CN114175886A

CN114175886A - Method for increasing near-surface air temperature and shallow soil temperature of frozen soil region

Info

Publication number: CN114175886A
Application number: CN202111491353.2A
Authority: CN
Inventors: 陈继
Original assignee: Northwest Institute of Eco Environment and Resources of CAS
Current assignee: Northwest Institute of Eco Environment and Resources of CAS
Priority date: 2021-12-08
Filing date: 2021-12-08
Publication date: 2022-03-15

Abstract

The invention discloses a method for increasing the temperature of near-surface air and shallow soil in a frozen soil area, and relates to the field of cold area engineering and environment; the method comprises the following steps: and covering the tailings on the soil surface of the frozen soil area. The method can widen the sustainable development mode of green utilization of tailing resources, and can realize the temperature rise of the near-surface air and shallow soil in the frozen soil area so as to promote the growth of vegetation.

Description

Method for increasing near-surface air temperature and shallow soil temperature of frozen soil region

Technical Field

The invention relates to the field of cold region engineering and environment, in particular to a method for increasing the temperature of near-surface soil and shallow soil in a frozen soil region.

Background

The cold region generally refers to a frozen soil region, and comprises an instant frozen soil region, a short-time frozen soil region, a seasonal frozen soil region and a permafrost region (China frozen soil (Zhouyou et al, 2000) and frozen soil engineering geological survey specifications GB 50324. sup. one-year-old 2014), even if the former three regions are not considered, the area of the permafrost region in the world is close to 3000 kilometres square, and the area of the permafrost region in China is about 200 kilometres square. Forests, grasslands, deserts and lichens are distributed in the wide areas, but the climate in the areas is cold, the annual average temperature is generally below 0 ℃, the annual average temperature is low, the growing season is short, and the ecological environment is extremely fragile. Under the influence of global climate change, excessive grazing and other human activities, the vegetation coverage of the area is reduced, the desertification area is increased, the safe operation of the engineering of the area and the sustainable development of agriculture, forestry and animal husbandry are threatened, the carbon emission of the area is increased, and the difficulty in realizing the global carbon peak reaching and carbon neutralization targets is obviously increased.

Meanwhile, the total amount of tailings in the world is sharply increased due to the dramatic increase in the demand of human resources. Taking waste gangue in coal mining as an example, coal gangue in China is accumulated and stockpiled by more than 50 hundred million tons at present, and the coal gangue is continuously increased at the speed of 6 hundred million tons per year. A large amount of tailings not only occupy a large amount of land, but also bring pollution to atmosphere, soil and water, and simultaneously cause new geological disasters.

The existing research results show that the suitable near-surface temperature and soil temperature are the basic conditions for seed germination and plant growth in nature. The suitable temperature ranges for different plants are different, and for the same plant, exceeding or falling below the temperature range will inhibit the growth and even cause the death. In cold regions, low temperature and soil temperature lead to the reduction of photosynthesis and respiration of plants, the reduction of water absorption rate of root systems, the reduction of biochemical and non-biochemical processes in soil, and the reduction of soil fertility, which are main factors leading to the slow growth of plants. Therefore, in cold regions, the higher the near-surface temperature and the soil temperature, the faster the plant grows.

At present, the problems of low temperature and soil temperature and insufficient growth accumulated temperature generally exist in cold regions or cold seasons, and various researches for increasing the temperature of near-surface air and soil are developed at present for promoting the germination of seeds and the growth of vegetation, wherein the researches comprise a greenhouse method, a mulching film method, a chemical and biological heating agent method, a solar heat collection method, a ground source heat pump method and the like, and the researches are mainly used for planting high-value-added economic crops or early-maturing crops such as vegetables and fruits in out-of-season (winter) or cold regions in a small-range area. The temperature increasing method has the disadvantages of complex process, high construction and operation cost, large workload of later maintenance, plastic pollution (such as mulching films or plastic greenhouses) in some cases, and inapplicability to the requirements of large-scale ecological restoration and grain crop planting in cold regions, and the method has no precedent for applying the method to the ecological restoration and the large-scale agricultural planting in forest regions and grassland regions with wide areas at present. At present, the development of an economical soil improvement technology suitable for wide-range popularization for large-range ecological restoration and promotion of crop cold season in cold regions is urgently needed.

