Determination method for phosphorus endogenous load of lake sediment

Abstract

The invention discloses a method for measuring phosphorus endogenous load of lake sediments. The method comprises the following steps: 1) measuring phosphorus reserve of the sediments; (2) calculating the phosphorus reserve of the sediments of the polluted layer; (3) measuring and calculating the phosphorus diffusion rate of the sediments; (4) calculating the phosphorus internal load of the sediments, wherein the calculation formula is N = m * Fd2; in the formula, N is the phosphorus internal load (unit: n) of the sediment, m is the phosphorus reserve (g) of the sediment of the pollution layer, and Fd is the phosphorus diffusion rate (mg.m <-2 >. D <-1 >) of the sediment. According to the method, the state of the phosphorus internal load of the lake sediment can be reflected more accurately and comprehensively, the evaluation index of the phosphorus internal load of the lake sediment is more standardized, and a reliable basis is provided for lake eutrophication control engineering measures and lake basin ecological protection formulating measures.

Description

Technical Field

[0001] This invention belongs to the field of lake nutrient determination technology, specifically relating to a method for determining the endogenous phosphorus load in lake sediments. Background Technology

[0002] Eutrophication of lakes is a water pollution phenomenon caused by nutrients in the overlying water. Phosphorus concentration is a key nutrient factor affecting algal biomass in lakes. When the phosphorus concentration in the overlying water exceeds 0.2 mg / L... -1 Eutrophication easily occurs when sediments are exposed to phosphorus. Nutrients in the overlying water mainly originate from external inputs and endogenous release from sediments. However, sediments are both a source and a sink of nutrients in the overlying water; endogenous phosphorus release from sediments is a result of the dynamic balance between sediments and overlying water. Sediments are usually the main source of phosphorus in the overlying water of lakes, and the phosphorus concentration in lake sediments is much higher than in the overlying water. High internal phosphorus loadings have been found in many shallow eutrophic lakes around the world and are considered a major reason for the delayed lake recovery after a reduction in external phosphorus inputs. Therefore, characterizing the contribution of phosphorus in sediments to phosphorus in the overlying water is crucial for evaluating the internal phosphorus loading in sediments.

[0003] Due to the uncertainty in methods for characterizing phosphorus loading in sediments, conflicting results have emerged from studies on phosphorus loading in lake sediments. Extensive research shows that phosphorus content in sediments is significantly higher than the phosphorus concentration in overlying water; ideally, all phosphorus in sediments could be considered to have entered the overlying water. Therefore, the phosphorus loading in sediments is primarily influenced by the phosphorus stockpile within the sediments. However, the rate at which phosphorus is released from sediments into the overlying water per unit time is crucial to the phosphorus concentration in the overlying water, and the diffusion rate of phosphorus from sediments into the overlying water is also a significant factor affecting the phosphorus loading within sediments. Therefore, the influence of endogenous phosphorus loading in sediments on the phosphorus concentration in the overlying water is affected by both the phosphorus stockpile in the sediments and the phosphorus release rate.

[0004] There is an urgent need for a more accurate and comprehensive method for measuring the endogenous phosphorus load in lake sediments, which can better reflect the phosphorus load status of lake sediments and standardize the evaluation of indicators. This would provide a reliable basis for engineering measures to control lake eutrophication and for formulating measures for the ecological protection of lake basins. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a method for measuring the endogenous phosphorus load in lake sediments that can more accurately and comprehensively reflect the phosphorus load status of lake sediments.

