Geochemical prediction and early warning of ecological environment security

One of the main purposes of regional eco-geochemical evaluation is to predict the future development trend of the studied ecosystem, and to give an early warning of the possible ecological risks at present and in the future, so as to guide the scientific decision-making of the government and realize the sustainable development of human society. Due to the limitation of samples, the contents discussed in this section only provide a research idea and specific methods, and the results are limited for reference only.

First, the concept and research ideas

(A) Basic concepts

Prediction refers to the qualitative and quantitative analysis and speculation of the future situation of the system by using certain methods on the basis of understanding the changing law of the objective environment and investigation and research.

The so-called early warning is to give an early warning to remind people to pay attention to the impending unbalanced state of the system, to monitor, track and predict the development and change process of the research system, and to give an early warning to the problems in order to take timely control measures and measures to push the system environment to a new and sustainable structural state.

Evaluation, prediction and early warning are closely related and different. Evaluation is to judge the actual ecological security and evaluate the influence of various geochemical indicators; Prediction is a scientific speculation based on the established model, focusing on the evolution trend of each factor index; Early warning is an early warning of the degree of danger according to the requirements of human sustainable development on the ecological environment on the basis of prediction, focusing on the influence and consequences of the evolution trend and speed of key indicators on the ecological environment.

Judging from various domestic research results, the theory and method of evaluation work are relatively mature; Although there are many forecasting methods and models for reference, they are not mature enough in the fields of ecological environment and geochemistry, that is, their practicability and accuracy are not ideal, and many forecasting theories and methods are still under study or improvement. At present, geochemical early warning is still in the exploration stage, because the environmental problems involved are often extensive, special, complex and technical, and the theory and technical methods to solve such problems are in the initial stage.

(B) the overall research ideas

The ideas and steps of this eco-environmental safety prediction are as follows: ① Determine the prediction and early warning objectives, and accurately grasp the harmful factors that affect the system safety, such as soil pollution by heavy metals such as Cd, Cr and Hg, soil acidification, natural radioactive anomalies, fluoride in shallow groundwater exceeding the standard, and heavy metal elements in agricultural products exceeding the standard; (2) Establish an early warning standard and a warning judgment model to study and judge the current operation stage of the ecosystem; ③ Choose scientific prediction methods (qualitative or quantitative), judge the future development trend of the predicted objects, give scientific evaluation on the rationality of the prediction results, make suggestions and provide decision-making services.

Second, land eco-geochemical early warning

(a) Terrestrial eco-geochemical early warning

Take the ecological risk assessment area determined by existing standards or research results as the ecological geochemical early warning area. * * * is divided into four categories (Figure 5-34): ① Hg, Zn, Cd, Cu, Pb, as, Cr and Ni, which are classified into Class III and Super Class III soils according to Soil Environmental Quality Standard (GB1561995). (2) The area where the fluorine content of shallow groundwater is greater than1mg/L (Class IV and Class V water) is the early warning area of endemic fluorosis; (3) According to the standards of the second national soil survey, the areas where the soil obviously lacks nutrients such as nitrogen, potassium, boron and molybdenum are designated as early warning areas; ④ Take the hidden danger area of radioactive pollution of soil natural elements such as U, Th and K as the early warning area.

1.Hg-Cr-Pb and other local heavy metal elements pollute the high-risk prediction area.

The local high-risk prediction areas of heavy metal pollution are scattered, which can be divided into three areas (A 1 ~ A3), with a total area of about 4 124km2, accounting for 7.59% of the study area. A 1 Heavy Metal Warning Zone is distributed in Yantai City, where Cd, Ni and Cu mainly exceed the standard, and Hg, Cr and As exceed the standard in some areas, covering an area of about 2680km2. The early warning area is located in important metallogenic areas such as gold, silver, copper, lead, zinc and graphite. The distribution characteristics of elements in the surface layer and deep soil in the early warning area are obviously different, and the cause of pollution may be mainly related to the superposition of associated heavy metal elements produced by mineralization and human activities in the later period. A2 heavy metal early warning zone is located in Linqu-Yishui, which is caused by Cr and Ni exceeding the standard, with an area of 1284km2, which is consistent with the spatial scope of basalts and Mesozoic volcanic rocks in Linqu Group and related to weathering and pedogenesis of basalts and Mesozoic volcanic rocks. A3 heavy metal warning zone is located in Wendeng-Chengshanjiao, which is mainly caused by Cu, Ni and local Cd exceeding the standard, with an area of 160km2, which is related to Neoarchean diorite, Jurassic adamellite and Cretaceous intermediate-acid rock mass. In addition, early warning zones for heavy metals are also scattered in Rizhao, Qingdao and Jimo-Jiaozhou areas. These areas are often the location of Mesozoic volcanic rocks, which are caused by the pollution caused by human activities superimposed on high geological background.

