In-situ determination device and method for soil or sediment denitrification in flooded environment

Abstract

An in-situ determination device and method for denitrification of soil or sediment in a flooded environment, belonging to the technical field of in-situ quantitative denitrification. The device includes a stainless-steel handle, an injection piston, a PVC cylinder, a stainless-steel cylinder, and a PE transparent bottle. The PVC cylinder and the stainless-steel cylinder are connected, and the PVC cylinder is arranged at the top of the stainless-steel cylinder. The stainless-steel handle is arranged on the outer side of the bottom of the PVC cylinder. The injection piston is movably connected inside the PVC cylinder. The PE transparent bottle is an annular body with an open top, a closed bottom, and a hollow interior, and the PE transparent bottle is sleeved on the outside of the PVC cylinder. The device of the present invention can establish a sealed environment in the field environment, avoiding the interference of N2 in the atmosphere, ensuring that the environmental conditions are consistent with the natural environment, sampling without damage by pressing the piston, without destroying the tank body, maintaining the sealed environment, and the water sample collection can be accurately measured, simple and accurate, and finally realizing the in-situ determination of the denitrification rate of soil or sediment in a flooded environment.

Description

Technical Field

[0001] The invention relates to the technical field of denitrification, and in particular to an in-situ determination device and method for soil or sediment denitrification in a flooded environment. Background Art

[0002] Denitrification can convert nitrate (NO3 - -N) is converted into N2 and returned to the atmospheric nitrogen reservoir, which is one of the main ways to remove active nitrogen under natural flooding environment. Under flooding conditions, the main product of denitrification is nitrogen (N2), accounting for more than 90% of the total product, and 78% of the atmospheric components are N2, resulting in a very high natural background concentration. For this reason, when measuring denitrification, strict sealing conditions are required to avoid the generation of bubbles to ensure that the sample is not disturbed by external N2, which has brought great difficulties to the quantitative determination of soil or sediment denitrification under flooding environment. Currently, most existing methods are to collect original soil columns and bring them back to the room for simulation cultivation, and a large amount of soil columns need to be collected in the field and transported back to the laboratory, which is a huge workload. In addition, during indoor simulation cultivation, the environmental conditions closely related to denitrification, such as temperature and dissolved oxygen, may deviate from those outdoors, resulting in indoor simulation experiments having certain limitations and being unable to truly represent the actual field conditions. Therefore, establishing an in-situ determination device and method for soil or sediment denitrification under flooding environment has important scientific significance for the study of soil or sediment denitrification under flooding environment. Summary of the invention

[0003] Technical problems solved: In view of the above technical problems, the present invention provides an in-situ determination device and method for denitrification of soil or sediment under a flooded environment, which can establish a sealed environment in the field environment, avoid the interference of N2 in the atmosphere, ensure that the environmental conditions are consistent with those in the natural environment, and non-destructively take samples by pressing the piston without destroying the tank body, so that the sealed environment can be maintained. The water sample collection can be accurately measured, which is simple and precise, and finally realizes the in-situ determination of the denitrification rate of soil or sediment under a flooded environment.

[0004] Technical solution: An in-situ determination device for denitrification of soil or sediment under flooded environment, the device comprises a stainless steel handle, an injection piston, a PVC cylinder, a stainless steel cylinder and a PE transparent bottle, the PVC cylinder and the stainless steel cylinder are both cylinders with openings at both ends and hollow inside, the PVC cylinder is a transparent cylinder, the outer surface of the PVC cylinder is provided with a scale, the PVC cylinder and the stainless steel cylinder are seamlessly connected and the PVC cylinder is arranged at the top of the stainless steel cylinder, the stainless steel handle is arranged outside the bottom of the PVC cylinder, and is used to insert and remove the stainless steel cylinder from the soil or sediment, the injection piston is movably connected to the inside of the PVC cylinder, the injection piston comprises a piston body, a PU tube and a valve switch, the head of the piston body is a rubber plug, the tail is a T-shaped push rod, and the outer diameter of the rubber plug is equal to the inner diameter of the PVC cylinder diameter, used to seal the PVC cylinder, the T-shaped push rod is used to pull the piston body, one end of the PU tube is arranged at the bottom center of the piston body, and the other end passes through and goes out of the center top of the piston body, the valve switch is arranged at the other end of the PU tube that passes through the center top of the piston body, the valve switch is used to collect water samples, and when sampling, the water outlet of the valve switch is connected to the headspace sampling bottle through a silicone tube. The valve switch is opened during sampling and kept closed at other times to ensure that the inside of the PVC cylinder is in a closed environment. The PE transparent bottle is an annular body with an open top, a closed bottom and a hollow inside. The PE transparent bottle sleeve is arranged on the outside of the PVC cylinder. When sampling, water samples can be injected into the ring to play a role of heat preservation and sealing, which can prevent the water sample in the PVC cylinder from forming bubbles on the PVC tube wall due to excessive air temperature, and can also play a sealing role.