[0006] The objective of this invention is achieved through the following technical solution: a method for determining the endogenous phosphorus load in lake sediments, characterized by comprising the following components: 1) Determination of sediment phosphorus reserves: Sediment columnar samples were collected using a sediment stratified sampler. The thickness δ of the sediment contamination layer was measured using a ruler. The sediment columnar samples were pushed out of the PVC pipe using a columnar piston. The sediment contamination layer columnar samples were separated using a mud-cutting blade. The sediment porosity Φ of the sediment columnar samples was determined by direct calculation method. The bulk density ρ of the sediment contamination layer was determined by ring cutter method. The sediment samples were freeze-dried, ground and passed through a 100-mesh sieve. The phosphorus content V of the sediment was determined by phosphomolybdenum blue spectrophotometer method. 2) The calculation formula for phosphorus reserves in contaminated sediments is as follows: m i =V / 1000×δ×ρ×10000×A; m=Σm i ; Where: m is the total phosphorus reserves in the lake's polluted layer sediments; m i V represents the phosphorus reserves in the contaminated sediment layer of the i-th region; V is the phosphorus content of the sediment (g·kg). -1 ); δ represents the thickness of the contaminated layer (m), typically 10cm for lakes, with the thickness in heavily polluted areas determined by actual measurements; ρ represents the bulk density of the sediment contaminated layer (g·cm³). -2 A represents the total area of ​​polluted sediments (m²). 2 ); 3) Determination and calculation of phosphorus diffusion rate in sediments: An in-situ sediment-water interface water quality sampler was used. A weight was used to insert the interstitial water sampling section of the sampler into the lake sediments. A boundary plate was used to leave the overlying water sampling section of the sampler above the sediment interface in the overlying water. After 7 days, the sampler was removed from the lake, and surface contaminants were cleaned. The sampler was placed with the sampling plate at the bottom and the protective plate at the top. The protective plate and the permeable membrane were removed, and the solution in the sampling chamber was removed with a pipette. The sampling chamber in the overlying water contained overlying water, and the sampling chamber in the sediment contained interstitial water. Interstitial water and overlying water samples were collected, and the phosphorus concentration in the interstitial water and overlying water at different depths was determined by ammonium molybdate spectrophotometry. The phosphorus diffusion rate in sediments is calculated using Frick's First Law, and the formula is as follows: ; In the formula: F d Phosphorus diffusion rate in sediments, mg / (m 2 ·d); Φ is the porosity of the sediment, %; D s m is the diffusion coefficient. 2 / s; It is the phosphorus concentration gradient through the sediment-water interface, mg / (L·cm). 4) Calculation of phosphorus loading in sediments, the formula is as follows: N=m×F d 2 ; In the formula: N is the internal phosphorus loading of sediment (unit: N), m is the phosphorus storage of contaminated sediment (g), and F d Phosphorus diffusion rate in sediments (mg·m -2 ·d -1 ).

[0007] Furthermore, in step 3), the D s The calculation method is as follows: When the sediment porosity Φ is less than or equal to 0.7, the formula is: D s =ΦD (Φ≤0.7) is used for calculation, where D=7.34 (D is the constant of Frick's first law); When the sediment porosity Φ is greater than 0.7, the formula is: D s = φD0 (Φ>0.7) is calculated, where D0=7.34+0.40(T—25℃), and T is the water temperature.

[0008] Furthermore, in step 3), the phosphorus concentration of overlying water and interstitial water in the sampling chambers at different depths of the in-situ sediment-water interface water quality sampler is subjected to exponential fitting with depth. The two sets of data on depth and phosphorus concentration are subjected to exponential fitting using Origin software. As the depth of overlying water and sediment increases, the phosphorus concentration decreases exponentially. The specific values ​​of the two parameters a and b in the following formula are obtained by exponential fitting using statistical software. Y=ae bX ; In the formula: Y is the phosphorus concentration in the water; X is the depth; a and b are parameters.

[0009] Furthermore, in step 3), The diffusion gradient is calculated using the following formula: .

