A method for accurately determining the depth of ecological dredging

Abstract

The present invention relates to the technical field of ecological environment governance, and proposes a method for accurately judging the depth of ecological dredging, which includes the following steps: setting sampling points in the target waters to conduct water sample and bottom mud surveys; stratifying the samples collected and surveyed in the above steps by sedimentology, and qualitatively analyzing the characteristics and thickness of the pollution layer, transition layer and normal layer according to the color, smell, particle size and viscosity of the bottom mud; using the Nemerow pollution index method to analyze the nutrient index of the bottom mud of each pollution layer divided in the above steps, and delineating the pollution level. Through the above technical scheme, the problems existing in the prior art are overcome, and the pollution characteristic factors, pollution levels and causes of water pollution determined from the three dimensions of "water body", "mud-water interface" and "bottom mud body" are comprehensively considered to scientifically determine the depth of ecological dredging, and the bottom mud that affects water pollution is removed to control the endogenous pollution of the bottom mud and improve the quality of the water environment.

Description

Technical Field

[0001] The present invention relates to the technical field of ecological environment governance, and in particular to a method for accurately judging the depth of ecological dredging. Background Art

[0002] The goal of ecological dredging is to remove polluted sediment and control endogenous pollution of sediment while minimizing the risk of water quality deterioration, creating conditions for the restoration of aquatic ecosystems and coordinating with the comprehensive water environment improvement plan to achieve the ultimate goal of improving the quality of the water environment. Before dredging, investigations and experiments should be conducted to scientifically select the dredging scope and dredging depth. Determining a reasonable dredging scope can avoid a series of problems such as failure to completely remove polluted sediment due to dredging, serious habitat damage caused by over-dredging, and excessive dredging costs. After determining the dredging scope of polluted sediment, it is necessary to further consider the appropriate dredging depth. Dredging depth is one of the key parameters of ecological dredging. The appropriateness of dredging depth is directly related to the effectiveness of ecological dredging and the cost of the project. Therefore, determining a reasonable ecological dredging depth is of great significance.

[0003] At present, doubts have been raised about using only the sediment evaluation method to determine the thickness of contaminated sediment dredging. It is recommended that the sediment pollution evaluation should be comprehensively considered, and the water quality pollution and mud-water interface changes before and after dredging should be considered, especially the exchange of pollutants between the sediment and the water body and the contribution of the sediment to water pollution. At present, the nitrogen and phosphorus exchange at the mud-water interface has been studied more in the scientific research field. The more mature methods include the overlying water method (adsorption and desorption, laboratory simulation cultivation method) and the pore water method (pore water diffusion model method). Among them, the commonly used overlying water method can more accurately describe the mud-water interface in the laboratory, but it is time-consuming; the pore water method is more efficient, but the results estimated by the formula are too idealized and divorced from the natural environmental conditions of the project. The calculated results do not have good reference value.

[0004] Therefore, it is extremely important to establish a simple, accurate, low-cost, and highly applicable scientific method based on the multidimensional space of the endogenous pollutant release interface to guide ecological dredging projects suitable for different sediment environmental conditions. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies in the prior art and provide a method for accurately judging the depth of ecological dredging, comprehensively considering the pollution characteristic factors, pollution level and causes of water pollution determined from the three dimensions of "water body", "mud-water interface" and "bottom mud body", scientifically determining the depth of ecological dredging, and utilizing it to remove the bottom mud that affects water pollution, control endogenous pollution of the bottom mud and improve the water environment quality.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for accurately determining the depth of ecological dredging comprises the following steps:

[0008] Step 1: Set up sampling points in the target waters and conduct water sampling and sediment surveys;

[0009] Step 2: Sedimentation-stratify the samples collected in step 1, qualitatively analyze the characteristics and thickness of the contaminated layer, transition layer and normal layer according to the color, odor, particle size and viscosity of the sediment, and draw a three-dimensional spatial distribution map of the sediment and a cross-section map of the sediment stratification;

[0010] Step 3: Analyze the nutrient index of the bottom mud of each pollution layer divided in step 2 using the Nemerow pollution index method and determine the pollution level;

