Method for determining lake nutrition degree and formulating management measures based on multiple variables

Abstract

The invention discloses a method for determining the nutrition degree of a lake and formulating management based on multiple variables in the technical field of lake management. The method comprises the following steps: 1) collecting total nitrogen and total phosphorus values observed in the lake history at the same time and the total nitrogen and total phosphorus entering amount of the lake in the last year; 2) carrying out data conversion; 3) determining joint distribution among the nutritional factors by using the converted data; 4) calculating a joint distribution function of the nutritional factors and chlorophyll a; 5) calculating a nutritional index threshold value Ks corresponding to a threshold value in the eutrophication threshold value table; the method comprises the following steps of (1) calculating Ks, (2) calculating Ks, (3) calculating Ks, (4) calculating Ks, (5) calculating Ks, (6) calculating a nutrition index Li corresponding to a lake observation value, (7) comparing Ks with Li to determine the nutrition degree corresponding to the lake in the observation period, and (8) analyzing the nutrition degree condition of the last year and formulating management measures The multivariable method for quantitatively comparing the nutrition degree of the lake is easy to popularize and use in water quality management of lakes in various nutrition states.

Description

Technical Field

[0001] The present invention relates to the technical field of lake management, and in particular to a method for determining the nutrient level of a lake and formulating management measures based on multiple variables. Background Art

[0002] Eutrophication is a serious problem in some of my country's lakes, severely impacting public health and water safety. Assessing and controlling lake eutrophication plays a crucial role in reducing algae concentrations and protecting lake water quality. Currently, lake eutrophication indicators are primarily tabulated, based on threshold values ​​for total nitrogen, total phosphorus, and chlorophyll a. However, since observed lake values ​​may not simultaneously meet these thresholds, determining a lake's nutrient status is challenging. Furthermore, some nutrient indices based on these tables often require subjective weighting, which compromises objectivity and complicates the formulation of lake water quality management measures. Summary of the Invention

[0003] In response to the shortcomings of the existing technology, the present invention provides a method for determining the nutrient level and management of lakes based on multiple variables. By utilizing the objective and nonlinear relationship between total nitrogen, total phosphorus and chlorophyll a in lakes, the nutrient levels of lakes can be quantitatively compared and lake management measures can be formulated. It is easy to promote and use in the water quality management of lakes in various nutrient states.

[0004] The object of the present invention is achieved by: a method for determining the nutrient content of a lake and formulating management measures based on multiple variables, comprising the following steps:

[0005] Step 1) Collect the total nitrogen and total phosphorus values ​​observed in the lake history, as well as the total nitrogen and total phosphorus inflows into the lake in the previous year;

[0006] Step 2) Perform data conversion;

[0007] Step 3) Use the transformed data to determine the joint distribution among nutritional factors;

[0008] Step 4) Calculate the joint distribution function of nutrient factors and chlorophyll a;

[0009] Step 5) Calculate the nutrient index threshold K corresponding to the threshold in the eutrophication threshold table s ;

[0010] Step 6) Calculate the trophic index L corresponding to the lake observation value i ;

[0011] Step 7) K s With L i Compare and determine the nutrient level of the lake during the observation period;

[0012] Step 8) Analyze the nutritional status of the previous year and formulate management measures.

[0013] Furthermore, step 1) specifically includes:

[0014] 1-1) Collect historical chlorophyll a observations of n groups of lakes with the required eutrophication levels, and denote the variable chlorophyll a as , and its i-th observation value is recorded as , where n is an integer greater than 500, i=1,2,3…n; and the number of observation data in the previous year is not less than 30;

[0015] 1-2) Collect the n sets of total nitrogen observations observed at the same time, and record the variable total nitrogen as , and its i-th observation value is recorded as ;

[0016] 1-3) Collect n sets of observations of total phosphorus simultaneously. The variable total phosphorus is recorded as , and its i-th observation value is recorded as .

[0017] 1-4) Collect and determine the total nitrogen and total phosphorus inflows into the lake in the previous year.

