River denitrification rate evaluation method based on high-frequency dissolved oxygen monitoring

Abstract

The invention discloses a determination method for acquiring a denitrification rate based on river dissolved oxygen high-frequency monitoring. The determination method comprises the following steps: S1, constructing a dynamic response model of the river denitrification rate to heterotrophic respiration; s11, carrying out in-situ high-frequency DO observation on different types of rivers, collecting a water sample, and measuring the concentrations of dissolved N2 and O2 in the collected water sample by adopting an MIMS technology; s12, on the basis of the O2 concentration data, the river heterotrophic oxygen respiration rate is calculated through an O2 mass balance model; s13, based on the N2 concentration data, calculating the river denitrification rate through an N2 mass balance model; s14, fitting the obtained series of heterotrophic respiration rates with the denitrification rate to obtain a dynamic response model between the denitrification rate and heterotrophic respiration; and S2, based on field real-time high-frequency monitoring dissolved oxygen observation data, simulating the river denitrification rate through the constructed dynamic response model. According to the invention, the problems that the traditional denitrification rate measurement cost is high and real-time continuous monitoring cannot be realized are solved, and in-situ, real-time and high-frequency monitoring of the denitrification rate is realized.

Description

Technical Field

[0001] This invention belongs to the field of denitrification rate measurement technology, and in particular, it is a method for evaluating river denitrification rate based on high-frequency dissolved oxygen monitoring. Background Technology

[0002] Denitrification is a key process in the nitrogen cycle of aquatic ecosystems, specifically referring to the process by which microorganisms reduce nitrates or nitrites to gaseous nitrogen (such as nitrous oxide and nitrogen gas) under anaerobic conditions. Accurately quantifying the denitrification rate is the scientific basis for assessing the self-purification capacity of water bodies, tracing the sources of nitrous oxide emissions, and formulating eutrophication control strategies. However, increasingly severe human activities have led to a continuous rise in nitrogen load in watersheds, making the accurate assessment of denitrification rates even more challenging. This technical bottleneck directly restricts the accurate construction of nitrogen cycle models for aquatic environments and also affects the effective remediation of high-nitrate water bodies.

[0003] Currently, mainstream measurement technologies each have their limitations: while membrane sample introduction mass spectrometry (MIMS) can monitor in situ... / Ar ratio enables high-frequency measurement, but the equipment is expensive and the technical threshold is high; isotope tracing methods (such as...) 15 While N) has high precision, it is extremely expensive and depends on non-in situ culture experiments; while the acetylene inhibition method is cheaper and more mature, the added inhibitors can interfere with microbial processes (such as inhibiting nitrification), which may lead to an underestimation of the rate, and it is ineffective in sulfate-reducing environments.

[0004] In summary, existing methods generally suffer from common drawbacks such as high cost, complex operation, or difficulty in achieving in-situ continuous monitoring, which seriously hinders a deeper understanding of the spatiotemporal dynamics of denitrification processes in aquatic ecosystems. Therefore, developing a new technology for low-cost, in-situ, high-frequency, and continuous monitoring of denitrification rates has become an urgent need in this field. Summary of the Invention

[0005] To address the aforementioned technical problems in existing technologies, this invention provides a method for assessing river denitrification rates based on high-frequency dissolved oxygen (DO) monitoring. This invention targets rivers with different land use types at the source watershed scale, using in-situ high-frequency DO concentration monitoring coupled with membrane sampling mass spectrometry to assess heterogeneous respiration and denitrification rates. By coupling heterogeneous respiration and denitrification processes, a dynamic model relating DO and denitrification rates is constructed, enabling high-resolution determination of river denitrification rates at spatiotemporal scales.

[0006] The technical solution adopted in this invention is: A method for determining denitrification rate based on high-frequency monitoring of dissolved oxygen in rivers, characterized by comprising the following steps: S1. Construct a dynamic response model of river denitrification rate to heterogeneous respiration; S11: Conduct in-situ high-frequency DO observations of different types of rivers, collect water samples, and use MIMS technology to determine the dissolved N2 and O2 concentrations of the collected water samples; S12: Based on the O2 concentration data measured by MIMS technology in step S11, the heterotrophic respiration rate of the river is calculated using the O2 mass balance model; S13: Based on the N2 concentration data measured by MIMS technology in step S11, the river denitrification rate is calculated using the N2 mass balance model; S14: Fit the series of heterogeneous respiration rates obtained in steps S12 and S13 to the denitrification rate. The dynamic response model between the denitrification rate and heterogeneous respiration is expressed as follows: (1) in, It is the rate of river denitrification. It is the rate of heterogeneous respiration. It is the maximum denitrification rate. It is the half-saturation constant; S2. Based on real-time high-frequency dissolved oxygen observation data in the field, the dynamic response model constructed in step S1 is used to simulate the river denitrification rate.

