Method for rapidly deducing denitrification rate of lake sediment by using water chlorophyll

Abstract

The application discloses a method for rapidly deducing the denitrification rate of lake sediments by using water chlorophyll, which comprises the following steps: (1) determining the water chlorophyll concentration of the corresponding point of the sediments; (2) selecting a segmented numerical model: according to the measured water chlorophyll concentration and the corresponding sediment denitrification rate, the parameters in the segmented numerical model are fitted to obtain the segmented numerical model; (3) deducing the denitrification rate of the sediments: the chlorophyll concentration is substituted into the selected numerical model to deduce the denitrification rate of the sediments. The application is aimed at the problems that the existing determination operation of the nitrification-denitrification coupled denitrification rate of the sediments is complicated, time-consuming and not suitable for large-scale sample determination, and provides a method for rapidly deducing the denitrification rate of the sediments by using water chlorophyll. The method for directly deducing the denitrification rate by using the easily measured index is simple, feasible and beneficial to high-frequency multi-point data acquisition.

Description

Technical Field

[0001] This invention relates to the field of aquatic ecological environment, specifically to a method for rapidly estimating the denitrification rate of lake sediments using chlorophyll in water. Background Technology

[0002] In recent years, with rapid economic development and increasing human activity, nitrogen and phosphorus emissions have risen sharply, leading to eutrophication and frequent cyanobacterial blooms in lakes and other water bodies. This, in turn, causes a series of aquatic ecological and environmental problems such as water quality deterioration and reduced biodiversity. Sediment denitrification is the main nitrogen removal pathway in lake ecosystems, regulating lake nutrient levels. Nitrification converts ammonia nitrogen, produced by the mineralization and decomposition of organic nitrogen, into nitrate nitrogen, while denitrification further converts nitrate nitrogen into nitrogen gas, releasing it into the atmosphere, thus permanently removing nitrogen from lakes. Therefore, sediment denitrification efficiency is one of the important ecological monitoring indicators for eutrophic lakes.

[0003] Currently, various methods are available for quantitatively assessing sediment denitrification processes, such as acetylene inhibition, isotope tracing, N2 flux, and mass balance methods (CN102128736B, CN111487365B). However, these methods all require artificial cultivation, which is not only cumbersome and time-consuming, making them unsuitable for large-scale sample analysis, but also unable to achieve historical data inversion and future scenario analysis. Summary of the Invention

[0004] Purpose of the invention: To address the problems existing in the prior art, this invention provides a method for rapidly estimating the denitrification rate of lake sediments using chlorophyll in water. The method of directly estimating the denitrification rate using easily measurable indicators is simple and feasible to operate, and is conducive to the acquisition of high-frequency, multi-site data. It effectively solves the problems of existing sediment nitrification-denitrification coupled denitrification rate measurement being cumbersome, time-consuming, and unsuitable for large-scale sample measurement, and also enables the inversion of historical data and future scenario analysis.

[0005] Technical solution: To achieve the above-mentioned objective, the present invention provides a method for rapidly estimating the nitrogen removal rate of lake sediments using chlorophyll in water, comprising the following steps:

[0006] (1) Determination of chlorophyll concentration in water:

[0007] Measure the chlorophyll concentration in the water at corresponding points in the sediment;

[0008] (2) Establishment of piecewise numerical model:

[0009] Based on the measured chlorophyll concentration in the water and the corresponding denitrification rate in the sediment, the parameters in the piecewise numerical model are fitted to obtain the piecewise numerical model.

[0010] (3) Estimation of sediment denitrification rate:

[0011] Substitute the chlorophyll concentration into the selected numerical model to estimate the sediment denitrification rate.

[0012] In step (1), the chlorophyll refers to chlorophyll a (Chl-a) in the water body overlying the sediment site to be tested.

[0013] In step (1), the concentration of chlorophyll in the water at the corresponding point of the sediment can be determined by traditional chemical methods, or by satellite remote sensing or sensors.

[0014] Preferably, the conventional chemical method includes the hot alcohol method for determining the chlorophyll concentration in the water at the corresponding sediment location or the acetone method for determining the chlorophyll concentration in the water at the corresponding sediment location.