[0011] Step 4: Analyze the heavy metal index of the sediment of each contaminated layer divided in step 2 by using the potential ecological risk index evaluation method, and define the potential ecological risk level. Use the potential ecological risk index evaluation method to evaluate the potential ecological risk of the heavy metal content in the sediment, and calculate its potential ecological risk coefficient and potential ecological risk index;

[0012] Step 5: Comprehensively analyze the nutrient pollution level of the proposed treatment area obtained in step 3 and the potential ecological risk level of heavy metals in the proposed treatment area obtained in step 4, and determine the pollution index and pollution level according to the maximum pollution degree index;

[0013] Step 6: Use a stratified water sampler to collect water samples from the water bodies corresponding to the sediment sampling sites surveyed in step 1. Collect 3 parallel samples from each sampling point, and use the modified Nemerow pollution index and water quality index method to evaluate the water quality level;

[0014] Step 7: Based on the pollution layer initially determined in step 2 and the pollution level evaluated in step 3, 10% to 20% of the sediment column samples are taken from the survey point in step 1 to analyze the sediment-water interface interaction; the column samples are sampled and tested every 10 cm, and adsorption and desorption tests are performed. Different methods are then used to detect the adsorption equilibrium interface release flux according to the characteristics of different sediments. Commonly used release flux test methods include laboratory simulation culture method and pore water diffusion model method;

[0015] Step 8: Combine the sediment qualitative preliminary pollution stratification in steps 2 to 4 with the sediment pollution index content and pollution level of each layer with the mud-water interface interaction in step 7, and then combine it with the water quality level analysis in step 6 to finally determine the equilibrium critical concentration, whether to dredge and the dredging point, and form a suitable ecological dredging interface;

[0016] Step 9: Based on the pollution stratification, sediment pollutant evaluation, mud-water interface interaction analysis, water quality grade assessment and pollution situation analysis of steps 2 to 8, a "two-body-one-face" coupling evaluation system of "water body", "sediment body" and "mud-water interface" is established to form a multi-dimensional evaluation system based on ecological dredging;

[0017] Step 10: The depth of ecological dredging of sediment is determined based on the adsorption equilibrium interface release flux in step 7, the pollution index and pollution level in step 5, and the biotoxic pollution evaluation, and the final dredging depth is determined based on the maximum value.

[0018] As a preferred embodiment of the present invention, in the feasibility study stage, the sampling survey in step 1 can arrange an exploration line of no more than 500m along the river longitudinally, and the number of sampling points in each exploration section should be no less than 3; in lake areas, block waters are arranged in a 100-200m grid or staggered plum blossom shape.

[0019] As a preferred embodiment of the present invention, in step 6, when evaluating the water quality level by the modified Nemerow pollution index and water quality index method, the pH value, nutrients: TN, TP and heavy metals: Hg, Cr, Cu, Cd, Pb, As, Zn, Se of the water sample are detected.

[0020] As a preferred embodiment of the present invention, the multidimensional evaluation system based on ecological dredging in step 9 includes "three dimensions" consisting of water body, bottom mud body and mud-water interface, and "seven methods" consisting of water quality index method, modified Nemerow pollution index method, adsorption-desorption method, laboratory simulation cultivation method, pore water diffusion model method, Nemerow pollution index method and potential ecological risk index method.

[0021] The beneficial effects of the present invention are:

[0022] 1. The present invention considers the three dimensions of water body, mud-water interface and bottom mud body as an organic whole. It is unscientific to conduct endogenous governance without any dimension, and it cannot eradicate or completely solve the problem of endogenous pollution governance. Therefore, the present invention conducts a comprehensive analysis of the mud-water interface assessment, the overlying water quality assessment and the bottom mud pollution assessment, and comprehensively evaluates the results to achieve different governance objectives. The maximum value is used to determine the final dredging depth as the main control standard, and the corresponding evaluation scheme is used to determine the precise dredging depth of the bottom mud used for ecological dredging of rivers, lakes and reservoirs. The method is simple, low-cost, scientific and reasonable, and highly operable. It is an important means to solve the problem of correct assessment of pollution and dredging depth guidance for endogenous governance of rivers and lakes;