[0007] Furthermore, in step S12, based on the O2 concentration obtained from MIMS, the heterotrophic respiration rate of the river is evaluated according to the O2 mass balance model, as shown in the following formula: (2) (3) in, yes t O2 concentration at time; It is the river depth; It is the time step; yes t Photosynthetically active radiative flux density at any given time; It is a primary productive force; It is the respiration of the ecosystem; It is the total daily solar radiation; yes t The dissolved oxygen equilibrium concentration at the corresponding temperature and pressure at any given time; It is the exchange rate of O2; Is t Time through Schmidt number ,Depend on The calculated O2 gas exchange rate; It is a standardized gas exchange rate, specifically referring to the gas transfer rate under ideal conditions of water temperature 20℃ and Schmidt number (Sc) of 600; The Schmidt coefficient is used, and the wind speed is <3.6 m / s. -1 Take 2 / 3 of the time, wind speed > 3.6 m / s -1 Take 1 / 2 at a time; It is the Schmidt constant of O2 at a specific temperature. The Schmidt constant of freshwater is a function of temperature (see 'Wanninkhof, R. Relationship between wind speed and gas exchange over the ocean. Journal of Geophysical Research-Oceans, 1992, 97(C5), 7373-7382.').

[0008] Furthermore, the heterotrophic respiration rate is obtained by subtracting autotrophic respiration from ecosystem respiration, as shown below: (4) It is the rate of heterotrophic respiration, i.e., the rate by which ER removes autotrophic respiration. A portion; AR as a certain proportion of GPP. Acquired, generally The value range is 0.30~0.71, and the average value is 0.50 ± 0.3.

[0009] Furthermore, in step S13, based on the N2 concentration obtained from MIMS, the river denitrification rate is evaluated according to the N2 mass balance model, as shown in the following formula: (5) (6) in, yes t N2 concentration at time; It is the denitrification rate; It is the river depth; yes t The equilibrium concentration of N2 at the corresponding temperature and pressure at any given time; Is t Time through Schmidt number ,Depend on The calculated N2 gas exchange rate; It is the Schmidt constant of N2 at a specific temperature. The Schmidt constant of freshwater is a function of temperature (see 'Wanninkhof, R. Relationship between wind speed and gas exchange over the ocean. Journal of Geophysical Research-Oceans, 1992, 97(C5), 7373-7382.'). The posterior distribution is estimated based on the model in step 102, while the denitrification rate and gas exchange rate for each sample are based on Bayesian simulation analysis of Markov chain Monte Carlo.

[0010] Furthermore, the time interval between water sample collections shall not exceed 4 hours.

[0011] The technical concept of this invention is to collect river water samples by in-situ high-frequency sensors and measure dissolved N2 and O2 concentration data by MIMS technology, construct a dynamic response model of river denitrification rate to heterogeneous respiration, and simulate the daily denitrification rate of the river based on the self-constructed dynamic response model, so as to realize in-situ, real-time and high-frequency monitoring of denitrification rate.

[0012] Compared with the prior art, the beneficial effects of the present invention are reflected in: 1. This invention utilizes an in-situ high-frequency dissolved oxygen sensor to measure dissolved oxygen concentration and obtain river denitrification rate, thereby achieving in-situ, real-time, and high-frequency monitoring of denitrification rate, which greatly improves the spatiotemporal resolution of monitoring and the response capability to instantaneous events.

[0013] 2. This invention ingeniously couples the difficult-to-measure denitrification rate with the heterogeneous respiration rate, which is easily obtained through in-situ dissolved oxygen data, to construct a dynamic response model between the two, thereby reducing the technical threshold and economic cost of long-term, large-scale monitoring.

[0014] 3. This invention, by introducing a model that includes "maximum denitrification rate" and "half-saturation constant", reflects the dynamic law that the denitrification rate is regulated by heterogeneous respiration and tends to saturate, reveals the core mechanism and has universality; this method can be flexibly applied to long-term ecological assessment and water quality management at the source watershed scale. Attached Figure Description

[0015] Figure 1 The flowchart is a method for determining the denitrification rate based on high-frequency monitoring of dissolved oxygen in rivers, according to the present invention.

[0016] Figure 2 This is a graph showing the variation of river denitrification rate according to the present invention.

[0017] Figure 3 The present invention provides the statistical distribution and range of variation of river denitrification rates. Detailed Implementation

[0018] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the scope of the present invention.

[0019] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0020] The present invention will now be described in detail with reference to the accompanying drawings and exemplary embodiments.