[0015] The hot alcohol method for determining the chlorophyll concentration at the corresponding sediment location is as follows: Take a water sample volume (L) V(sample). Filter V(sample) volume (L) of the water sample using a GF / C membrane. Place the membrane in a glass tube, add 5 mL of 90% hot alcohol at 90℃, heat in a water bath for approximately 2 minutes, let stand in the dark for 4 hours, and then filter. Record the filtrate volume V(filter). Measure the absorbance at 665 nm and 750 nm, obtaining the absorbance difference, which is recorded as A(before acidification). Add one drop of 1 mol / L hydrochloric acid directly to a cuvette, and measure the absorbance again at 665 nm and 750 nm, obtaining the absorbance difference, which is recorded as A(after acidification). Calculate the chlorophyll concentration using C(μg / L) = (A(before acidification) - A(after acidification)) × 27.9 × 1000 × V(filter) / V(sample).

[0016] Specifically, 50 mL of water sample was filtered using a GF / C membrane. The membrane was placed in a glass tube, and 5 mL of 90% hot ethanol was added. The mixture was heated in a water bath for approximately 2 minutes, allowed to stand in the dark for 4 hours, and then filtered. The absorbance was measured at 665 nm and 750 nm. The chlorophyll concentration was calculated using the formula: C(μg / L) = (Result before acidification - Result after acidification) × 27.9 × 1000 × V(extraction) / V(filtration).

[0017] Specifically, the acetone method for determining the chlorophyll concentration of water at corresponding sediment locations involves taking a water sample of volume V, filtering it through a cellulose acetate membrane, fully dissolving the membrane in acetone solution, extracting the sample, centrifuging it, and taking the supernatant volume V1. The absorbance values ​​are then measured at wavelengths of 630 nm, 645 nm, 663 nm, and 750 nm, and calculated using the following relationship:

[0018]

[0019] Where V is the volume of the water sample (L); V1 is the volume of the extract (L); and σ is the optical path length of the cuvette (cm).

[0020] Further, 50 mL of water sample (V) was filtered through a 0.45 μm cellulose acetate membrane, and the filter membrane was fully dissolved in 10 mL of 90% acetone solution. Extraction was carried out at 4 °C for 24 h, centrifuged at 5000 rpm for 10 min, and the volume of the supernatant (L) was taken as V1. The absorbance values ​​were measured at wavelengths of 630 nm, 645 nm, 663 nm, and 750 nm (A630, A645, A663, and A750, respectively) and calculated.

[0021] In step (2), the piecewise numerical model is an empirical numerical model established by chlorophyll concentration and sediment denitrification rate. Specifically, when the chlorophyll concentration x ≤ 73.2 μg / L, the sediment denitrification rate is directly proportional to chlorophyll, and the sediment denitrification rate y conforms to the quantitative relationship y = 0.0085x + 0.2363 with the chlorophyll a concentration x; when the chlorophyll concentration x > 73.2 μg / L, the sediment denitrification rate is inversely proportional to chlorophyll, and the sediment denitrification rate y conforms to the quantitative relationship y = -0.003x + 1.0783 with the chlorophyll a concentration x. Based on the chlorophyll a concentration in the water body, the required piecewise numerical model is selected, and the chlorophyll concentration is substituted to deduce the sediment denitrification rate at each sampling point.

[0022] The method described in this invention for rapidly estimating the coupled nitrogen removal rate of lake sediments using chlorophyll in water bodies is applied to the estimation of nitrogen reduction in lake sediments.

[0023] Nitrification-denitrification coupled nitrogen removal in sediments is a major nitrogen removal pathway in lake ecosystems and a key nitrogen transformation pathway monitored by water environment managers and researchers. Aquatic algae not only provide substrates and carbon sources for sediment nitrification and denitrification but also create anaerobic environments for denitrification; therefore, algal biomass is closely related to the nitrogen removal rate. This invention provides a method to rapidly deduce the nitrification-denitrification coupled nitrogen removal rate in sediments based on the quantitative relationship between sediment nitrogen removal rate and chlorophyll concentration in overlying water.

