CN110658327B - River basin surface source heavy metal silt enrichment ratio calculation method based on sediment analysis - Google Patents

Abstract

The invention discloses a basin surface source heavy metal silt enrichment ratio calculation method based on sediment analysis, which comprises the steps of selecting a typical small basin; collecting the column core of the sediment, and determining the heavy metal content and total phosphorus content of different sediment depth layers²¹⁰Pb_exAn activity value; measuring mass deposition rate values of layers with different depths and deposition flux values of heavy metal and total phosphorus; establishing the heavy metal and total phosphorus deposition flux of the drainage basinLong-term quantitative relationships between values; collecting background soil of a drainage basin and measuring heavy metal and total phosphorus content values in the background soil; and establishing a long-term quantitative relation between the concentration ratios of the heavy metals in the drainage basin and the total phosphorus silt. The method has the advantages that the relation can be applied to other similar drainage basins by only establishing the long-term quantitative relation between the non-point source heavy metal and the total phosphorus silt enrichment ratio in a typical drainage basin based on sediment analysis, and the non-point source heavy metal silt enrichment ratio of the applied drainage basin can be quickly obtained.

Description

Calculation method of sediment enrichment ratio of non-point source heavy metals in watershed based on sediment analysis

technical field

The invention belongs to the technical field of non-point source pollution prevention and control in a watershed, and relates to a method for calculating the enrichment ratio of heavy metal sediment in a non-point source of a watershed based on sediment analysis.

Background technique

Agricultural non-point source pollution has gradually become a key factor restricting the improvement of my country's water environment quality. Various chemical substances remaining in farmland soil are the main non-point source pollutants. They will eventually enter rivers, lakes and other water bodies with the erosion of soil under rainfall conditions, thus causing a series of water environment quality problems. At present, most of the agricultural non-point source pollution research carried out in my country focuses on carbon, nitrogen, phosphorus and other nutrients, and solves the problem of eutrophication of water bodies in the river basin. However, there is still not much attention to toxic heavy metals that pose a huge threat to ecological security and human health. . To carry out research on agricultural non-point source pollution, it is necessary to clarify the characteristics of the loss of non-point source pollutants in the river basin, so as to provide technical support for the subsequent implementation of effective prevention and control measures. Soil erosion caused by surface runoff is an important form of agricultural non-point source pollution. Soil erosion processes tend to transport fine-grained matter, resulting in surface runoff typically enriched with more contaminants than source soil. Therefore, the sediment enrichment ratio is considered to be an important parameter for the study of the characteristics of the loss of non-point source pollutants in the basin and the construction of water quality models. Due to the high attention paid to the eutrophication of water bodies in the early days, the research on the loss characteristics of non-point source nitrogen and phosphorus in the watershed has been relatively mature at home and abroad, and an empirical formula for the calculation of the sediment enrichment ratio has been established. However, research on this aspect of heavy metals is relatively lagging behind. Different heavy metals have different sediment enrichment ratios, and are affected by the basin climate, topography, hydrology and other conditions. Through the establishment of runoff plots to carry out long-term positioning observation experiments, foreign scholars have carried out research work on the enrichment ratio of different heavy metal sediments. In contrast, the research on agricultural non-point source pollution in my country started relatively late, and a comprehensive and systematic database has not yet been established. At the same time, since many areas do not have the conditions for carrying out long-term field observation experiments, some scholars directly refer to the existing research results of sediment enrichment ratio abroad when conducting research on the loss characteristics of heavy metals from non-point sources in the basin, which increases the uncertainty of the research. . As the final "sink" of watershed materials, sediments can reflect the loss characteristics of non-point source pollutants on the whole watershed scale. Therefore, by establishing a quantitative relationship between heavy metals and total phosphorus sediment enrichment ratios in typical small watersheds based on sediment analysis, the heavy metal sediment enrichment ratios can be estimated based on the total phosphorus sediment enrichment ratios in similar watersheds. Since the collection and analysis of sediments are very simple and easy, the workload of establishing runoff plots in the basin to carry out long-term positioning observation experiments is greatly saved. In view of the above background, in order to calculate the agricultural non-point source heavy metal sediment enrichment ratio in different watersheds more quickly and efficiently, this patent application establishes a method for calculating the basin non-point source heavy metal sediment enrichment ratio based on sediment analysis. Select typical watersheds to establish a long-term quantitative relationship between non-point source heavy metals and total phosphorus sediment enrichment ratio, and apply the obtained quantitative relationship to other similar watersheds. Accumulation ratio to quickly obtain the heavy metal sediment enrichment ratio of the application watershed.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method for calculating the enrichment ratio of non-point source heavy metals and sediments in a river basin based on sediment analysis. The long-term quantitative relationship between the ratios can be applied to other similar watersheds, and the enrichment ratio of non-point source heavy metal sediments in the applied watershed can be quickly obtained.