Disclosure of Invention

The invention aims to provide a method for increasing the temperature of the near-surface air and the shallow soil in the frozen soil area, which aims to solve the problems in the prior art.

In order to achieve the purpose, the invention provides the following scheme:

the invention provides a method for increasing the temperature of near-surface soil and shallow soil in a frozen soil area, which comprises the following steps: and covering the tailings on the soil surface of the frozen soil area.

Further, the tailings have an apparent reflectivity of no greater than 20% to solar radiation.

Further, the particle size of the tailings is 2 mm-10 cm.

Further, the coverage thickness of the tailings is 5 mm-10 cm.

Further, the coverage degree of the tailings covered soil is not less than 50%.

The invention discloses the following technical effects:

the invention not only realizes the daytime temperature increase of near-surface atmosphere and shallow soil in a small-range treatment area, but also can prolong the heat release time of the soil at night, slow down the rate of heat release from the soil after sunset to the atmosphere and increase the temperature of the shallow soil at night, and promote the germination of seeds and the growth of vegetation by advancing the green-turning period of the vegetation, accelerating the growth rate in summer and postponing the withering and yellow time before cold season on the basis of the daytime heat release rate of the soil in the small-range treatment area, the asymmetry of solar radiation heat absorption in the daytime and the radiation heat release at night and the weakening of convection heat transfer in a tailing stone layer.

The invention widens the current recycling mode of the tailings, can promote the green mining of mining industry and the development of circular economy, can realize the long-term sustainable utilization of resources, can realize the natural temperature rise of near-surface atmosphere and shallow soil while changing the tailings into valuables, has the advantages of mild temperature rise process, proper temperature rise amplitude, direct temperature rise effect, zero energy consumption and zero maintenance in the operation process, and is suitable for ecological restoration in large-scale cold areas or the promotion of the growth of field crops. The method adopted by the invention can realize the distributed direct utilization of solar energy resources, has high efficiency, zero energy consumption, no maintenance and low cost, and is expected to be used for ecological restoration in large-scale areas of cold regions.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.

FIG. 1 is a graph of the daily change in air temperature and precipitation during a field trial;

FIG. 2 is a schematic view showing a cross-sectional structure of soil according to example 1;

FIG. 3 is a comparison of soil temperature at 10cm and 20cm depths for a control site and a test site;

FIG. 4 is a comparison of the air temperature at a height of 2m near the surface of the ground in summer between the control site and the test site;

FIG. 5 shows the vegetation status of the control and test fields 38 days after the start of the test;

FIG. 6 shows the warming effect of the soil under different covering layer thicknesses of the gangue;

FIG. 7 is a graph showing the effect of convective cooling on temperature increase for different tailing sizes.

Detailed Description

Reference will now be made in detail to various exemplary embodiments of the invention, the detailed description should not be construed as limiting the invention but as a more detailed description of certain aspects, features and embodiments of the invention.

It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Further, for numerical ranges in this disclosure, it is understood that each intervening value, between the upper and lower limit of that range, is also specifically disclosed. Every smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in a stated range is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference herein for the purpose of disclosing and describing the methods and/or materials associated with the documents. In case of conflict with any incorporated document, the present specification will control.

It will be apparent to those skilled in the art that various modifications and variations can be made in the specific embodiments of the present disclosure without departing from the scope or spirit of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification. The description and examples are intended to be illustrative only.

As used herein, the terms "comprising," "including," "having," "containing," and the like are open-ended terms that mean including, but not limited to.

In order to realize the effect of remarkably increasing the temperature of near-surface and shallow soil and promoting ecological restoration, the direct total solar radiation value received by the natural surface of the earth in each year is not less than 4000 MJ/square meter in an area to be covered with dark or black tailing materials, the direct total solar radiation value received by vegetation in the growing period is not less than 2000 MJ/square meter, and the cumulative days of continuously not less than 0 ℃ in daily average temperature (average value in many years) in the year are not less than 90 days.

