salt concentration, and simultaneously observing vegetation growth status to obtain vadose zone salt concentration profiles and vegetation growth status observation data corresponding to each groundwater depth includes: Preliminary salt concentration measurements were performed along the depth direction in the vadose zone to obtain a preliminary salt concentration distribution.

[0048] The thickness of the sampling layer is determined based on the preliminary salt concentration distribution.

[0049] The method for determining the sampling layer thickness based on the preliminary salt concentration distribution includes: The concentration difference at each depth sampling point is obtained by subtracting the solubility of each salt group in the groundwater from the salt concentration at each depth sampling point in the preliminary salt concentration distribution.

[0050] The method for obtaining the concentration difference value corresponding to each depth sampling point by subtracting the solubility of each salt group in groundwater from the salt concentration at each depth sampling point in the preliminary salt concentration distribution includes: Obtain the solubility of each salt group in the groundwater.

[0051] The solubility of each salt group is subtracted from the salt concentration at each depth sampling point in the preliminary salt concentration distribution to obtain the concentration difference value of each salt group at each depth sampling point.

[0052] The minimum value among the concentration differences of each salt group at each depth sampling point is determined as the concentration difference at the corresponding depth sampling point.

[0053] The depth corresponding to the depth sampling point with the smallest concentration difference is determined as the encryption depth.

[0054] For example, a groundwater level monitoring well No. 1 is set up in the target area. An automatic pressure-type water level sensor is installed in the well. The data acquisition interval is set to 24 hours. The observation is carried out continuously for 12 months to obtain groundwater depth data corresponding to 365 observation times. During the observation period, the groundwater depth fluctuates between 152cm and 478cm.

[0055] The vadose zone thickness was taken as 600 cm below the surface, covering the maximum fluctuation range of groundwater depth during the observation period. Twelve depth sampling points, numbered D1 to D12, were set at 50 cm intervals along the 600 cm depth range, corresponding to depths of 25 cm, 75 cm, 125 cm, 175 cm, 225 cm, 275 cm, 325 cm, 375 cm, 425 cm, 475 cm, 525 cm, and 575 cm, respectively. The depth sampling point numbers are denoted as follows. , Number the soil samples as 1, 2, ..., 12, corresponding to D1 to D12 respectively. Collect soil samples at each point, prepare an extract at a water-to-soil ratio of 5:1, and measure the conductivity of the extract. Based on the pre-established linear regression relationship between conductivity and salt concentration, the salt concentration of the extract at the corresponding depth sampling point was calculated. : , The unit is g / L. The unit is mS / cm. The regression coefficient was obtained by fitting paired data of regional soil leachate conductivity and salt concentration determined by chemical titration, with a goodness of fit of 0.96. The preliminary salt concentration distribution was obtained as follows: D1 corresponds to 18.6 g / L, D2 to 14.2 g / L, D3 to 10.5 g / L, D4 to 7.8 g / L, D5 to 5.6 g / L, D6 to 3.9 g / L, D7 to 2.3 g / L, D8 to 2.0 g / L, D9 to 2.6 g / L, D10 to 3.1 g / L, D11 to 3.5 g / L, and D12 to 3.6 g / L. The salt concentration first decreases and then increases along the depth direction, reaching the lowest value across the entire depth range near D8.

[0056] A comprehensive water quality analysis was conducted on the groundwater in the target area. The salt content of the groundwater was classified into four groups: sodium chloride, sodium sulfate, magnesium sulfate, and calcium sulfate. The salt group classification numbers are denoted as follows: , Numbers 1, 2, 3, and 4 correspond to sodium chloride, sodium sulfate, magnesium sulfate, and calcium sulfate, respectively. The measured groundwater temperature is 18℃. Values ​​for sodium chloride solubility are taken from the solubility data table corresponding to 18℃. The solubility of sodium sulfate is 358 g / L. The solubility of magnesium sulfate is 190 g / L. The solubility of calcium sulfate is 353 g / L. It is 2.1 g / L.

[0057] Solubility of sodium chloride Solubility of sodium sulfate Solubility of magnesium sulfate Solubility of calcium sulfate The concentration differences between these values ​​and the salt concentrations corresponding to D1 to D12 are calculated to obtain the concentration differences of the four salt groups at each depth sampling point: ,in, For the first The salt concentration corresponding to each depth sampling point For the first The depth sampling point corresponds to the first The concentration difference between the salt groups; Greater than At that time, the corresponding salt group was in the first... At depth sampling point D8, which is in a supersaturated state, the concentration difference is still calculated as an absolute value. Taking 8 as an example, the corresponding concentration difference is 356.0 g / L for sodium chloride, 188.0 g / L for sodium sulfate, 351.0 g / L for magnesium sulfate, and 0.1 g / L for calcium sulfate.

[0058] The minimum concentration difference among the four salt groups at each depth sampling point is determined as the concentration difference at that depth sampling point: .

[0059] Concentration difference corresponding to depth sampling point D8 The concentration is 0.1 g / L, corresponding to the salt grouping of calcium sulfate ( (Equal to 4). The concentration differences from D1 to D12 were calculated using the same method. The corresponding salt groups were all calcium sulfate, with D1 being 16.5 g / L, D2 being 12.1 g / L, D3 being 8.4 g / L, D4 being 5.7 g / L, D5 being 3.5 g / L, D6 being 1.8 g / L, D7 being 0.2 g / L, D9 being 0.5 g / L, D10 being 1.0 g / L, D11 being 1.4 g / L, and D12 being 1.5 g / L.

[0060] Comparing the concentration differences corresponding to D1 to D12, the concentration difference of 0.1 g / L at depth sampling point D8 is the smallest among the 12 values. Therefore, the depth of 375 cm corresponding to depth sampling point D8 is determined as the densification depth. The salt concentration of 2.0 g / L at the densification depth is related to the calcium sulfate solubility. (2.1 g / L) is the closest, corresponding to the depth position of calcium sulfate component in the vadose zone that is closest to saturation precipitation.

[0061] It should be noted that the salt concentration of the leachate used to determine the densification depth in this step is not on the same dimension as the solubility of groundwater salt components (pore water concentration scale). The absolute value of the concentration difference obtained by direct subtraction is not strictly equal to the difference between the in-situ pore water salt concentration and solubility. However, the water content of the vadose zone usually changes continuously and gradually along the depth direction without abrupt changes. The conversion ratio of leachate salt concentration to pore water salt concentration between adjacent sampling points (50 cm apart) is similar. Therefore, the relative magnitude of the leachate salt concentration difference can be used to identify the depth area with the smallest concentration difference. This can be used to roughly and reliably locate the depth range where salt components are relatively closer to saturation precipitation, thus meeting the location requirement of determining the densification depth.

[0062] Using the encryption depth as the center, the thickness of the sampling layer is determined by a geometric progression towards both the groundwater surface and the surface.