[0010] The beneficial effects of this invention are: it can more accurately and comprehensively reflect the state of phosphorus load in lake sediments, and the evaluation index of phosphorus load in lake sediments is more standardized, providing a reliable basis for the formulation of engineering measures to control lake eutrophication and ecological protection policies for lake basins. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the method of the present invention; Figure 2 These are sampling points for measuring phosphorus load in Erhai Lake sediments; Figure 3 The thickness of the sediment contamination layer at different sampling points in Erhai Lake; Figure 4 The phosphorus content is measured at different sampling points in various areas of Erhai Lake; Figure 5 These are the phosphorus reserves at different sampling points in various areas of Erhai Lake; Figure 6 The average annual phosphorus diffusion rate of sediments from different sampling points in various lake areas of Erhai Lake; Figure 7 This refers to the changes in sediment load in different areas of Erhai Lake in different months; Figure 8 It represents the changes in sediment load at different points in different areas of Erhai Lake. Detailed Implementation

[0012] The present invention will now be described in detail with reference to the accompanying drawings. Example

[0013] 1. Calculation model for phosphorus loading in sediments: Phosphorus content in sediments is much higher than the phosphorus concentration in overlying water. Ideally, all phosphorus in sediments could enter the overlying water. Therefore, the internal phosphorus loading in sediments is mainly affected by the phosphorus stockpile in the sediments. However, the rate at which phosphorus is released from sediments into the overlying water per unit time is crucial to the phosphorus concentration in the overlying water, and the diffusion rate of phosphorus from sediments to the overlying water is also an important factor affecting the internal phosphorus loading in sediments. Therefore, the influence of the internal phosphorus loading in sediments on the phosphorus concentration in the overlying water is affected by both the phosphorus stockpile in the sediments and the phosphorus release rate. In summary, the internal loading of sediments is the ability of phosphorus in sediments to migrate into the overlying water, i.e., the kinetic energy of migration. Therefore, referring to the law of conservation of mass-energy in physics, the relationship between kinetic energy, mass, and velocity can be defined as: E = m × c 2 (E is kinetic energy, m is mass, and c is velocity), the formula for calculating the load within sediments is derived as follows: N=m×F d 2 ; Where: N is the internal phosphorus loading of sediments (unit: n); m is the phosphorus reserves of contaminated sediments (g); F d Phosphorus diffusion rate in sediments (mg·m -2 ·d -1 ).

[0014] 2. Determination of phosphorus loading in sediments: 2.1 Classification of different contaminated areas in sediments The lake sediments were divided into four zones: a depth greater than 10m, a depth of 4-10m, a depth of less than 4m with aquatic vegetation, and a depth of less than 4m without aquatic vegetation. The area of ​​each zone was measured to determine the contaminated sediment area for that zone, and the total contaminated sediment area A was calculated from the total contaminated sediment area of ​​all zones. Sampling points were established in each zone to collect sediment column samples, and the pollutant data were the average of all sampling points.

[0015] 2.1 Determination of sediment phosphorus reserves: Sediment columnar samples were collected using a sediment stratification sampler (Type 3 gravity hammer sediment sampler, manufactured by Beijing Zhonghe Technology Co., Ltd.). The thickness of the sediment contamination layer (a dark, blackish layer) was observed through the PVC pipe of the sediment stratification sampler, and the thickness δ of the sediment contamination layer was measured using a ruler. The sediment columnar sample was pushed out of the PVC pipe using a columnar piston, and the sediment contamination layer columnar sample was separated using a mud-cutting blade. The sediment porosity Φ and the bulk density ρ of the sediment contamination layer were determined using the direct calculation method (GB / T50123-2019) (bulk density was determined by the ring cutter method (NY / T1121.4-2006)). The sediment samples were freeze-dried, ground through a 100-mesh sieve, and the sediment phosphorus content V was determined using the phosphomolybdenum blue spectrophotometer method.