The technical scheme adopted in the present invention is to carry out according to the following steps:

Step 1: Select a typical small watershed;

Step 2: Collect sediment cores, and measure heavy metals, total phosphorus content and ²¹⁰ Pb _ex activity values in layers with different deposition depths;

Step 3: Determine the quality deposition rate value of different depth layers and the deposition flux value of heavy metals and total phosphorus;

Step 4: Establish a long-term quantitative relationship between heavy metals and total phosphorus deposition flux values in the basin;

Step 5: Collect the background soil of the watershed and determine the content of heavy metals and total phosphorus in it;

Step 6: Establish a long-term quantitative relationship between heavy metals in the basin and the enrichment ratio of total phosphorus and sediment.

Further, step 1 selects a typical small watershed as the study area. In order to ensure the smooth progress of sediment collection, the outlet of the watershed needs to have a relatively stable sedimentary environment that is convenient for sediment collection; secondly, in order to extend the calculation formula obtained in the study to other similar watersheds In order to calculate the heavy metal enrichment ratio of non-point sources in other watersheds, the selected watershed must also be representative, and its climate, topography, hydrology, as well as the land use types, soil types and background values covered must be representative.

Further, in step 2, a columnar sampler was used to obtain the sediment core at the outlet of the watershed, and it was carefully divided and bagged at a thickness of 1 cm on site. After the samples were brought back to the laboratory, they were naturally air-dried, and the agate was ground through a 100-mesh nylon sieve. After being digested by the HNO ₃ -HF-HClO ₄ method, inductively coupled plasma emission spectrometer was used to determine the content of heavy metals and total phosphorus. The activity value of ²¹⁰ Pb _ex (atmospheric source ²¹⁰ Pb) was determined by energy spectrometer.

Further, in step 3, based on the ²¹⁰ Pb _ex activity values of the layers with different deposition depths obtained in step 2, the CRS (Constant Rate Supply) model is applied to calculate the mass deposition rate values of each layer. The formula for calculating the mass deposition rate is:

where R(Z) is the mass deposition rate of the Z depth layer (mg/cm ² ·a); I(Z) is the cumulative amount of ²¹⁰ Pb _ex (Bq/cm ² ) of each deposited layer below the depth Z; A(Z) is the ²¹⁰ Pb _ex activity (Bq/kg) in the Z-depth layer; λ is the ²¹⁰ Pb decay constant (0.03114/a).

Multiply the mass deposition rate value of each deposition depth layer and the heavy metal and total phosphorus content values determined in step 2, respectively, to calculate their drainage flux values. The formula for calculating the deposition flux is:

S(Z)=R(Z)×C(Z)

where S(Z) is the deposition flux of the Z-depth layer (ug/cm ² ·a); R(Z) is the mass deposition rate of the Z-depth layer (mg/cm ² ·a); C(Z) is the Z-depth layer Concentration content of the layer (mg/kg).