[0063] The method of determining the sampling layer thickness by taking the encryption depth as the center and proceeding towards the groundwater surface and the land surface respectively according to a geometric sequence includes: The difference between the maximum and minimum values ​​of the root distribution density of vegetation within the depth range adjacent to the encryption depth is obtained to obtain the variation range of root distribution density.

[0064] The ratio of the variation range of root distribution density to the preset baseline value of variation range is determined as the common ratio of the geometric sequence.

[0065] The method for determining the preset change range benchmark value includes: Along the depth direction, the depth corresponding to the depth sampling point where the change amplitude first falls below the preset concentration change threshold is determined as the starting depth at which the salt concentration no longer changes with depth.

[0066] The depth range between the starting depth and the bottom of the vadose zone is defined as the reference depth range.

[0067] Obtain the difference between the maximum and minimum values ​​of the vegetation root distribution density within the reference depth range, and determine the difference as a preset variation range benchmark value.

[0068] By multiplying the preset initial sampling layer thickness by the common ratio layer by layer, the sampling layer thicknesses extending towards the groundwater surface and the surface are obtained respectively.

[0069] The vadose zone was divided into sampling layers according to the thickness of the sampling layer. Soil samples were collected layer by layer and the salt concentration was measured to obtain the vadose zone salt concentration profile corresponding to each groundwater burial depth.

[0070] For example, the depth range adjacent to the 375cm densification depth is 25cm above and below, i.e., 350cm to 400cm, with the boundary falling at the midpoint between the initial salt concentration distribution sampling points D7 (325cm) and D9 (425cm). Within the 350cm to 400cm depth range, the root distribution density of vegetation was measured using a root drill combined with a root image analyzer, in cm / cm³. The measured values ​​at depths of 350cm, 360cm, 375cm, 390cm, and 400cm were 0.52cm / cm³, 0.47cm / cm³, 0.31cm / cm³, 0.38cm / cm³, and 0.42cm / cm³, respectively. The lowest value in the range was observed at 375cm, corresponding to the near-saturation precipitation of calcium sulfate at this densification depth, and the gypsum crystals formed in the soil hindering root penetration. The maximum root distribution density within the 350cm to 400cm depth range is denoted as... The minimum value is denoted as , It is 0.52 cm / cm³. The root distribution density variation range is 0.31 cm / cm³, denoted as [missing information]. : .get It is 0.21 cm / cm³.

[0071] Comparing the salt concentration variations at adjacent depth sampling points from D1 to D12 along the depth direction: D8 to D9: 0.6 g / L; D9 to D10: 0.5 g / L; D10 to D11: 0.4 g / L; D11 to D12: 0.1 g / L. The criterion is: .

[0072] The preset concentration change threshold is 0.15 g / L, which is based on 1.5 times the accuracy of the conductivity method (±0.1 g / L) to avoid misjudgment due to detection errors. The change range from D11 to D12 is 0.1 g / L, which is lower than the preset concentration change threshold of 0.15 g / L. This is the first occurrence of the sub-threshold range along the depth direction. The depth of 525 cm corresponding to D11 is determined as the starting depth at which the salt concentration no longer changes with depth.

[0073] The depth range between the initial depth of 525 cm and the bottom of the vadose zone of 600 cm was defined as the reference depth range, with a length of 75 cm. Within this reference depth range, the root density was measured: 0.34 cm / cm³ at 525 cm, 0.30 cm / cm³ at 550 cm, 0.24 cm / cm³ at 575 cm, and 0.18 cm / cm³ at 600 cm. The maximum root density within the reference depth range was recorded as [value missing]. The minimum value is denoted as , It is 0.34 cm / cm³. The value is 0.18 cm / cm³, and the preset variation range baseline value is denoted as [value missing]. : .get It is 0.16 cm / cm³.

[0074] The variation range of root distribution density Compared with the preset change range benchmark value The ratio of the two numbers is determined as the common ratio of the geometric sequence. : 1.31. When the variation range of root distribution density is less than the preset variation range benchmark value, the common ratio is less than 1, and the sampling layer thickness decreases to both sides. The lower limit of the sampling layer thickness is set to 5cm to avoid the sampling layer thickness approaching 0, which would lead to ineffective sampling. In this example, the variation range of root distribution density is greater than the preset variation range benchmark value, the common ratio is greater than 1, and the sampling layer thickness increases to both sides.

[0075] The preset initial sampling layer thickness is denoted as , A value of 10cm is used, based on the minimum depth of a single operation of the ring sampler. A central sampling layer is defined with a densification depth of 375cm as the center, ranging from 370cm to 380cm in depth, with a thickness of [missing information]. This serves as the starting layer for expansion to both sides. The sampling layer numbers for expansion to both sides are denoted as... , Take 2, 3, ..., the first The layer thickness of the sampling layer is denoted as : .

[0076] This indicates the operation of rounding to the nearest integer in centimeters. It is 13cm. It is 17cm. It is 22cm. It is 29cm. It is 38cm. It is 50cm. It is 66cm. It is 86cm. The value is 113cm. When the cumulative calculated value of the sampling layer thickness after expanding layer by layer according to the common ratio exceeds the boundary distance in the corresponding direction, the thickness of the last sampling layer in the corresponding direction is adjusted to the difference between the boundary distance and the accumulated thickness, and this is taken as the last sampling layer in the corresponding direction, and expansion according to the common ratio is no longer continued.

[0077] The sampling layer extends upwards from the upper boundary of the central sampling layer at 370cm on one side of the Earth's surface, with a distance of 370cm between it and the 0cm surface. to The total thickness is 321cm, and the remaining distance is 370 minus 321 equals 49cm, which is less than... The calculated value is 113cm. The thickness of the last sampling layer on the surface side is adjusted to 49cm. There are a total of 10 layers on the surface side, including the central sampling layer, with depth ranges of 357cm to 370cm (13cm), 340cm to 357cm (17cm), 318cm to 340cm (22cm), 289cm to 318cm (29cm), 251cm to 289cm (38cm), 201cm to 251cm (50cm), 135cm to 201cm (66cm), 49cm to 135cm (86cm), and 0cm to 49cm (49cm, the last layer).

[0078] The groundwater level extends downwards from the lower boundary of the central sampling layer by 380cm, and the distance between it and the bottom of the vadose zone (600cm) is 220cm. to The total thickness is 169cm, and the remaining distance is 220 minus 169 equals 51cm, which is less than... The calculated value is 66cm. The thickness of the last sampling layer on the groundwater surface side is adjusted to 51cm. There are a total of 8 layers on the groundwater surface side, including the central sampling layer, with depth ranges of 380cm to 393cm (13cm), 393cm to 410cm (17cm), 410cm to 432cm (22cm), 432cm to 461cm (29cm), 461cm to 499cm (38cm), 499cm to 549cm (50cm), and 549cm to 600cm (51cm, the last layer). The entire depth range of the vadose zone is divided into 17 sampling layers according to the above division.

