Model method for estimating drainage basin soil organic carbon density by using water optical characteristic parameters

Abstract

The invention discloses a model method for estimating drainage basin soil organic carbon density by using water optical characteristic parameters, relates to a method for estimating drainage basin soil organic carbon density, and belongs to the field of water and soil environment parameter evaluation. The invention aims to solve the problems of long time consumption and high cost of the existing method for measuring the organic carbon density of the soil. The method comprises the following steps: 1, obtaining water body sample data; 2, obtaining soil sample data; and 3, on the basis of the boundary vector data of the 9 large watersheds in China, the water body sample data and the soil sample data correspond to each other, a linear regression model of SPSS software is utilized to construct the relationship between the soil organic carbon density SOCD and the water body absorption coefficient aCDOM (355), and the final model SOCD = 1.22 * aCDOM (355) + 0.087. By monitoring the concentration change of the CDOM in the water body, the migration and transformation rules of the organic carbon density of the soil in the surrounding watershed can be known. The method is of great significance in understanding earth carbon cycle, protecting ecological environment, guiding agricultural production and the like.

Description

Technical Field

[0001] The invention relates to a method for estimating soil organic carbon density in a watershed, and belongs to the field of water body and soil environmental parameter evaluation. Background Art

[0002] Soil erosion is an important factor leading to the loss of soil organic carbon pool and soil degradation. Soil organic carbon (SOC) refers to various positively charged carbon-containing organic compounds in the soil and is an extremely important component of the soil. Colored dissolved organic matter (CDOM) is the colored part of dissolved organic matter (DOM) and is an important type of absorber of ultraviolet light and visible blue light in water. Soil organic carbon is one of the important sources of CDOM. When organic matter in the soil is dissolved and released into the water, the colored part forms CDOM. Therefore, the content and composition of soil organic carbon will directly affect the concentration and characteristics of CDOM in the water. In addition, CDOM in the water will also affect the dynamic balance of soil organic carbon. Soil organic carbon will decompose and transform under the action of microorganisms, and these processes will also affect the concentration and composition of CDOM in the water. For example, the decomposition of soil organic carbon will produce a series of intermediates, which may contain colored substances, thereby increasing the concentration of CDOM in the water. The absorption and fluorescence characteristics of CDOM can reflect the source and transformation process of organic matter in water bodies, and thus provide important information for studying the migration and transformation of soil organic carbon. At the same time, CDOM in water bodies may also return to the soil through processes such as sedimentation and adsorption, and interact with soil organic carbon.

[0003] At present, the measurement of soil organic carbon and its density mainly uses instruments such as element analyzers to determine the carbon content in soil samples, burn soil samples at high temperatures, and measure the amount of carbon dioxide released during the combustion process to infer the carbon content in the soil. Soil bulk density is one of the important factors affecting soil carbon density. Therefore, before determining soil carbon density, it is necessary to accurately determine the soil bulk density. This can be achieved by using tools such as ring cutters for field measurements and further processing and analysis in the laboratory. The process is cumbersome and complicated, the economic cost is high, and the experimental data acquisition cycle time is long. The absorption coefficient of CDOM, an optically active substance in water bodies, is mainly measured by ultraviolet spectrophotometers, which can quickly obtain relevant CDOM data. The measurement of soil organic carbon can be obtained by measuring the absorption coefficient of CDOM in water bodies, and the source and composition of soil organic carbon and its density can be inferred. However, there is currently no numerical estimation method based on the optical properties of CDOM in the country and the black soil region of Northeast China to estimate the soil organic carbon density in the surrounding watershed. Summary of the invention

[0004] The purpose of the present invention is to solve the problem that the current method of measuring soil organic carbon density is time-consuming and costly, and to provide a model method for estimating the soil organic carbon density of a watershed by using optical characteristic parameters of water bodies.