[0005] Preferably, the PU tube has an outer diameter of 4 mm and an inner diameter of 3 mm.

[0006] Preferably, the inner diameter of the PVC cylinder is 70 mm.

[0007] Preferably, the inner diameter of the PE transparent bottle is 10 cm.

[0008] Preferably, the height of the PVC cylinder is not less than 30 cm.

[0009] The determination method based on the above-mentioned soil or sediment denitrification in-situ determination device under flooding environment comprises the following steps:

[0010] Step 1. Insert the bottom of the PVC cylinder and the stainless steel cylinder into the soil through the stainless steel handle of the in-situ determination device for denitrification of soil or sediment under flooding environment, and ensure that at the beginning of the experiment, the soil fits closely with the PVC cylinder and the stainless steel cylinder to form a strictly sealed environment;

[0011] Step 2. Before sampling, pull out the injection piston, fill the PVC cylinder with water sample, and then gently stir clockwise for 30 seconds with a glass rod to ensure that the water sample is uniform and does not disturb the soil or sediment. Open the valve switch and insert the piston vertically into the PVC cylinder to ensure that there are no bubbles at the bottom of the piston. Quickly close the valve switch and inject the same water sample as in the PVC cylinder into the upper part of the piston and the PE transparent plastic bottle;

[0012] Step 3. Let it stand for 4-6 hours so that the dissolved N2 in the in-situ determination device for denitrification of soil or sediment under flooding environment can be evenly mixed. When sampling starts, read the scale of the PVC cylinder first and record the volume V. Then connect the valve switch outlet with a silicone tube, open the valve, and press the injection piston by hand at the same time. The water in the PVC cylinder flows out through the PU tube in the center of the piston and finally enters the headspace sampling bottle through the silicone tube. When the water sample overflows more than 1.5 times the volume of the sampling bottle and overflows the silicone tube, quickly tighten the bottle cap to ensure that there are no bubbles in the bottle. Store the collected water sample at 4°C and determine the concentration C of dissolved N2 in the water. After completing the sample collection, close the valve switch and record the volume of the water sample discharged during sampling ΔV according to the scale marked on the outer wall of the PVC cylinder. After an interval of at least 2 hours, start the second sampling. The process is as above. Collect 4-5 samples continuously and the sampling is completed.

[0013] Step 4. The volume of water sample discharged each time is different. According to the change of volume, the concentration of dissolved N2 in the water measured by each sampling is calibrated. The following formula is used to calibrate the N2 concentration C I : In the formula, C I Indicates the dissolved N2 concentration of the water sample after calibration for the i-th sampling, μmol·L -1 ;

[0014] C i Indicates the dissolved N2 concentration of the water sample measured at the i-th sampling, μmol·L -1 ;

[0015] V i It represents the volume of water sample in the sampler at the time of sampling for the i-th time, mL;

[0016] k = n-1, n represents the number of sampling times;

[0017] V0 represents the volume of water sample in the sampler at the first sampling, mL;

[0018] ΔV represents the amount of water consumed per sampling, mL;

[0019] Step 5. Obtain the calibrated concentration and calculate the N2 emission flux using the following formula: Where F represents the N2 emission flux, mg·N·m -2 ·d-1 ;

[0020] Indicates the change in dissolved N2 concentration in the sampler, in μmol·L -1 ·h -1 ;

[0021] V represents the initial volume of the sampler, and A represents the bottom area of ​​the sampler, so is the sampler height, h / cm;

[0022] 24 means 24 hours / day;

[0023] 28 represents the molar mass of N2;

[0024] 10 represents the volume and area conversion unit [10 3 (L converted to m 3 )×10 -2 (cm to m conversion)].