[0016] 2.2 Calculation of phosphorus reserves in contaminated sediments, such as... Figure 1 As shown, the calculation formula is: m i =V / 1000×δ×ρ×10000×A; m=Σm i ; Where: m is the total phosphorus reserves in the lake's polluted layer sediments; m i V represents the phosphorus reserves in the contaminated sediment layer of the i-th region; V is the phosphorus content of the sediment (g·kg). -1 ); δ represents the thickness of the contaminated layer (m), typically 10cm for lakes, with the thickness in heavily polluted areas determined by actual measurements; ρ represents the bulk density of the sediment contaminated layer (g·cm³). -2 A represents the total area of ​​polluted sediments (m²). 2 ).

[0017] 2.3 Methods for determining and calculating the phosphorus diffusion rate in sediments: An in-situ sediment-water interface water quality sampler (see Chinese invention patent "In-situ Sediment-Water Interface Water Quality Sampler and Sampling Method" CN 101608982 B) was used. A weight was used to insert the interstitial water sampling section of the sampler into the lake sediments. A boundary plate was used to leave the overlying water sampling section above the sediment interface in the overlying water. After 7 days, the sampler was removed from the lake, its surface cleaned, and the sampling plate placed below and the protective plate above. The protective plate and permeable membrane were removed, and the solution in the sampling chambers was removed using a pipette. The sampler has 40 sampling chambers longitudinally: 10 in the overlying water (containing overlying water) and 30 in the sediment (containing interstitial water). Interstitial water and overlying water samples were collected, and the phosphorus concentration in the interstitial water and overlying water at different depths was determined using ammonium molybdate spectrophotometry to calculate the phosphorus diffusion rate.

[0018] The rate of phosphorus diffusion from sediments is calculated according to Frick's First Law, such as... Figure 1 As shown, the calculation formula is: ; In the formula: F d Phosphorus diffusion rate in sediments, mg / (m 2 ·d); Φ is the porosity of the sediment, %; D s m is the diffusion coefficient. 2 / s; It is the phosphorus concentration gradient through the sediment-water interface, mg / (L·cm).

[0019] Among them, D s The calculation method is as follows: When the sediment porosity Φ is less than or equal to 0.7, the formula is: D s =ΦD (Φ≤0.7) is used for calculation, where D=7.34 (D is the constant of Frick's first law); When the sediment porosity Φ is greater than 0.7, the formula is: D s = φD0 (Φ>0.7) is calculated, where D0=7.34+0.40(T—25℃), and T is the water temperature.

[0020] The phosphorus concentration of overlying water and interstitial water in the sampling chambers at different depths of the in-situ sediment-water interface water quality sampler was subjected to exponential fitting with depth. The two sets of data on depth and phosphorus concentration were subjected to exponential fitting using Origin software. As the depth of overlying water and sediment increased, the phosphorus concentration decreased exponentially. The specific values ​​of the two parameters a and b in the following formula were obtained by exponential fitting using statistical software.

[0021] Y=aebX ; In the formula: Y is the phosphorus concentration in the water; X is the depth; a and b are parameters; The diffusion gradient is calculated using the following formula: .

[0022] 2.4 Calculation of phosphorus loading in sediments, see [reference needed]. Figure 1 The calculation formula is: N=m×F d 2 ; In the formula: N is the internal phosphorus loading of sediment (unit: n), m is the phosphorus storage of contaminated sediment (g), and F d Phosphorus diffusion rate in sediments (mg·m -2 ·d -1 ).

[0023] 3. Assessment of sediment load in Erhai Lake: Erhai Lake is the second largest lake in Yunnan Province, with a maximum depth of 20 meters. Since the 1980s, due to human disturbance, the lake has transitioned from an oligotrophic to a eutrophic state, especially after a large-scale algal bloom in 2003. In recent years, with increased efforts in comprehensive management, water quality has gradually improved. However, the phosphorus content in sediments has been gradually increasing. When external sources are effectively controlled, the internal load of sediments becomes a significant factor affecting eutrophication. Therefore, accurately assessing the internal load of sediments is crucial for controlling eutrophication in Erhai Lake.