[0079] The frequency of simultaneous observation of soil salinity and vegetation growth status was set to once every 15 days, which is lower than the frequency of automatic monitoring of groundwater depth over 24 hours. This takes into account the field work cycle and testing costs of destructive soil sampling. During the 12-month observation period, stratified collection and measurement data were obtained at 24 observation times. The groundwater depth values ​​corresponding to the 24 observation times were all determined by taking the record value that is closest to the time in the 24-hour monitoring record of the automatic pressure water level sensor. Taking one observation time as an example, the recorded groundwater depth was 461cm. The vadose zone ranged from 0cm above the ground to 461cm below the groundwater depth. The sampling layers involved were 9 layers on the surface side (0cm to 370cm), 1 layer in the center (370cm to 380cm), and 4 layers on the groundwater surface side (380cm to 461cm, i.e., 380cm to 393cm, 393cm to 410cm, 410cm to 432cm, and 432cm to 461cm). The subsequent 3 layers on the groundwater surface side (461cm to 499cm, 499cm to 549cm, and 549cm to 600cm) were not sampled because their depth exceeded the groundwater depth of 461cm at the corresponding observation time and they were in the saturated zone below the groundwater surface. Soil samples were collected layer by layer from 14 sampling layers, and the salinity concentration at the corresponding depth of each sampling layer was measured. The salinity profile of the vadose zone was obtained by conversion using the conductivity method: 19.4 g / L from 0 cm to 49 cm, 17.0 g / L from 49 cm to 135 cm, 13.4 g / L from 135 cm to 201 cm, 9.5 g / L from 201 cm to 251 cm, 6.7 g / L from 251 cm to 289 cm, and 289 cm to 318 cm. The concentrations were as follows: 4.9 g / L at 318 cm to 340 cm, 3.7 g / L at 340 cm to 357 cm, 3.0 g / L at 357 cm to 370 cm, 2.5 g / L at 370 cm to 380 cm, 2.2 g / L at 380 cm to 393 cm, 2.4 g / L at 380 cm to 393 cm, 2.8 g / L at 393 cm to 410 cm, 3.1 g / L at 410 cm to 432 cm, and 3.3 g / L at 432 cm to 461 cm. Using the same method, stratified data collection and measurement were performed at the remaining 23 observation times, resulting in vadose zone salinity profiles corresponding to the 24 observation times in the groundwater depth time series.

[0080] At the same observation time when soil samples were collected, the transpiration rate of vegetation was measured to obtain observation data on vegetation growth status corresponding to each groundwater depth.

[0081] The method for measuring the transpiration rate of vegetation at the same observation time when soil samples are collected, and obtaining observation data on vegetation growth status corresponding to different groundwater depths, includes: Obtain meteorological data corresponding to the same observation time as the transpiration rate measurement; calculate the potential transpiration rate based on the meteorological data; divide the transpiration rate by the potential transpiration rate to obtain the transpiration rate ratio.

[0082] The observation time when the transpiration rate ratio is lower than the preset transpiration rate ratio is defined as the suppressed state, and the observation time when the transpiration rate ratio is not lower than the preset transpiration rate ratio is defined as the normal state, so as to obtain the vegetation growth status observation data corresponding to each groundwater depth.

[0083] Obtain the distribution density of vegetation roots along the depth direction.

[0084] For example, tamarisk trees growing around groundwater monitoring well No. 1 were selected as the measurement objects. Three tamarisk trees with uniform growth and similar age were chosen. A heat diffusion stem flow meter probe was installed on the current year's lignified branches of each tree, with the probe inserted to a depth of 2 cm. The stem flow rate was recorded, and the transpiration water consumption per tree was converted according to the sapwood area. Combined with the canopy projection area of ​​each tree, the transpiration rate per unit area was converted. The average value of the three measurement results was taken as the transpiration rate at the corresponding observation time, denoted as . Stem flow measurements and soil salinity stratification were conducted simultaneously, with each measurement frequency being once every 15 days.

[0085] An automatic weather station was set up next to the monitoring well, and the daily maximum temperature, daily minimum temperature, and daily average temperature were recorded at the same observation time as the evaporation rate measurement, and denoted as follows: , , The unit is °C; the astronomical radiation expressed as evaporation equivalent is obtained by combining the observation date and the latitude of the target area, and is denoted as... The unit is mm / d. Potential transpiration rate is characterized by reference evapotranspiration, denoted as . Calculated according to the Hargreaves-Samani reference evaporation empirical formula: .

[0086] The unit is mm / d. Taking one observation time as an example, the groundwater depth is 461 cm, which is the same time as the measurement of the salinity profile in the vadose zone. It is 32℃. It is 18℃. It is 25℃. From the table, we get 14.6 mm / d. Substituting this into the calculation, we get... The flow rate was 5.38 mm / d; the corresponding observation time was measured using the stem flow method. It is 1.98 mm / d.

[0087] evaporation rate Divide by potential transpiration rate The ratio of transpiration rates is obtained and denoted as . : 0.37.

[0088] The preset transpiration rate ratio is denoted as The method for obtaining the values ​​is as follows: Within the target area, monitoring sections where the groundwater depth has remained stable at 200cm for an extended period and where the root system can sustainably utilize capillary water were selected as unrestricted water control points. The transpiration rate ratios for 36 sunny days were measured using the same stem flow method. The mean was 0.93, and the standard deviation was 0.06. Subtracting twice the standard deviation from the mean yielded the result. It is 0.81.

[0089] It is 0.37, lower than The corresponding observation time was determined to be in a suppressed state. Using another observation time as a control, at a groundwater depth of 198 cm, the measured... It is 3.2 mm / d. It is 3.6 mm / d. It is 0.89, not lower than The condition was determined to be normal. The transpiration rate ratio was calculated for each of the 24 observation times during the observation period using the same method and compared with... By comparison, we obtained the vegetation growth status observation data corresponding to the 24 observation times.

[0090] The root density along the depth direction was measured once at the beginning of the observation period and not repeated within the 12-month observation period. The data was based on the fact that the spatial distribution pattern of the root system in perennial deep-rooted plants of the genus *Tamarix* changes over an annual period, and the rate of change is significantly slower than that of the vadose zone salinity profile. This data was considered a relatively stable background parameter during the observation period. It should be noted that this method is only applicable to deep-rooted perennial plants such as *Tamarix* with interannually stable root spatial patterns. If the target vegetation is shallow-rooted, annual, or has a root distribution that exhibits significant plasticity in response to water and salinity conditions, the root density should be measured synchronously with the vadose zone salinity profile and repeated at the same frequency.

