A method for assessing the release potential of nitrogen and phosphorus nutrients from lake sediments

Abstract

The present invention relates to the field of pollution control and environmental management, specifically, to a method for evaluating the release potential of nitrogen and phosphorus nutrients in lake sediments. The method comprises the following steps: collecting sediment and overlying water samples, and obtaining in-situ environmental data of the sampling point at the same time; determining the physical and chemical properties of lake sediments, and calculating the nitrogen and phosphorus storage flux of lake sediments; conducting static release culture and interstitial water diffusion model experiments based on the in-situ environmental data of the sampling point, determining the total nitrogen and total phosphorus content of the interstitial water and the overlying water, and calculating the nitrogen and phosphorus release flux of lake sediments; expert scoring and evaluation; giving weights to the cumulative release potential and immediate release potential of nitrogen and phosphorus nutrients, and adding and calculating to obtain the release potential value of nitrogen and phosphorus nutrients in lake sediments. The present invention comprehensively evaluates the release potential of nitrogen and phosphorus nutrients in lake sediments, and provides an important basis for lake water environment evaluation and ecological environment management decision-making.

Description

Technical Field

[0001] The invention relates to the technical field of marine ecosystem health assessment, and in particular to a method for assessing the release potential of nitrogen and phosphorus nutrients in lake sediments. Background Art

[0002] In recent years, the eutrophication of lakes in my country has become increasingly serious. With the in-depth advancement of water pollution control, the exogenous nitrogen and phosphorus loads of lakes have been effectively controlled, and endogenous release has become a key factor causing the decline in water environment quality and the degradation of water ecological functions. Sediments, as an important component of lake ecosystems, are important storage carriers of nitrogen and phosphorus nutrients in lakes and are also the key to endogenous release. When external conditions change, nitrogen and phosphorus nutrients in sediments will continue to respond and change. Under the combined action of physical, chemical, biological and other factors, the accumulated nitrogen and phosphorus nutrients will exchange nitrogen and phosphorus nutrients with the overlying water body through the sediment-water interface, forming endogenous release pollution. The release of nitrogen and phosphorus nutrients in lake sediments has the characteristics of accumulation and immediacy. Among them, accumulation refers to the fact that sediments act as the "sink" of pollutants, which accumulate a certain amount of nitrogen and phosphorus nutrients and then cause continuous release. The cumulative release potential can be characterized by storage flux; immediacy refers to the fact that when there is a nitrogen and phosphorus concentration gradient between sediments and overlying water bodies at a certain moment, it triggers the immediate release of sediment nutrients, and sediments become the "source" of lake pollutants. The immediate release potential can be characterized by release flux. At present, many scholars have conducted research on the release potential of nitrogen and phosphorus in sediments in response to the ecological and environmental risks brought by the endogenous release of nitrogen and phosphorus nutrients in lake sediments. Liu Tao et al. (2012) used the pore water diffusion flux model to calculate the release flux of nitrogen and phosphorus nutrients, and obtained the maximum adsorption amount of nitrogen and phosphorus nutrients by fitting the adsorption isotherm with the modified Langmuir equation, and then judged the endogenous release risk of lakes. Chen Chao et al. (2014) conducted a sediment-water interface microenvironment release experiment to calculate the potential release rate of nitrogen and phosphorus nutrients to judge their release potential. Wang Wenwen et al. (2017) used the continuous fractional extraction method to study the spatial distribution characteristics of nutrients, and then used the flooding culture method to calculate the diffusion flux of nutrients to judge the release potential of sediments. However, most of these studies are based on continuous monitoring of the changes in the concentration of nutrients in the overlying water or calculating the concentration of nutrients in the pore water of the sediment according to Fick's law. They only consider the immediate characteristics of sediment nutrient release and ignore the cumulative release effect determined by the nitrogen and phosphorus nutrients stored in the sediments. They cannot fully describe the release potential of sediment nutrients. At present, there is no consensus on the estimation method of the release potential of nitrogen and phosphorus nutrients from lake sediments. Under natural conditions, the cumulative and immediate release of nitrogen and phosphorus nutrients are both necessary conditions for the risk of endogenous release of pollutants. They are equally important and indispensable. In addition, the release of nitrogen and phosphorus nutrients from lake sediments is uncertain. Factors such as lake water environment quality, hydrological and hydrodynamic conditions, and water ecological conditions will affect the release of nitrogen and phosphorus nutrients from sediments. The cumulative release potential and the immediate release potential cannot be regarded as a simple additive relationship. It is necessary to comprehensively consider the characteristics of the study area and assign weights. In the process of comprehensive evaluation of the release potential of the two, it is necessary to consider the actual ecological and environmental factors and social development factors in the study area, and to effectively avoid the subjectivity of artificial weighting.The present invention mainly considers the cumulative release potential and immediate release potential of nitrogen and phosphorus nutrients in sediments. Different from the weighting method of the multi-attribute index system, for the weighting process of two indicators, the multiplication of weights will lead to a "multiplier effect" where the larger one is larger and the smaller one is smaller, which is not very applicable. The linear weight addition of the distribution coefficient is prone to problems such as "excellent", "strong" or "poor" weights. Summary of the invention