[0024] 3.1. Regional division of Erhai Lake sediments: Erhai Lake is naturally shaped like an "ear," forming three lake areas: northern, central, and southern. Figure 2 As shown, the northern lake area is divided into four sampling points based on water depth and aquatic plant distribution: Sampling point 2 in Shaping Bay (water depth within 4m with aquatic plants), Sampling point 1 in Hongshan Bay (water depth 4-10m), Sampling point 3 in the open water area (water depth 4-10m), and Sampling point 4 in Xizhou Bay (water depth within 4m with aquatic plants). The central lake area is divided into four sampling points based on water depth and aquatic plant distribution: Sampling point 5 in areas without aquatic plants within 4m, Sampling point 6 in areas with water depths of 4-10m, and Sampling point 7 in areas with depths greater than 10m. (The text abruptly ends here.) Sampling point 8 was used in areas with a maximum water depth of over 10m; sampling point 9 was used in areas with aquatic plants within 4m of water depth; and sampling point 10 was used in the narrowest area of ​​Erhai Lake, 4-10m deep. In the southern lake area, based on water depth and aquatic plant distribution, sampling point 11 was used in areas with a water depth of 4-10m; sampling point 12 was used in areas without aquatic plants within 4m of water depth; sampling point 13 was used in areas with a water depth of over 10m; sampling point 14 was used in the Haidong Bay area with a water depth of over 10m; and sampling point 15 was used in areas with aquatic plants within 4m of water depth. The total area of ​​polluted sediment, A, was measured.

[0025] 3.2 Assessment of the thickness of the sediment contamination layer in Erhai Lake: Sediment columnar samples were collected from different locations using a sediment stratification sampler. The thickness of the sediment contamination layer was determined by observing the color of different sediment layers. The upper layer of the sediment columnar samples was a yellow herbaceous layer, below which was a black sludge layer (sediment contamination layer), below which was a grayish-white transition layer, and below that was the lake parent material layer. The thickness (δ) of the sediment contamination layer was measured using a ruler. The thickness of the sediment contamination layer at different locations in Erhai Lake is shown in the figure. Figure 3 As shown.

[0026] 3.3 Assessment of Phosphorus Reserves in Sediments: After determining the thickness of the sediment contamination layer, a columnar sediment sample was pushed out of the PVC pipe using a piston rod. The columnar sediment sample was then separated using a mud-cutting blade. The sediment porosity Φ and the bulk density ρ of the sediment contamination layer were determined using the direct calculation method (GB / T50123-2019) (bulk density was determined by the ring cutter method (NY / T1121.4-2006)). The sediment sample was freeze-dried, ground through a 100-mesh sieve, and the phosphorus content V was determined using a phosphomolybdenum blue spectrophotometer. The formula for calculating sediment phosphorus reserves is: m = V / 1000 × δ × ρ × 10000 × A. Phosphorus content at different sampling sites in various areas of Erhai Lake is shown below. Figure 4 As shown, the phosphorus reserves at different sampling sites in various areas of Erhai Lake are as follows: Figure 5 As shown.

[0027] 3.4 Assessment of phosphorus diffusion flux in sediments: An in-situ sediment-water interface water quality sampler was used. A weight was used to insert the interstitial water sampling section of the sampler into the lake sediments. A boundary plate was used to leave the overlying water sampling section above the sediment interface in the overlying water. After 7 days, the sampler was removed from the lake, its surface cleaned, and the sampler was placed with the sampling plate at the bottom and the protective plate on top. The protective plate and permeable membrane were removed, and the solution in the sampling chambers was removed using a pipette. The sampler had 40 sampling chambers arranged longitudinally: 10 in the overlying water (containing overlying water) and 30 in the sediment (containing interstitial water). Interstitial water and overlying water samples were collected. The phosphorus concentration in the interstitial water and overlying water at different depths was determined using ammonium molybdate spectrophotometry to calculate the phosphorus diffusion rate. The formula used was: Calculate the phosphorus diffusion rate. The annual average phosphorus diffusion rate of sediments from different sampling points in various areas of Erhai Lake is shown below. Figure 6 As shown.