[0024] This invention addresses the problems of cumbersome, time-consuming, and unsuitable-for-large-scale sediment denitrification rate measurement in existing methods. It provides a method for rapidly estimating sediment denitrification rate using water chlorophyll. This method allows for convenient and large-scale acquisition of water chlorophyll concentration through chemical analysis, satellite remote sensing, or sensors, thereby directly estimating the denitrification rate of bottom sediments. This invention's method for directly estimating denitrification rate using easily measurable indicators is simple and feasible, and beneficial for acquiring high-frequency, multi-site data.

[0025] The method of this invention indirectly determines complex indicators using a simple and readily available index. By directly inputting the easily measurable index, results with high consistency with traditional complex methods can be obtained. This invention establishes a numerical model to replace traditional methods. Only a simple and easily measurable index needs to be input to deduce complex and difficult-to-measure indicators, making it very convenient and easy to implement. For example, in underwater terrain, there is no need for underwater surveying; it can be directly scanned by a drone on the water surface, making it simple and easy to implement.

[0026] This invention, by establishing a specific piecewise numerical model, discovers for the first time that the sediment denitrification rate is directly proportional to low chlorophyll concentration and inversely proportional to high chlorophyll concentration. Therefore, the required piecewise numerical model is selected based on the chlorophyll concentration of the water body. In specific applications, the selection of the piecewise numerical model is based on chlorophyll concentration, determining that the sediment denitrification rate is directly proportional to low chlorophyll concentration and inversely proportional to high chlorophyll concentration, and a specific numerical model is established. When applying this specific numerical model, a mathematical relationship is established between chlorophyll and the measured denitrification rate; the denitrification rate is obtained by directly inputting chlorophyll.

[0027] When the chlorophyll concentration x ≤ 73.2 μg / L, the sediment denitrification rate is directly proportional to the chlorophyll concentration, and the sediment denitrification rate y conforms to the quantitative relationship y = 0.0085x + 0.2363 with the chlorophyll a concentration x; when the chlorophyll concentration x > 73.2 μg / L, the sediment denitrification rate is inversely proportional to the chlorophyll concentration, and the sediment denitrification rate y conforms to the quantitative relationship y = -0.003x + 1.0783 with the chlorophyll a concentration x.

[0028] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0029] Compared to traditional methods, this invention eliminates the need for collecting bottom sediments and time-consuming ex-situ culture, directly estimating the denitrification rate using easily measurable surface water indicators. This method, which directly derives the denitrification rate from easily measurable indicators, is simple and feasible, facilitating the acquisition of high-frequency, multi-site data. It effectively solves the problems of existing sediment nitrification-denitrification coupled denitrification rate measurements being cumbersome, time-consuming, and unsuitable for large-scale sample testing. Furthermore, it enables the inversion of historical data and future scenario analysis.

[0030] This invention can determine the chlorophyll concentration in water at corresponding sediment locations using traditional chemical methods, and can also reduce the time required to acquire a single data point from daily to second-level direct output by connecting with remote sensing satellites, sensors, and other technologies. Attached Figure Description

[0031] Figure 1 A schematic diagram of the process for estimating sediment denitrification rate using chlorophyll in water;

[0032] Figure 2This serves as a comparative verification of traditional measurements and model projections of sediment denitrification rates.

[0033] Figure 3 Spatial patterns of nitrogen removal rates in Taihu Lake sediments in 2005 and 2015. Detailed Implementation

[0034] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0035] Example 1

[0036] Model validation and application were conducted using Taihu Lake as the model. Taihu Lake is a typical eutrophic lake, and its sediment denitrification process plays a crucial role in controlling trophic levels. Therefore, sediment denitrification efficiency is one of the important ecological monitoring indicators for Taihu Lake. Based on the spatial characteristics of Taihu Lake sediments and referring to the long-term observation sites of the Taihu Lake Ecosystem National Field Scientific Observation and Research Station, 16 sampling points were selected for model validation. The coordinates of each sampling point are shown in Table 1. After collecting the overlying water, chlorophyll a was analyzed using the hot ethanol method: A water sample of volume V (sample) was filtered through a GF / C membrane. The membrane was placed in a glass tube, and 5 mL of 90% hot ethanol at 90℃ was added. The sample was heated in a water bath for about 2 minutes, allowed to stand in the dark for 4 hours, and then filtered. The volume of the filtrate (L) was recorded as V (filter). The absorbance was measured at 665 nm and 750 nm, and the absorbance difference was recorded as A (before acid). One drop of 1 mol / L hydrochloric acid was added directly to a cuvette, and the absorbance was measured again at 665 nm and 750 nm, and the absorbance difference was recorded as A (after acid). The chlorophyll concentration was calculated according to C (μg / L) = (A (before acid) - A (after acid)) × 27.9 × 1000 × V (filter) / V (sample), as shown in Table 1.