[0018] Furthermore, step 2) specifically includes the following steps:

[0019] 2-1) Arrange the observed values ​​of chlorophyll a from smallest to largest, and record the i-th observed value as the k-th. Calculate the observed value of chlorophyll a using the following formula: The corresponding transformed observations :

[0020] ;

[0021] The transformed variable chlorophyll a is recorded as ;

[0022] 2-2) Calculate the observed values ​​of total nitrogen and total phosphorus after conversion using the same method as step 2-1) and record them as as well as , the variables total nitrogen and total phosphorus are respectively as well as .

[0023] Furthermore, the step 3) specifically includes the following steps:

[0024] 3-1) Calculation as well as Kendall rank correlation coefficient between ;

[0025] 3-2) Calculate using the following formula :

[0026] ;

[0027] where:

[0028] ;

[0029] The above equation is solved by finite volume method.

[0030] 3-3) Calculate the joint distribution of total nitrogen and total phosphorus after transformation by the following formula:

[0031] .

[0032] Further, the step 4) specifically includes the following steps:

[0033] 4-1) Substitute the simultaneously observed n groups of (X , ) into the joint distribution function , get n groups of values, denoted as , and find out their corresponding , i=1, 2, 3…n; The corresponding variable is denoted as ;

[0034] 4-2) Calculate the Kendall rank correlation coefficient between and ; ;

[0035] 4-3) Calculate by the following formula:

[0036] ;

[0037] where:

[0038] ;

[0039] The above equation is solved by finite volume method.

[0040] 4-4) Calculate the joint distribution function F of the total nitrogen, total phosphorus and chlorophyll a of the nutrient factor by the following formula:

[0041] .

[0042] Further, the step 5) specifically includes the following steps:

[0043] 5-1) According to the method of step 2) to step 4), calculate the value corresponding to the joint distribution function F corresponding to the threshold value in the eutrophication threshold table, denoted as M s , s=1, 2, 3:

[0044] Table 1 Eutrophication threshold table

[0045]

[0046] 5-2) Substitute M s into the following formula to calculate the corresponding eutrophication index threshold K s :

[0047] ;

[0048] wherein, is the cumulative distribution function of standard normal distribution.

[0049] Further, the step (6) specifically comprises the following steps:

[0050] 6-1) According to the method of step 2) to step 4), the corresponding value of the joint distribution function F of the observed values of chlorophyll a, total nitrogen and total phosphorus of n groups of lakes is calculated, and is recorded as N i , i = 1, 2, 3, …, n.

[0051] 6-2) Substitute N i into the following formula to calculate the corresponding eutrophication index L i :

[0052] ;

[0053] wherein, is the cumulative distribution function of standard normal distribution.

[0054] Further, the step 7) specifically comprises the following steps:

[0055] 7-1) Arrange K s from small to large, and record them as K1, K2, K3, respectively.

[0056] 7-2) Compare the values of n eutrophication indexes L i , i = 1, 2, 3, …, n with K s in turn, if less than or equal to K1, the state of the lake corresponding to the observed value is oligotrophic; if between K1 and K2, the state of the lake corresponding to the observed value is mesotrophic; if between K2 and K3, it is eutrophication state; if the value is greater than K3, it is higher than the eutrophication state.

[0057] Further, the step 8) specifically comprises the following steps:

[0058] 8-1) Sort the obtained lake eutrophication state, and stipulate that the score of oligotrophic state is -1, the score of mesotrophic state is 0, the score of eutrophication state is 1, and the score of higher than eutrophication state is 2.

[0059] 8-2) Calculate the average of the observation value of the lake in the last year. If it is between -0.5 to 0.5, the lake is in an ideal state, and the maximum allowable amount of total nitrogen and total phosphorus into the lake of this year can be the same as that of the last year; if it is less than or equal to -0.5, calculate the relative deviation from -0.5, denoted as a%, and the maximum allowable amount of total nitrogen and total phosphorus into the lake of this year is increased by 0.1 x a% based on the total nitrogen and total phosphorus into the lake of the last year; if it is greater than or equal to 0.5, calculate the relative deviation from 0.5, denoted as b%, and the maximum allowable amount of total nitrogen and total phosphorus into the lake of this year is reduced by 0.1 x b% based on the total nitrogen and total phosphorus into the lake of the last year.