Figure 5-34 Early Warning Map of Land Quality in Eastern Shandong

Heavy metal elements are highly toxic elements. For example, cadmium can cause pain, cardiovascular diseases and cancers (such as bone cancer, gastrointestinal cancer, rectal cancer, esophageal cancer and prostate cancer). Arsenic pollution can stimulate skin cancer, lung cancer, liver cancer, kidney cancer and bladder cancer, and also lead to high-risk diseases such as cardiovascular disease and glucose metabolism disorder. The pollution of heavy metals in soil directly pollutes vegetables and other foods. Finally, people eat food, so that carcinogenic toxic substances enter the human body. Therefore, attention should be paid to the high-risk areas of local heavy metal pollution, and it is suggested to establish a soil environmental monitoring network as soon as possible to prevent agricultural products from exceeding the standard and affecting human health.

2. Early warning area of endemic fluorosis

Two areas (B 1 ~ B2) were delineated, with a total area of 3033km2. Weifang north (B 1), the west is not closed, with an area of 668km2；; Gaomi-Changyi (B2) covers an area of 2,365 square kilometers. The fluorine content of groundwater in this area exceeds 65438 0 mg/L, and locally exceeds 2 mg/L. Due to various reasons, the drinking water problem of residents in high fluorine area has not been completely solved, which is the key area for the prevention and control of endemic fluorosis in Shandong Province. The influence of human economic activities on fluorine in shallow groundwater is weak, mainly due to the pollution caused by wastewater and sewage irrigation from industrial and mining enterprises in some areas or points; The research shows that the high fluorine shallow groundwater in this area mainly comes from the high fluorine strata of Laiyang Formation, Qingshan Formation and Wangshi Formation, and is concentrated in the water under the control of topography, evaporation power, loose sediments and groundwater depth.

3. The soil obviously lacks nutrients such as nitrogen, potassium, boron and molybdenum, and there is an acidification danger zone.

This study found that the contents of Mn, TFe2O3 and other nutrient elements in this area are unbalanced, and there is a lack of total N, total P, organic matter and beneficial trace elements B and Mo in a large area. People's traditional concept of fertilization attaches the most importance to nitrogen fertilizer, phosphorus fertilizer and organic fertilizer, which can be improved by fertilization, but people seldom pay attention to B and Mo in mineral fertilizers and trace fertilizers, which will affect the flowering and fruiting of crops and are important factors to determine crop yield. Both the total amount and effective amount of elements B and Mo in this area are lacking in a large area, and some areas are seriously lacking. The effective amount of soil elements is directly related to crops. According to the standard of the second national soil survey, the areas where the available forms of nitrogen, potassium, boron and molybdenum are deficient at the same time are taken as early warning areas to remind local farmers to pay attention to fertilization so as to change the phenomenon of crop element deficiency. A total of four early warning zones are designated, which are located in Junan-Linshu (C 1) with an area of1525km2; ; South of Jiaonan (C2), with an area of 281km2; ; Jimo city East (C3) covers an area of 850 square kilometers, and Weihai City and its surrounding areas (C4) cover a total area of 524 square kilometers.

4. Hidden danger areas of uranium, thorium and potassium natural radioactive pollution

Except Qingdao, the ground γ -ray spectrum measurement has not been carried out in other areas of the investigation area. Based on the content characteristics of radioactive elements U, th and k2o in soil, and according to the empirical relationship between the content values of the three elements and the radioactive γ value, it is converted into U equivalent (UE = U+0.43th+1.826kK2O, U, Th and K2O are the contents in soil respectively, and the unit of U and Th content is 65433.