[0037] Based on the measured chlorophyll concentration in the water and the corresponding sediment denitrification rate (obtained using the conventional N2 flux method described below), a piecewise linear fit was performed to establish a mathematical model. When the chlorophyll concentration x ≤ 73.2 μg / L, the sediment denitrification rate is directly proportional to chlorophyll, and the sediment denitrification rate y conforms to the quantitative relationship y = 0.0085x + 0.2363 with the chlorophyll a concentration x; when the chlorophyll concentration x > 73.2 μg / L, the sediment denitrification rate is inversely proportional to chlorophyll, and the sediment denitrification rate y conforms to the quantitative relationship y = -0.003x + 1.0783 with the chlorophyll a concentration x. Based on the chlorophyll a concentration in the water, the required piecewise numerical model was selected, and the sediment denitrification rate at each sampling point was calculated by substituting the chlorophyll concentration. The specific process is as follows: Figure 1 As shown in Table 1, the obtained denitrification rates are as follows.

[0038] Simultaneously, the traditional N2 flux method was used to determine the sediment denitrification rate: sediment column samples were collected simultaneously from various sampling points. The N2 flux was measured using a closed static incubation method. During sample collection, a movable rubber piston was placed above the experimental column. Water samples were collected at the lower outlet of the column by slowly pressing the piston down at 5-minute intervals, for a total of 5 samplings. Samples were stored in headspace vials (12 mL, Labco Limited, UK). 20 μL of saturated HgCl2 was added using a syringe to fix the samples for analysis. Each sampling included three replicates. The N2 content in the water samples was determined using a membrane interface mass spectrometer (MIMS) with an O2:Ar ratio. The results were linearly fitted to obtain the N2 concentration change rate.

[0039]

[0040] In the above formula, F represents the N2 release flux at the sediment-water interface, in μmol·m⁻¹. -2 ·h -1 h is the height of the water covering the experimental column; d(C) / dt is the rate of change of N2 concentration in the covering water, μmol·m -3 ·h -1 The denitrification rates at each site are shown in Table 1 (measured values). Verification was performed through comparison.

[0041] Table 1 Model Validation

[0042]

[0043] As shown in Table 1, the method of this invention directly derives the nitrogen removal rate using an easily measurable index (chlorophyll), which is simple and feasible to operate and beneficial for acquiring high-frequency, multi-site data; at the same time, the model derivation method of this invention has high consistency with traditional experimental methods. Figure 2 The main advantages of this invention are that it is basically the same as the traditional method in terms of accuracy and repeatability. In addition, the method of this invention is more convenient, lower cost and easier to scale up, while the traditional method has a complicated procedure and higher requirements for the measurement equipment.

[0044] Example 2

[0045] Using the method of Example 1 of this invention, based on historical water chlorophyll a concentration ( Figure 3 This allows for the historical inversion of nitrogen removal rates in Taihu Lake sediments in 2005 and 2015. The data shows that the nitrogen removal rate in Taihu Lake sediments generally showed an increasing trend over the 10-year period. Figure 3 Traditional methods require physical samples, making it impossible to analyze historical patterns in sediment denitrification rates. This invention, however, can extrapolate based on satellite remote sensing data, which effectively acquires historical data.

[0046] Example 3

[0047] Example 3 uses the same method as Example 1, except that the acetone method is used to determine the chlorophyll concentration of the water at the corresponding sediment location. Specifically, 50 mL of water sample is taken, filtered through a 0.45 μm cellulose acetate membrane, and the filter membrane is fully dissolved in 10 mL of 90% acetone solution. Extraction is carried out at 4°C for 24 h to obtain an extract volume (L) of V1. The extract is centrifuged at 5000 rpm for 10 min, and the supernatant is taken. The absorbance values ​​are measured at wavelengths of 630 nm, 645 nm, 663 nm, and 750 nm (A630, A645, A663, and A750, respectively), and calculated using the following relationship:

[0048]

[0049] Where V is the volume of the water sample (L); V1 is the volume of the extract (L); and σ is the optical path length of the cuvette (cm).