[0023] 2. The present invention couples the three dimensions of "water body", "mud-water interface" and "bottom mud body" as an organic whole for evaluation, and establishes a multi-dimensional evaluation system of "three dimensions" and "seven methods", and proposes characteristic detection indicators for evaluating river, lake and reservoir pollution, which can more effectively judge the causes of internal pollution in water bodies and the depth of dredging for bottom mud pollution, and solve the limitations of the current evaluation standards for bottom mud pollution and the problems of traditional single-dimensional water management that only treats the symptoms but not the root causes;

[0024] 3. Sedimentology is used to qualitatively divide the bottom mud of rivers, lakes and reservoirs into different pollution layers. The nutrient pollution degree of each pollution layer is evaluated by Nemerow pollution index method. The heavy metal pollution risk is evaluated by potential ecological risk coefficient. The pollution level is preliminarily determined by comprehensively considering the nutrient and heavy metal pollution. The Nemerow pollution index is combined with the water quality index method to evaluate the water quality level of the overlying water. The cause of water pollution is analyzed through the interaction between mud and water interface. The precise layer of sediment pollution release is determined so that appropriate endogenous control measures can be taken to control it.

[0025] 4. The present invention proposes a mud-water interface evaluation method suitable for different engineering conditions, which can accurately determine the pollutant content when dynamic equilibrium is reached, determine the "source" or "sink" of river, lake and reservoir bottom mud, and the dredging depth, etc. This evaluation method is scientific, reasonable, simple, feasible and highly accurate;

[0026] 5. The modified Nemerow pollution index method for evaluating water quality of the present invention takes into account the weight of each pollution factor in water quality evaluation and incorporates important pollution factors into the calculation to avoid the disadvantages of the traditional Nemerow pollution index method that overemphasizes the impact of the pollution factor with the highest concentration on water quality and ignores the serious harm of important pollution factors that are difficult to handle to water quality;

[0027] 6. The present invention takes into account multiple evaluation methods such as Nemerow pollution index method, heavy metal potential ecological risk index method, adsorption and desorption method, laboratory simulation cultivation method or pore water diffusion model method when evaluating the sediment dredging depth. The maximum value is used to determine the final dredging depth, which considers pollution indicators more comprehensively and avoids ignoring the effects of factors that have a greater impact on water quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a multi-dimensional evaluation system diagram of water body, mud-water interface and bottom mud body of the present invention;

[0029] Figure 2 It is a layout diagram of the exploration lines and exploration points in the engineering design stage of the present invention;

[0030] Figure 3 A pollution degree classification diagram of ecological dredging contaminated soil of the present invention;

[0031] Figure 4It is the Tir value diagram of various heavy metals of the present invention;

[0032] Figure 5 It is an evaluation diagram of the ecological risk coefficient and ecological risk index of the present invention;

[0033] Figure 6 This is a risk screening value diagram of agricultural land soil pollution in the present invention;

[0034] Figure 7 It is a heavy metal risk screening value selection diagram of the present invention;

[0035] Figure 8 It is a water pollution level reference diagram of the present invention;

[0036] Fig. 9 It is a reference diagram of the weights and standardization factor values ​​of each indicator of the water quality index of the present invention;

[0037] Fig.10 It is a water quality index level and classification level diagram of the present invention;

[0038] Fig.11 This is a comprehensive determination diagram of the pollution depth of the bottom mud of rivers, lakes and reservoirs in the present invention. DETAILED DESCRIPTION

[0039] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and the best embodiment. Based on the embodiments in the invention, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the invention.

[0040] Embodiment 1:

[0041] like Figure 1-11 As shown, this embodiment proposes a method for accurately determining the depth of ecological dredging, comprising the following steps:

[0042] Step 1: Collect and survey water and sediment samples in the rivers, lakes and reservoirs to be treated.

[0043] During the feasibility study stage, an exploration line of no more than 500m can be arranged along the longitudinal direction of the river, and the number of sampling points in each exploration section should be no less than 3; in lake areas, block waters should be arranged in a 100-200m grid or staggered plum blossom shape; irregular waters should be arranged according to the actual situation and the above-mentioned spacing principles.

[0044] During the engineering design phase, the spacing between exploration lines and points should comply with the Figure 2 and meet the following requirements:

[0045] ① When the pollution distribution, topography, and rock and soil properties change significantly, the number of exploration points should be increased;

[0046] ② The number of exploration points in a small local area or isolated area shall not be less than 3;

[0047] ③ Exploration points should be densely deployed at river intersections, historical sewage outlets, river estuaries, lake bays, water sources, important tourist areas and waters with severe water pollution based on actual conditions.