According to the relationship between γ radiation dose rate and U-equivalent measured in Qingdao, the lower limit of U-equivalent anomaly 17.02× 10-6 (equivalent to the average value of U-equivalent content+1.67 times standard deviation) corresponds to γ radiation dose rate of about163.16. Taking the lower limit of U-equivalent anomaly as the representative, seven natural radioactive early warning zones of uranium, thorium and potassium were delineated, with a total area of 2 1, 4 1.2 km2, It is distributed in Linqu Yishui (D 1 area of 506.0km2), northern Junan County (D2 area of 578.3km2), northeastern Qingdao (D3 area of 64.8km2), northeastern Zhaoyuan (D4 area of 66.8km2) and northern Haiyang (D5 area). Only the No.2 early warning area in northern Junan County is composed of strata.

(2) Temporal and spatial variation and prediction of soil elements in northern Qingdao.

1. Feasibility analysis

In 2003, supported by the cooperation project between the Ministry of Land and Resources and Qingdao Municipal People's Government, Qingdao Institute of Marine Geology conducted soil sampling and analysis in the north of Qingdao. The sampling in this study (2007) was four years apart from the sampling in 2003, and the repeated sampling area was 2200km2, and the corresponding unit data was 553 groups. The sampling density, sampling method and inspection index are exactly the same. The samples are undertaken by the Testing Center of Institute of Geophysical and Geochemical Exploration, Chinese Academy of Geological Sciences. The analysis methods and quality monitoring requirements of the two samples are basically the same, and various monitoring methods such as standard samples, password samples and monitoring samples are adopted to ensure the reliability of the analysis quality. These two batches of data provide high-quality data for studying the temporal and spatial changes of regional soil geochemical environment.

Compare statistical characteristic values (median, average, correlation coefficient, etc.). ), and judge the change of soil element content in this area. Because the accumulation rate of soil elements is basically linear in the short term, we can use the accumulation rate of soil elements in the last four years to predict the change of soil element content in the next few years, and use the soil environmental quality standard (GB15618-1995) or other standards to make geochemical maps or evaluation maps with the same color band and isoline. Through comparison, we can find the soil.

2. Study on temporal and spatial changes of soil elements.

Table 5-8 shows that the accumulation trend of elements such as P, OrgC, Ba, La, Ag, B, W, Ga, Ge and Co in the soil of northern Qingdao is obvious during the four years from 2003 to 2007. The relative accumulation speed of heavy metal elements in soil is the fastest, and the content increased by 4% in four years, followed by Cr and Pb, indicating that the enrichment of heavy metal elements in soil in northern Qingdao is very obvious in recent four years, and the soil acidification (pH decline) is remarkable.

Correlation analysis shows (Table 5-8) that MgO, Tl, As, La, Sc, Y, Zr, Ce, Na2O, Nb, Fe2O3, Ni, Mn, Co, Cr, V, Sr, Ti, Be, Ba, Rb, K2O and other elements are significantly positively correlated between the two batches of data, and their scatter distribution is approximately linear. It shows that the pollution of industrial and agricultural production, transportation and living activities has little influence, and the element content has little change. The correlation coefficients of Sn, C, N, Bi, Hg, Ge, Cd, Au, Cl, Ag, OrgC, I, Ga and Pb are small, and the variation coefficients of Bi, Hg, Cd, Au, Cl, Ag and Pb are also large. It can be seen from the scatter distribution diagram that the correlation differences between Hg, Cd, N and OrgC are mainly in a few.

Table 5-8 Statistical Parameters of Soil Element Content in Northern Qingdao (2003-2007)

sequential

Note: The number of statistical samples is 554, and the contents of oxides, total carbon, organic carbon and N are in%, with Au in 10-9 and other elements in 10-6. PH is dimensionless, and the relative accumulation rate (%) = (C2007-C2003) × 65438.

Figure 5-35 Scatter Diagram of Mercury and Cadmium in Two Sampling Soils

3.3. Environmental quality prediction. Cadmium and mercury

In a short time, the accumulation rate of soil elements is basically linear, which is the basis for predicting the change of environmental quality of elements in soil at a certain time in the future. This time, only the environmental quality changes of Cd and Hg in soil in 20 15, 2020 and 2030 were predicted. Firstly, the predicted values of Cd and Hg of each sample unit (with an area of 4km2) in the topsoil in 20 15, 2020 and 2030 are calculated according to the formula (5-2), and then the predicted values are calculated according to the Soil Environmental Quality Standard (GB1518—18).