[0060] In the present application, environmental studies show that the degree of lake nutrition is closely related to total nitrogen, total phosphorus and chlorophyll a; and the existing evaluation methods of the degree of lake nutrition are also mostly based on these three indicators. Specifically, the threshold of the degree of lake nutrition is generally listed in table form; but in most cases, the observation values of the lake do not meet the threshold values listed in the table, which makes it difficult to effectively evaluate the degree of lake nutrition. On the other hand, the eutrophication index based on these three environmental variables often needs to determine the weight manually, which makes the evaluation results have a certain subjectivity and brings difficulties to the development of management measures. The present application overcomes the above two shortcomings and proposes a new method.

[0061] Compared with the prior art, the present application has the beneficial effects that the present application makes full use of the statistical relationship of objective observation data, and almost has no step of artificial subjective intervention, which overcomes the shortcomings of strong subjectivity of the existing methods and is easy to popularize in the determination of the water quality management target of each lake. BRIEF DESCRIPTION OF DRAWINGS

[0062] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description only are the embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of the provided drawings.

[0063] Figure 1 The flowchart of the present application. DETAILED DESCRIPTION

[0064] With reference to the accompanying drawings, the technical solutions in the embodiments of the present application will be described clearly and completely. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the scope of the present application.

[0065] Embodiments

[0066] The present application will be further described below in combination with the accompanying drawings and the actual observation data of a lake in the east of China.

[0067] As shown in a multivariate method for determining and comparing the degree of lake nutrition: Figure 1

[0068] Step 1) According to the requirements of the present specification, 656 sets of data of simultaneously observed chlorophyll a, total nitrogen and total phosphorus in the history of the lake are collected.

[0069] 1-1) The observed values of chlorophyll a in the history of the lake of 656 sets of eutrophication degree are collected, and the variable chlorophyll a is denoted as Chl, the i-th observed value of which is denoted as Chli, i=1, 2, 3, …, 656; wherein the number of observed values of the previous year is 56.

[0070] 1-2) 656 sets of observed values of total nitrogen simultaneously observed are collected, and the variable total nitrogen is denoted as TN, the i-th observed value of which is denoted as Tni, i=1, 2, 3, …, 656.

[0071] 1-3) 656 sets of observed values of total phosphorus simultaneously observed are collected, and the variable total phosphorus is denoted as TP, the i-th observed value of which is denoted as Tpi, i=1, 2, 3, …, 656.

[0072] 1-4) The amount of total nitrogen entering the lake in the previous year of the lake is collected and determined as 3280 tons, and the amount of total phosphorus entering the lake is collected and determined as 932 tons.

[0073] Step 2) The 656 sets of chlorophyll a observation values are arranged from small to large, and the rank k of each observation value is recorded, and the converted value of each set of chlorophyll a observation values is calculated by the following formula:

[0074]

[0075] The observed values of total nitrogen and total phosphorus are converted by the same method, and

[0076] Step 3) The Kendall rank correlation coefficient between the converted total nitrogen and total phosphorus observation values is calculated​​​​​​​​​ In this example, 0.76; the equation is solved by finite volume method:

[0077]

[0078] wherein:

[0079]

[0080] In this example, 1.32. The joint distribution function of total nitrogen and total phosphorus is obtained as:

[0081]

[0082] Step 4) Substitute the 656 groups of total nitrogen and total phosphorus converted total phosphorus observation values into the above formula to obtain the corresponding 656 groups of values, and the corresponding random variable is denoted as ; and calculate its Kendall rank correlation coefficient with the converted chlorophyll a ; in this example, 0.85. Use the integral equation in the above steps to obtain the corresponding 1.68; the joint distribution function of total nitrogen, total phosphorus and chlorophyll a is obtained as:

[0083]

[0084] Step 5) Calculate the F corresponding to the threshold values in the table below using the above steps.