[0025] Preferably, in step 1, the in-situ determination device for denitrification of soil or sediment under flooding environment is implanted into the soil through the bottom of the PVC cylinder and the stainless steel cylinder via the stainless steel handle at least 12 hours in advance.

[0026] Preferably, the water sample in step 2 is field water, river water or culture medium.

[0027] Preferably, in step three, the concentration C of soluble N2 in water is determined by a membrane injection mass spectrometer.

[0028] Beneficial effects: 1. The device of the present invention can establish a sealed environment in the field environment, avoiding the interference of N2 in the atmosphere, ensuring that the environmental conditions are consistent with the natural environment, and the sampling process does not need to destroy the soil, and the sealed environment can be maintained.

[0029] 2. The water sample collection method of the present invention is simple and accurate, and can realize the in-situ determination of the denitrification rate of soil or sediment in a flooded environment.

[0030] 3. The method of the present invention avoids the deviation between indoor simulation experiments and outdoor ones, and realizes the in-situ accurate quantification of denitrification rate of soil or sediment under flooding environment. Compared with the nitrate disappearance method, the method of the present invention shows that NO3 - -N recovery rate was 34.81%-37.01%. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a schematic diagram of the structure of the sampling device of the present invention;

[0032] Figure 2 This is a schematic diagram of the determination of the denitrification rate of Wuzhai soil in Example 2;

[0033] Figure 3 This is a graph showing the change of solubility N2 over time in Example 2;

[0034] Figure 4 This is a schematic diagram showing the increase of soluble N2 over time in Example 3;

[0035] Figure 5 For NO3 in Example 3 - - Schematic diagram of N decreasing over time.

[0036] The numbers in the figure represent the following: 1. Stainless steel handle; 2. Valve switch; 3. Injection piston; 4. PU tube; 5. PVC cylinder; 6. PE transparent bottle; 7. Stainless steel cylinder. DETAILED DESCRIPTION

[0037] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0038] Example 1

[0039] The water sample in this embodiment is river water.

[0040] An in-situ measurement device for soil or sediment denitrification in a flooded environment, see Figure 1The device includes a stainless steel handle 1, an injection piston 3, a PVC cylinder 5, a stainless steel cylinder 7 and a PE transparent bottle 6. The PVC cylinder 5 and the stainless steel cylinder 7 are both hollow cylinders with openings at both ends. The PVC cylinder 5 is a transparent cylinder. The outer surface of the PVC cylinder 5 is provided with scales. The PVC cylinder 5 and the stainless steel cylinder 7 are seamlessly connected and the PVC cylinder 5 is arranged at the top of the stainless steel cylinder 7. The stainless steel handle 1 is arranged on the outside of the bottom of the PVC cylinder 5 and is used to insert and remove the stainless steel cylinder 7 from the soil or sediment. The injection piston 3 is movably connected to the inside of the PVC cylinder 5. The injection piston 3 includes a piston body, a PU tube 4 and a valve switch 2. The head of the piston body is a rubber plug and the tail is a T-shaped push rod. The outer diameter of the rubber plug is equal to the inner diameter of the PVC cylinder 5, which is used to seal the PVC Cylinder 5, T-shaped push rod is used to pull the piston body, one end of the PU tube 4 is set at the bottom center of the piston body, and the other end penetrates and passes through the top center of the piston body. The valve switch 2 is set at the other end of the PU tube 4 that passes through the top center of the piston body. The valve switch 2 is used to collect water samples. When sampling, the water outlet of the valve switch 2 is connected to the headspace sampling bottle through a silicone tube. The valve switch is opened during sampling and kept closed at other times to ensure that the inside of the PVC cylinder 5 is in a closed environment. The PE transparent bottle 6 is an annular body with an open top, a closed bottom and a hollow inside. The PE transparent bottle 6 is sleeved on the outside of the PVC cylinder 5. When sampling, water samples can be injected into the annular ring to play a role of heat preservation and sealing, which can prevent the water sample in the PVC cylinder 5 from forming bubbles on the wall of the PVC cylinder 5 due to the high air temperature, and can also play a sealing role. The outer diameter of the PU tube is 4mm and the inner diameter is 3mm. The inner diameter of the PVC cylinder is 70mm. The inner diameter of the PE transparent bottle is 10cm. The height of the PVC cylinder is 50cm.

