Prediction method for dissolved oxygen exchange flux of water body sediment-overlying water interface

Abstract

The invention provides a water body sediment-overlying water interface dissolved oxygen exchange flux prediction method, and belongs to the technical field of water ecological environment, and the method comprises the following steps: monitoring a target water body, and collecting sediment samples and environmental data information; the method comprises the following steps: simulating an oxygen consumption culture process of sediment isolated air through a laboratory, constructing a target water body-sediment oxygen consumption rate model, and obtaining oxygen consumption kinetic parameters; according to the oxygen consumption kinetic parameters, establishing a dissolved oxygen exchange flux prediction model of the water body sediment and the overlying water interface; and utilizing the dissolved oxygen exchange flux prediction model to predict the dissolved oxygen exchange flux of the water body sediment and the overlying water interface under different sediment suspension and dissolved oxygen content conditions. By means of the method, the exchange flux of the sediment-overlying water interface of dissolved oxygen under various conditions is predicted, the influence of oxygen-consuming substances released by the sediment on water environment oxygen deficit under the conditions is better evaluated, and theoretical and method guidance is provided for preventing and improving water body oxygen deficit.

Description

Technical Field

[0001] The present invention relates to the technical field of water ecological environment, and particularly relates to a method for predicting the dissolved oxygen exchange flux at the water-sediment overlying water interface. Background Art

[0002] Dissolved oxygen is one of the important indicators for evaluating the water environment quality, which can effectively reflect the water quality changes in the water environment in a timely manner and has an important impact on aquatic organisms and the aquatic environment. Water sediment plays a complex and crucial role in the water ecological environment, participating in the cycle of substances in the water body, absorbing and storing pollutants to reduce their concentration in the water, but it can also release pollutants under specific conditions, causing secondary pollution. The exchange flux of dissolved oxygen at the water-sediment overlying water interface refers to the amount of dissolved oxygen consumed by the oxidation of oxygen-consuming substances such as organic matter and reducing inorganic salts in the bottom sediment by biological and abiotic means. In water ecological systems such as rivers, lakes, and reservoirs, the oxygen-consuming substances released by sediment resuspension account for a large proportion, even up to more than 50% of the total amount of oxygen-consuming substances in the water body. Therefore, accurately evaluating and predicting the exchange flux of dissolved oxygen at the water-sediment overlying water interface is of great significance for studying and evaluating the dynamic changes of dissolved oxygen in the water body, material cycle, and ecosystem function.

[0003] With global climate change, extreme weather events occur frequently. Events such as heavy rain and floods cause significant changes in river hydrodynamics, easily leading to a large amount of sediment suspension, resulting in a sharp change in the exchange flux of dissolved oxygen at the water-sediment overlying water interface (WSI), and causing sudden hypoxia in the water body. At the same time, in the coastal plain water network, due to the phenomenon of tidal saltwater intrusion and the widespread use of sluice gates for water control. When the sluice gates are opened, water flow is generated, causing sediment resuspension, which will also cause changes in the dissolved oxygen flux at the WSI interface and lead to hypoxia in local river sections. Therefore, it is necessary to predict the dissolved oxygen exchange flux at the WSI interface under specific sediment suspension conditions. Traditional observation methods (such as the bottom incubator method) evaluate the oxygen exchange flux at the WSI interface by enclosing the sediment and its overlying water and analyzing the change law of dissolved oxygen over time. The sediment is mostly in a static state, but the complex hydrodynamic conditions in the real water environment will inevitably cause resuspension of the surface sediment, so there is a possibility of underestimation. In recent years, the eddy covariance method has also been applied to the evaluation of the dissolved oxygen exchange flux at the WSI interface, which can evaluate the dissolved oxygen exchange flux at the WSI interface under different horizontal flow velocity conditions, but the simulated horizontal flow velocity is relatively low (<10 cm / s), and it cannot simulate the exchange flux of dissolved oxygen at the WSI interface under the condition of high sediment suspension caused by strong turbulence (such as the average vertical flow velocity is not zero). To solve the problem of predicting the exchange flux of dissolved oxygen at the WSI interface caused by the oxygen-consuming substances released from the sediment in this situation, it is urgent to develop a method that can accurately predict the exchange flux of dissolved oxygen at the WSI interface under various situations. Summary of the Invention

[0004] The object of the present invention is to provide a method capable of efficiently and accurately predicting the dissolved oxygen exchange flux at the WSI interface under different sediment suspension states and overlying water dissolved oxygen contents.