[0085] Table 1 Eutrophication threshold table

[0086]

[0087] Substitute the obtained F values into the inverse function of the standard normal distribution function respectively to calculate the corresponding values, which are -2.52, -1.93, -0.560

[0088] Step 6) Convert the 656 groups of chlorophyll a, total nitrogen and total phosphorus observation values into values according to the methods of steps 2-4 to calculate the joint distribution function F corresponding to the values of the lake chlorophyll a, total nitrogen and total phosphorus observation values, and substitute the results into the following formula to obtain the corresponding nutrition index L i .

[0089]

[0090] wherein, is the cumulative distribution function of the standard normal distribution.

[0091] Step 7) Compare the nutrition index corresponding to the 656 groups of observation values with the nutrition index threshold value respectively to determine their nutrition state.

[0092] ​​Step 8) According to the score of the lake nutrition status obtained in the last step, the score of all observation values of the lake in the last year is assigned, wherein the score of the oligotrophic state is -1, the score of the mesotrophic state is 0, the score of the eutrophic state is 1, and the score of the state higher than the eutrophic state is 2. Further, the average score of all observation values of the lake in the last year is calculated; in this case, the average score is -0.16, which is between -0.5 and 0.5, so the maximum allowable amount of total nitrogen and total phosphorus into the lake in this year can be used as the amount of total nitrogen and total phosphorus into the lake in the last year, i.e. 3280 tons and 932 tons, respectively.

[0093] The above description of the embodiments is only used to help understand the method of the present application and its core idea. It should be noted that for those skilled in the art, without departing from the principles of the present application, the present application can be improved and modified in several ways, and these improvements and modifications also fall within the protection scope of the claims of the present application.

Claims

1. A method for determining the trophic state of a lake and developing management measures based on multivariate, characterized in that, The method comprises the following steps: Step 1) collecting total nitrogen and total phosphorus values observed at the same time in the history of the lake, and total nitrogen and total phosphorus amounts entering the lake in the previous year of the lake; Step 2) data transformation; Step 3) determining the joint distribution of the nutrients by using the transformed data; Step 4) calculating the joint distribution function of the nutrients and chlorophyll a; Step 5) calculating the nutrient index threshold value K corresponding to the threshold value in the eutrophication threshold table s ; Step 6) Calculate the trophic index L corresponding to the lake observation i ; Step 7) K s and L i Determine the corresponding degree of nutrition of the lake during the observation period by comparison. Step 8) analyzing the nutrient status in the previous year and formulating management measures.

2. A method for determining the trophic status of a lake and developing management measures based on multivariate, according to claim 1, characterized in that, Step 1) specifically comprises: 1-1) Collecting historical observation values of chlorophyll-a of n groups of lakes which need to be eutrophication, and the variable chlorophyll-a is recorded as The i-th observation value of which is recorded as Wherein, n is an integer greater than 500, i = 1, 2, 3…n; wherein, the observation data of the last year is not less than 30; 1-2) Collecting the observed values of n sets of total nitrogen observed at the same time, and the variable total nitrogen is denoted as , the i-th observation of which is denoted as ; 1-3) Collect n sets of simultaneous observations of total phosphorus, the variable total phosphorus is denoted by , and the ith observation is denoted by ; 1-4) collecting and determining the total nitrogen and total phosphorus amounts entering the lake in the previous year of the lake.

3. A method for determining the trophic status of a lake and developing management measures based on multivariate, according to claim 2, characterized in that, Step 2) specifically comprises the following steps: 2-1) The observed values of chlorophyll a are arranged in ascending order, and the i-th observed value is arranged in the k-th position, and the observed value of chlorophyll a is calculated by the following formula The corresponding transformed observed value : ； Transformed variable chlorophyll a is denoted as ; 2-2) Calculate the observed values of total nitrogen and total phosphorus after conversion by the same method as in step 2-1), and denote them as and respectively. and respectively.