[0028] 3.5 Assessment of phosphorus load in sediments of Erhai Lake in different seasons and regions: Internal phosphorus loading in sediments is the result of the dynamic balance between phosphorus adsorption and release between lake sediments and overlying water. Therefore, internal phosphorus loading reflects both the sediment's ability to diffuse into the overlying water and its ability to prevent phosphorus migration from the overlying water into the sediment. By measuring sediment diffusion rates and phosphorus reserves in the polluted layer at various locations in different areas of Erhai Lake on the 5th of each month, the model formula: N = m × F was used. d 2 The internal loading of sediments at sampling points in different seasons and regions of Erhai Lake was estimated, such as... Figure 7 As shown, the phosphorus loading in Erhai Lake sediments ranged from -0.9671 to 0.4584 from January to December. It was negative in June, July, and October, and positive in other months. June and July are the rainy season in Erhai Lake, resulting in higher input of external pollutants and the deposition of exogenous phosphorus in the sediments. In October, Erhai Lake begins to store water, reducing water flow and allowing phosphorus from the overlying water to migrate into the sediments. January saw the highest phosphorus loading in sediments, as the water level and quality were better in January. Figure 8 As shown, the annual average internal phosphorus loading of sediments at different sampling sites in different areas of Erhai Lake ranges from -0.0799 to 0.3123. Negative values ​​are observed at sampling sites 6, 7, and 15, while positive values ​​are observed at other sites. The water body of Erhai Lake generally flows from northwest to southeast. According to the contour lines of the Erhai Lake bottom (see...),... Figure 1 Locations 6 and 7 are situated on the sloping bottom of Erhai Lake. Due to the influence of water flow, the bottom sediment at these two locations is eroded, resulting in less pollutant deposition. The sediments primarily adsorb phosphorus from the overlying water. Location 15 is located at the only outlet in the lower reaches of Erhai Lake. Affected by the Erhai Reservoir, the water flow is slower from October to May of the following year, leading to phosphorus deposition from the northern inflow into the sediments at this location. Location 2 has the highest phosphorus loading in the sediments. This location is situated in Shaping Bay, where the water is shallow and aquatic plants are abundant, resulting in a higher phosphorus diffusion rate and thus a higher phosphorus loading in the sediments.

[0029] 4. Validation of sediment internal loading assessment methods: 4.1 Correlation analysis of phosphorus loading, content, and diffusion flux in sediments from different areas of Erhai Lake with overlying water quality and aquatic environment: Phosphorus loading in lake sediments has a significant impact on phosphorus concentration in the overlying water, and its magnitude is influenced by physicochemical factors in the overlying water. The correlation analysis of phosphorus loading, phosphorus content, phosphorus diffusion flux, and overlying water physicochemical factors at different locations in Erhai Lake is shown in Tables 1.1 and 1.2. Phosphorus loading in sediments showed a highly significant positive correlation with active phosphorus, transparency, and dissolved oxygen in the overlying water, and a significant positive correlation with dissolved inorganic phosphorus. Phosphorus content showed a significant positive correlation with total phosphorus in the overlying water. It is evident that sediment loading primarily affects the dissolved phosphorus content in the overlying water, and is influenced by water depth and dissolved oxygen content. The correlation coefficient between sediment phosphorus loading at different locations in Erhai Lake and the water quality and aquatic environment of the overlying water is higher than that between sediment phosphorus content and phosphorus diffusion flux. The sediment phosphorus loading proposed in this paper can better reflect the interaction between phosphorus in sediments and the water quality and aquatic environment of the overlying water.

[0030] Table 1.1 Correlation analysis of phosphorus loading, content, and diffusion flux in sediments from different areas of Erhai Lake with overlying water quality and aquatic environment

[0031] Note: n=15, * indicates significance level, ** indicates extremely significant level.