[0048] The drilling holes should be arranged according to the pollution situation and geological conditions of the environmental protection dredging area. The spacing between exploration lines and exploration points is determined in the attached Figure 2 .

[0049] When there are significant changes in pollution distribution, topography, and rock and soil properties within the designed dredging depth, the number of exploration points should be increased, and the number of exploration points in small and isolated areas should not be less than 3.

[0050] Step 2: stratify the samples collected in step 1 using the sedimentology method, qualitatively analyze the characteristics and thickness of the contaminated layer, transition layer and normal layer based on the color, odor, particle size and viscosity of the sediment, and draw a three-dimensional spatial distribution map of the sediment and a cross-sectional map of the sediment stratification.

[0051] Step 3: Analyze the nutrient index of the bottom mud of each pollution layer divided in step 2 using the Nemerow pollution index method and define the pollution level. The Nemerow pollution index formula is estimated according to formula (1):

[0052] PN={[(PI 均 2 )+(PI 最大 2 )] / 2} 1 / 2 …………(1)

[0053] Where: PI 均 is the average single pollution index; PI 最大 It is the largest single pollution index.

[0054] The single pollution index (PI) of ecological dredging contaminated soil is calculated according to formula (2).

[0055] PI=C i / S i …………………………………………(2)

[0056] Where: C i is the measured value of pollution index of ecological dredging contaminated soil; S i The reference value required for soil pollutant quality calculation (the reference value can be selected according to the evaluation target, and can be a reference value, a risk screening value, a quantile value of a certain confidence level, etc.). The detectable polluted sediment indicators include pH value, nutrients (TN, TP, organic matter) and heavy metals (Hg, Cr, Cu, Cd, Pb, Ni, As, Zn).

[0057] The pollution level of ecological dredging contaminated soil is divided according to the Nemerow Pollution Index (PN). See the attached Figure 3 .

[0058] Step 4: Analyze the heavy metal index of the sediment of each contaminated layer divided in step 2 using the potential ecological risk index evaluation method, and define the potential ecological risk level. According to the "Soil Environmental Quality Agricultural Land Soil Pollution Risk Control Standard (Trial)" (GB15618-2018), the potential ecological risk index evaluation method is used to evaluate the potential ecological risk of the heavy metal content in the sediment. Calculate its potential ecological risk coefficient (E i f ) and potential ecological risk index (RI).

[0059] 1) Single heavy metal pollution coefficient C i f .

[0060] C i f =C i D / C i R ………………………………(3)

[0061] Where: C i f is the pollution coefficient of a single heavy metal; C i D is the measured value of a single sediment heavy metal concentration; C i R It is the background reference value or standard of a single heavy metal.

[0062] 2) Potential ecological risk coefficient Eir of single heavy metal.

[0063] E i f =T i f ×C i f ………………………………(4)

[0064] Where: T i f It is the toxicity response coefficient of a single heavy metal, reflecting the toxicity level of the heavy metal and the sensitivity of the water body to heavy metal pollution. The detectable heavy metal indicators include Hg, Cr, Cu, Cd, Pb, Ni, As, and Zn.

[0065] Various heavy metals i f See attached for value Figure 4 .

[0066] 3) Heavy metal potential ecological risk index RI

[0067]

[0068] 4) Evaluation indicators

[0069] The evaluation of ecological risk coefficient and ecological risk index is attached. Figure 5 .

[0070] C i n The value is determined based on the Soil Environmental Quality Agricultural Land Soil Pollution Risk Control Standard (Trial) (GB15618-2018). Figure 6 The risk screening value corresponding to the paddy field with pH ≥ 7.5; other heavy metals are selected from the attached Figure 6 The risk screening values ​​corresponding to other items in pH ≥ 7.5 are used as reference values ​​for this calculation. For details, see the attached Figure 6 .

[0071] Step 5, comprehensively analyze the nutrient pollution level of the proposed treatment area obtained in step 3 and the potential ecological risk level of heavy metals in the proposed treatment area obtained in step 4, and determine the pollution index and pollution level according to the maximum pollution degree index.