[0091] The measurement method is the same as that used for measuring the root distribution density of vegetation within the depth range adjacent to the densification depth and within the reference depth range, employing the root drilling method combined with a root image analyzer. The root distribution density of vegetation at the sampling points corresponding to depths D1 to D12 is denoted as... , The meanings of the depth sampling point numbers are the same: D1 is 0.15cm / cm³, D2 is 0.22cm / cm³, D3 is 0.29cm / cm³, D4 is 0.35cm / cm³, D5 is 0.41cm / cm³, D6 is 0.47cm / cm³, D7 is 0.50cm / cm³, D8 is 0.31cm / cm³, consistent with the measured value at 375cm within the adjacent depth range of the densified depth, D9 is 0.40cm / cm³, D10 is 0.37cm / cm³, D11 is 0.34cm / cm³, consistent with the measured value at 525cm within the reference depth range, and D12 is 0.24cm / cm³, consistent with the measured value at 575cm within the reference depth range. The 12 measured values ​​corresponding to D1 to D12, together with the measured values ​​of 0.52cm / cm³, 0.47cm / cm³, 0.38cm / cm³, and 0.42cm / cm³ at 350cm, 360cm, 390cm, and 400cm in the adjacent depth range of the densification depth, and the measured values ​​of 0.30cm / cm³ and 0.18cm / cm³ at 550cm and 600cm in the reference depth range, together constitute the distribution density profile of vegetation roots along the depth direction, covering 18 measuring points in the depth range of 25cm to 600cm.

[0092] S2. Convert the salinity profile of the vadose zone corresponding to each groundwater depth into an osmotic pressure profile.

[0093] The method for converting the salinity profile of the vadose zone corresponding to each groundwater depth into an osmotic pressure profile includes: Obtain the water content profile of the vadose zone along the depth direction, the solubility of each salt component in the groundwater, and the initial concentration percentage of each salt component in the groundwater.

[0094] Based on the salt concentration profile and water content profile of the vadose zone, the salt concentration is converted into pore water salt concentration at each depth.

[0095] Based on the initial concentration ratio of each salt group in the groundwater, the salt concentration in the pore water is allocated to the corresponding concentration of each salt group.

[0096] The smaller value between the allocated concentration of each salt component and the solubility of the corresponding salt component is determined as the dissolved concentration of the corresponding salt component.

[0097] Divide the dissolved concentration and solubility of each salt component by its corresponding molar mass to obtain the molar concentration of each salt component. Calculate the osmotic pressure of each salt component at each depth and sum them to obtain the osmotic pressure profile. The formula for calculating the osmotic pressure of each salt component is as follows: .

[0098] in, For the first Each salt group corresponds to a specific osmotic pressure; For the first The van der Hoff coefficients corresponding to each salt group; For the first The molar concentration of the dissolved state corresponding to each salt group; It is the gas constant; This is the thermodynamic temperature corresponding to the water temperature; For the first The molar concentration of the solubility corresponding to each salt group; This is the preset concentration correction factor.

[0099] For example, at sampling points corresponding to depths D1 to D12, soil moisture content was measured point-by-point using a time-domain reflectometry probe, simultaneously with the measurement at the same depth points as the vadose zone salinity profile, thus obtaining a moisture content profile of the vadose zone along the depth direction. The moisture content corresponding to the sampling layer (370cm to 380cm) at the densified depth of 375cm is denoted as... Actual measurement The value is 0.18, with units of g water / g dry soil. In the comprehensive water quality analysis of the groundwater in the target area, the initial concentration percentages of four salt groups—sodium chloride, sodium sulfate, magnesium sulfate, and calcium sulfate—in the total dissolved salts of the groundwater are also given, denoted as [missing information]. , , , , It is 0.45. It is 0.30. It is 0.20. It is 0.05.

[0100] Taking the sampling layer from 370cm to 380cm at the observation time corresponding to a groundwater depth of 461cm as an example, the measured salt concentration profile of the vadose zone in the 370cm to 380cm sampling layer was 2.2g / L. The leachate was prepared with a water-to-soil ratio of 5:1 to ensure that the salt concentration of the leachate was lower than the in-situ pore water salt concentration. The product of the leachate salt concentration and the water-to-soil ratio was divided by the water content. The pore water salt concentration is calculated and denoted as . 61.1 g / L.

[0101] Pore ​​water salinity concentration Multiply by the initial concentration percentage of each of the four salt groups respectively. The allocated concentrations for each salt group are obtained and denoted as follows: The sodium chloride concentration was obtained. The sodium sulfate concentration is 27.5 g / L. The magnesium sulfate concentration is 18.3 g / L. The calcium sulfate concentration is 12.2 g / L. It is 3.06 g / L.

[0102] Each salt group is assigned its corresponding concentration. Solubility of corresponding salt components The smaller value in the range is determined as the dissolved concentration of the corresponding salt group. Sodium chloride (27.5g / L) less than (358g / L) Take 27.5 g / L of sodium sulfate. (18.3g / L) less than (190g / L) Take 18.3 g / L; magnesium sulfate (12.2g / L) less than (353g / L) Take 12.2 g / L of calcium sulfate. (3.06 g / L) greater than (2.1g / L) Pick The concentration was 2.1 g / L, which corresponds to the calcium sulfate component reaching a saturated precipitation state in the sampling layer from 370 cm to 380 cm. This is consistent with the judgment that the calcium sulfate component at the densification depth of 375 cm is close to saturated precipitation and forms gypsum crystals that hinder root penetration.

[0103] It should be noted that the smaller value is used to correct the situation where the calcium sulfate component should not be fully included in the osmotic pressure contribution at a fixed proportion due to precipitation. The allocated concentrations of the three components, sodium chloride, sodium sulfate, and magnesium sulfate (27.5, 18.3, and 12.2 g / L), are all lower than their respective solubilities, and no precipitation has occurred. The fixed proportion allocation result is consistent with the actual pore water concentration.

[0104] In the formula for calculating osmotic pressure and Must be molar concentration, already obtained and All values ​​are mass concentrations. The molar mass corresponding to each salt group is taken and denoted as... Sodium chloride Sodium sulfate has a concentration of 58.44 g / mol. Magnesium sulfate has a concentration of 142.04 g / mol. Calcium sulfate has a concentration of 120.37 g / mol. The concentration is 136.14 g / mol. Divide the mass concentration by the molar mass and multiply by 1000 to convert it to molar concentration, in mol / m³. Sodium chloride It is 470.6 mol / m³. It is 6125.9 mol / m³; sodium sulfate It is 128.8 mol / m³. It is 1337.7 mol / m³; magnesium sulfate It is 101.4 mol / m³. It is 2932.6 mol / m³; calcium sulfate It is 15.4 mol / m³. It is 15.4 mol / m³. and The values ​​are equal, indicating that the calcium sulfate component is in a saturated state.