Study on agricultural eco-geochemistry in eastern Shandong Province

Where: △Ci is the annual average change of elements in four years, Ci2007 and Ci2003 are the measured content values of elements in 2007 and 2003 respectively, and Ci is the predicted content value after n years. This study takes n = 8,13,23.

As can be seen from Figure 5-36, with the passage of time, the area of super-II soil of Cd and Hg elements gradually increases. Especially Cd-II soil area increased obviously. 20 15, the area of Cd-II soil will appear locally. In 2020, the soil area of CD-II will gradually expand, and in 2030, the soil area of CD-II will gradually expand, resulting in "point source" inferior soil. According to statistics, the soil area of CD-II will increase by 382km2 from 2007 to 2030, with an average annual increase of 65,438km2. The predicted trend of mercury is slightly different from that of cadmium. Compared with 2007, the change of Hg was the biggest in 20 15, and the second or third type of Hg soil appeared. The area of super second-class soil is 35km2, accounting for 65438 0.59% of the study area. However, the forecast results did not change significantly in 2020 and 2030, and the distribution area basically did not change significantly. From the analysis of toxicity and ecological effects of heavy metals, we should pay attention to the prediction results of Cd and Hg.

Fig. 5-36 Prediction map of environmental quality of soil heavy metals Cd and Hg in northern Qingdao in the next 30 years.

A—Environmental quality map of soil cadmium in a—2007; B-20 15 soil Cd environmental quality prediction map; C—Prediction map of soil cadmium environmental quality in c—2020; D—Prediction map of soil cadmium environmental quality in d—2030; E—Environmental quality map of soil mercury in e—2007; F-20 15 soil mercury environmental quality prediction map; G—Prediction map of soil mercury environmental quality in g—2020; H—Prediction Map of Soil Mercury Environmental Quality in h—2030

Three. Early warning and prediction of regional ecological security

(A) early warning concept

1) There is a quantitative linear relationship model between As, Cd, Pb, Se in wheat seeds and the contents of corresponding elements in soil, and variables such as pH or OrgC (Table 5-5), which is the premise of regional ecological security early warning; Using the element (index) content obtained from multi-objective investigation to predict the element content in crop seeds growing on it, so as to realize the early warning of ecological environment safety in the whole region.

2) The early warning of regional ecological security mainly considers the safety of wheat, and adopts three-level early warning mode, namely alarm, safer and safer level. According to the content of heavy metal elements in wheat seeds and related standards, when the content of heavy metal elements in wheat seeds exceeds the hygienic limit standard, it can be "alarmed" and the map can be painted red, indicating that the pollution in this area has been serious and must be treated or re-planned; If the quality of wheat is higher than the safety standard of green food but lower than the hygienic limit standard, it can be considered that the area is at a safe level and the map can be painted yellow; If the seed quality is higher than the safety standard of green food, it can be considered that the area is at a high safety level and can be marked green on the map. If the standard limits of elements are consistent (such as Cd, Zn, Cu, Cr), the diagram is represented as two color areas, namely, red "alarm area" and green "safety area".

3) The hygienic limit standard of selenium in wheat seeds is 0.3× 10-6. Combined with Qin Jian 'an et al. (1989), the early warning limit of wheat was determined when studying the relationship between endemic diseases and environment. When the selenium content of wheat seeds is less than 0.04× 10-6, it is selenium-deficient wheat, and the picture is pink. Samples with contents between 0.04× 10-6 and 0.07× 10-6 are called selenium-enriched wheat, and the picture is yellow. Samples with seed contents between 0.07× 10-6 and 0.3× 10-6 are called selenium-enriched wheat, and the picture is green. The sample with seed content > 0.3× 10-6 is called out-of-gauge food, and the picture is dark red.

4) Through the analysis of the present situation, put forward the control scheme, predict and warn the ecological security after the control, and compare the effects before and after the control. For example, by improving the soil pH value, that is, changing the soil pH value, the change of ecological security in the study area was discussed.

(2) Early warning results of regional ecological security

It can be seen from Table 5-9 and Table 5- 10 that most of the wheat in the study area is safe at present. Except Cr, the safe areas of Hg, Pb, Cd, as, Cu and other elements in wheat seeds are all above 98%, and the safe areas of As and Cu are 100%.