[0003] The present invention constructs a quantitative evaluation method for the release potential that comprehensively considers the accumulation and immediacy of nitrogen and phosphorus nutrients in lake sediments, taking into account both the continuous release caused by nitrogen and phosphorus nutrients stored in sediments and the immediate release at a certain moment caused by the change in concentration gradient between sediments and water bodies. By calculating the storage flux and release flux of nitrogen and phosphorus in sediments, the cumulative release potential and timely release potential of nitrogen and phosphorus in sediments are determined respectively, and the subjective and objective combined weighting method is used to comprehensively reflect the importance of accumulation and immediacy as well as the subjective intention of decision makers, so as to accurately and scientifically estimate the release potential of nitrogen and phosphorus nutrients in lake sediments and provide scientific decision-making for lake eutrophication control.

[0004] In order to achieve the above object, the present invention mainly provides the following technical solutions:

[0005] A method for evaluating the release potential of nitrogen and phosphorus nutrients in lake sediments comprises the following steps:

[0006] Step 1, collecting sediment and overlying water samples, and obtaining in-situ environmental data of the sampling points;

[0007] Step 2, determining the physical and chemical properties of lake sediments, calculating the nitrogen and phosphorus storage fluxes of lake sediments, and characterizing the cumulative release potential of nitrogen and phosphorus nutrients in lake sediments;

[0008] Step 3, according to the in-situ environmental data of the sampling point, static release culture and interstitial water diffusion model experiments are carried out, sediments and overlying water bodies are placed in a columnar tube, interstitial water of sediments in different layers is collected at different times, and then the total nitrogen and total phosphorus contents of the interstitial water and the overlying water are measured, and the nitrogen and phosphorus release fluxes of the lake sediments are calculated to characterize the immediate release potential of nitrogen and phosphorus nutrients in the lake sediments;

[0009] Step 4: Experts scored and evaluated the cumulative release potential and immediate release potential of nitrogen and phosphorus nutrients in sediments according to the characteristics of the study area, and subjectively weighted them to obtain the indicator weight α i ; The entropy weight method is used to objectively weight the cumulative release potential and immediate release potential of nitrogen and phosphorus nutrients in sediments calculated in steps 2 and 3 to obtain the indicator weight β i; The combined weights of the cumulative release potential and immediate release potential of nitrogen and phosphorus nutrients in sediments are obtained by subjective and objective combined weighting. The reasonable value range of the combined weight is the intersection of the subjective weight neighborhood and the objective weight neighborhood. The intersection boundary is and The combined weight in the intersection can reflect the importance ranking of subjective and objective weights, and also reflect the importance intensity information of subjective and objective weights. Formula (1) is used

[0010]

[0011]

[0012] In the formula, α i is the subjective weight, β i is the objective weight obtained by entropy weight method, is the objective function, which requires that the deviation between the combined weight of the two fluxes and the weight obtained by objective weighting be minimized; the constraint condition w i ≥w j , i<j ensures that the combined weight of the flux satisfies the importance information of the subjective weight; the constraint condition The interval of the combined weight is limited. It is ensured that the sum of the combined weights is 1;

[0013] Set the constraint conditions and solve the combined weighted optimization model to obtain the combined weights w of the cumulative release potential and immediate release potential of nitrogen and phosphorus nutrients in sediments. i ;

[0014] Step 5, assign weights to the cumulative release potential and immediate release potential of nitrogen and phosphorus nutrients, add them up and calculate the release potential value of nitrogen and phosphorus nutrients in lake sediments.

[0015] In the above-mentioned method for evaluating the release potential of nitrogen and phosphorus nutrients from lake sediments, the in-situ environmental data of the sampling points include the temperature, redox potential, pH value of the lake sediments measured on site, and the temperature, redox potential, and pH value of the water body.

[0016] In the above-mentioned method for assessing the release potential of nitrogen and phosphorus nutrients from lake sediments, the physical properties are particle density, porosity, average sedimentation rate and water content.

[0017] In the above-mentioned method for assessing the release potential of nitrogen and phosphorus nutrients in lake sediments, the chemical properties are the chemical properties of the sediments, i.e., the total nitrogen and total phosphorus contents of the sediments.