[0105] The van der Hoff coefficients for the four salt groups were determined by measuring the osmotic pressure of solutions with pore water concentrations close to those in this example using the freezing point depression method. The values ​​were then converted to the degree of ionization. Sodium chloride showed near-complete ionization. Take 1.9; sodium sulfate exhibits partial ion pair effect. Take 2.6; magnesium sulfate ion pair effect is significant. Take 1.3; calcium sulfate has the strongest ion-pair effect. Take 1.2. The thermodynamic temperature corresponding to the water temperature. Based on a groundwater temperature of 18℃, The K value is 291.15 K. (Gas constant) Take 8.314 J / (mol·K). Preset concentration correction factor. The deviation was obtained by comparing the calculated ideal van der Hoff value with the measured osmotic pressure by the freezing point depression method, and the result was fitted when the salt concentration was close to the solubility. The value was set to 0.15.

[0106] Will , , , , , Substitute into the osmotic pressure calculation formula: The sodium chloride was calculated. 2166.1 kPa; Sodium sulfate 811.9 kPa; magnesium sulfate 319.2 kPa; calcium sulfate The value is 51.5 kPa.

[0107] The four salt groups were assigned their corresponding osmotic pressures. , , , The osmotic pressure profile was obtained by summing the values ​​at each depth. The osmotic pressures corresponding to the sampling layers from 370cm to 380cm were 2166.1kPa, 811.9kPa, 319.2kPa, and 51.5kPa, respectively, resulting in a total calculated value of 3348.7kPa. The same method was used to calculate and sum the values ​​for each of the remaining sampling layers, yielding the osmotic pressure profile corresponding to a groundwater depth of 461cm at the corresponding observation time. The same method was then used to repeat the calculation of the vadose zone salinity profiles corresponding to each of the 24 observation times within the observation period, resulting in osmotic pressure profiles corresponding to each of the 24 observation times in the groundwater depth time series.

[0108] The osmotic pressure profile and the root distribution density along the depth direction are multiplied point by point at the same depth to obtain the root stress intensity profile corresponding to each groundwater depth; the peak value in the root stress intensity profile is identified.

[0109] The method for identifying peak values ​​in the root stress intensity profile includes: Linear interpolation of the osmotic pressure profile yields the interpolated osmotic pressure profile.

[0110] The distribution density of vegetation roots along the depth direction is interpolated using cubic splines to obtain the interpolated root distribution density profile.

[0111] The interpolated osmotic pressure profile and the interpolated root distribution density profile are multiplied point by point at the same depth to obtain the interpolated root stress intensity profile.

[0112] Identify peak values ​​in the interpolated root stress intensity profile.

[0113] The peak value was determined as the root permeability stress level at the corresponding groundwater depth, and the time series of root permeability stress levels corresponding to the observation time was obtained.

[0114] For example, the osmotic pressures corresponding to the four salt groups are shown. , , , The osmotic pressure profile is obtained by summing the values ​​at each depth, denoted as . The sampling layer corresponding to 370cm to 380cm The value was 3348.7 kPa. Using the same method, the summation was performed layer by layer for the remaining 13 sampling layers corresponding to the observation time at a groundwater depth of 461 cm. The midpoint depth of the 14 sampling layers was... The values ​​are as follows: 48921.8 kPa at 24.5 cm, 45127.9 kPa at 92 cm, 29713.2 kPa at 168 cm, 17563.6 kPa at 226 cm, 11469.3 kPa at 270 cm, 7865.4 kPa at 303.5 cm, 5769.4 kPa at 329 cm, 4604.8 kPa at 348.5 cm, 3822.6 kPa at 363.5 cm, 3348.7 kPa at 375 cm, 3461.4 kPa at 386.5 cm, 3651.3 kPa at 401.5 cm, 3538.6 kPa at 421 cm, and 3232.7 kPa at 446.5 cm.

[0115] The interpolation step size is denoted as , A thickness of 1cm is used, with the narrowest sampling layer among the 14 sampling layers being 10cm, to avoid peak localization being limited by interpolation resolution. The depth variable is denoted as... The lower bound of the interpolation is taken as the measured starting depth of the vegetation root distribution density at 25 cm, and the upper bound is taken as the depth of the midpoint of the deepest sampling layer of the osmotic pressure profile at the corresponding observation time, which is 446.5 cm. The depths corresponding to two adjacent osmotic pressures are denoted as... , The corresponding osmotic pressure is denoted as , , lie in and When the interval is between, the interpolated osmotic pressure profile calculation formula is: .

[0116] When the value is 100cm, it is located at 92cm from the sampling point. (45127.9 kPa) and 168 cm ( The interpolation calculation is between 29713.2 kPa and 29713.2 kPa. The value is 43505.3 kPa.

[0117] Cubic spline interpolation was performed on the root distribution density along the depth direction. The interpolation nodes were taken from the sampling points at depths D1 to D12, as well as the denser sampling points within the adjacent depth range and the reference depth range, totaling 18 depth points. Natural boundary conditions were used, meaning the second derivative of the interpolation curve was zero at 25 cm and 600 cm. The interpolated root distribution density profile is denoted as […]. . When the height is 100cm, it is located at 75cm. (0.22cm / cm³) and 125cm ( On spline curves between 0.29 cm / cm³, interpolation calculations were performed. It is 0.2559 cm / cm³.

[0118] Interpolated osmotic pressure profile Interpolated root distribution density profile Multiplying the results point by point at the same depth yields the interpolated root stress intensity profile, denoted as . The unit is kPa·cm / cm³. Get the corresponding values ​​for 25cm, 50cm, 75cm, 100cm, 125cm, 150cm, 175cm, 200cm, 225cm, 250cm, 275cm, 300cm, 325cm, 350cm, 375cm, 400cm, and 425cm. The values ​​are, in order: 7334.1, 8743.1, 10138.3, 11132.6, 11146.1, 10712.5, 9886.4, 8710.4, 7287.0, 6332.7, 5137.8, 3946.1, 3049.1, 2353.8, 1038.7, 1525.6, and 1396.2.

[0119] Calculate point by point within a depth range of 25cm to 446.5cm with a step size of 1cm. Identify the peak value in the interpolated root stress intensity profile; the peak value appears in... At 113cm, corresponding to The pressure is 40868.6 kPa. It is 0.274 cm / cm³, peak value The value is 11196.5. The peak value appears in the middle of the interpolation range and does not fall at the 25cm or 446.5cm boundary; if the peak value appears at the boundary of the interpolation range, it is still treated as the value at the boundary. The value is determined as the peak value and no further processing is performed.