Further, in step 4, based on the deposition flux values of heavy metals and total phosphorus at different depths obtained in step 3, regression analysis is applied to establish a long-term quantitative relationship between them. The formula for the quantitative relationship is y=ax+b, where y is the heavy metal deposition flux value, x is the total phosphorus deposition flux value, and a and b are constants in the formula.

Further, step 5 collects several background soil samples in the whole watershed. After air-drying, grinding and sieving in the laboratory, after digestion by HNO ₃ -HF-HClO ₄ method, inductively coupled plasma emission spectrometer was used to determine the content of heavy metals and total phosphorus.

Further, in step 6, based on the long-term quantitative relationship between heavy metals and total phosphorus deposition flux values in the watershed obtained in step 4, and the background soil value of the watershed obtained in step 5, an empirical model for the migration of adsorbed pollutants is used to establish the relationship between heavy metals in non-point sources and total phosphorus in the watershed. Long-term quantitative relationship between phosphorus and sediment enrichment ratios.

The empirical model for the migration of adsorbed pollutants is:

L=C×Q×η

Among them, L is the adsorption loss load (g/km ² ); C is the background soil value of the watershed (mg/kg); Q is the soil erosion amount of the watershed (t/km ² ), and η is the sediment enrichment ratio (dimensionless) .

The long-term quantitative relationship between heavy metals and total phosphorus sediment enrichment ratio in the basin is as follows:

Among them, η _i is the sediment enrichment ratio of heavy metal i in the basin (dimensionless); ηtotal _phosphorus is the sediment enrichment ratio of total phosphorus in the basin (dimensionless); Li is the adsorption loss load of heavy metal _i in the basin (g/ km ² ); L _{total phosphorus} is the adsorbed loss load of total phosphorus in the watershed (g/km ² ); A _i is the ratio of heavy metal i and total phosphorus in the watershed to the soil background value (dimensionless); a and b are the heavy metals and the total phosphorus in the watershed The constant in the quantitative relationship formula of total phosphorus deposition flux value; x is the total phosphorus deposition flux value (ug/cm ² ·a).

Among them, x of the watershed to be calculated is obtained through steps 2 and 3, and η _{total phosphorus} is obtained according to the empirical formula proposed by Menzel RG. The empirical calculation formula of ηtotal _phosphorus is:

lnηtotal _phosphorus =2-0.2×lnQ

Among them, ηtotal _phosphorus is the sediment enrichment ratio (dimensionless) of total phosphorus in the watershed; Q is the soil erosion amount (t/km ² ) in the watershed.

Description of drawings

Fig. 1 is a flow chart of the method for calculating the enrichment ratio of heavy metal sediments from non-point sources in the basin based on sediment analysis;

Figure 2 is a schematic diagram of the changes in the deposition fluxes of heavy metals and total phosphorus in the watershed;

Figure 3 is a schematic diagram of the correlation between heavy metals and total phosphorus deposition flux in the watershed.

Detailed ways

The present invention will be described in detail below with reference to specific embodiments.

Figure 1 shows the flow chart of the calculation method for the enrichment ratio of heavy metals in non-point sources in the basin based on sediment analysis. The implementation steps are as follows:

step 1

In this case, the Menglianggu small watershed located in the upper reaches of the Yihe River in the Yimeng Mountains of my country is selected as an example for analysis. This small agricultural watershed is representative in the Yimeng Mountains, with forest land and arable land accounting for more than 70% of the total watershed area, and there is no obvious source of industrial pollution.