4. A method for determining the trophic status of a lake and developing management measures based on multivariate, according to claim 3, characterized in that, The step 3) specifically comprises the following steps: 3-1) Calculations and Kendall rank correlation coefficient between ; 3-2) Calculated using the formula : ； Wherein: ； The above equation is solved by using the finite volume method; 3-3) calculating the joint distribution of the transformed total nitrogen and total phosphorus by using the following formula: 。 5. A method for determining the trophic status of a lake and developing management measures based on multivariate, according to claim 4, characterized in that, The step 4) specifically comprises the following steps: 4-1) n groups of simultaneous observations (X1, Y1), (X2, Y2), (X3, Y3), …, (Xn, Yn) are made. , ) Substitute the joint distribution function into the n groups of values, denoted as , and find the corresponding , i = 1, 2, 3…n. The corresponding variable is denoted as ; 4-2) Calculations and Kendall rank correlation coefficient between ; 4-3) Calculated using the formula : ； Wherein: ； The above equation is solved by using the finite volume method; 4-4) calculating the joint distribution function F of the nutrients total nitrogen, total phosphorus and chlorophyll a by using the following formula: 。 6. A method for determining the trophic status of a lake and developing management measures based on multivariate, according to claim 5, characterized in that, The step 5) specifically comprises the following steps: 5-1) The value of the joint distribution function F corresponding to the threshold value in the eutrophication threshold table is calculated according to the method of steps 2) - 4), and is denoted as M s , s = 1,2,3: Table 1 eutrophication threshold table ； 5-2) Calculate M s The corresponding nutrition index threshold K is calculated by substituting the values into the following formula, respectively s : ； wherein is the cumulative distribution function of the standard normal distribution.

7. A method for determining the trophic status of a lake and developing management measures based on multivariate, according to claim 6, characterized in that, The step (6) specifically comprises the following steps: 6-1) According to the method of step 2) - step 4), the value corresponding to the joint distribution function F corresponding to the observed values of n groups of lakes of chlorophyll a, total nitrogen and total phosphorus is calculated, and is recorded as N i , i = 1, 2, 3, …, n; 6-2) The N i The corresponding nutrition index L is calculated by substituting the values into the following equation i : ； wherein is the cumulative distribution function of the standard normal distribution.

8. A method for determining the trophic status of a lake and developing management measures based on multivariate, according to claim 7, characterized in that, The step 7) specifically comprises the following steps: 7-1) K s In ascending order, respectively, K1, K2, K3; 7-2) Compare the n nutrition indices L in turn i , i-1, 2, 3, …, n and K s The value of the observation value corresponding to the lake state is poor nutrition if it is less than or equal to K1; if it is between K1 and K2, the observation value corresponding to the lake state is medium nutrition; if it is between K2 and K3, it is eutrophication state; if the value is greater than K3, it is higher than the eutrophication state.

9. A method for determining the trophic status of a lake and developing management measures based on multivariate, according to claim 8, characterized in that, The step 8) specifically comprises the following steps: 8-1) ranking the obtained lake nutrient status, and setting the score of the oligotrophic state as -1, the score of the mesotrophic state as 0, the score of the eutrophic state as 1, and the score of the state higher than the eutrophic state as 2; 8-2) calculating the average score of the observed values in the previous year of the lake. If the average score is between -0.5 and 0.5, the lake nutrient status is ideal, and then the maximum allowable amounts of total nitrogen and total phosphorus entering the lake in the current year can be the same as the total nitrogen and total phosphorus amounts entering the lake in the previous year of the lake; if the average score is less than or equal to -0.5, the relative deviation of the average score from -0.5 is calculated and recorded as a%, and the maximum allowable amounts of total nitrogen and total phosphorus entering the lake in the current year are increased based on the total nitrogen and total phosphorus amounts entering the lake in the previous year of the lake, and the increase ratio is 0.1×a%; if the average score is greater than or equal to 0.5, the relative deviation of the average score from 0.5 is calculated and recorded as b%, and the maximum allowable amounts of total nitrogen and total phosphorus entering the lake in the current year are reduced based on the total nitrogen and total phosphorus amounts entering the lake in the previous year of the lake, and the reduction ratio is 0.1×b%.

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