Table 5-9 Early Warning Results of Ecological Security of Cadmium, Chromium, Copper and Zinc in Wheat in the Study Area

Table 5- 10 Early Warning Results of Wheat Ecological Security in Study Area

Most of the wheat seeds in the study area are safe, accounting for 97.33% of the whole area, the yellow area is about 2.33% safe, and only 0.34% of the wheat areas with red alarm exceeding the standard are scattered, which is related to the point source pollution of soil caused by human activities. The red warning zone of wheat seed Cd exceeding the standard is about 1.35%, which is mainly due to the high Cd content and low pH value in the soil, which leads to the increase of Cd absorption rate of wheat seeds. The red warning zone of wheat seed Cr exceeding the standard is about 7. 13%, which is the main factor affecting the comprehensive quality of wheat in this area. Previous studies have shown that the excessive chromium content in wheat seeds is the result of the comprehensive action of soil organic carbon, pH, CEC and other physical and chemical indicators, and the total chromium content is high.

The red warning zone of wheat seed mercury exceeding the standard is about 1.32%, which is mainly related to the excessive mercury content in soil caused by gold mines and mine pollution. The yellow safer area is mainly distributed in the periphery of the early warning area. The mercury content of wheat seeds is higher than the green standard and lower than the limited standard, and it is in a transitional area, so attention should be paid to prevention, as shown in Figure 5-37.

The prediction results of selenium content in wheat seeds show that the overall selenium content in wheat is low, with selenium deficiency and selenium deficiency accounting for 96.50%, of which wheat samples with selenium content less than 0.04× 10-6 account for 46.07%. The selenium content of wheat samples ranged from 0.04×10-6 to 0.07×10-6, accounting for 50.43%. Only 3.47% of the samples with selenium content of 0.07×10-6 ~ 0.3×10-6 are selenium-enriched, which is a good selenium-enriched wheat planting area. Only 0.03% of the areas with excessive selenium content in wheat have issued a red warning, which is mainly related to "point source" pollution, as shown in Figure 5-38.

Figure 5-37 Early Warning Diagram of Mercury Ecological Security in Regional Wheat

The "one-vote veto" method of seven elements, such As As, Hg, Pb, Cd, Cr, Cu and Zn, was used to comprehensively evaluate the current situation of wheat ecological security in the study area (Table 5-10; Figure 5-39), the results show that most of the wheat in the study area is safe, accounting for 90. 15% of the whole area, of which the safe area accounts for 86. 14% and the safer area accounts for 4.0 1%. About 9.85% of the red alert wheat areas exceed the standard, mainly in the west of the study area, while most areas in the middle and east of the study area can carry out large-scale agricultural product planting and the development of famous green food.

(3) Prediction and early warning of the future trend of regional ecological security

With the continuous improvement of industrialization and agricultural intensification, the pollution of heavy metal elements such as Cd and Cr in soil and soil acidification have become a major obstacle to the safe production of agricultural products. Previous studies have shown that the enrichment coefficients of Cd and Cr in wheat seeds are significantly correlated with pH value, and the functional relationship is as follows.

Study on agricultural eco-geochemistry in eastern Shandong Province

According to the measured soil pH value, cadmium and chromium contents, the estimated values of cadmium and chromium in wheat seeds can be obtained by the above formula. In order to highlight the change of wheat seed content caused by the change of soil pH value, the following changes have been made in the division of evaluation criteria for Cd and Cr elements in wheat seeds:

On the wheat Cd safety warning map, the Cd content of seeds is less than 0. 1× 10-6, which is green food safety, and is represented by green in the map. The Cd content of seeds is between 0.1×10-6 ~ 0.2×10-6, which is shown in yellow. The content of Cd in seeds is between 0.2×10-6 and 0.4×10-6, which exceeds the national food safety standard, but is lower than the international food standard, and is indicated by light red in the figure. The content of Cd in seeds is > 0.4× 10-6, which exceeds the international food standard, and is indicated in red in the figure.

Figure 5-38 Early Warning Map of Ecological Security of Selenium in Wheat in the Region

The content of Cr in seeds is less than 1.0× 10-6, which is green food safety, and is indicated by green in the figure. The Cr content of seeds is between1.0×10-6 ~1.5×10-6, which is indicated by yellow in the figure (warning zone). The Cr content of seeds is between1.5×10-6 ~ 2.0×10-6, which is indicated by light red in the figure (alarm area); The Cd content of seeds is more than 2.0× 10-6, which is more than twice the food hygiene limit. It is indicated in red in the figure (serious alarm).