[0018] Among them, the cumulative release potential of nitrogen and phosphorus nutrients in sediments is expressed by the nitrogen and phosphorus storage flux in lake sediments, and the calculation formula is:

[0019] BF j =C i,j ×S×ρ d ×10 -4 (2)

[0020] Where BF j is the storage flux of nitrogen and phosphorus in the outcropping sediment at sampling point j (g·m -2 ·a -1 );C i,j is the nitrogen and phosphorus content of the sediment exposed at sampling point j (mg·kg -1 ); S is the sedimentation rate of the sediment (cm·a -1 );ρ d is the dry density of the sediment (g·cm -3 ).

[0021] In the above-mentioned evaluation method for the release potential of nitrogen and phosphorus nutrients in lake sediments, the immediate release potential of nitrogen and phosphorus nutrients in sediments is expressed by the nitrogen and phosphorus release flux of lake sediments, and the calculation formula is:

[0022]

[0023] In the formula, F j represents the release flux of TN and TP in the sediment at sampling point j (g·m -2 ·d -1 ); represents the sediment porosity; D s represents the actual diffusion coefficient of nitrogen and phosphorus at the sediment-water interface (m 2 ·d -1 ); Represents the concentration gradient of total nitrogen or total phosphorus at the mud-water interface (g·m -3 ·m -1 ).

[0024] In the above-mentioned evaluation method for the release potential of nitrogen and phosphorus nutrients in lake sediments, the subjective weighting takes the cumulative release potential and immediate release potential of nitrogen and phosphorus nutrients in sediments as the criterion layer, selects ten indicators that affect the cumulative release and immediate release of nitrogen and phosphorus nutrients in sediments, and constructs an evaluation index system for the release potential of nitrogen and phosphorus nutrients in lake sediments.

[0025] In the above-mentioned method for evaluating the release potential of nitrogen and phosphorus nutrients from lake sediments, the indicators of the cumulative release potential are the degree of eutrophication of the water body, the organic matter content in the sediments, the redox conditions of the sediments, the productivity of the lake ecosystem and the degree of nitrogen and phosphorus load from external inputs.

[0026] In the above-mentioned method for evaluating the release potential of nitrogen and phosphorus nutrients in lake sediments, the indicators of immediate release potential are the environmental conditions of lake water bodies, the hydrodynamic conditions of water bodies, the physical properties of sediments, the properties of nitrogen and phosphorus nutrients in sediments, and the degree of interference from human activities.

[0027] In the above-mentioned evaluation method for the release potential of nitrogen and phosphorus nutrients in lake sediments, the subjectively weighted experts score the contribution of the cumulative release potential and immediate release potential of nitrogen and phosphorus nutrients in sediments to the release potential of lake nutrients according to the characteristics of the study area, with a total score of 100. Subsequently, the expert scoring sheets are summarized, the scores of each indicator are summed up, and the respective weights and their corresponding criterion layer indicator weights are calculated to obtain the subjective weights of the cumulative release potential and immediate release potential of nitrogen and phosphorus nutrients in sediments.

[0028] In the above-mentioned evaluation method for the release potential of nitrogen and phosphorus nutrients in lake sediments, the cumulative release potential and immediate release potential of nitrogen and phosphorus nutrients in the sediments are subjectively weighted to obtain the indicator weight α i The weight obtained by subjective weighting emphasizes the importance of the two potential attributes themselves. The entropy weight method is used to objectively weight the cumulative release potential and immediate release potential of nitrogen and phosphorus nutrients in sediments to obtain the indicator weight β i The weight obtained by objective weighting takes into account the strength information between the two indicators based on the size of the discrimination.

[0029] In the above-mentioned evaluation method for the release potential of nitrogen and phosphorus nutrients in lake sediments, the formula for calculating the annual release potential of nitrogen and phosphorus nutrients in sediments is:

[0030] R=(w1×BF j +w2×F j ×365)×T(4)

[0031] Where R is the release potential of nitrogen and phosphorus nutrients in sediments (g·m -2 ), T is the release time (a).

[0032] By means of the above technical solution, the method for evaluating the release potential of nitrogen and phosphorus nutrients in lake sediments proposed by the present invention has at least the following advantages:

[0033] The method for evaluating the release potential of nitrogen and phosphorus nutrients from lake sediments provided by the present invention comprehensively describes the cumulative and immediate impacts of the release of nitrogen and phosphorus nutrients from lake sediments, scientifically empowers and strengthens the rationality of subjective decision-making intentions and cumulative and immediate release research, comprehensively evaluates the release potential of nitrogen and phosphorus nutrients from lake sediments, overcomes the limitation of traditional methods for evaluating the release potential of nitrogen and phosphorus nutrients that only considers the immediate release of sediments, and provides an important basis for lake water environment evaluation and ecological environmental management decision-making.

[0034] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the preferred embodiments of the present invention are described in detail as follows. DETAILED DESCRIPTION

[0035] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation method, structure, characteristics and effects of the evaluation method for the release potential of nitrogen and phosphorus nutrients in lake sediments proposed by the present invention are described in detail below in combination with the preferred embodiments. In the following description, different "one embodiment" or "embodiment" do not necessarily refer to the same embodiment. In addition, specific features, structures, or characteristics in one or more embodiments may be combined in any suitable form.