In the following examples, the coverage of the tailings covered soil is not less than 50%.

Example 1

The implementation time is as follows: 2021, 7/month 1 to 9/month 30.

The implementation place is as follows: the Qinghai-Tibet plateau cocoa West Lao ventral G109 region has a mileage of 3061, a north latitude of 34 degrees 51 ', an east longitude of 92 degrees 56', and an altitude of 4700 m.

Climate conditions: the invention mainly aims at cold regions such as permafrost regions and the like with insufficient positive accumulated temperature and difficult ecological restoration in the growing period. Starting from 6 months and 3 days, the average temperature of the test site is higher than zero 0 ℃ in continuous days; the average daily temperature was below 0 ℃ in the beginning of 10 months and 4 days. During the test period from 7 months and 1 day to 9 months and 30 days in 2021, the lowest instantaneous temperature is-4.3 ℃, the lowest daily average temperature is 0.41 ℃, the highest instantaneous temperature is 17.1 ℃, the highest daily average temperature is 10.1 ℃ and the maximum daily rainfall is 13.2 mm. The average air temperature during this period was 5.8 ℃, the accumulated temperature 529 ℃ was integrated, and the rainfall was integrated to 210mm (fig. 1).

Treating a tailing material: selecting waste deep-color or black gangue tailings (other deep-color/black metal or nonmetal tailings can also be used, and the apparent reflectivity to solar radiation cannot be more than 20%), crushing the gangue, selecting crushed materials with the particle size of 2 mm-4 cm after sorting, and sending the crushed materials to a test site for later use.

Construction of a test site: a field with flat terrain is selected in a test area, the length and the width of the field are all about 10 meters, one half of the field is used as a test field, the other half of the field is used as a control field without measures, and yellow silt is arranged on the shallow layer of the field.

In the beginning of 7 months, the test site is ploughed, and then a layer of sorted waste rock with the thickness of about 10cm is paved on the test site (figure 2). And then broadcasting plateau native grass seed ryegrass seeds on a test field and a control field paved with the gangue layer, broadcasting about 2000 g of grass seeds on a field with the square meter of 100, harrowing for 7-8 times by using harrows, wherein the length of the teeth of the harrows is about 7 cm, and the sowing depth of the grass seeds is about 2-5 cm. The grass seeds are not rained for a few days before being broadcast, the surface soil is dry, manual watering and film covering are carried out 3 days after the grass seeds are broadcast, and the film covering is removed after two weeks. No additional fertilization is carried out in the whole planting process. After the watering is finished until the growth season is finished, other manual treatment is not carried out on the field.

Sensor layout: in the process of building a test field, temperature sensors are respectively arranged at the depth of 10cm and 20cm below the surface layers of the central positions of the two fields, air temperature sensors are respectively arranged at the position 2m above the two fields, 1 rain gauge cylinder is arranged at the adjacent region of the field, and the air temperature sensors are arranged in a radiation-proof cover. The temperature sensor is produced in a key laboratory of frozen soil engineering country, the precision is +/-0.05 ℃, and the sensitivity is 0.01 ℃; the rain gauge adopts T-200B, the precision is 0.5 mm, and the sensitivity is 0.05 mm.

The data acquisition instrument is arranged: the data acquisition instrument is a CR3000 universal data acquisition instrument of Campbell company in America, the sampling frequency of the temperature probe is 1 time in 10 seconds, the storage frequency is 1 time in 30 minutes, and the temperature storage data is an average value of half an hour; the sampling and storing frequency of the rain gauge is 30 minutes, and the rain data is an accumulated value.

And (3) analyzing a temperature rise result: table 1 lists the instantaneous temperature extremes for 10cm soil temperature, 20cm soil temperature and 2m air temperature, daily average and integrated temperature data for different sites during the main growth period from 7 months 15 to 8 months 15 and the difference between the two sites. The temperature at the test site was higher than the control site except for the lowest instantaneous air temperature at 2m height. Compared with a control field, the temperature of the soil at different depths of the test field is basically higher by more than 3 ℃, the average temperature value at the height of 2 meters is basically higher by about 0.5 ℃, the accumulated temperature of the soil at different depths is higher by 100 ℃ per day, and the accumulated temperature of the air at the height of 2 meters is also higher by 16 ℃ per day.