[0041] The determination method based on the above-mentioned soil or sediment denitrification in-situ determination device under flooding environment comprises the following steps:

[0042] Step 1. At least 12 hours in advance, the in-situ determination device for denitrification of soil or sediment under flooding environment is implanted into the soil through the stainless steel handle 1 to ensure that the soil, the PVC cylinder 5 and the stainless steel cylinder 7 are closely fitted to form a strictly sealed environment when the experiment starts;

[0043] Step 2. Before sampling, pull out the injection piston 3, fill the PVC cylinder 5 with water sample, and then gently stir clockwise for 30 seconds with a glass rod to ensure that the water sample is uniform and does not disturb the soil or sediment. Open the valve switch 2, insert the injection piston 3 vertically into the PVC cylinder 5, ensure that there are no bubbles at the bottom of the injection piston 3, quickly close the valve switch 2, and inject the same water sample as in the PVC cylinder 5 into the upper part of the injection piston 3 and the PE transparent bottle 6;

[0044] Step 3. Let it stand for 4-6 hours so that the dissolved N2 in the in-situ determination device for denitrification of soil or sediment under flooding environment can be evenly mixed. When sampling starts, first read the scale of the PVC cylinder 5 and record the volume V. Then connect the water outlet of the valve switch 2 with a silicone tube, open the valve switch 2, and press the injection piston 3 by hand at the same time. The water in the PVC cylinder 5 flows out through the PU tube 4 in the center of the injection piston 3, and finally enters the headspace sampling bottle through the silicone tube. When the water sample overflows more than 1.5 times the volume of the sampling bottle and overflows the silicone tube, quickly tighten the bottle cap to ensure that there are no bubbles in the bottle. Store the collected water sample at 4°C and determine the concentration C of dissolved N2 in the water by a membrane injection mass spectrometer. After completing the sample collection, close the valve switch 2, and record the volume of the water sample discharged during sampling ΔV according to the scale marked on the outer wall of the PVC cylinder 5. After an interval of at least 2 hours, start the second sampling. The process is as above. Collect 4-5 samples continuously and the sampling is completed.

[0045] Step 4. The volume of water sample discharged each time is different. According to the change of volume, the concentration of dissolved N2 in the water measured by each sampling is calibrated. The following formula is used to calibrate the N2 concentration C I : In the formula, C I Indicates the dissolved N2 concentration of the water sample after calibration for the i-th sampling, μmol·L -1 ;

[0046] C i Indicates the dissolved N2 concentration of the water sample measured at the i-th sampling, μmol·L -1 ;

[0047] Vi represents the volume of water sample in the sampler at the i-th sampling, mL;

[0048] k = n-1, n represents the number of sampling times;

[0049] V0 represents the volume of water sample in the sampler at the first sampling, mL;

[0050] ΔV represents the amount of water consumed per sampling, mL;

[0051] Step 5. Obtain the calibrated concentration and calculate the N2 emission flux using the following formula: Where F represents the N2 emission flux, mg·N·m -2 ·d -1 ;

[0052] Indicates the change in dissolved N2 concentration in the sampler, in μmol·L -1 ·h -1 ;

[0053] V represents the initial volume of the sampler, and A represents the bottom area of ​​the sampler, so is the sampler height, h / cm;

[0054] 24 means 24 hours / day;

[0055] 28 represents the molar mass of N2;

[0056] 10 represents the unit of volume and area conversion [10 3 (L to m conversion 3 )×10 -2 (cm to m conversion)].