[0050] Example 4

[0051] Example 4 uses the same method as Example 1, except that satellite remote sensing or sensors are used to determine the chlorophyll concentration in the water at the corresponding sediment location.

Claims

1. A method for rapidly deriving the denitrification rate of lake sediments using the chlorophyll of water bodies, characterized in that, Includes the following steps: (1) Determination of chlorophyll concentration in water: Measure the chlorophyll concentration in the water at corresponding points in the sediment; (2) Selection of piecewise numerical models: Based on the measured chlorophyll concentration in the water and the corresponding denitrification rate in the sediment, the parameters in the piecewise numerical model were fitted to obtain the piecewise numerical model. (3) Estimation of sediment denitrification rate: Substitute the chlorophyll concentration to be measured into the selected numerical model to estimate the nitrogen removal rate of the sediment. The piecewise numerical model mentioned in step (2) is a numerical model established by chlorophyll concentration and sediment denitrification rate. Specifically, when the chlorophyll concentration x ≤ 73.2 μg / L, the sediment denitrification rate is directly proportional to chlorophyll, and the sediment denitrification rate y conforms to the quantitative relationship y = 0.0085x + 0.2363 with the chlorophyll a concentration x; when the chlorophyll concentration x > 73.2 μg / L, the sediment denitrification rate is inversely proportional to chlorophyll, and the sediment denitrification rate y conforms to the quantitative relationship y = -0.003x + 1.0783 with the chlorophyll a concentration x. Based on the chlorophyll a concentration of the water body, the required piecewise numerical model is selected, and the chlorophyll concentration is substituted to deduce the sediment denitrification rate of each sampling point. 2.The method for quickly deriving the denitrification rate of lake sediment by using the water body chlorophyll according to claim 1, characterized in that, The chlorophyll mentioned in step (1) refers to chlorophyll a in the water body overlying the sediment site to be tested, named Chl-a.

3. The method for rapidly estimating the nitrogen removal rate of lake sediments using chlorophyll in water, as described in claim 1, is characterized in that... In step (1), the concentration of chlorophyll in the water body at the corresponding point of sediment can be determined by traditional chemical methods, or by satellite remote sensing or sensors.

4. The method for rapidly estimating the denitrification rate of lake sediments using chlorophyll in water, as described in claim 3, is characterized in that... The traditional chemical methods include the hot alcohol method for determining the chlorophyll concentration in the water at the corresponding sediment location or the acetone method for determining the chlorophyll concentration in the water at the corresponding sediment location.

5. The method for rapidly estimating the nitrogen removal rate of lake sediments using chlorophyll in water, as described in claim 4, is characterized in that... The hot alcohol method measures the sediment corresponding point water body chlorophyll concentration: take water sample volume V 样 , filter with GF / C membrane, add the membrane into hot alcohol, heat in water bath, avoid light, stand, filter after, record the filtrate volume V 滤 , respectively measure the absorbance under 665 nm and 750 nm conditions, get the absorbance difference, record as A 酸前 , drop hydrochloric acid, respectively measure the absorbance under 665 nm and 750 nm conditions, get the absorbance difference, record as A 酸后 ; according to C (μg / L) =(A 酸前 - A 酸后 )× 27.9 × 1000 × V 滤 / V 样 , calculate to obtain the chlorophyll concentration.

6. The method for rapidly estimating the denitrification rate of lake sediments using chlorophyll in water according to claim 4, characterized in that, The acetone method for determining the chlorophyll concentration (Chla) at corresponding sediment locations involves taking water samples, filtering them through a cellulose acetate membrane, fully dissolving the membrane in acetone, extracting the chlorophyll, centrifuging, and measuring the absorbance of the supernatant at wavelengths of 630 nm, 645 nm, 663 nm, and 750 nm. The absorbance is then calculated using the following relationship: ； Where V is the volume of the water sample in L; V1 is the volume of the supernatant in L; and σ is the optical path length of the cuvette in cm.

7. The application of the method for rapidly estimating the nitrogen removal rate of lake sediments using chlorophyll in water bodies as described in claim 1 in the estimation of nitrogen reduction in lake sediments.

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