[0032] Table 1.2 Correlation analysis of phosphorus loading, content and diffusion flux in sediments of different areas of Erhai Lake with overlying water quality and aquatic environment

[0033] Note: n=15, * indicates significance level, ** indicates extremely significant level.

[0034] The internal phosphorus loading in sediments is a comprehensive reflection of sediment phosphorus reserves and sediment phosphorus diffusion flux; therefore, it can be expressed by the formula "N = m × c". 2 "Calculating the internal phosphorus load in sediments can better reflect the impact of phosphorus in sediments on overlying water than using sediment phosphorus content and phosphorus diffusion flux alone. It can assess the internal load in lakes with different eutrophication levels, evaluate the control effect of aquatic plants and dredging engineering measures on the internal load in lake sediments, and thus reveal the ability of lake sediment phosphorus to influence overlying water."

[0035] 4.2 Assessment of phosphorus load in sediments from different lakes Table 2 shows the estimated phosphorus loading in sediments of different lakes and wetlands using a model. The sediment phosphorus loading ranged from -0.0004 to 595684.60. The phosphorus loading in the sediments of eutrophic lakes Taihu and Dianchi was significantly higher than that of the mesotrophic lake Erhai. The phosphorus content and phosphorus diffusion flux in the sediments of Dianchi were both higher than those of Erhai. The phosphorus content in the sediments of Taihu was lower than that of Erhai, but the phosphorus diffusion flux was much higher. According to the model, the phosphorus loading in the sediments of Taihu was higher than that of Erhai. Compared to Meiliang Bay, which had better water quality, East Taihu, with its poorer water quality, had lower sediment phosphorus content and higher phosphorus diffusion flux, resulting in an 11.8-fold increase in sediment phosphorus loading according to the model. The summer sediment phosphorus loading in the eutrophic lake Chaohu was -0.0004, mainly due to the influence of higher external phosphorus input concentrations. Using a model, calculations were performed on the experimental results from the technical literature published by Palmer-Felgate (Palmer-Felgate EJ, Bowes MJ, Stratford C, Neal C, MacKenzie S. Phosphorus release from sediments in a treatment wetland: Contrast between DET and EPC0 methodologies[J]. Ecological Engineering, 2011, 37: 826–832. https: / / doi.org / 10.1016 / j.ecoleng.2010.12.024). The results showed that dredging slightly increased the phosphorus content in the sediment, but reduced the phosphorus diffusion flux, resulting in a 90% reduction in the internal phosphorus load of the sediment. Planting aquatic plants increased the phosphorus content in the sediment, but reduced the phosphorus diffusion flux, resulting in a 90% reduction in the internal phosphorus load of the sediment.

[0036] Table 2 Phosphorus loading in sediments from different lake wetlands

[0037] It is evident that, using the model proposed in this invention to calculate sediment phosphorus loading, the sediment phosphorus loading in eutrophic lakes is higher than that in mesotrophic lakes. When the exogenous phosphorus input is high, the ability of eutrophic lake sediments to prevent phosphorus migration into sediments is far greater than that in mesotrophic lakes. Planting aquatic plants and dredging can both significantly reduce sediment phosphorus loading. Therefore, the sediment phosphorus loading calculated by the model proposed in this invention reflects the influence of phosphorus in sediments on overlying water better than sediment phosphorus content and phosphorus diffusion flux. When diffusion flux is negative, phosphorus loading is also negative, reflecting the ability of sediments to prevent phosphorus from overlying water from depositing into sediments. A positive sediment phosphorus loading reflects the ability of sediments to supply phosphorus to overlying water.