[0005] To achieve the above object, the present invention proposes a method for predicting the dissolved oxygen exchange flux at the water-sediment overlying water interface, comprising the following steps:

[0006] S1: Monitor the environmental data of the target water body, and collect sediment samples and environmental data information;

[0007] S2: Simulate the oxygen-consuming culture process of the sediment isolated from air in the laboratory, measure the dissolved oxygen concentration in the overlying water at different culture times, thereby construct the sediment oxygen-consuming rate model of the target water body, and obtain the oxygen-consuming kinetic constant k through regression calculation;

[0008] S3: Establish a prediction model for the dissolved oxygen exchange flux at the water-sediment and overlying water interface according to the oxygen-consuming kinetic constant k;

[0009] S4: Use the prediction model to predict the dissolved oxygen exchange flux at the water-sediment and overlying water interface under different sediment suspension and dissolved oxygen content conditions.

[0010] Further, the environmental data information includes the dissolved oxygen concentration C in the overlying water DO,w , the overlying water temperature T, the water depth h w , the bulk density ρ of the surface sediment s , the content C of the oxygen-consuming substances that can be released in the surface sediment OD,s and the suspended particle content C ss .

[0011] Further, in step S2, the expression of the sediment aerobic rate model is:

[0012]

[0013] wherein, C DO,0 is the initial dissolved oxygen concentration in the overlying water during the oxygen-consuming culture of the sediment at temperature T; C DO,t is the dissolved oxygen concentration in the overlying water after the sediment oxygen-consuming culture for time t; a is the dissolved oxygen concentration in the overlying water when the sediment oxygen-consuming culture reaches stability, and k is the kinetic constant of the sediment oxygen-consuming process to be obtained.

[0014] Further, the stable dissolved oxygen concentration a is the dissolved oxygen concentration in the overlying water when the sediment oxygen-consuming culture reaches stability, and is also defined as the stable value when the dissolved oxygen concentration no longer changes significantly during the oxygen-consuming culture process, and is determined through experiments.

[0015] Further, in step S3, the expression of the dissolved oxygen exchange flux prediction model is as follows:

[0016] Flux DO@SWI =-k×C DO,w ×C OD,s ×ρ s ×h s

[0017] In the formula, Flux DO@SWI is the dissolved oxygen exchange flux at the water-sediment overlying water interface (mg m -2 day -1 ), k is the kinetic constant of the sediment oxygen consumption process obtained in step S2 (L day -1 mg -1 ), h s is the equivalent stacking thickness of suspended sediment (m), C DO,w is the dissolved oxygen concentration in the target water body (mg L -1 ); C OD,s is the content of oxygen-consuming substances that can be released in the water sediment (mg g -1 ); ρ s is the bulk density of the water sediment (g m -3 )

[0018] Further, the equivalent stacking thickness h s of the suspended sediment is obtained by on-site measurement or estimated by the following estimation formula:

[0019]

[0020] where C ss is the suspended particle content in the overlying water; h w is the water depth; ρ s is the bulk density of the water sediment, w is the sediment resuspension contribution coefficient, which is mainly affected by the water flow velocity, and its value range is 50%-100%. The lower limit is taken at low water flow velocity (<0.1 m / s), and the upper limit is taken when the water flow velocity exceeds 1 m / s.

[0021] Further, in step S2, the experimental conditions of the oxygen consumption culture process include: the sediment suspension state is maintained by mechanical stirring; the water temperature is controlled within the range of the actual temperature of the target water body ±1°C; the determination threshold of the dissolved oxygen concentration change is no more than 0.1 mg / L per hour.

[0022] Compared with the prior art, the advantages of the present invention are as follows:

[0023] 1. Compared with the traditional eddy covariance method which is only applicable to low flow velocity conditions, the present invention adopts a numerical method to calculate the dissolved oxygen exchange flux at the water-sediment interface. By artificially simulating the oxygen consumption process of the target water sediment in the laboratory, the oxygen consumption kinetic constant is obtained, and then a prediction model for the dissolved oxygen exchange flux at the WSI interface is constructed. Under different prediction scenarios, according to the release amount of sediment resuspension or the content of suspended solids in water and the dissolved oxygen concentration in the overlying water, the exchange flux is predicted, establishing a close connection between the oxygen-consuming substances in the sediment and the dissolved oxygen in the water body. It can not only reflect the scientificity and rationality of the quantification process, effectively improve the speed and accuracy of the quantitative assessment of the dissolved oxygen exchange flux at the water-sediment interface, but also accurately predict the dissolved oxygen exchange flux at the WSI interface under different sediment suspension states and overlying water dissolved oxygen contents, facilitating a better assessment of the impact of sediment-released oxygen-consuming substances on water environment hypoxia in this situation, breaking through the technical bottleneck of predicting the dissolved oxygen WSI interface exchange flux under high sediment suspension in a strong turbulence environment, solving the problem of underestimating the release of oxygen-consuming substances by traditional methods, and providing a more accurate tool for water environment risk assessment.