[0072] Step 6: Collect water samples from the water bodies corresponding to the sediment sampling sites surveyed in step 1 using a stratified water sampling device. Collect 3 parallel samples from each sampling point and evaluate the water quality level using the modified Nemerow pollution index and water quality index method. pH value, nutrients (TN, TP) and heavy metals (Hg, Cr, Cu, Cd, Pb, As, Zn, Se) can be detected.

[0073] The modified Nemerow pollution index (NPI) is calculated according to formula (6).

[0074] NPI={[(N max 2 )+(F wei 2 )] / 2} 1 / 2 (6)

[0075] N i =C i / S i (7)

[0076]

[0077]

[0078] Where: NPI is the modified Nemerow pollution index; N maxis the maximum value of single factor evaluation of n evaluation indicators; F wei is the weighted average value of single factor evaluation of n evaluation indicators; N i is the single factor evaluation value C of factor i i is the measured value of index i; S i is the standard value of the i indicator; a i is the weight of index i; S max is the maximum value among all factor standard values.

[0079] The Nemerow Pollution Index (NPI) for water pollution evaluation is attached. Figure 8 .

[0080] After optimization and improvement by researchers, 3 to 5 representative indicators can be selected for water quality evaluation. The calculation formula of water quality index (WQI) is as follows:

[0081]

[0082] Where: WQI is the water quality index; C i is the standardized factor value of index i; P i is the weight of the i indicator. The detectable indicators include nutrients (TN, NH3-N, NO3-N, NO2-N, C, SRP, TP) and other categories (T, BOD5, pH, EC, COD Mn , DO, TDS, Ca 2+ Mg 2+ , Cl - 、SO4 2- , TC, FC, TUR, TSS, TOP, TON). The weight values ​​of various physical and chemical indicators refer to the attached Fig. 9 Specific WQI levels and classification levels are as follows Fig.10 .

[0083] Step 7, based on the pollution layer initially determined in step 2 and the pollution level evaluated in step 3 (generally the pollution level exceeds mild pollution or the potential ecological risk is), 10% to 20% of the sediment column samples are taken from the survey point in step 1 to analyze the sediment-water interface interaction. The column samples are sampled and tested every 10 cm, and adsorption and desorption tests are performed. Different methods are used to detect the adsorption equilibrium interface release flux according to the characteristics of different sediments. The commonly used release flux (release rate) test methods are laboratory simulation culture method and pore water diffusion model method.

[0084] Adsorption-desorption method:

[0085] The linear regression equations of initial concentration and adsorption-desorption amount of different types of simulated water bodies were established, and the zero-point equilibrium concentration (adsorption-desorption amount Q = 0) and the water quality category (NH4 +-N, P content) comparison, when the zero-point equilibrium concentration of the sediment at a certain depth is greater than the target water quality category, the sediment has a risk of release to the water body and is evaluated as a contaminated soil layer that will affect the water quality. Otherwise, it has an adsorption effect on the water body and is evaluated as a normal soil layer.

[0086] Adsorption / release calculation formula:

[0087] Q=(C0-C e )×V / W……………………(11)

[0088] Where: Q is the adsorption amount (mg / kg); C0 is the initial concentration (mg / L); C e is the equilibrium concentration (mg / L); V is the volume of solution added to the sample (50mL); W is the dry weight of sediment (kg). It can detect indicators of nutrients (NH3-N, TDN, SRP, TDP) and heavy metals (Hg, Cr, Cu, Cd, Pb, As, Zn, Se).

[0089] Laboratory simulation culture test (disturbance simulation analysis):

[0090] The sediment disturbance mode device is set with four external dynamic conditions: "stationary", "disturbance", "large-scale disturbance" and "severe disturbance", which correspond to the stirring speeds of the electronic constant speed stirrer of 0r / min, 100r / min, 120r / min and 160r / min. When simulating seasonal environment, the simulation test is carried out in a constant temperature incubator with the corresponding seasonal temperature set.