[0005] The model method for estimating the soil organic carbon density in a watershed using water body optical characteristic parameters is carried out in the following steps:

[0006] 1. Obtain water sample data: Take typical lakes in Northeast China as sampling points, obtain 593 sample points of CDOM concentration in 279 lakes in Northeast China, collect surface water from lakes, collect 2L water samples from each sampling point, and immediately put them into the refrigerator for dark storage. All water samples were filtered within two days, and the filtered samples were refrigerated and stored at 4℃, and optical absorption parameters were tested. The water absorption coefficient a was used to calculate the absorption coefficient of the water body. CDOM (355) represents the CDOM concentration of the water sample;

[0007] 2. Obtain soil sample data: Soil samples were collected from the 0-10 cm soil surface layer within a 5 km buffer zone around 279 lakes. 5-8 soil samples were collected around each lake and placed in sealed containers. A total of 720 surface soil samples were collected. The soil bulk density was measured using the ring knife method. The soil organic carbon content was measured using the external heating-potassium dichromate titration method. The soil organic carbon density SOCD is equal to the soil organic carbon content TOC multiplied by the soil bulk density BD. The average soil organic carbon density of the 279 lakes was calculated.

[0008] 3. Based on the boundary vector data of China's nine major river basins, all samples were divided into 279 sub-basins, and the water sample data and soil sample data were matched, that is, there were 279 pairs of water and soil sample data, of which 175 sample point water and soil sample data were used for model construction, and 104 sample point water and soil sample data were used for model verification;

[0009] The linear regression model of soil organic carbon density SOCD and water absorption coefficient a was constructed using SPSS software. CDOM (355), the final model SOCD = 1.22*a CDOM (355)+0.087.

[0010] The optical absorption parameter testing method described in step 1 is as follows:

[0011] First, the water sample was filtered using a 47 μm glass fiber microporous filter membrane to obtain a primary filtered water sample;

[0012] The primary filtered water sample was then filtered through a 0.22 μm polycarbonate membrane to obtain the water sample for CDOM testing;

[0013] The water sample for CDOM test was placed in a cuvette, ultrapure water was used as a reference, and the absorbance of the water sample for CDOM test at 200nm–800nm ​​was measured using a Shimadzu UV spectrophotometer UV-2660. CDOM The absorption coefficient of (355) indicates the CDOM concentration.

[0014] By monitoring the concentration changes of CDOM in water bodies, the present invention can understand the migration and transformation rules of soil organic carbon density in surrounding watersheds. These are of great significance for understanding the earth's carbon cycle, protecting the ecological environment, and guiding agricultural production. According to the model method of the present invention, water samples are collected in the black soil area of ​​Northeast China, and CDOM sample filtration and ultraviolet spectrophotometer absorption coefficient a are measured in the laboratory. CDOM (355) measured using SOC = 1.22*a CDOM (355)+0.087 can be used to estimate the average soil organic carbon density within a 5 km buffer zone around the water body, without measuring soil organic carbon and soil bulk density. This method can quickly obtain the soil organic carbon density around the watershed. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is the location map of water bodies in Northeast China in the present invention;

[0016] Figure 2 It is the relationship between the water CDOM absorption coefficient and the surrounding soil organic carbon density in Experiment 1;

[0017] Figure 3 This is a comparison chart between the measured value of soil organic carbon density in Experiment 1 and the model estimated value. DETAILED DESCRIPTION

[0018] The technical solution of the present invention is not limited to the specific implementation modes listed below, but also includes any combination of the specific implementation modes.

[0019] Specific implementation method 1: This implementation method uses the optical characteristic parameters of water bodies to estimate the density of organic carbon in watershed soil in accordance with the following steps:

[0020] 1. Obtain water sample data: Take typical lakes in Northeast China as sampling points, obtain 593 sample points of CDOM concentration in 279 lakes in Northeast China, collect surface water from lakes, collect 2L water samples from each sampling point, and immediately put them into the refrigerator for dark storage. All water samples were filtered within two days, and the filtered samples were refrigerated and stored at 4℃, and optical absorption parameters were tested. The water absorption coefficient a was used to calculate the absorption coefficient of the water body. CDOM (355) represents the CDOM concentration of the water sample;

[0021] 2. Obtain soil sample data: Soil samples were collected from the 0-10 cm soil surface layer within a 5 km buffer zone around 279 lakes. 5-8 soil samples were collected around each lake and placed in sealed containers. A total of 720 surface soil samples were collected. The soil bulk density was measured using the ring knife method. The soil organic carbon content was measured using the external heating-potassium dichromate titration method. The soil organic carbon density SOCD is equal to the soil organic carbon content TOC multiplied by the soil bulk density BD. The average soil organic carbon density of the 279 lakes was calculated.