[0024] 2. By simulating the suspension state in the laboratory and combining with the kinetic model, the present invention can accurately predict the dissolved oxygen exchange flux at the sediment-water interface under dynamic conditions, significantly improving the applicability and reliability of the prediction.

[0025] 3. Through the oxygen consumption culture experiment with air isolation in the laboratory, a rate model based on the oxygen consumption kinetic constant is established, and key parameters such as the equivalent thickness of suspended sediment and the resuspension contribution coefficient are introduced to quantify the dynamic relationship between the oxygen-consuming substances in the sediment and the dissolved oxygen in the water body. The model calibrates the parameters through regression analysis to ensure scientificity and reproducibility.

[0026] 4. In the process of constructing the prediction model, the present invention integrates actual environmental parameters such as the dissolved oxygen concentration in the overlying water, temperature, water depth, suspended particle content, and sediment bulk density, comprehensively reflecting the complex influences of hydrodynamic conditions, sediment characteristics, and environmental factors, making the prediction results closer to the complex real scenario.

[0027] 5. Through numerical modeling and localization of environmental parameters, the present invention significantly improves the prediction efficiency, is applicable to different water body types (rivers, lakes, reservoirs, etc.) and various scenario simulations (such as large changes in sediment suspension amount, fluctuations in dissolved oxygen concentration, etc.), and has a wide application range. At the same time, the case verification of the present invention shows that the prediction results of the prediction model under different conditions are consistent (such as the flux linearly increasing with the increase in suspension amount), verifying the robustness of the method of the present invention. Description of the Drawings

[0028] Figure 1Schematic flow chart of the prediction method for the dissolved oxygen exchange flux at the water-sediment overlying water interface proposed by the present invention. Detailed implementation manners

[0029] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be further described below.

[0030] For different sediment suspension conditions (such as the release of aerobic substances in sediments caused by the opening of the dam sluice for water discharge or the release of aerobic substances in sediments during a rainstorm), in this embodiment, taking a coastal sluice section of a certain river in the lower reaches of the Yangtze River as an example, a prediction method for the dissolved oxygen exchange flux at the water-sediment overlying water interface is proposed. As Figure 1 shown, the method includes the following steps:

[0031] S1: Monitor the environmental data of the target water body, and collect sediment samples and environmental data;

[0032] In this embodiment, the target water body is a coastal sluice section of a certain river in the lower reaches of the Yangtze River. Monitor the coastal sluice section of a certain river in the lower reaches of the Yangtze River, collect surface sediment samples (<5 cm), and measure the dissolved oxygen concentration (C DO,w = 8 mg / L) in the overlying water, the overlying water temperature (T = 32 °C), the water depth (h w = 1.4 m), the bulk density of the surface sediment (ρ s = 2.21×10 6 g / m 3 ), the content of oxygen-consuming substances that can be released in the surface sediment (C OD,s = 0.067 mg / g), and the content of suspended particles in the overlying water (C ss = 850 g / m 3 ).

[0033] S2: Construct and train the sediment oxygen consumption rate model of the target water body, and obtain the oxygen consumption kinetic constant k through regression calculation;

[0034] In this embodiment, 10 g, 25 g, and 50 g of surface sediment are respectively weighed and placed in glass bottles containing 1 L of oxygen-rich water (the bottom area is about 64 cm 2 , and the water depth is about 16 cm). Control the water temperature at 32 ± 1 °C, mechanically stir to keep the sediment in a suspended state, isolate the air and start the oxygen consumption culture process, record the change of the dissolved oxygen concentration in the overlying water with time until the change of the dissolved oxygen concentration is less than 0.1 mg / L. Through the following expression 1, construct the sediment oxygen consumption rate model and train it. After training, use the least squares method for regression calculation to obtain the average value of the oxygen consumption kinetic constant k = -3.45 L / (mg·day);

[0035]

[0036] S3: Establish a prediction model for the dissolved oxygen exchange flux at the water - sediment interface of the water body. The expression of this model is:

[0037] Flux DO@SWI =-k×C DO,w ×C OD,s ×ρ s ×h s

[0038] In the formula, Flux DO@SWI is the dissolved oxygen exchange flux at the water - sediment interface of the water body, and h s is the equivalent stacking thickness of suspended sediments;

[0039] The specific prediction model for the dissolved oxygen exchange flux in this embodiment is:

[0040] Flux DO@SWI =3.45 (L / (mg·day))×C DO,w (mg / L)×0.067 (mg / g)×(2.21×10 6 )(g / m 3 )×h s (m);

[0041] Among them, the equivalent stacking thickness of suspended sediments

[0042] S4: Predict the dissolved oxygen exchange flux at the water - sediment interface of the water body under different environmental conditions:

[0043] In this embodiment, for the given conditions of sediment suspension amount and dissolved oxygen content, predict the dissolved oxygen exchange flux at the water - sediment interface of the water body. The prediction results are shown in Table 1 below:

[0044] Table 1

[0045]

[0046] Through the method of this embodiment, the efficient and accurate prediction of the dissolved oxygen exchange flux at the water - sediment interface of the water body under different environmental conditions is successfully realized.

[0047] The above is only the preferred embodiment of the present invention and does not impose any limitation on the present invention. Any person skilled in the art within the technical field, without departing from the technical solution of the present invention, makes any form of equivalent substitution or modification and other changes to the technical solution and technical content disclosed by the present invention, which are still within the content of the technical solution of the present invention and still fall within the protection scope of the present invention.

Claims

1. A prediction method for the dissolved oxygen exchange flux at the water-sediment overlying water interface, characterized in that It includes the following steps: S1: Monitor the environmental data of the target water body, and collect sediment samples and environmental data information; S2: Simulate the oxygen-consuming culture process of the sediment isolated from air in the laboratory, measure the dissolved oxygen concentration in the overlying water at different culture times, thereby construct the sediment oxygen-consuming rate model of the target water body, and obtain the oxygen-consuming kinetic constant k through regression calculation; S3: Establish a prediction model for the dissolved oxygen exchange flux at the interface between the water body sediment and the overlying water according to the oxygen-consuming kinetic constant k; S4: Use the prediction model to predict the dissolved oxygen exchange flux at the interface between the water body sediment and the overlying water under different sediment suspension and dissolved oxygen content conditions.

2. The prediction method for the dissolved oxygen exchange flux at the water sediment-overlying water interface according to claim 1, wherein The environmental data information includes the dissolved oxygen concentration C in the overlying water DO,w , the overlying water temperature T, the water depth h w , the bulk density ρ of the surface sediment s , the content C of oxygen-consuming substances that can be released in the surface sediment OD,s and the content C of suspended particles ss .

3. The prediction method of the dissolved oxygen exchange flux at the water sediment-overlying water interface according to claim 1, characterized in that In step S2, the expression of the sediment oxygen-consuming rate model is: Among them, C DO,0 is the initial concentration of dissolved oxygen in the overlying water; C DO,t is the dissolved oxygen concentration after time t; a is the stable concentration of dissolved oxygen, and k is the kinetic constant of the oxygen consumption process.

4. The prediction method for the dissolved oxygen exchange flux at the water sediment-overlying water interface according to claim 2, characterized in that, The stable dissolved oxygen concentration a is the dissolved oxygen concentration in the overlying water when the oxygen consumption of the sediment culture reaches stability, which is determined by experiments.

5. The prediction method for the dissolved oxygen exchange flux at the water sediment-overlying water interface according to claim 1, characterized in that, In step S3, the expression of the dissolved oxygen exchange flux prediction model is: Flux DO@SWI =-k×C DO,w ×C OD,s ×ρ s ×h s where Flux DO@SWI is the dissolved oxygen exchange flux at the water-sediment interface, h s is the equivalent accumulated thickness of suspended sediment, k is the kinetic constant of the sediment oxygen consumption process, C DO,w is the dissolved oxygen concentration in the target water body; C OD,s is the content of oxygen-consuming substances that can be released in the water sediment; ρ s is the bulk density of the water sediment.

6. The prediction method of the dissolved oxygen exchange flux at the water sediment-overlying water interface according to claim 5, wherein The equivalent accumulated thickness h of the suspended sediment s is obtained through on-site measurement or estimated by the following estimation formula: Among them, C ss is the content of suspended particles in the overlying water; h w is the water depth; ρ s is the bulk density of the water body sediment, and w is the contribution coefficient of sediment resuspension.

7. The prediction method of the dissolved oxygen exchange flux at the water-sediment overlying water interface according to claim 1, wherein In step S2, the experimental conditions of the oxygen-consuming culture process include: the sediment suspension state is maintained by mechanical stirring; the water temperature is controlled within the range of the actual temperature of the target water body ±1°C; the determination threshold of the change in dissolved oxygen concentration is not more than 0.1 mg / L per hour.

Images