[0036] This embodiment discloses a method for evaluating the release potential of nitrogen and phosphorus nutrients in lake sediments, comprising the following steps:

[0037] Step 1, collecting sediment and overlying water samples, and obtaining in-situ environmental data of the sampling points;

[0038] Step 2, determining the physical and chemical properties of lake sediments, calculating the nitrogen and phosphorus storage fluxes of lake sediments, and characterizing the cumulative release potential of nitrogen and phosphorus nutrients in lake sediments;

[0039] Step 3, according to the in-situ environmental data of the sampling point, static release culture and interstitial water diffusion model experiments are carried out, sediments and overlying water bodies are placed in a columnar tube, interstitial water of sediments in different layers is collected at different times, and then the total nitrogen (TN) and total phosphorus (TP) contents of the interstitial water and the overlying water are measured, and the nitrogen and phosphorus release fluxes of the lake sediments are calculated to characterize the immediate release potential of nitrogen and phosphorus nutrients in the lake sediments;

[0040] Step 4: Experts scored and evaluated the cumulative release potential and immediate release potential of nitrogen and phosphorus nutrients in sediments according to the characteristics of the study area, and subjectively weighted them to obtain the indicator weight α i ; The entropy weight method is used to objectively weight the cumulative release potential and immediate release potential of nitrogen and phosphorus nutrients in sediments calculated in steps 2 and 3 to obtain the indicator weight β i ; The combined weights of the cumulative release potential and immediate release potential of nitrogen and phosphorus nutrients in sediments are obtained by subjective and objective combined weighting. The reasonable value range of the combined weight is the intersection of the subjective weight neighborhood and the objective weight neighborhood. The intersection boundary is and The combined weight in the intersection can reflect the importance ranking of subjective and objective weights, and can also reflect the importance strength information of objective weights. Formula (1) is used

[0041]

[0042]

[0043] In the formula, α i is the subjective weight, β i is the objective weight obtained by entropy weight method, is the objective function, which requires that the deviation between the combined weight of the two fluxes and the weight obtained by objective weighting be minimized; the constraint condition w i ≥w j , i<j ensures that the combined weight of the flux satisfies the importance information of the subjective weight; the constraint condition The interval of the combined weight is limited. Ensure that the combined weights satisfy the sum of the weights to be 1; set constraints, and solve the combined weighted optimization model to obtain the combined weights w of the cumulative release potential and immediate release potential of nitrogen and phosphorus nutrients in sediments i ;

[0044] Step 5, assign weights to the cumulative release potential and immediate release potential of nitrogen and phosphorus nutrients, add them up and calculate the release potential value of nitrogen and phosphorus nutrients in lake sediments.

[0045] In the above-mentioned evaluation method for the release potential of nitrogen and phosphorus nutrients from lake sediments, the in-situ environmental data of the sampling points include the temperature, redox potential, and pH value of the lake sediments measured on site, as well as the temperature, redox potential, and pH value of the water body. Specifically, multiple sampling points are set up in the study area, and the collected sediments and overlying water samples are sealed and stored at low temperatures and transported back to the laboratory.

[0046] In the above-mentioned method for evaluating the release potential of nitrogen and phosphorus nutrients in lake sediments, the physical properties are particle density, porosity, average sedimentation rate and water content.

[0047] In the above-mentioned method for evaluating the release potential of nitrogen and phosphorus nutrients in lake sediments, the chemical properties are the chemical properties of the sediments, namely, the total nitrogen and total phosphorus content of the sediments.

[0048] Among them, the cumulative release potential of nitrogen and phosphorus nutrients in sediments is expressed by the nitrogen and phosphorus storage flux in lake sediments, and the calculation formula is:

[0049] BF j =C i,j ×S×ρ d ×10 -4 (2)

[0050] Where BF j is the storage flux of nitrogen and phosphorus in the outcropping sediment at sampling point j (g·m -2 ·a-1 );C i,j is the nitrogen and phosphorus content of the sediment exposed at sampling point j (mg·kg -1 ); S is the sedimentation rate of the sediment (cm·a -1 );ρ d is the dry density of the sediment (g·cm -3 ).

[0051] In the above-mentioned evaluation method for the release potential of nitrogen and phosphorus nutrients in lake sediments, the immediate release potential of nitrogen and phosphorus nutrients in sediments is expressed by the nitrogen and phosphorus release flux of lake sediments, and the calculation formula is:

[0052]

[0053] In the formula, F j represents the release flux of TN and TP in the sediment at sampling point j (g·m -2 ·d -1 ); represents the sediment porosity; D s represents the actual diffusion coefficient of nitrogen and phosphorus at the sediment-water interface (m 2 ·d -1 ); Represents the concentration gradient of total nitrogen or total phosphorus at the mud-water interface (g·m -3 ·m -1 ).