1) Assuming that the content of heavy metal elements in soil remains unchanged, which is mainly affected by acidification factors such as acid precipitation, soil erosion and human activities, it is assumed that the soil pH will decrease by 0.2 unit, 0.5 unit, 0.7 unit and 1 unit after several years, and the ecological security of wheat in the whole region will be predicted.

2) Assuming that the content of heavy metal elements in soil remains unchanged, by increasing the pH value of acidic soil, it can be concluded that when the pH value of acidic soil increases by 0.2 unit, 0.5 unit, 0.7 unit and 1 unit, the ecological security of wheat in the whole region can be predicted.

From Table 5- 1 1 and Figure 5-40, it can be seen that after the soil pH value in the study area increased by 0.2 unit, the red warning zone and yellow warning zone of Cd element quickly changed to green safety zone, making the green safety zone of wheat Cd quality reach 100%. However, when the degree of soil acidification in the study area increases 1 pH, there will be a red alarm of 0.97%, which is more than three times the current red alarm area.

Figure 5-39 Early Warning Diagram of Wheat Comprehensive Ecological Security

Table 5- 1 1 Changes of early warning area of wheat seeds Cd and Cr when soil pH value changes in the study area (soil Cd and Cr contents remain unchanged)

Fig. 5-40 Early Warning of Regional Wheat Cadmium Ecological Security (pH Change)

A- regional wheat Cd ecological security map (pH decreased by 0.2 units) B- regional wheat Cd ecological security map (pH decreased by 0.5 units)

C- regional wheat Cd ecological security map (pH decreased by 0.7 units) D- regional wheat Cd ecological security map (pH decreased 1 unit)

Figure 5-4 1 shows the change table and trend diagram of Cr early warning area when the soil pH value changes in the study area. As can be seen from Figure 54 1, the wheat quality in the red warning area in the study area will change to the green safety area with the increase of soil pH, that is, the Cr green safety area of wheat can reach 99.09% when the soil pH increases by 0.7 units, which can greatly improve the deterioration trend of farmland ecological security, which is a necessary measure to improve the ecological security in the study area in the future.

Figure 5-4 1 Early Warning Trend of Wheat Chromium Ecological Security and Changes of Soil pH

Fourthly, the present situation and early warning of soil acid buffering capacity.

Soil acidification is a phenomenon that soil pH decreases under natural and man-made conditions. The natural process of soil acidification is very slow, but in recent decades, the process of soil acidification has been greatly accelerated due to human influence. There are two main human factors affecting soil acidification. One is that atmospheric environmental pollution leads to an increase in acid deposition, which accelerates soil acidification in areas affected by acid deposition. Another important factor is improper agricultural measures. These agricultural measures mainly include: ① planting leguminous crops and forage grass, improving the level of soil organic nitrogen through biological nitrogen fixation, and the mineralization, nitrification and subsequent leaching of organic nitrogen lead to soil acidification; (2) removing alkaline substances from soil by harvesting animal and plant products; ③ The application of chemical fertilizer, especially ammonium nitrogen fertilizer, is also an important reason for accelerating soil acidification.

(1) Establishment of soil acidification model based on base ion.

Soil acidification is related to the leaching of soil base ions. On the one hand, after acid precipitation is input into the topsoil, alkaline ions in the soil are mainly leached, which reduces the pH value of the soil and eventually leads to soil acidification; On the other hand, with the excessive application of nitrogen fertilizer, when hydrothermal conditions are suitable, it will be rapidly hydrolyzed and formed, and continue to be nitrated into ions, increasing the release of H+ ions and producing soil acidity. In addition, ions are easy to combine with base cations in soil, which will lead to the leaching of base cations in soil with the leaching of ions, while the reduction of base cations in soil will lead to soil acidification. In addition, crop harvesting can also reduce potassium, sodium, calcium and magnesium ions in the soil. Therefore, this study takes the correlation between the content of basic ions (basic elements) in soil and pH value as a model to predict soil acidification, and discusses the changing trend of soil pH value caused by the change of soil basic ions through the model.