[0022] 3. Based on the boundary vector data of China's nine major river basins, all samples were divided into 279 sub-basins, and the water sample data and soil sample data were matched, that is, there were 279 pairs of water and soil sample data, of which 175 sample point water and soil sample data were used for model construction, and 104 sample point water and soil sample data were used for model verification;

[0023] The linear regression model of soil organic carbon density SOCD and water absorption coefficient a was constructed using SPSS software. CDOM (355), the final model SOCD = 1.22*a CDOM (355)+0.087.

[0024] Specific implementation method 2: This implementation method is different from specific implementation method 1 in that the optical absorption parameter testing method in step 1 is as follows:

[0025] First, the water sample was filtered using a 47 μm glass fiber microporous filter membrane to obtain a primary filtered water sample;

[0026] The primary filtered water sample was then filtered through a 0.22 μm polycarbonate membrane to obtain the water sample for CDOM testing;

[0027] The water sample for CDOM test was placed in a cuvette, ultrapure water was used as a reference, and the absorbance of the water sample for CDOM test at 200nm–800nm ​​was measured using a Shimadzu UV spectrophotometer UV-2660. CDOM The absorption coefficient of (355) represents the CDOM concentration. The rest is the same as the first embodiment.

[0028] The following experiments were used to verify the effect of the present invention:

[0029] Experiment 1:

[0030] The model method for estimating the soil organic carbon density in a watershed using water body optical characteristic parameters is carried out in the following steps:

[0031] 1. Obtain water sample data: Taking the Northeast region ( Figure 1) Typical lakes were used as sampling points. 593 sampling points of CDOM concentrations were obtained from 279 lakes in Northeast China. 2L of water samples were collected from the surface water of the lakes. They were immediately placed in a refrigerator for dark storage. All water samples were filtered within two days. The filtered samples were stored at 4°C and tested for optical absorption parameters. The water absorption coefficient a was used. CDOM (355) represents the CDOM concentration of the water sample;

[0032] 2. Obtain soil sample data: Soil samples were collected from the 0-10 cm soil surface layer within a 5 km buffer zone around 279 lakes. 5-8 soil samples were collected around each lake and placed in sealed containers. A total of 720 surface soil samples were collected, and the soil bulk density was measured using the ring knife method (place the ring knife holder on a ring knife of known weight, slightly apply vaseline on the inner wall of the ring knife, and press the edge of the ring knife vertically downward into the soil until the ring knife tube is filled with the sample. If the soil is hard, the ring knife handle can be gently tapped with a hammer. Use a soil cutter to cut the soil sample around the ring knife, take out the ring knife filled with soil, and carefully cut off the ring knife. Remove the excess soil at both ends so that the soil volume is exactly the volume of the ring cutter, and wipe off the soil outside the ring cutter. Immediately cover the two ends of the ring cutter to prevent water evaporation. Weigh the weight of the wet soil in the ring cutter and the weight of the ring cutter, and record the data. At the same time, use an aluminum box to sample and determine the natural moisture content of the soil. Calculate the soil bulk density according to the formula. ), the soil organic carbon content is measured using the external heating-potassium dichromate titration method (LY / T1237-1999), and the soil organic carbon density (SOCD) is equal to the soil organic carbon content (TOC) multiplied by the soil bulk density (BD). The average value of the soil organic carbon density of 279 lakes is calculated;

[0033] 3. Based on the boundary vector data of China's nine major river basins, all samples were divided into 279 sub-basins, and the water sample data and soil sample data were matched, that is, there were 279 pairs of water and soil sample data, of which 175 sample point water and soil sample data were used for model construction, and 104 sample point water and soil sample data were used for model verification;