[0057] Example 2

[0058] The same as Example 1, except that in this example, the denitrification rate of Wuzhai soil was measured using an in-situ measuring device, the water sample was field water, and NO3 - -N content: 5.6 mg·L -1 , see Figure 2 The in-situ measuring device was inserted into the rice field at a depth of 15 cm. After the PVC cylinder was filled with field water, the height was 15 cm. Sampling was performed according to step 3, and samples were collected at 0, 4, 8, 12, and 24 hours. After concentration calibration, the time was used as the horizontal axis and N2 was used as the vertical axis to obtain like Figure 3 As shown, a, b, and c represent three repetitions.

[0059] As shown in Table 1, there is a very good correlation between the increase in soluble N2 solubility and time, indicating that this method is effective.

[0060] Table 1 Correlation between soluble N2 and time

[0061]

[0062] The denitrification rate was calculated. As shown in Table 2, the denitrification rate of the unfertilized Wuzhai soil was 0.542-9.13 mg·N·m -2 ·day -1 , different sample time points have large spatial variability (CV = 25.3%);

[0063] Table 2 Denitrification rate of Wuzhai soil

[0064]

[0065] Example 3

[0066] As in Example 1, the denitrification rate of Wuzhai soil was measured using an in-situ measurement device and compared with the nitrate disappearance method.

[0067] The in-situ measuring device was inserted into the rice field at a depth of 15 cm, and the water sample containing nitrate was added to the in-situ measuring device.- -N concentration is 10 mg·L -1 The samples were collected according to the method described in Example 1 at 0, 4, 8, 12, and 24 hours, and the dissolved N2 concentration was determined by membrane inlet mass spectrometry (MIMS). The NO3 in the water samples was determined by spectrophotometer. - -N concentration, after concentration calibration, with time as the horizontal axis and concentration as the vertical axis, we get N2( Figure 4 ) and NO3 - -N( Figure 5 ) changes over time, Figure 4 and Figure 5 a, b, and c represent three repetitions.

[0068] Table 3 Comparison of the results of N2 direct determination method and nitrate disappearance method

[0069]

[0070] As shown in Table 3, the NO3 - -34.81%-37.01% of N was converted into N2.