[0054] In the above-mentioned evaluation method for the release potential of nitrogen and phosphorus nutrients in lake sediments, the subjective weighting takes the cumulative release potential and immediate release potential of nitrogen and phosphorus nutrients in sediments as the criterion layer, selects ten indicators that affect the cumulative release and immediate release of nitrogen and phosphorus nutrients in sediments (see Table 1 Expert scoring table for the release potential of nitrogen and phosphorus nutrients in lake sediments), and constructs an evaluation index system for the release potential of nitrogen and phosphorus nutrients in lake sediments.

[0055] Table 1 Expert scoring table for the release potential of nitrogen and phosphorus nutrients in lake sediments

[0056]

[0057]

[0058] By setting the above-mentioned indicator layers and evaluation basis, we can systematically consider the impact of lake hydrology, water environment, water ecology and human activities on the release of nitrogen and phosphorus nutrients from lake sediments, provide a basis for expert scoring and evaluation, and fully and comprehensively characterize the potential for nitrogen and phosphorus nutrient release from lake sediments.

[0059] In the above-mentioned method for evaluating the release potential of nitrogen and phosphorus nutrients from lake sediments, the indicators of the cumulative release potential are the degree of eutrophication of the water body, the organic matter content in the sediments, the redox conditions of the sediments, the productivity of the lake ecosystem and the degree of nitrogen and phosphorus load from external inputs.

[0060] In the above-mentioned method for evaluating the release potential of nitrogen and phosphorus nutrients in lake sediments, the indicators of immediate release potential are the environmental conditions of lake water bodies, the hydrodynamic conditions of water bodies, the physical properties of sediments, the properties of nitrogen and phosphorus nutrients in sediments, and the degree of interference from human activities.

[0061] In the above-mentioned evaluation method for the release potential of nitrogen and phosphorus nutrients in lake sediments, the subjectively weighted experts score the contribution of the cumulative release potential and immediate release potential of nitrogen and phosphorus nutrients in sediments to the release potential of lake nutrients according to the characteristics of the study area, with a total score of 100. Subsequently, the expert scoring sheets are summarized, the scores of each indicator are summed up, and the respective weights and their corresponding criterion layer indicator weights are calculated to obtain the subjective weights of the cumulative release potential and immediate release potential of nitrogen and phosphorus nutrients in sediments.

[0062] In the above-mentioned evaluation method for the release potential of nitrogen and phosphorus nutrients in lake sediments, the cumulative release potential and immediate release potential of nitrogen and phosphorus nutrients in the sediments are subjectively weighted to obtain the indicator weight α i The weight obtained by subjective weighting emphasizes the importance of the two potential attributes themselves. The entropy weight method is used to objectively weight the cumulative release potential and immediate release potential of nitrogen and phosphorus nutrients in sediments to obtain the indicator weight β i The weight obtained by objective weighting takes into account the strength information between the two indicators based on the size of the discrimination.

[0063] In the above-mentioned evaluation method for the release potential of nitrogen and phosphorus nutrients in lake sediments, the formula for calculating the annual release potential of nitrogen and phosphorus nutrients in sediments is:

[0064] R=(w1×BF j +w2×F j ×365)×T (4)

[0065] Where R is the release potential of nitrogen and phosphorus nutrients in sediments (g·m -2 ), T is the release time (a).

[0066] The method for evaluating the release potential of nitrogen and phosphorus nutrients from lake sediments provided by the present invention comprehensively describes the cumulative and immediate impacts of the release of nitrogen and phosphorus nutrients from lake sediments, scientifically empowers and strengthens the rationality of subjective decision-making intentions and cumulative and immediate release research, comprehensively evaluates the release potential of nitrogen and phosphorus nutrients from lake sediments, overcomes the limitation of traditional methods for evaluating the release potential of nitrogen and phosphorus nutrients that only considers the immediate release of sediments, and provides an important basis for lake water environment evaluation and ecological environmental management decision-making.

[0067] In the process of expert evaluation in step 4, the present invention invites a number of experts in the field of water environment protection who are familiar with the study area and have sufficient experience and knowledge to form an evaluation team. By complementing and correcting the opinions of experts in different fields, one-sided judgments are avoided and the risk of bias is reduced, thereby ensuring that the evaluation process is comprehensive, accurate and reliable.

[0068] When weighting the two potentials subjectively and objectively, the importance ranking of subjective weights and the importance strength of objective weights are given priority, and then the importance strength of subjective weights and the importance ranking of objective weights are taken into account. A reasonable interval of combined weights is constructed to take into account the importance ranking of subjective weights and the importance strength of objective weights. The reasonable value interval of combined weights is the "intersection" of the attribute subjective weight neighborhood δ and the objective weight neighborhood δ. The intersection boundary is and The combined weights in the intersection can not only reflect the importance ranking of subjective and objective weights, but also reflect the importance intensity information of objective weights.