[0120] The depth at which this peak is located also has a high osmotic pressure level. (40868.6 kPa) and high root distribution density ( The value of 0.274 cm / cm³ represents the local depth where the coupling effect between osmotic stress and root distribution is strongest. The osmotic stress experienced by the roots at this depth dominates the overall water physiological response of the plant. In contrast, the coupling effect is weaker in shallower layers with higher osmotic pressure but sparser root distribution (such as at 24.5 cm) or deeper layers with denser root distribution but lower osmotic pressure (such as around 325 cm), and neither layer dominates the overall plant response. Therefore, this peak value, rather than the whole profile area integral or weighted average, is used as the root osmotic stress level.

[0121] It should be noted that when the local osmotic stress in the root system reaches a high level, signaling substances such as abscisic acid (ABA) can be synthesized and transported to the aboveground parts to induce stomatal closure. This chemical signal transduction pathway is determined by the severity of local stress and is not weakened by the hydraulic compensation water absorption of roots at other depths. Therefore, peak stress has an independent dominant role in the overall plant response.

[0122] The peak value of 11196.5 was determined to be the root infiltration stress level corresponding to a groundwater depth of 461 cm. The observation time number is denoted as follows. , Numbered 1, 2, ..., 24, corresponding to the 24 observation times within the observation period, the observation time corresponding to a groundwater depth of 461cm is recorded as the 10th observation time. Equal to 10. Root osmotic stress level is denoted as... , The value was 11196.5. The same method was used to repeat the interpolation, multiplication, and peak value identification for the osmotic pressure profiles corresponding to the remaining 23 observation times. The lower bound of the interpolation was taken as 25 cm, and the upper bound varied with the groundwater depth at the corresponding observation time. The depth of the midpoint of the deepest sampling layer of the osmotic pressure profile at the corresponding observation time was taken to obtain the root osmotic stress level corresponding to each of the 24 observation times. to This constitutes a time series of root osmotic stress levels.

[0123] S3. Divide the root osmotic stress level time series into several intervals according to the numerical values ​​from small to large, and count the proportion of the inhibited state in the corresponding vegetation growth status observation data for each interval to obtain the inhibited proportion sequence; identify the position in the inhibited proportion sequence where the proportion growth rate changes from increasing to decreasing, and determine the root osmotic stress level corresponding to the position as the osmotic stress threshold.

[0124] For example, the groundwater depth and root infiltration stress level corresponding to the 24 observation times during the observation period are respectively. The vegetation growth status observation data were calculated one by one according to the established method, and the results are as follows: The value equals 1, and the groundwater depth is 165cm. The value is 2640.5, which is normal. The value is 2, and the groundwater depth is 152cm. The value is 2590.0, which is normal. The value is 3, and the groundwater depth is 178cm. The value is 2831.0, which is normal. The value is 4, and the groundwater depth is 210cm. The value is 4193.0, which is normal. The value is 5, and the groundwater depth is 245cm. The value is 4640.5, which is normal. The value is 6, and the groundwater depth is 268cm. The value is 6296.0, which is normal. The value is 7, and the groundwater depth is 295cm. The value is 6215.5, which is normal. The value is 8, and the groundwater depth is 312cm. The value is 7250.0, which is normal. The value is 9, and the groundwater depth is 338cm. The value is 7191.0, which is normal. The value is 10, and the groundwater depth is 461cm. The value is 11196.5, which is suppressed; The value is 11, and the groundwater depth is 355cm. The value is 8625.5, which is normal. The value is 12, and the groundwater depth is 372cm. The value is 8310.0, which is normal. The value is 13, and the groundwater depth is 390cm. The value is 9873.0, indicating suppression. The value is 14, and the groundwater depth is 405cm. The value is 9000.5, which is suppressed; The value is 15, and the groundwater depth is 418cm. The value is 10871.0, indicating suppression. The value is 16, and the groundwater depth is 430cm. The value is 10113.0, indicating suppression. The value is 17, and the groundwater depth is 442cm. The value is 11855.0, indicating suppression. The value is 18, and the groundwater depth is 455cm. The value is 10225.5, which is suppressed; The value is 19, and the groundwater depth is 470cm. The value is 12953.0, indicating suppression. The value is 20, and the groundwater depth is 478cm. The value is 11381.0, indicating suppression. The value is 21, and the groundwater depth is 460cm. The value is 12768.0, indicating suppression. The value is 22, and the groundwater depth is 425cm. The value is 10370.5, indicating suppression. The value is 23, and the groundwater depth is 380cm. The value was 8438.0, indicating suppression. The value is 24, and the groundwater depth is 300cm. The value is 6508.0, which is normal.

[0125] The 24 root osmotic stress levels were sorted in ascending order of value, and the sorting number was denoted as follows: , Take 1, 2, ..., 24, and sort them. The root osmotic stress level corresponding to position is denoted as . The corresponding vegetation growth status observation data are rearranged synchronously with the sorting.

[0126] The interval division method is as follows: set a preset sample size for each interval. , Not less than 3 to ensure statistical representativeness; number of intervals Divide the total number of observation times by The result is rounded down, and must be at least 5 to capture the trend of changes in the suppressed proportion; if it is not divisible, the remainder is included in the last interval. In this example, the total number of observation times is 24. Take 4. The value is 6, satisfying both of the above constraints. The interval index is denoted as... , Take 1, 2, ..., 6, and sort them. Ranked first The observation data of the four root system osmotic stress levels and vegetation growth status corresponding to the position are classified into the first... A range.

[0127] Interval 1 corresponds to the 1st to 4th positions in the ranking, with root osmotic stress levels of 2590.0, 2640.5, 2831.0, and 4193.0, respectively, and all corresponding vegetation growth status observations are normal. Interval 2 corresponds to the 5th to 8th positions in the ranking, with root osmotic stress levels of 4640.5, 6215.5, 6296.0, and 6508.0, and all corresponding vegetation growth status observations are normal. Interval 3 corresponds to the 9th to 12th positions in the ranking, with root osmotic stress levels of 7191.0, 7250.0, 8310.0, and 8438.0, and corresponding vegetation growth status observations are normal, normal, normal, and inhibited. Interval 4 corresponds to positions 13 to 16 in the ranking, with root osmotic stress levels of 8625.5, 9000.5, 9873.0, and 10113.0, corresponding to vegetation growth status observations of normal, inhibited, inhibited, and inhibited, respectively. Interval 5 corresponds to positions 17 to 20 in the ranking, with root osmotic stress levels of 10225.5, 10370.5, 10871.0, and 11196.5, all corresponding to inhibited vegetation growth status observations. Interval 6 corresponds to positions 21 to 24 in the ranking, with root osmotic stress levels of 11381.0, 11855.0, 12768.0, and 12953.0, all corresponding to inhibited vegetation growth status observations.

[0128] interval The corresponding suppressed ratio is denoted as The calculation formula is: ;in, For interval The interval corresponds to the number of samples in the suppressed state in the vegetation growth status observation data. The number of suppressed state samples corresponding to intervals 1 to 6 are 0, 0, 1, 3, 4, and 4 respectively, and the suppression ratio sequence is as follows: Equal to 0, Equal to 0, It equals 0.25. It equals 0.75. Equals 1, It equals 1.