Statistic the data of surface soil 13 674 samples in the whole region, and draw the relationship diagram between the sum of K, Ca, Na and Mg and soil pH after taking the average value of a certain content range (Figure 5-42). It can be clearly seen from Figure 5-42 that the relationship between soil pH and base ion content has the characteristics of piecewise function, which can be expressed by the following four linear equations. When solving the equation simultaneously, the intersections of (5.47, 5.89), (7. 13, 5.59) and (7.64, 5.79) can be obtained from left to right respectively.

Fig. 5-42 Relationship between main basic ion content and pH value in soil

1) Total amount of Y-based ions = 0.1372xph+5.1408, R=0.348, n = 31(pH ≤ 5.40);

2) Total amount of Y-based ions =-0. 1846 xph+6.9025, R=0.658, n = 81(5.40 < pH ≤ 7.10);

3) the total amount of Y-based ions = 0.3962 xph+2.76 14, R=0.608, n = 36 (7.10 < pH ≤ 7.80);

4) Total amount of Y-based ions = 1.2374 xph+3.6995, R=0.82 1, n = 27 (pH > 7.80).

As can be seen from Figure 5-42, when the soil pH value is greater than pH>7.64 and the soil is eroded by acidic substances, the pH value in the soil keeps a relatively small change by neutralizing a large number of metal ions. At this time, a large number of metal ions in the soil played a very obvious acid buffering role; However, when the soil pH is alkaline between 7. 13 ~ 7.64, the buffering ability of base ions to soil acidity decreases, the acid-base neutralization basically disappears, and the soil pH value decreases rapidly. Therefore, the area with soil pH value of 7. 13 ~ 7.64 is regarded as the early warning area of alkaline soil acidification. When the soil pH is between 5.47 and 7.13, the soil pH will increase with the loss of base ions. However, when the soil pH is less than 5.47 and it is acidic, a large number of base ions in the soil are leached due to the invasion of acidic substances. When the leached base ions are not supplemented, they lose the ability to buffer the acidity of the soil, and the soil begins to acidify rapidly, and the soil pH is 5.47.

(2) Early warning of soil acid buffering capacity in the study area

According to the geochemical model of soil acidification, the early warning standard is as follows:

The pH > 7.64 is defined as a high safety zone, which is represented by dark green, indicating that the soil in this area has strong acid buffering capacity and is a safety zone. The pH = 7. 13 ~ 7.64 is defined as the early warning zone of alkaline soil acidification, which is expressed in pink, indicating that the buffering capacity of soil is in the transition state from alkaline to acidic, and the buffering capacity of soil is weak, but if the pH value of soil is increased after treatment, the buffering capacity of acid will change rapidly. In the range of pH = 5.57 ~ 7. 13, the soil pH increased rapidly with the leaching of soil base ions, that is, when K+Ca+Na+Mg in the soil decreased from 5.89% to 5.59%, the soil pH increased rapidly from 5.47 to 7. 13, which indicated that the soil in this area also had strong acid buffer. The pH = 5.47 ~ 5.57 near the critical point of acidification of acidic soil is defined as a transitional warning zone, which is expressed in orange, indicating that the buffering capacity of soil is in a transitional state and close to the acidification explosion point. Once the environment deteriorates, it will cause an explosion, which requires high vigilance. The area with pH < 5.47 is defined as the early warning area of acid soil acidification, which is indicated in red, indicating that the soil basically loses its acid buffering capacity and needs to be alarmed. If we want to improve the acid buffering capacity, we must make great efforts to greatly improve the pH value of the soil. ..

As can be seen from Figure 5-43, nearly half of the soil in the study area has strong acid buffering capacity, but nearly 34.43% of the soil in the whole area has serious acidification problem, and the acid buffering capacity is not optimistic. The early warning area of alkaline soil acidification accounts for 13.84%, which is mainly distributed in the west of Weihe River and the east and south of Yantai City. Nearly 20.59% of the whole region is in the danger zone (acid soil early warning zone), which is distributed in the southern bedrock area, the south-central Yishu fault zone, the western part of Yantai City and most parts of Weihai. In these areas, it is urgent to increase the pH value to avoid the loss of acid buffering capacity due to acidification.

Figure 5-43 Early Warning Diagram of Acidic Buffering Capacity of Surface Soil