TABLE 1 comparison of the Main temperature index of the control and test sites

Fig. 3 and 4 show the average half-hour-daily temperature change results during the main growth period of 7 months 15 to 8 months 15 at 10cm soil, 20cm soil and 2m near the surface of two test sites during the field test. At the same relative position, the temperature of the test site is higher than that of the control site at different times every day. Compared with a control field, the daily average temperature of 10cm soil, 20cm soil and 2m near the earth surface of the test field is higher by 3.4 ℃, 3.2 ℃ and 0.5 ℃, the average temperature difference in half an hour is respectively 2.7 ℃, 3.1 ℃ and 0.4 ℃, and the average temperature difference in half an hour is 4.6 ℃, 3.3 ℃ and 0.7 ℃ when the average temperature difference in half an hour is maximum.

Vegetation growth condition comparison: FIG. 5 shows that the vegetation is sparse in the control field without the gangue temperature increasing measure, the coverage is only about 10%, and the vegetation height is small. On the test field heated by black gangue, the vegetation coverage is nearly 90%, the leaf color is dark green, the stem leaves are stout, and the grassland productivity is far higher than that of a control field.

Experimental example 1

In order to realize the effect of effectively increasing the near-surface air temperature and the shallow soil temperature, the tailing material for covering the surface of the ground is dark or black tailing which has good solar radiation absorption and obvious temperature increasing effect. In this example, the tailing material has an apparent reflectivity of no greater than 10% to solar radiation. The apparent reflectivity is directly related to the solar warming effect, and the smaller the apparent reflectivity is, the more remarkable the radiation warming effect is. Considering that the apparent reflectance of conventional planting soil is generally 25 to 35%, in order to ensure the warming effect of the present measure, it should be ensured that the apparent reflectance of the cover layer to solar radiation is not more than 20% during the design period of use.

The minimum thickness of the tailing ore covering layer used by the invention can resist the influence of wind erosion and water erosion, and the influence of construction process, terrain and landform is properly considered, so as to basically cover the original natural earth surface and realize the long-term and high-efficiency absorption of solar radiation. Referring to the concept of ecology, the coverage (Cs) of the temporary tailing ore is equal to the proportion of the vertical projection area of the ground surface tailing stones, and the coverage of the tailing stones is not lower than 50%. The apparent reflectivity of the land surface soil is generally 10-35%, and the apparent reflectivity delta of the soil in the test area is assumed_{Soil for soil}30% of the reflectance of the tailings _{Stone (stone)}10%, when the ground tailing coverage (Cs) is 50%, the apparent reflectance δ of the ground surface becomes δ_{Soil for soil}×(1-Cs)+δ_{Stone (stone)}And the multiplied Cs is 20 percent, and meets the requirement that the apparent reflectivity is not more than 20 percent. To ensure this coverage requirement, the thinnest thickness is no less than 5 mm.

From the effect of radiation temperature increase, the maximum thickness of the tailing stone covering layer is obtained by the following method:

based on a finite element method, a one-dimensional model for calculating the soil temperature under the coal gangue layer is established, and the model is calibrated by using the measured data under the condition of 10cm coal gangue coverage. Based on the calibrated model, numerical simulation is carried out on the soil temperature at the shallow layer 10cm, 20cm, 30 cm, 40 cm and 50 cm under the coal gangue covering layer of 10cm, 20cm, 30 cm, 40 cm and 50 cm of the cacao west in the abdominal region of the Qinghai-Tibet plateau during the growing season from 7 months to 8 months. FIG. 6 is the effect of temperature increase under different thickness conditions of the gangue cover layer (the soil temperature at different depths under the gangue cover layer is subtracted by the ground temperature of the natural field). As can be seen from fig. 6, the temperature increasing effect on the underlying soil at different depths is not increased significantly with the increase of the thickness of the covering layer of the tailing stones from 10cm to 50 cm, and some temperature increases or even decreases. Thus, a smaller cover layer thickness is beneficial to the warming of the underlying soil from the standpoint of temperature considerations. Therefore, the thickness of the tailings covering layer is not more than 10 cm.