[0129] The increment of the inhibition ratio between adjacent intervals is denoted as , Taking 1, 2, ..., 5, the calculation formula is: .

[0130] Equal to 0, It equals 0.25. It equals 0.5. It equals 0.25. The value equals 0. The increment sequence rises from 0 to 0.25 and 0.5, then falls back to 0.25 and 0. The maximum value is obtained at the point where the increment sequence is located. Previously, they increased one by one, in The values ​​then decrease sequentially, indicating the point where the proportional growth rate changes from increasing to decreasing, corresponding to the transition from interval 3 to interval 4. If multiple consecutive maximum values ​​appear in the incremental sequence, the transition position corresponding to the side with the smaller root osmotic stress level value is taken; if the maximum increment occurs in... or Reduce the sample size of the preset single interval (No less than 3) Re-partition, expand the number of intervals and re-bind.

[0131] Identify the increment of the suppressed proportion in the adjacent intervals that reach the maximum value. Then, the interval corresponding to this increment Sort position position (i.e., interval) The root osmotic stress level corresponding to the starting sorting position is determined as the osmotic stress threshold.

[0132] Following the method described above, The maximum value of the incremental sequence corresponds to the transition from interval 3 to interval 4. The root osmotic stress level corresponding to the 13th position in the sorting of interval 4 is determined as the osmotic stress threshold, denoted as . , It is 8625.5.

[0133] S4. Output the groundwater ecological water level when the root infiltration stress level reaches the infiltration stress threshold, which is the groundwater burial depth corresponding to each observation time.

[0134] For example, the root permeability stress level is only taken at the groundwater depth corresponding to the 24 observation times. Observation times in the groundwater depth time series where root permeability stress level calculations were not performed are not included in this step. The root permeability stress levels corresponding to the 24 observation times in chronological order are as follows: to ,in It is 8625.5, which is close to the osmotic stress threshold. (8625.5) values ​​are equal, indicating that the root osmotic stress level has reached the osmotic stress threshold. The groundwater depth corresponding to 11 is 355cm, and the output groundwater ecological water level is 355cm. The corresponding vegetation growth status observation data is normal. The infiltration stress threshold is taken from the boundary position where the inhibition ratio begins to rise rapidly at the interval statistical level, which does not contradict whether the vegetation growth status observation data of a single observation is in an inhibited state.

[0135] When multiple observation times in the root infiltration stress level time series show that the root infiltration stress level is equal to the infiltration stress threshold, the one with the smallest corresponding groundwater depth value is taken as the groundwater ecological water level, so that the groundwater ecological water level is biased towards the shallow depth side, leaving a margin for ecological protection.

[0136] Example 2: Based on the same inventive concept, such as Figure 2 As shown, this embodiment also provides a groundwater ecological water level determination system based on vegetation ecological response, the system comprising: The multi-source observation data acquisition module is used to collect groundwater depth at each observation time during the observation period in the target area; at each observation time, soil samples are collected in layers of the vadose zone and the salt concentration is measured, and the vegetation growth status is observed simultaneously to obtain the vadose zone salt concentration profile and vegetation growth status observation data corresponding to each groundwater depth; and the distribution density of vegetation roots along the depth direction is obtained.

[0137] The permeability stress level calculation module is used to convert the vadose zone salinity concentration profile corresponding to each groundwater depth into an osmotic pressure profile; multiply the osmotic pressure profile by the root distribution density along the depth direction at the same depth point by point to obtain the root stress intensity profile corresponding to each groundwater depth; identify the peak value in the root stress intensity profile; determine the peak value as the root permeability stress level at the corresponding groundwater depth, and obtain the root permeability stress level time series corresponding to the observation time.

[0138] The osmotic stress threshold identification module is used to divide the root osmotic stress level time series into several intervals according to the numerical values ​​from small to large, and to count the proportion of the inhibited state in the corresponding vegetation growth status observation data in each interval to obtain the inhibited proportion sequence; to identify the position in the inhibited proportion sequence where the proportion growth rate changes from increasing to decreasing, and to determine the root osmotic stress level corresponding to the position as the osmotic stress threshold.

[0139] The ecological water level determination and output module is used to output the groundwater ecological water level when the root seepage stress level reaches the seepage stress threshold at each observation time.

[0140] It should be noted that the specific methods by which each module performs operations in the system described in the above embodiments have been described in detail in the embodiments related to the method, and will not be elaborated here.

[0141] Finally, it should be noted that although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for determining groundwater ecological water level based on vegetation ecological response, characterized in that, The method includes: During the observation period in the target area, groundwater depth was collected at each observation time. At each observation time, soil samples were collected from the vadose zone and the salt concentration was measured. The vegetation growth status was observed simultaneously to obtain the vadose zone salt concentration profile and vegetation growth status observation data corresponding to each groundwater depth. The distribution density of vegetation roots along the depth direction was obtained. The salinity profiles of the vadose zone corresponding to each groundwater depth are converted into osmotic pressure profiles. The osmotic pressure profiles are multiplied by the root distribution density along the depth direction at the same depth point by point to obtain the root stress intensity profiles corresponding to each groundwater depth. The peak values ​​in the root stress intensity profiles are identified. The peak values ​​are determined as the root osmotic stress levels at the corresponding groundwater depths to obtain the root osmotic stress level time series corresponding to the observation time. The time series of root osmotic stress levels was divided into several intervals according to the numerical values ​​from small to large. The proportion of the inhibited state in the corresponding vegetation growth status observation data of each interval was counted to obtain the inhibited proportion sequence. The position where the proportion growth rate of the inhibited proportion sequence changed from increasing to decreasing was identified, and the root osmotic stress level corresponding to the position was determined as the osmotic stress threshold. The groundwater ecological water level is output as the groundwater depth at which the root infiltration stress level reaches the infiltration stress threshold, corresponding to the groundwater depth at each observation time.

2. The method for determining groundwater ecological water level based on vegetation ecological response according to claim 1, characterized in that, The method for collecting soil samples from the vadose zone at different observation times, measuring salt concentration, and simultaneously observing vegetation growth status to obtain vadose zone salt concentration profiles and vegetation growth status observation data corresponding to each groundwater depth includes: Preliminary salt concentration measurements were performed along the depth direction in the vadose zone to obtain a preliminary salt concentration distribution. The thickness of the sampling layer was determined based on the preliminary salt concentration distribution. The vadose zone was divided into sampling layers according to the thickness of the sampling layer. Soil samples were collected layer by layer and the salt concentration was measured to obtain the vadose zone salt concentration profile corresponding to each groundwater depth. At the same observation time when soil samples were collected, the transpiration rate of vegetation was measured to obtain observation data on vegetation growth status corresponding to each groundwater depth.