[0091] The method for calculating the release rate of laboratory simulated culture is as follows:

[0092]

[0093] Where: R is the release rate of a substance, the unit is mg / m 2 d(or mg / m 2 ·h); V is the volume of overlying water in the sediment (L); C n and C i-1 is the nutrient concentration of the samples collected for the nth and i-1th times (mg / L); C0 is the initial nutrient concentration of the overlying water (mg / L); V i is the sampling volume (L); C a is the nutrient concentration of the added water (mg / L); A is the cross-sectional area of ​​the water and sediment column in the stirring device (m 2); t is the nutrient release time (d or h); if the gas exchange at the interface is not considered, the calculated result is the apparent release rate of a nutrient. It can detect nutrient (TN, NH3-N, NO3-N, TDN, TP, SRP, TDP) and heavy metal (Hg, Cr, Cu, Cd, Pb, As, Zn, Se) indicators.

[0094] Pore ​​water diffusion model estimation method:

[0095] The siphon method was used to collect the overlying water 10 cm above the sediment and placed in a polyethylene bottle, which was then stored at 4°C and brought back to the laboratory; the sediment column samples were collected using a sediment column collector, and then frozen and transported to the laboratory for cutting and sampling, and the sediment column samples of the contaminated layer were divided into several layers at required intervals. The water content of the sediment was tested, the pore water of the sediments at different depths was extracted, and the release flux was calculated.

[0096] This method only explores the nitrogen and phosphorus exchange process at the sediment-water interface, assuming that the material exchange process between the sediment and the overlying water is in equilibrium. It can be considered that molecular diffusion is the main way for sediment ammonia nitrogen to migrate to the overlying water through the interstitial water. At this time, the molecular diffusion between the interstitial water of the sediment and the overlying water conforms to the Fick law molecular diffusion model, and its diffusion rate can be obtained by Fick's first law and calculated using formula 13. When the diffusion rate is positive, it means that ammonia nitrogen or soluble phosphorus diffuses from the sediment to the overlying water, and when the diffusion rate is negative, it means that ammonia nitrogen or soluble phosphorus diffuses from the overlying water to the sediment.

[0097]

[0098] Where: F is the ammonia nitrogen release rate through the interface between sediment and overlying water (mg / m 2 d; is the porosity of surface sediments (%), replaced by the relative water content of fresh sediments; D s is the effective molecular diffusion coefficient corrected for porosity (cm 2 / s), which can be calculated by empirical formula (Formula 10, 11); is the ammonia nitrogen concentration gradient between surface sediment pore water and overlying water (10 - 3 mg / cm 4 ).

[0099]

[0100]

[0101] Where: D0 is the ideal diffusion coefficient of nutrients in infinite dilution solution, for NH4 + -N:D0=17.6×10- 6 cm 2 / s; TDP: 6.8×10 -6 cm 2 / s(DIP:7.0×10 -6 cm 2 / s); COD: 6.7×10 -10 cm 2 / s. It can detect indicators of nutrients (NH3-N, TDN, SRP, TDP) and heavy metals (Hg, Cr, Cu, Cd, Pb, As, Zn, Se).

[0102] Step 8: Combine the sediment qualitative preliminary pollution stratification in steps 2 to 4 with the sediment pollution index content and pollution level of each layer with the mud-water interface interaction in step 7, and then combine it with the water quality level analysis in step 6 to finally determine the equilibrium critical concentration, whether to dredge and the dredging point, and form a suitable ecological dredging interface. The coupled evaluation system of ecological dredging "water body", "mud-water interface" and "sediment body" is shown in Figure 2 .

[0103] Step 9: Based on the pollution stratification, sediment pollutant evaluation, mud-water interface interaction analysis, water quality grade assessment and pollution situation analysis of steps 2 to 8, a "two-body-one-face" coupling evaluation system of "water body", "sediment body" and "mud-water interface" is established to form a multi-dimensional evaluation system based on ecological dredging (see Figure 2 ), this method system includes the "three dimensions" of water body, bottom mud body and mud-water interface, and the "seven methods" of water quality index method, modified Nemerow pollution index method, adsorption-desorption method, laboratory simulation cultivation method, pore water diffusion model method, Nemerow pollution index method and potential ecological risk index method. And extract the characteristic indicators that can be detected by each method in ecological dredging engineering.

[0104] Step 10, the depth of ecological dredging of the sediment is determined by comprehensively considering the adsorption equilibrium interface release flux in step 7, the pollution index and pollution level in step 5, and the biological toxic pollution evaluation, and the final dredging depth is determined by the maximum value.