[0021] refer to Figure 1 The present invention provides a method for determining the denitrification rate based on high-frequency monitoring of dissolved oxygen in rivers, comprising the following steps: S1. Construct a dynamic response model of river denitrification rate to heterogeneous respiration; S11: Conduct in-situ high-frequency dissolved oxygen observations of different types of rivers, collect water samples, and use MIMS technology to determine the dissolved N2 and O2 concentrations of the collected water samples; S12: Based on the O2 concentration data measured by MIMS technology in step S11, the heterotrophic respiration rate of the river is calculated using the O2 mass balance model; S13: Based on the N2 concentration data measured by MIMS technology in step S11, the river denitrification rate is calculated using the N2 mass balance model; S14: Fit the series of heterogeneous respiration rates obtained in steps S12 and S13 to the denitrification rate. The dynamic response model between the denitrification rate and heterogeneous respiration is expressed as follows: (1) in, It is the rate of river denitrification. It is the rate of heterogeneous respiration. It is the maximum denitrification rate. It is the half-saturation constant; S2. Based on real-time high-frequency dissolved oxygen observation data in the field, the dynamic response model constructed in step S1 is used to simulate the river denitrification rate.

[0022] In one embodiment, in step S12, based on the O2 concentration obtained from MIMS, the heterotrophic respiration rate of the river is evaluated according to the O2 mass balance model, as shown in the following formula: (2) (3) in, yes t O2 concentration at time; It is the river depth; It is the time step; yes t Photosynthetically active radiative flux density at any given time; It is a primary productive force; It is the respiration of the ecosystem; It is the total daily solar radiation; yes t The dissolved oxygen equilibrium concentration at the corresponding temperature and pressure at any given time; It is the exchange rate of O2; Is t Time through Schmidt number ,Depend on The calculated O2 gas exchange rate; It is a standardized gas exchange rate, specifically referring to the gas transfer rate under ideal conditions of water temperature 20℃ and Schmidt number (Sc) of 600; The Schmidt coefficient is used, and the wind speed is <3.6 m / s. -1 Take 2 / 3 of the time, wind speed > 3.6 m / s -1 Take 1 / 2 at a time; This is the Schmidt constant of O2 at a specific temperature. The Schmidt constant of freshwater is a function of temperature (see 'Wanninkhof, R. Relationship between wind speed and gas exchange over the ocean. Journal of Geophysical Research-Oceans, 1992, 97(C5), 7373-7382.'). Using a non-uniform distribution, i.e., a normal distribution or a log-normal distribution, as the prior probability, Correlation was established with hydrological parameters; GPP (3.1 ± 6.0 g O2 m -2 d -1 ) and ER (7.1 ± 7.1 g O2 m -2 d -1 The prior probability of ) is based on the range described in the literature.

[0023] In one embodiment, the heterotrophic respiration rate is obtained by subtracting autotrophic respiration from ecosystem respiration, as shown below: (4) It is the rate of heterotrophic respiration, i.e., the rate by which ER removes autotrophic respiration. A portion; AR as a certain proportion of GPP. Acquired, generally The value range is 0.30~0.71, and the average value is 0.50 ± 0.3.

[0024] In one embodiment, in step S13, based on the N2 concentration obtained from MIMS, the river denitrification rate is evaluated according to the N2 mass balance model, as shown in the following formula: (5) (6) in, yes t N2 concentration at time; It is the denitrification rate; It is the river depth; yes t The equilibrium concentration of N2 at the corresponding temperature and pressure at any given time; Is t Time through Schmidt number ,Depend on The calculated N2 gas exchange rate; It is the Schmidt constant of N2 at a specific temperature. The Schmidt constant of freshwater is a function of temperature (see 'Wanninkhof, R. Relationship between wind speed and gas exchange over the ocean. Journal of Geophysical Research-Oceans, 1992, 97(C5), 7373-7382.'). The posterior distribution is estimated based on the model in step 102, with a denitrification rate of (2.2 ± 4.1 g Nm). -2 d -1 The prior values ​​are based on the literature range, while the denitrification rate and gas exchange rate of each sample are based on Bayesian simulation analysis of Markov chain Monte Carlo.

[0025] In one embodiment, the time interval between water sample collections does not exceed 4 hours.

[0026] refer to Figure 2 and Figure 3 In one embodiment of the present invention, a typical headwaters basin located in Henan Province was selected, with a basin area of ​​39,000 square kilometers. The main land use types covered by the eight selected headwater rivers include forest land, agriculture, and urban land.

[0027] From May to December 2020, in-situ high-frequency dissolved oxygen (DOO) monitoring was conducted on rivers with different land use types. Dissolved oxygen sensors were used to acquire surface water temperature and dissolved oxygen concentration data every 15 minutes. In addition, parameters such as river length, width, depth, flow velocity, and slope were measured to construct a basic database.