[0038] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A method for determining the endogenous phosphorus load in lake sediments, characterized in that... Includes the following: 1) Determination of sediment phosphorus reserves: Sediment columnar samples were collected using a sediment stratified sampler. The thickness δ of the sediment contamination layer was measured using a ruler. The sediment columnar samples were pushed out of the PVC pipe using a columnar piston. The sediment contamination layer columnar samples were separated using a mud-cutting blade. The sediment porosity Φ of the sediment columnar samples was determined by direct calculation method. The bulk density ρ of the sediment contamination layer was determined by ring cutter method. The sediment samples were freeze-dried, ground and passed through a 100-mesh sieve. The phosphorus content V of the sediment was determined by phosphomolybdenum blue spectrophotometer method. 2) The calculation formula for phosphorus reserves in contaminated sediments is as follows: m i =V / 1000×δ×ρ×10000×A; m=Σm i ; Where: m is the total phosphorus reserves in the lake's polluted layer sediments; m i V represents the phosphorus reserves in the contaminated sediment layer of the i-th region; V is the phosphorus content of the sediment (g·kg). -1 ); δ represents the thickness of the contaminated layer (m), typically 10cm for lakes, with the thickness in heavily polluted areas determined by actual measurements; ρ represents the bulk density of the sediment contaminated layer (g·cm³). -2 A represents the total area of ​​polluted sediments (m²). 2 ); 3) Determination and calculation of phosphorus diffusion rate in sediments: An in-situ sediment-water interface water quality sampler was used. A weight was used to insert the interstitial water sampling section of the sampler into the lake sediments. A boundary plate was used to leave the overlying water sampling section of the sampler above the sediment interface in the overlying water. After 7 days, the sampler was removed from the lake, and surface contaminants were cleaned. The sampler was placed with the sampling plate at the bottom and the protective plate at the top. The protective plate and the permeable membrane were removed, and the solution in the sampling chamber was removed with a pipette. The sampling chamber in the overlying water contained overlying water, and the sampling chamber in the sediment contained interstitial water. Interstitial water and overlying water samples were collected, and the phosphorus concentration in the interstitial water and overlying water at different depths was determined by ammonium molybdate spectrophotometry. The phosphorus diffusion rate in sediments is calculated using Frick's First Law, and the formula is as follows: ； In the formula: F d Phosphorus diffusion rate in sediments, mg / (m³) 2 ·d); Φ is the porosity of the sediment, %; D s m is the diffusion coefficient. 2 / s; It is the phosphorus concentration gradient through the sediment-water interface, mg / (L·cm). 4) Calculation of phosphorus loading in sediments, the formula is as follows: N=m×F d 2 ; In the formula: N is the internal phosphorus loading of sediment (unit: n), m is the phosphorus storage of contaminated sediment (g), and F d Phosphorus diffusion rate in sediments (mg·m -2 ·d -1 ).

2. The method for determining the endogenous phosphorus load in lake sediments according to claim 1, characterized in that: In step 3), the D s The calculation method is as follows: When the sediment porosity Φ is less than or equal to 0.7, the formula is: D s =ΦD (Φ≤0.7) is used for calculation, where D=7.34 (D is the constant of Frick's first law); When the sediment porosity Φ is greater than 0.7, the formula is: D s = φD0 (Φ> 0.7) is calculated, where D0=7.34+0.40(T—25℃), and T is the water temperature.

3. The method for determining the endogenous phosphorus load in lake sediments according to claim 2, characterized in that: In step 3), the phosphorus concentration of overlying water and interstitial water in the in-situ sediment-water interface water quality sampler at different depths is subjected to exponential fitting with depth. The two sets of data on depth and phosphorus concentration are subjected to exponential fitting using Origin software. As the depth of overlying water and sediment increases, the phosphorus concentration decreases exponentially. The specific values ​​of the two parameters a and b in the following formula are obtained by exponential fitting using statistical software. Y=ae bX ; In the formula: Y is the phosphorus concentration in the water; X is the depth; a and b are parameters.

4. The method for determining the endogenous phosphorus load in lake sediments according to claim 3, characterized in that: In step 3), The diffusion gradient is calculated using the following formula: .

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