[0034] The linear regression model of soil organic carbon density SOCD and water absorption coefficient a was constructed using SPSS software. CDOM (355) (In SPSS software, click "Analysis" - "Regression" - "Linear Regression" to enter the linear regression analysis interface. In the linear regression analysis interface, import the dependent variable (SOCD) and the independent variable (CDOM) into the corresponding boxes. Click the "Statistics" button and select the required statistical options, such as regression coefficient, model fit, and estimated value.), the final model SOCD = 1.22*a CDOM (355)+0.087

[0035] Plot the water absorption coefficient aCDOM In the rectangular coordinate system with (355) as the horizontal axis and soil organic carbon density as the vertical axis, the correlation coefficient can reach 0.73 ( Figure 2 ), and the linear relationship was verified by using the remaining 104 water and soil sample data to verify the measured data. The horizontal axis is the measured value. The measured value is brought into the above final model, and the calculated result is recorded as the estimated value as the vertical axis. The results of the comparison between the measured value and the model estimated value show that the correlation slope is 0.75 and the correlation coefficient is 0.72 ( Figure 3 ).

[0036] Since the sampling points are widely and evenly distributed within the black soil region of Northeast China, the soil organic carbon density calculated by the method of the present invention has a very high credibility.

[0037] The optical absorption parameter testing method described in step 1 is as follows:

[0038] First, the water sample was filtered using a 47 μm glass fiber microporous filter membrane to obtain a primary filtered water sample;

[0039] The primary filtered water sample was then filtered through a 0.22 μm polycarbonate membrane to obtain the water sample for CDOM testing;

[0040] The water sample for CDOM test was placed in a cuvette, ultrapure water (Milli-Q IQ 7000 system) was used as a reference, and the absorbance of the water sample for CDOM test at 200nm–800nm ​​was measured using a Shimadzu UV spectrophotometer UV-2660. CDOM The absorption coefficient of (355) indicates the CDOM concentration.

Claims

1. A model method for estimating soil organic carbon density in a watershed using water body optical characteristic parameters, characterized by The model method for estimating the soil organic carbon density in a watershed using water body optical characteristic parameters is carried out in the following steps:

1. Obtain water sample data: Take typical lakes in Northeast China as sampling points, obtain 593 sample points of CDOM concentration in 279 lakes in Northeast China, collect surface water from lakes, collect 2L water samples from each sampling point, and immediately put them into the refrigerator for dark storage. All water samples were filtered within two days, and the filtered samples were refrigerated and stored at 4℃, and optical absorption parameters were tested. The water absorption coefficient a was used to calculate the absorption coefficient of the water body. CDOM (355) represents the CDOM concentration of the water sample; 2. Obtain soil sample data: Soil samples were collected from the 0-10 cm soil surface layer within a 5 km buffer zone around 279 lakes. 5-8 soil samples were collected around each lake and placed in sealed containers. A total of 720 surface soil samples were collected. The soil bulk density was measured using the ring knife method. The soil organic carbon content was measured using the external heating-potassium dichromate titration method. The soil organic carbon density SOCD is equal to the soil organic carbon content TOC multiplied by the soil bulk density BD. The average soil organic carbon density of the 279 lakes was calculated.

3. Based on the boundary vector data of China's nine major river basins, all samples were divided into 279 sub-basins, and the water sample data and soil sample data were matched, that is, there were 279 pairs of water and soil sample data, of which 175 sample point water and soil sample data were used for model construction, and 104 sample point water and soil sample data were used for model verification; The linear regression model of soil organic carbon density SOCD and water absorption coefficient a was constructed using SPSS software. CDOM (355), the final model SOCD = 1.22*a CDOM (355)+0.

087.

2. The model method for estimating soil organic carbon density in a watershed using water body optical characteristic parameters according to claim 1 is characterized in that The optical absorption parameter testing method described in step 1 is as follows: First, the water sample was filtered using a 47 μm glass fiber microporous filter membrane to obtain a primary filtered water sample; The primary filtered water sample was then filtered through a 0.22 μm polycarbonate membrane to obtain the water sample for CDOM testing; The water sample for CDOM test was placed in a cuvette, ultrapure water was used as a reference, and the absorbance of the water sample for CDOM test at 200nm–800nm ​​was measured using a Shimadzu UV spectrophotometer UV-2660. CDOM The absorption coefficient of (355) indicates the CDOM concentration.

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