[0028] River water samples of different types were collected every 30 minutes for a total of 24 hours. After pretreatment, the N2 / Ar and O2 / Ar ratios were determined using MIMS technology to calculate the N2 and O2 concentrations.

[0029] Heterogeneous respiration rates on a daily scale of 5–12 months in different types of rivers simulated in step S1. ) and denitrification rate ( This leads to the construction of an intrinsic dynamic response model. This model not only describes the quantitative relationship between the two but also introduces the maximum denitrification rate (…). ), half-saturation constant ( Key parameters such as ) were used to characterize the kinetics of denitrification as a function of microbial metabolic activity.

[0030] Fifty rivers of different types were selected, and based on high-frequency dissolved oxygen concentration monitoring data from January to December 2021, the daily-scale primary productivity, ecosystem respiration, and heterogeneous respiration rate of the rivers were simulated.

[0031] Figure 2 The figure shows the dynamic changes in the daily denitrification rate of a certain river from January to December 2021. Figure 3 The statistical distribution and range of denitrification rates for 50 rivers are shown, along with the mean (solid line) and median (dashed line) of the river denitrification rates.

[0032] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for determining denitrification rate based on high-frequency monitoring of dissolved oxygen in rivers, characterized in that, Includes the following steps: S1. Construct a dynamic response model of river denitrification rate to heterogeneous respiration; S11: Conduct in-situ high-frequency dissolved oxygen observations of different types of rivers, collect water samples, and use MIMS technology to determine the dissolved N2 and O2 concentrations of the collected water samples; S12: Based on the O2 concentration data measured by MIMS technology in step S11, the heterotrophic respiration rate of the river is calculated using the O2 mass balance model; S13: Based on the N2 concentration data measured by MIMS technology in step S11, the river denitrification rate is calculated using the N2 mass balance model; S14: Fit the series of heterogeneous respiration rates obtained in steps S12 and S13 to the denitrification rate. The dynamic response model between the denitrification rate and heterogeneous respiration is expressed as follows: （1） in, It is the rate of river denitrification. It is the rate of heterogeneous respiration. It is the maximum denitrification rate. It is the half-saturation constant; S2. Based on real-time high-frequency dissolved oxygen observation data in the field, the dynamic response model constructed in step S1 is used to simulate the river denitrification rate.

2. The method for determining denitrification rate based on high-frequency monitoring of dissolved oxygen in rivers as described in claim 1, characterized in that, In step S12, based on the O2 concentration obtained from MIMS, the heterotrophic respiration rate of the river is evaluated according to the O2 mass balance model, as shown in the following formula: （2） （3） in, yes t O2 concentration at time; It is the river depth; It is the time step; yes t Photosynthetically active radiative flux density at any given time; It is a primary productive force; It is the respiration of the ecosystem; It is the total daily solar radiation; yes t The dissolved oxygen equilibrium concentration at the corresponding temperature and pressure at any given time; It is the exchange rate of O2; Is t Time through Schmidt number ,Depend on The calculated O2 gas exchange rate; It is a standardized gas exchange rate, specifically referring to the gas transfer rate under ideal conditions of water temperature 20℃ and Schmidt number (Sc) of 600; The Schmidt coefficient is used, and the wind speed is <3.6 m / s. -1 Take 2 / 3 of the time, wind speed > 3.6 m / s -1 Take 1 / 2 at a time; It is the Schmidt constant of O2 at a specific temperature, while the Schmidt constant of fresh water is a function of temperature.

3. The method for determining denitrification rate based on high-frequency monitoring of dissolved oxygen in rivers as described in claim 2, characterized in that, The heterotrophic respiration rate is obtained by subtracting autotrophic respiration from ecosystem respiration, as shown below: （4） It is the rate of heterotrophic respiration, i.e., the rate by which ER removes autotrophic respiration. A portion; AR as a certain proportion of GPP. Acquired.

4. The method for determining denitrification rate based on high-frequency monitoring of dissolved oxygen in rivers as described in claim 1, characterized in that, In step S13, based on the N2 concentration obtained from MIMS, the river denitrification rate is evaluated according to the N2 mass balance model, as shown in the following formula: （5） （6） in, yes t N2 concentration at time; It is the denitrification rate; It is the river depth; yes t The equilibrium concentration of N2 at the corresponding temperature and pressure at any given time; Is t Time through Schmidt number ,Depend on The calculated N2 gas exchange rate; It is the Schmidt constant of N2 at a specific temperature; the Schmidt constant of fresh water is a function of temperature. The posterior distribution is estimated based on the model in step 102, while the denitrification rate and gas exchange rate for each sample are based on Bayesian simulation analysis of Markov chain Monte Carlo.

5. The method for determining denitrification rate based on high-frequency monitoring of dissolved oxygen in rivers as described in claim 1, characterized in that, The time interval for collecting water samples shall not exceed 4 hours.

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