3. The method for determining groundwater ecological water level based on vegetation ecological response according to claim 2, characterized in that, The method for determining the sampling layer thickness based on the preliminary salt concentration distribution includes: The concentration difference between each salt group in the groundwater is obtained by subtracting the solubility of each salt group from the salt concentration at each depth sampling point in the preliminary salt concentration distribution. The depth corresponding to the depth sampling point with the smallest concentration difference is determined as the encryption depth; Using the encryption depth as the center, the thickness of the sampling layer is determined by a geometric progression towards both the groundwater surface and the surface.

4. The method for determining groundwater ecological water level based on vegetation ecological response according to claim 3, characterized in that, The method for obtaining the concentration difference value corresponding to each depth sampling point by subtracting the solubility of each salt group in groundwater from the salt concentration at each depth sampling point in the preliminary salt concentration distribution includes: Obtain the solubility of each salt group in groundwater; The solubility of each salt component is subtracted from the salt concentration at each depth sampling point in the preliminary salt concentration distribution to obtain the concentration difference value of each salt component at each depth sampling point. The minimum value among the concentration differences of each salt group at each depth sampling point is determined as the concentration difference at the corresponding depth sampling point.

5. The method for determining groundwater ecological water level based on vegetation ecological response according to claim 3, characterized in that, The method of determining the sampling layer thickness by taking the encryption depth as the center and proceeding towards the groundwater surface and the land surface respectively according to a geometric sequence includes: The difference between the maximum and minimum values ​​of the root distribution density of vegetation within the depth range adjacent to the encryption depth is obtained to obtain the variation range of root distribution density; The ratio of the variation range of root distribution density to the preset baseline value of variation range is determined as the common ratio of the geometric sequence; By multiplying the preset initial sampling layer thickness by the common ratio layer by layer, the sampling layer thicknesses extending towards the groundwater surface and the surface are obtained respectively.

6. The method for determining groundwater ecological water level based on vegetation ecological response according to claim 5, characterized in that, The method for determining the preset change range benchmark value includes: Along the depth direction, the depth corresponding to the depth sampling point where the change amplitude first falls below the preset concentration change threshold is determined as the starting depth at which the salt concentration no longer changes with depth; The depth range between the starting depth and the bottom of the vadose zone is defined as the reference depth range; Obtain the difference between the maximum and minimum values ​​of the vegetation root distribution density within the reference depth range, and determine the difference as a preset variation range benchmark value.

7. The method for determining groundwater ecological water level based on vegetation ecological response according to claim 2, characterized in that, The method for measuring the transpiration rate of vegetation at the same observation time when soil samples are collected, and obtaining observation data on vegetation growth status corresponding to different groundwater depths, includes: Obtain meteorological data corresponding to the same observation time as the transpiration rate measurement; calculate the potential transpiration rate based on the meteorological data; divide the transpiration rate by the potential transpiration rate to obtain the transpiration rate ratio. The observation time when the transpiration rate ratio is lower than the preset transpiration rate ratio is defined as the suppressed state, and the observation time when the transpiration rate ratio is not lower than the preset transpiration rate ratio is defined as the normal state, so as to obtain the vegetation growth status observation data corresponding to each groundwater depth.

8. The method for determining groundwater ecological water level based on vegetation ecological response according to claim 1, characterized in that, The method for converting the salinity profile of the vadose zone corresponding to each groundwater depth into an osmotic pressure profile includes: Obtain the water content profile along the depth direction of the vadose zone, the solubility of each salt component in the groundwater, and the initial concentration percentage of each salt component in the groundwater; Based on the salt concentration profile and water content profile of the vadose zone, the salt concentration is converted into pore water salt concentration at each depth. Based on the initial concentration ratio of each salt component in the groundwater, the pore water salt concentration is allocated to the corresponding allocated concentration of each salt component. The smaller value between the allocated concentration of each salt component and the solubility of the corresponding salt component is determined as the dissolved concentration of the corresponding salt component. Divide the dissolved concentration and solubility of each salt component by its corresponding molar mass to obtain the molar concentration of each salt component. Calculate the osmotic pressure of each salt component at each depth and sum them to obtain the osmotic pressure profile. The formula for calculating the osmotic pressure of each salt component is as follows: ； in, For the first Each salt group corresponds to a specific osmotic pressure; For the first The van der Hoff coefficients corresponding to each salt group; For the first The molar concentration of the dissolved state corresponding to each salt group; It is the gas constant; This is the thermodynamic temperature corresponding to the water temperature; For the first The molar concentration of the solubility corresponding to each salt group; This is the preset concentration correction factor.

9. The method for determining groundwater ecological water level based on vegetation ecological response according to claim 1, characterized in that, The method for identifying peak values ​​in the root stress intensity profile includes: Linear interpolation is performed on the osmotic pressure profile to obtain the interpolated osmotic pressure profile; The distribution density of vegetation roots along the depth direction is interpolated using cubic splines to obtain the interpolated root distribution density profile. The interpolated osmotic pressure profile and the interpolated root distribution density profile are multiplied point by point at the same depth to obtain the interpolated root stress intensity profile. Identify peak values ​​in the interpolated root stress intensity profile.

10. A groundwater ecological water level determination system based on vegetation ecological response, used to perform the method according to any one of claims 1 to 9, characterized in that, The system includes: The multi-source observation data acquisition module is used to collect groundwater depth at each observation time during the observation period in the target area; at each observation time, soil samples are collected in layers of the vadose zone and the salt concentration is measured, and the vegetation growth status is observed simultaneously to obtain the vadose zone salt concentration profile and vegetation growth status observation data corresponding to each groundwater depth; and the distribution density of vegetation roots along the depth direction is obtained. The permeability stress level calculation module is used to convert the vadose zone salinity concentration profile corresponding to each groundwater depth into an osmotic pressure profile; multiply the osmotic pressure profile by the root distribution density along the depth direction at the same depth point by point to obtain the root stress intensity profile corresponding to each groundwater depth; identify the peak value in the root stress intensity profile; determine the peak value as the root permeability stress level at the corresponding groundwater depth, and obtain the root permeability stress level time series corresponding to the observation time; The osmotic stress threshold identification module is used to divide the root osmotic stress level time series into several intervals according to the numerical values ​​from small to large, and to count the proportion of the inhibited state in the corresponding vegetation growth status observation data in each interval to obtain the inhibited proportion sequence; to identify the position in the inhibited proportion sequence where the proportion growth rate changes from increasing to decreasing, and to determine the root osmotic stress level corresponding to the position as the osmotic stress threshold. The ecological water level determination and output module is used to output the groundwater ecological water level when the root seepage stress level reaches the seepage stress threshold at each observation time.

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