[0105] Note: If the heavy metals do not present potential ecological risks or their biological toxicity is medium or below, A2 or A3 will not be considered in the comprehensive determination of sediment contamination depth.

[0106] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for accurately determining the depth of ecological dredging, characterized in that: The following steps are involved: Step 1: Set up sampling points in the target waters and conduct water sampling and sediment surveys; Step 2: Sedimentation-stratify the samples collected in step 1, qualitatively analyze the characteristics and thickness of the contaminated layer, transition layer and normal layer according to the color, odor, particle size and viscosity of the sediment, and draw a three-dimensional spatial distribution map of the sediment and a cross-section map of the sediment stratification; Step 3: Analyze the nutrient index of the bottom mud of each pollution layer divided in step 2 using the Nemerow pollution index method and determine the pollution level; Step 4: Analyze the heavy metal index of the sediment of each contaminated layer divided in step 2 by using the potential ecological risk index evaluation method, and define the potential ecological risk level. Use the potential ecological risk index evaluation method to evaluate the potential ecological risk of the heavy metal content in the sediment, and calculate its potential ecological risk coefficient and potential ecological risk index; Step 5: Comprehensively analyze the nutrient pollution level of the proposed treatment area obtained in step 3 and the potential ecological risk level of heavy metals in the proposed treatment area obtained in step 4, and determine the pollution index and pollution level according to the maximum pollution degree index; Step 6: Use a stratified water sampler to collect water samples from the water bodies corresponding to the sediment sampling sites surveyed in step 1. Collect 3 parallel samples from each sampling point, and use the modified Nemerow pollution index and water quality index method to evaluate the water quality level; Step 7: Based on the pollution layer initially determined in step 2 and the pollution level evaluated in step 3, 10% to 20% of the sediment column samples are taken from the survey point in step 1 to analyze the sediment-water interface interaction; the column samples are sampled and tested every 10 cm, and adsorption and desorption tests are performed. Different methods are then used to detect the adsorption equilibrium interface release flux according to the characteristics of different sediments. Commonly used release flux test methods include laboratory simulation culture method and pore water diffusion model method; Step 8: Combine the sediment qualitative preliminary pollution stratification in steps 2 to 4 with the sediment pollution index content and pollution level of each layer with the mud-water interface interaction in step 7, and then combine it with the water quality level analysis in step 6 to finally determine the equilibrium critical concentration, whether to dredge and the dredging point, and form a suitable ecological dredging interface; Step 9: Based on the pollution stratification, sediment pollutant evaluation, mud-water interface interaction analysis, water quality grade assessment and pollution situation analysis from steps 2 to 8, a "two-body and one-face" coupling evaluation system of "water body", "sediment body" and "mud-water interface" is established, forming a multi-dimensional evaluation system based on ecological dredging; Step 10: The depth of ecological dredging of sediment is determined based on the adsorption equilibrium interface release flux in step 7, the pollution index and pollution level in step 5, and the biotoxic pollution evaluation, and the final dredging depth is determined based on the maximum value.

2. A method for accurately determining the depth of ecological dredging according to claim 1, characterized in that: During the feasibility study stage, the sampling survey in step 1 may be conducted along a longitudinal exploration line of no more than 500 m in length for the river, and the number of sampling points for each exploration section should be no less than 3. In lake areas, block waters may be arranged in a 100-200 m grid or staggered plum blossom pattern.

3. A method for accurately determining the depth of ecological dredging according to claim 1, characterized in that: In step 6, when evaluating the water quality level by using the modified Nemerow pollution index and water quality index method, the pH value, nutrients: TN, TP and heavy metals: Hg, Cr, Cu, Cd, Pb, As, Zn, Se of the water sample are detected.

4. A method for accurately determining the depth of ecological dredging according to claim 1, characterized in that: The multidimensional evaluation system based on ecological dredging in step 9 includes "three dimensions" consisting of water body, bottom mud body and mud-water interface, and "seven methods" consisting of water quality index method, modified Nemerow pollution index method, adsorption-desorption method, laboratory simulation cultivation method, pore water diffusion model method, Nemerow pollution index method and potential ecological risk index method.

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