Step 2

After the preliminary field investigation, a columnar sampler was used to obtain a 25cm-deep sediment core at about 1km upstream of the outlet of the watershed, and it was carefully divided and bagged at a thickness of 1cm on site. After the samples were brought back to the laboratory, they were naturally air-dried, and the agate was ground through a 100-mesh nylon sieve. After being digested by the HNO ₃ -HF-HClO ₄ method, the content of heavy metals and total phosphorus was determined by inductively coupled plasma emission spectrometer. High-purity germanium with low background γ was used. The activity value of ²¹⁰ Pb _ex (atmospheric source ²¹⁰ Pb) was determined by energy spectrometer. Taking Pb and Cu as an example, the measurement results of layers with different deposition depths are shown in Table 1. It can be seen from the table that the Pb content range is 29.86-37.98mg/kg, the Cu content range is 34.84-47.07mg/kg, the total phosphorus content range is 398.02-1381.28mg/kg, and the ²¹⁰ Pb _ex activity range is 4.15-12.12Bq/ kg. This method is not limited to the above two heavy metals, and is also applicable to other heavy metals measured in sediments.

Table 1 Heavy metals, total phosphorus content and ²¹⁰ Pb _ex activity values in layers with different deposition depths

Step 3

Based on the ²¹⁰ Pb _ex activity values of the layers with different deposition depths obtained in step 2, the CRS model was used to calculate the mass deposition rate values of each layer. The formula for calculating the mass deposition rate is:

where R(Z) is the mass deposition rate of the Z depth layer (mg/cm ² ·a); I(Z) is the cumulative amount of ²¹⁰ Pb _ex (Bq/cm ² ) of each deposited layer below the depth Z; A(Z) is the ²¹⁰ Pb _ex activity (Bq/kg) in the Z-depth layer; λ is the ²¹⁰ Pb decay constant (0.03114/a).

Multiply the mass deposition rate value of each deposition depth layer with the Pb, Cu, and total phosphorus content values determined in step 2 to obtain their drainage flux values. The formula for calculating the deposition flux is:

S(Z)=R(Z)×C(Z)

where S(Z) is the deposition flux of the Z-depth layer (ug/cm ² ·a); R(Z) is the mass deposition rate of the Z-depth layer (mg/cm ² ·a); C(Z) is the Z-depth layer Concentration content of the layer (mg/kg).

As shown in Figure 2, the Pb deposition flux is 13.93-23.10ug/cm ² ·a, the Cu deposition flux is 16.73-26.36ug/cm ² ·a, and the total phosphorus deposition flux is 191.03-814.23ug/cm ² ·a a. According to the chronological time series reflected by the sediment core, the historical trends of the sedimentary fluxes of Pb and Cu and total phosphorus in the basin are roughly the same.

Step 4

Based on the deposition flux values of Pb, Cu and total phosphorus at different depth layers obtained in step 3, regression analysis was applied to establish a long-term quantitative relationship between them. As shown in Fig. 3, there is a good correlation between Pb, Cu and total phosphorus deposition flux values in the watershed, and their R ² values are 0.70 and 0.83, respectively, indicating that they have similar loss characteristics. The quantitative relationship formulas obtained are:

Pb: y=0.0080x+14.881

Cu: y=0.0125x+16.057

Wherein y is the heavy metal deposition flux value (ug/cm ² ·a); x is the total phosphorus deposition flux value (ug/cm ² ·a).

Step 5

Several 100-120 cm deep natural woodland soil samples were collected throughout the watershed. After air-drying, grinding and sieving in the laboratory, after digestion by HNO ₃ -HF-HClO ₄ method, the inductively coupled plasma emission spectrometer was used to determine the content of heavy metals and total phosphorus. The background content of Pb in the watershed soil was 20.37 mg/kg, the background content of Cu was 21.82 mg/kg, and the background content of total phosphorus was 664.27 mg/kg.

Step 6

Based on the long-term quantitative relationship between Pb, Cu and total phosphorus deposition flux values in the watershed obtained in step 4, and the soil background value obtained in step 5, an empirical model for the migration of adsorbed pollutants was used to establish the non-point source Pb, Cu and total phosphorus in the watershed Long-term quantitative relationship between sediment enrichment ratios. The quantitative relationship formulas obtained are:

where η _Pb is the sediment enrichment ratio of Pb in the watershed (dimensionless); η _Cu is the sediment enrichment ratio of Cu in the watershed (dimensionless); ηtotal _phosphorus is the sediment enrichment ratio of total phosphorus in the watershed (dimensionless) ; x is the total phosphorus deposition flux value in the basin (ug/cm ² ·a).