Claims

1. A method for determining soil or sediment denitrification in situ determination under flooded environment, the device comprising a stainless steel handle, an injection piston, a PVC cylinder, a stainless steel cylinder and a PE transparent bottle, the PVC cylinder and the stainless steel cylinder are both cylinders with openings at both ends and hollow inside, the PVC cylinder is a transparent cylinder, the outer surface of the PVC cylinder is provided with scales, the PVC cylinder and the stainless steel cylinder are seamlessly connected and the PVC cylinder is arranged at the top of the stainless steel cylinder, the stainless steel handle is arranged outside the bottom of the PVC cylinder, and is used to insert and remove the stainless steel cylinder from the soil or sediment, the injection piston is movably connected to Inside the PVC cylinder, the injection piston includes a piston body, a PU tube and a valve switch. The head of the piston body is a rubber plug, and the tail is a T-shaped push rod. The outer diameter of the rubber plug is equal to the inner diameter of the PVC cylinder and is used to seal the PVC cylinder. The T-shaped push rod is used to pull the piston body. One end of the PU tube is arranged at the bottom center of the piston body, and the other end passes through and passes through the center top of the piston body. The valve switch is arranged at the other end of the PU tube passing through the center top of the piston body. The PE transparent bottle is an annular body with an open top, a closed bottom and a hollow interior. The PE transparent bottle sleeve is arranged on the outside of the PVC cylinder; it is characterized in that The following steps are involved: Step 1. Insert the bottom of the PVC cylinder and the stainless steel cylinder into the soil through the stainless steel handle of the in-situ determination device for denitrification of soil or sediment under flooding environment, and ensure that at the beginning of the experiment, the soil fits closely with the PVC cylinder and the stainless steel cylinder to form a strictly sealed environment; Step 2. Before sampling, pull out the injection piston, fill the PVC cylinder with water sample, and then gently stir clockwise for 30 seconds with a glass rod to ensure that the water sample is uniform and does not disturb the soil or sediment. Open the valve switch and insert the piston vertically into the PVC cylinder to ensure that there are no bubbles at the bottom of the piston. Quickly close the valve switch and inject the same water sample as in the PVC cylinder into the upper part of the piston and the PE transparent plastic bottle; Step 3. Let it stand for 4-6 hours so that the dissolved N2 in the in-situ determination device for denitrification of soil or sediment under flooding environment can be evenly mixed. When sampling starts, read the scale of the PVC cylinder first and record the volume V. Then connect the valve switch outlet with a silicone tube, open the valve, and press the injection piston by hand at the same time. The water in the PVC cylinder flows out through the PU tube in the center of the piston and finally enters the headspace sampling bottle through the silicone tube. When the water sample overflows more than 1.5 times the volume of the sampling bottle, gently pull out the silicone tube, quickly tighten the bottle cap to ensure that there are no bubbles in the bottle, store the collected water sample at 4℃ and determine the concentration C of dissolved N2 in the water. After completing the sample collection, close the valve switch and record the volume of the water sample discharged during sampling ΔV according to the scale marked on the outer wall of the PVC cylinder. After an interval of at least 2 hours, start the second sampling. The process is as above. Collect 4-5 samples continuously and the sampling is completed. Step 4. The volume of water sample discharged each time is different. According to the change of volume, the concentration of dissolved N2 in the water measured by each sampling is calibrated. The following formula is used to calibrate the N2 concentration C I : In the formula, C I Indicates the dissolved N2 concentration of the water sample after calibration for the i-th sampling, μmol·L -1 ; C i Indicates the dissolved N2 concentration of the water sample measured at the i-th sampling, μmol·L -1 ; V i It represents the volume of water sample in the sampler at the time of sampling for the i-th time, mL; k = n-1, n represents the number of sampling times; V0 represents the volume of water sample in the sampler at the first sampling, mL; ΔV represents the amount of water consumed per sampling, mL; Step 5. Obtain the calibrated concentration and calculate the N2 emission flux using the following formula: Where F represents the N2 emission flux, mg·N·m -2 ·d -1 ; Indicates the change in dissolved N2 concentration in the sampler, in μmol·L -1 ·h -1 ; V represents the initial volume of the sampler, and A represents the bottom area of ​​the sampler, so is the sampler height, h / cm; 24 means 24 hours / day; 28 represents the molar mass of N2; 10 represents the unit of volume and area conversion [10 3 (L to m conversion 3 )×10 -2 (cm to m conversion)].

2. The method for measuring denitrification in situ of soil or sediment under flooding environment according to claim 1, characterized in that: In the step 1, at least 12 hours in advance, the in-situ determination device for denitrification of soil or sediment under flooding environment is implanted into the soil through the bottom of the PVC cylinder and the stainless steel cylinder through the stainless steel handle.

3. The method for measuring denitrification in situ of soil or sediment under flooding environment according to claim 1, characterized in that: The water sample in step 2 is field water, river water or culture medium.

4. The method for measuring denitrification in situ of soil or sediment under flooding environment according to claim 1, characterized in that: In the step three, the concentration C of soluble N2 in water is measured by membrane injection mass spectrometer.

5. The method for measuring denitrification in situ of soil or sediment under flooding environment according to claim 1, characterized in that: The outer diameter of the PU tube is 4 mm, and the inner diameter is 3 mm.

6. The method for measuring denitrification in situ of soil or sediment under flooding environment according to claim 1, characterized in that: The inner diameter of the PVC cylinder is 70 mm.

7. The method for measuring denitrification in situ of soil or sediment under flooding environment according to claim 1, characterized in that: The inner diameter of the PE transparent bottle is 10 cm.

8. The method for measuring denitrification in situ of soil or sediment under flooding environment according to claim 1, characterized in that: The height of the PVC cylinder is not less than 30 cm.

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