[0069] For the weighted calculation of the two indicators of cumulative release potential and immediate release potential, the combined weighting model that takes into account both "sequence information" and "intensity information" can effectively avoid the influence of "multiplier effect" and distribution coefficient on the evaluation. At the same time, the subjective and objective combined weighting method can not only comprehensively consider the cumulative and immediate impact of sediment release, but also make up for the uncertainty of the evaluation by combining subjective opinions with objective data. It can also flexibly allocate weights to the release potential of nitrogen and phosphorus nutrients in lake sediments according to the actual environmental characteristics and influencing factors, ensuring that the results are comprehensive and accurate, providing scientific background information for the prevention and control of endogenous pollution in lakes and the improvement of water quality, and is of great significance for formulating lake management decision-making plans and improving the efficiency of environmental management.

[0070] The evaluation method of the present invention is further described below with reference to specific embodiments.

[0071] The evaluation process of the release potential of nitrogen and phosphorus nutrients in the sediments of a certain lake is used as an example to illustrate. According to the literature, the average sedimentation rate of a certain lake is S j 3.2mm·a -1 At the same time, the basic properties of the sediments were obtained through laboratory measurements. Porosity According to the formula: Calculated. Dry density according to the formula: Get, where W c is the water content of sediment (%); ρ s is the particle density of the sediment (g·cm -3 );ρ w Take 1 (g·cm -3 ). The actual diffusion coefficient of nitrogen and phosphorus at the sediment-water interface is D s According to the porosity of the sediment Calculate, where hour, when hour, );D0 is the diffusion coefficient of the ideal solution (cm 2 ·s -1 ), the Stokes-Einstein equation is used to correct the temperature effect of the ideal diffusion coefficient. The concentration gradient of sediment nutrients at the sediment-water interface The result is obtained by fitting the exponential curve of nutrients and depth between the interstitial water of 0-5 cm and the overlying water of 0-5 cm in the sediment. The nitrogen and phosphorus nutrient storage flux and release flux of lake sediments are calculated according to formulas (1) and (2). The calculation process and results are shown in Table 2.

[0072] Table 2 Calculation results of nitrogen and phosphorus nutrient storage flux and release flux in sediments

[0073]

[0074]

[0075] The storage flux and release flux of nitrogen and phosphorus nutrients in the sediments calculated in Table 2 show that the cumulative release potential of nitrogen nutrients in the sediments of sampling points A to E in this lake is 0.30 g·a -1 ·m -2 , 0.15g·a -1 ·m -2 , 1.40 g·a -1 ·m -2 , 0.47g·a -1 ·m -2 , 0.03g·a -1 ·m -2 ; The cumulative release potential of phosphorus nutrients is 0.20g·a -1 ·m -2 , 0.14 g·a -1 ·m -2 , 0.24g·a -1 ·m -2 , 0.19 g·a -1 ·m-2 , 0.07g·a -1 ·m -2 The immediate release potential of nitrogen nutrient salts in the sediments at sampling points A to E is 2.76 g·m -2 ·d -1 , 0.85g·m -2 ·d -1 , 2.23 g·m -2 ·d -1 , 0.72 g·m -2 ·d -1 , 1.36 g·m -2 ·d -1 ; The immediate release potential of phosphorus nutrient is 0.043 g·m -2 ·d -1 , 0.048 g·m -2 ·d -1 , 0.044 g·m -2 ·d -1 , 0.058 g·m -2 ·d -1 , 0.033 g·m -2 ·d -1 .

[0076] For a long time, a certain lake has been seriously eutrophicated by the discharge of domestic sewage and industrial sewage from surrounding villages and factories, and the nitrogen and phosphorus nutrient load in the sediment is high. In recent years, in order to ensure the ecological water use of the lake and restore the health of the lake ecosystem, the relevant environmental management departments have carried out ecological water replenishment projects and ecological dredging projects. External water replenishment, dredging projects and the removal of embankments and dikes have seriously changed the hydrodynamic conditions of a certain lake, and the endogenous pollution of the lake has intensified. Ten experts in the field of water environment protection research with different backgrounds were invited to judge and score the contribution of the cumulative release potential and immediate release potential of nitrogen and phosphorus nutrients in the sediment of a certain lake to the release potential according to the evaluation indicators in Table 1, and the results are shown in Table 3. According to the expert scores, the subjective weight coefficients of the cumulative release potential and immediate release potential of nitrogen and phosphorus in the sediment are calculated and added as 0.4 and 0.6. The subjective weighting results show that the "sequence information" of the two potentials, that is, the importance ranking is: immediate release potential> cumulative release potential.