Collect sediments in the watershed to be calculated, measure the total phosphorus concentration and mass deposition rate in the sediments, calculate the total phosphorus deposition flux value, and put the η _{total phosphorus} value obtained from the existing empirical formula into the above relationship, namely The Pb and Cu sediment enrichment ratios of the watershed to be calculated in the current year can be obtained.

The present invention selects typical small watersheds; collects sediment cores, measures heavy metals, total phosphorus content values and ²¹⁰ Pb _ex activity values in different deposition depth layers; ; Establish the long-term quantitative relationship between heavy metals and total phosphorus deposition flux in the watershed; collect background soil in the watershed and determine the content of heavy metals and total phosphorus; establish long-term quantitative relationship between heavy metals and total phosphorus and sediment enrichment ratios in the watershed. The invention also has the following advantages: 1. only need to establish a long-term quantitative relationship between heavy metals and total phosphorus sediment enrichment ratios in typical small watersheds, and the formula can be applied to other similar watersheds to calculate the heavy metal sediment enrichment ratios; 2. . After the calculation formula is established, the sediment enrichment ratio of the current year in the basin can be calculated from the total phosphorus sediment enrichment ratio only by collecting sediments in the application basin, which is simple and easy to implement.

The above is only a preferred embodiment of the present invention, and does not limit the present invention in any form. Any simple modifications, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention belong to the present invention. within the scope of the technical solution of the invention.

Claims (6)

1. The method for calculating the concentration ratio of the heavy metal silt of the watershed non-point source based on sediment analysis is characterized by comprising the following steps of:

step 1: selecting a typical small watershed;

step 2: collecting the column core of the sediment, and determining the heavy metal content and total phosphorus content of different sediment depth layers²¹⁰Pb_exAn activity value;

and 3, step 3: measuring mass deposition rate values of layers with different depths and deposition flux values of heavy metal and total phosphorus;

and 4, step 4: establishing a long-term quantitative relation between the watershed heavy metal and the total phosphorus deposition flux value;

and 5: collecting background soil of a drainage basin and measuring the content values of heavy metals and total phosphorus in the background soil;

step 6: establishing a long-term quantitative relation between the concentration ratios of heavy metals in the watershed and the total phosphorus sediment;

and step 6, establishing a long-term quantitative relationship between the river basin surface source heavy metal and the total phosphorus sediment concentration ratio by applying an adsorption state pollutant migration empirical model based on the long-term quantitative relationship between the river basin heavy metal and the total phosphorus deposition flux value obtained in the step 4 and the river basin soil background value obtained in the step 5, wherein the adsorption state pollutant migration empirical model is as follows:

L＝C×Q×η

wherein L is the adsorption state loss load; c is a watershed soil background value; q is the erosion amount of the soil in the watershed, and eta is the silt enrichment ratio;

the long-term quantitative relation formula between the concentration ratio of the heavy metal in the drainage basin and the total phosphorus silt is as follows:

wherein eta_iThe silt concentration ratio of the heavy metal i in the drainage basin is shown; eta_{Total phosphorus}The silt concentration ratio of the total phosphorus in the drainage basin is obtained; l is_iThe load is the adsorption state loss load of the heavy metal i in the drainage basin; l is_{Total phosphorus}The load is lost in the adsorption state of the total phosphorus in the drainage basin; a. the_iThe ratio of the drainage basin heavy metal i to the soil background value of total phosphorus; a and b are constants in a quantitative relation formula of the heavy metal in the watershed and the total phosphorus deposition flux value; x is the total phosphorus deposition flux value;

wherein, x of the watershed to be calculated is obtained through the steps 2 and 3, eta_{Total phosphorus}Eta is obtained from the empirical formula proposed by Menzel R.G_{Total phosphorus}The empirical formula of (2) is:

lnη_{total phosphorus}＝2-0.2×lnQ

Wherein eta_{Total phosphorus}The silt enrichment ratio of the total phosphorus in the basin is obtained; q is the erosion amount of the soil in the drainage basin.