In order to realize the effect of obviously increasing the temperature of the near-surface soil and the shallow soil, the convection effect in the tailing rock mass layer is fully eliminated. In the research process, natural convection or forced convection is found to occur in the rock block layer when the temperature of the surface layer is lower than the temperature of the bottom of the rock block layer or under the action of near-surface wind. In permafrost regions, this convective action of the rock layer is often used to cool the frozen ground. In the invention, the convection effect in the tailing rock block layer limits the heating effect of the tailing rock block layer. In order to enhance the warming effect of the tailings cover layer, the existence of such convective cooling effect in the tailings cover layer must be avoided as much as possible. The literature, "Experimental study on flowing effect of particulate size on flowing effect of used-rock layer under closed and open tops" shows that the convective cooling effect is different in the rock layers with different particle sizes. Figure 7 lists the results of the test on different particle size rock coatings after the temperature at the bottom of the rock coating has stabilized over 8 cycles of temperature fluctuation. The test environment temperature is sine wave change, the wave amplitude is 15 ℃, and the average temperature is 0.5 ℃. The smallest average particle size tested was 8.3 cm and the largest was 27.1 cm. As can be seen from fig. 2, the convective cooling effect of the bulk layer increases with increasing particle size. At a particle size of 10.5 cm, the convective cooling effect of the tailing lump layer is substantially eliminated. Thus, the maximum particle size of the rock in the tailings overburden is 10 cm. The particle size of the tailing lump stones is less than 2mm, wind erosion is easy to occur, the ground surface is exposed, the temperature increase effect is weakened, and secondary disasters such as wind-blown sand and the like are easy to form, so the minimum particle size of the tailing lump stones is set to be 2 mm.

Comparative example 1

In the vicinity of the test site of example 1, a 10m × 5m site with a flat topography was selected, and the soil surface was covered with a light-colored stone having a particle size of 2mm to 4 cm (apparent reflectance for solar radiation: 30%) and a thickness of 10cm under the same conditions as in example 1, and the daily average temperature of 10cm, 20cm soil and 2m near the surface was counted over the period of 7 months 15 to 8 months 15, and the results are shown in table 2.

Comparative example 2

The difference is that the soil surface is covered with wheat straw with the covering thickness of 10cm, the daily average temperature of 10cm soil, 20cm soil and 2 meters near the surface is counted from 7 months 15 to 8 months 15, and the result is shown in table 2.

TABLE 2 comparison of the heating effects of the reference site and other comparison sites

The data presented in table 2 show that the experimental example 1 using coal gangue is significantly higher than the comparative example 1 using common rock block and the comparative example 2 using straw regardless of the average soil temperature per day of 10cm, the average soil temperature per day of 20cm or the near-surface air temperature at a height of 2 m.

The above-described embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the scope of the present invention, and various modifications and improvements of the technical solutions of the present invention can be made by those skilled in the art without departing from the spirit of the present invention, and the technical solutions of the present invention are within the scope of the present invention defined by the claims.

Claims

1. A method for increasing the temperature of near-surface air and shallow soil in a frozen soil area is characterized by comprising the following steps of: and covering the tailings on the soil surface of the frozen soil area.

2. The method for increasing the near-surface air temperature and the shallow soil temperature of the frozen soil region as claimed in claim 1, wherein the visible reflectivity of the tailings to solar radiation is not more than 20%.

3. The method for increasing the near-surface air temperature and the shallow soil temperature of the frozen soil region according to claim 1, wherein the particle size of the tailings is 2 mm-10 cm.

4. The method for increasing the near-surface air temperature and the shallow soil temperature of the frozen soil region according to claim 1, wherein the coverage thickness of the tailings is 5 mm-10 cm.

5. The method for increasing the near-surface air temperature and the shallow soil temperature of the frozen soil region according to claim 1, wherein the coverage degree of the tailings covered soil is not less than 50%.