[0077] Table 3 Results of experts’ scoring and weighting of the potential for cumulative release and immediate release of sediments from a lake

[0078]

[0079]

[0080] The entropy weights of the cumulative release potential and immediate release potential of nitrogen and phosphorus in sediments are calculated by the formula The probability of getting two potentials is given by (where K = 1 / ln2 = 1.44) and the information entropy is E1 = 1.61; E2 = 2.13. According to the formula The entropy weights are calculated to be 0.45 and 0.55. The weights obtained by the entropy weight method indicate the "intensity information" of the two potentials. In terms of the importance of the indicator attributes, the immediate release potential is greater than the cumulative release potential. The combined weighting method is used to obtain the weights. According to the constraints in formula (4), As the objective function, the reasonable value range of the weight of the sediment cumulative release potential is [0.4, 0.45], and the reasonable value range of the weight of the sediment immediate release potential is [0.55, 0.6]. According to the constraint condition w in formula (4), i …w j , i<j, the sediment cumulative release potential and immediate release potential obtained by combined weighting should satisfy the order of importance of subjective weights, that is, the immediate release potential weight ≥ the cumulative release potential weight. In addition, the sum of the sediment cumulative release potential and the immediate release potential weight is 1, and the objective weight β obtained by entropy weight i Substitute into the objective function In the above equations, the combined weights of the cumulative release potential and the immediate release potential of sediment nitrogen that meet the constraints within the interval are calculated to be 0.45 and 0.55. The combined weights of the cumulative release potential and the immediate release potential of sediment phosphorus are obtained by the same method as 0.49 and 0.51. This combined weight not only satisfies the importance ranking determined by experts based on the characteristics of a lake, but also takes into account the importance intensity information between the potential values. Substituting the combined weight into formula (4), it is found that the annual release potential of sediment nitrogen nutrients at sampling points A to E in the lake is 0.55 g·m -2 , 0.17 g·m -2 , 0.45g·m -2 , 0.14 g·m -2 , 0.27 g·m -2 ; The potential release value of phosphorus nutrients in sediments is 0.0081 g·m -2 , 0.0090g·m -2 , 0.0083g·m -2 , 0.0109 g·m -2 , 0.0062g·m -2 The average annual release potential of nitrogen nutrients in the lake sediments is 0.32 g·m -2 The annual release potential of phosphorus nutrient is 0.0085 g·m -2 Based on the obtained nitrogen and phosphorus nutrient release potential of lake sediments, areas with high nutrient release potential are identified, prevention and mitigation measures are taken for specific sources or regions, and lake ecological management strategies are refined to provide scientific basis and data support for decision makers to specify environmental management policies.

[0081] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A method for evaluating the release potential of nitrogen and phosphorus nutrients in lake sediments, characterized in that: The steps include: Step 1, collecting sediment and overlying water samples, and obtaining in-situ environmental data of the sampling points; Step 2, determining the physical and chemical properties of lake sediments, calculating the nitrogen and phosphorus storage fluxes of lake sediments, and characterizing the cumulative release potential of nitrogen and phosphorus nutrients in lake sediments; Step 3, according to the in-situ environmental data of the sampling point, static release culture and interstitial water diffusion model experiments are carried out, sediments and overlying water bodies are placed in a columnar tube, interstitial water of sediments in different layers is collected at different times, and then the total nitrogen and total phosphorus contents of the interstitial water and the overlying water are measured, and the nitrogen and phosphorus release fluxes of lake sediments are calculated to characterize the immediate release potential of nitrogen and phosphorus nutrients in lake sediments; Step 4: Experts scored and evaluated the cumulative release potential and immediate release potential of nitrogen and phosphorus nutrients in sediments according to the characteristics of the study area, and subjectively weighted them to obtain the indicator weight α i ; The entropy weight method is used to objectively weight the cumulative release potential and immediate release potential of nitrogen and phosphorus nutrients in sediments calculated in steps 2 and 3 to obtain the indicator weight β i ; The combined weights of the cumulative release potential and immediate release potential of nitrogen and phosphorus nutrients in sediments are obtained by subjective and objective combined weighting. The reasonable value range of the combined weight is the intersection of the subjective weight neighborhood and the objective weight neighborhood. The intersection boundary is and The combined weight in the intersection adopts formula (1): where α i is the subjective weighting weight, β i is the objective weight obtained by the entropy weight method, is the objective function, that is, it is required that the deviation between the combined weight of the two fluxes and the weight obtained by objective weighting is minimized; the constraint condition w i ≥w j .i < j ensures that the combined weight of the fluxes satisfies the importance information of the subjective weight; the constraint condition limits the interval of the combined weight, guarantees that the combined weight satisfies that the sum of the weights is 1; Set the constraint conditions and solve the combined weighted optimization model to obtain the combined weights w of the cumulative release potential and immediate release potential of nitrogen and phosphorus nutrients in sediments. i ; Step 5, assign weights to the cumulative release potential and immediate release potential of nitrogen and phosphorus nutrients, add them up and calculate the release potential value of nitrogen and phosphorus nutrients in lake sediments.