2. The method for calculating the silt enrichment ratio of the heavy metals in the watershed non-point source based on the sediment analysis of claim 1, which is characterized in that: in the step 1, a typical small watershed is selected as a research area, and in order to ensure smooth collection of sediments, a relatively stable deposition environment convenient for sediment collection is required at an outlet of the watershed; secondly, in order to popularize the calculation formula obtained by research into other similar watersheds for calculating the non-point source heavy metal enrichment ratio of other watersheds, the selected watersheds must be representative, and the climate, the terrain, the hydrology, the covered land utilization type, the soil type and the background value of the selected watersheds need to be representative.

3. The method for calculating the silt enrichment ratio of the heavy metals in the watershed non-point source based on the sediment analysis of claim 1, which is characterized in that: step 2, a sediment column core is obtained at the outlet of the fluid area by using a column-shaped sampler, the sediment column core is carefully cut and bagged according to the thickness of 1cm on site, the sample is taken back to a laboratory and then is naturally dried, and agate is ground and sieved by a 100-mesh nylon sieve and then is subjected to HNO₃–HF–HClO₄After the digestion, the heavy metal and total phosphorus content values are measured by adopting an inductively coupled plasma emission spectrometer, and the heavy metal and total phosphorus content values are measured by adopting a high-purity germanium low-background gamma energy spectrometer²¹⁰Pb_exAnd (4) an activity value.

4. The method for calculating the concentration ratio of the heavy metal sediment in the watershed non-point source based on the sediment analysis as claimed in claim 1, wherein the method comprises the following steps: the step 3 is based on the layers with different deposition depths obtained in the step 2²¹⁰Pb_exAnd (3) calculating the mass deposition rate value of each layer by using a CRS model, wherein the mass deposition rate calculation formula is as follows:

wherein R (Z) is the mass deposition rate of the Z depth layer; i (Z) for deposition layers below depth Z²¹⁰Pb_ex(ii) an accumulated amount; a (Z) is a Z depth layer²¹⁰Pb_exActivity; λ is²¹⁰The Pb decay constant; and (3) multiplying the mass deposition rate value of each deposition depth layer by the heavy metal and total phosphorus content values measured in the step (2) respectively, and calculating the watershed deposition flux values, wherein the deposition flux calculation formula is as follows:

S(Z)＝R(Z)×C(Z)

wherein S (Z) is the deposition flux of the Z depth layer; r (Z) is the mass deposition rate of the Z depth layer; c (Z) is the concentration content of the Z depth layer.

5. The method for calculating the silt enrichment ratio of the heavy metals in the watershed non-point source based on the sediment analysis of claim 1, which is characterized in that: and 4, establishing a long-term quantitative relation between the heavy metals in different depth layers and the total phosphorus deposition flux value obtained in the step 3 by applying regression analysis, wherein the formula form of the quantitative relation is y ═ ax + b, y is the heavy metal deposition flux value, x is the total phosphorus deposition flux value, and a and b are constants in the formula.

6. The method for calculating the silt enrichment ratio of the heavy metals in the watershed non-point source based on the sediment analysis of claim 1, which is characterized in that: step 5, collecting a plurality of background soil samples in the whole watershed range, air-drying, grinding and sieving in a laboratory, and then HNO₃–HF–HClO₄And (4) after the method digestion, measuring the heavy metal and total phosphorus content value by using an inductively coupled plasma emission spectrometer.

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