2. The method for evaluating the release potential of nitrogen and phosphorus nutrients in lake sediments according to claim 1, characterized in that: The in-situ environmental data of the sampling points include the temperature, redox potential, pH value of lake sediments measured on site, and the temperature, redox potential, pH value of water bodies.

3. The method for evaluating the release potential of nitrogen and phosphorus nutrients in lake sediments according to claim 1, characterized in that: The physical properties are particle density, porosity, average sedimentation rate and water content, The chemical properties are the total nitrogen and total phosphorus content of the sediment, Among them, the cumulative release potential of nitrogen and phosphorus nutrients in sediments is expressed by the nitrogen and phosphorus storage flux in lake sediments, and the calculation formula is: BF j =C i,j ×S×ρ d ×10 -4 (2) Where BF j is the storage flux of nitrogen and phosphorus in the outcropping sediment at sampling point j (g·m -2 ·a -1 );C i,j is the nitrogen and phosphorus content of the sediment exposed at sampling point j (mg·kg -1 ); S is the sedimentation rate of the sediment (cm·a -1 );ρ d is the dry density of the sediment (g·cm -3 ).

4. The method for evaluating the release potential of nitrogen and phosphorus nutrients in lake sediments according to claim 1, characterized in that: The immediate release potential of nitrogen and phosphorus nutrients in sediments is expressed by the nitrogen and phosphorus release flux of lake sediments, and the calculation formula is: In the formula, F j represents the release flux of TN and TP in the sediment at sampling point j (g·m -2 ·d -1 ); represents the sediment porosity; D s represents the actual diffusion coefficient of nitrogen and phosphorus at the sediment-water interface (m 2 ·d -1 ); Represents the concentration gradient of total nitrogen or total phosphorus at the mud-water interface (g·m -3 ·m -1 ).

5. The method for evaluating the release potential of nitrogen and phosphorus nutrients in lake sediments according to claim 1, characterized in that: The subjective weighting takes the cumulative release potential and immediate release potential of nitrogen and phosphorus nutrients in sediments as the criterion layer, selects ten indicators that affect the cumulative release and immediate release of nitrogen and phosphorus nutrients in sediments, and constructs an evaluation index system for the release potential of nitrogen and phosphorus nutrients in lake sediments.

6. The method for evaluating the release potential of nitrogen and phosphorus nutrients in lake sediments according to claim 5, characterized in that: The indicators of cumulative release potential are the degree of eutrophication of water bodies, the content of organic matter in sediments, the redox conditions of sediments, the productivity of lake ecosystems and the degree of nitrogen and phosphorus load from external inputs.

7. The method for evaluating the release potential of nitrogen and phosphorus nutrients in lake sediments according to claim 5, characterized in that: The indicators of immediate release potential are the environmental conditions of lake water, the hydrodynamic conditions of the water, the physical properties of sediments, the properties of nitrogen and phosphorus nutrients in the sediments, and the degree of interference from human activities.

8. The method for evaluating the release potential of nitrogen and phosphorus nutrients in lake sediments according to claim 1, characterized in that: The subjectively weighted experts scored the contribution of the cumulative release potential and immediate release potential of nitrogen and phosphorus nutrients in sediments to the release potential of lake nutrients based on the characteristics of the study area, with a total score of 100. The expert scoring sheets were then summarized, the scores of each indicator were summed up, and their respective weights and their corresponding criterion layer indicator weights were calculated to obtain the subjective weights of the cumulative release potential and immediate release potential of nitrogen and phosphorus nutrients in sediments.

9. The method for evaluating the release potential of nitrogen and phosphorus nutrients in lake sediments according to claim 1, characterized in that: Subjectively weight the cumulative release potential and immediate release potential of nitrogen and phosphorus nutrients in the sediment to obtain the indicator weight α i The weight obtained by subjective weighting emphasizes the importance of the two potential attributes themselves. The entropy weight method is used to objectively weight the cumulative release potential and immediate release potential of nitrogen and phosphorus nutrients in sediments to obtain the indicator weight β i The weight obtained by objective weighting takes into account the strength information between the two indicators based on the degree of discrimination.

10. The method for evaluating the release potential of nitrogen and phosphorus nutrients in lake sediments according to claim 1, characterized in that: The formula for calculating the annual release potential of nitrogen and phosphorus nutrients in sediments is: R=(w1×BF j +w2×F j ×365)×T(4) Where R is the release potential of nitrogen and phosphorus nutrients in sediments (g·m -2 ), T is the release time (a).

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