Xiaoqing River originates from various springs in Jinan, starts from Mulizhuang in the west and flows into Laizhou Bay in the east, with a total length of 237 km and a drainage area of 10 336 km2. Xiaoqing River Basin is an important economic development zone in Shandong Province, with Zibo, an important industrial town, Guangrao and Shengli oil fields, emerging industrial cities, complete industrial categories and scattered township enterprises. There are many kinds of crops, not only wheat, corn and cotton, but also the well-known Yellow River, Mingshui rice, Zhangqiu green onion and Shouguang vegetables. Huantai, the first grain-producing county in the north, is located in the south-central part of the work area. However, since 1970s, with the rapid development of cities and industrial and mining enterprises in Jinan, Zibo, Qilu Petrochemical and other basins, the discharge of industrial wastewater and domestic sewage has increased year by year, and the sewage discharge in the whole basin accounts for more than two thirds of the annual average runoff of Xiaoqing River, resulting in the deterioration of the water environment and serious water pollution in Xiaoqing River, which has seriously exceeded the standard of agricultural irrigation water quality in many places. Due to the shortage of agricultural water, the area of sewage irrigation is expanding, and the accumulation of heavy metals and organic pollutants such as Gr, Pb and Cu in soil is doubled by sewage irrigation, which leads to the serious decline of soil environmental quality and the quality of agricultural and livestock products in sewage irrigation area. According to statistics, the over-standard rate of heavy metals in grain crops in major sewage irrigation areas in the province is 25%. In recent decades, the incidence of cancer, liver disease and fetal malformation has increased significantly in polluted areas along the Yangtze River.

Therefore, it is of great significance to study the soil environmental quality along the Xiaoqing River, find out the soil environmental pollution situation along the Xiaoqing River, evaluate the soil environmental quality, and put forward the countermeasures and measures for soil improvement, so as to improve the quality of agricultural products in the study area and protect people's health.

The study area starts from Jinan in the west and ends at the mouth of Bohai Sea in the east. Qu Di-gaoqing county-chunhua town in the north and Zouping-Huantai in the south. It has jurisdiction over 8 counties and cities including Jinan, Zibo, Dongying, Weifang and Binzhou, including Zhangqiu, Jiyang, Zouping, Gaoqing, Boxing, Huantai, Guangrao and Shouguang.

(I) Characteristics of geochemical content of elements in Xiaoqing River Basin

1. Statistical characteristics of soil elements along Xiaoqing River

See Table 3- 17 for the distribution of soil elements along Xiaoqing River. Among the 25 elements and indicators analyzed, the arithmetic mean values of most elements before and after excluding abnormal values are not much different, only the mean values of Cr, Hg, Mo, Se and S are quite different, and Cr changes from 81.21×10-6 to 72.44× 64. Mercury changed from 52.8× 10 -9 to 29.6× 10 -9, molybdenum from 0.657× 10 -6 to 0.589× 10 -6, and selenium from 0.25×16.

As far as the coefficient of variation is concerned, the coefficient of variation of 20 of the 25 indicators is within 0.5, and the elements or indicators with high data dispersion are S, Hg, Cr, Se and Zn, and their original values are 5.74, 2.03, 0.79, 0.69 and 0.64 respectively. After excluding outliers, the coefficients of variation of these five indicators are 0.30, 0.35 and 0.64 respectively.

Table 3- 17 Characteristic Parameter Table of Geochemical Content of Surface Soil Components in Xiaoqing River Basin

As far as the distribution of background values of elements is concerned, the elements such as As, Hg, Mo, SiO2 _ 2 _ 2, Al _ 2O _ 3, TFE _ 2O _ 3 and K _ 2O in the soil background in this area are basically close to those in the lower reaches of the Yellow River, while Na _ 2O, P and B are slightly lower, while Cd, Co, Cr, Cu, F, Mn, Ni, Pb, etc. The elements of Co, Mn, Mo, Pb and Na2 O in the soil along the Xiaoqing River are obviously lower than the average value of Shandong Province, among which Mo is only 0. 1 times that of Shandong Province, while As, B, Cd, Cr, F, Hg, Ni, Zn, Se, TFe2 O3, MgO and CaO are all higher than those of Shandong Province, among which CaO, MgO and Cd are all higher. As, Hg, Mo, Se, Pb and Zn in the soil along the Xiaoqing River are obviously lower than the average value of China's soil, among which Hg and Mo are only 0.46 and 0.3 times of that of China's soil, while Cd, Cr, F, Cu, Ni, MgO, CaO and Na2 O are higher than that of China's soil, among which MgO and CaO are 1.84 and 2 respectively.

2. Distribution characteristics of soil elements in the upper, middle and lower reaches of Xiaoqing River

By comparing the statistical data of surface soil element content in different sections of the upper, middle and lower reaches of Xiaoqing River (Figure 3-3 1), it can be found that the background values of F, Mn, Al2 O3, S, MgO and K2 O in the upper reaches are lower than those in the middle and lower reaches, while SiO2 _ 2 and Na2 O are the highest in the upper reaches, and other elements are higher than those in the lower reaches but lower than those in the middle reaches. The background values of As, B, Cu, Cd, Cr, Co, F, Hg, Mn, Ni, Pb, Zn and se in the middle reaches of the soil are higher than those in the upper and lower reaches of the soil, in which Cd, Hg and Se are respectively 1.3, 1.6 and 1.4 times that in the lower reaches of the soil.

Figure 3-3 1 background value map of soil elements in upper, middle and lower reaches of Xiaoqing River

3. Distribution characteristics of soil elements on the north and south banks of Xiaoqing River

Comparing the statistics of background values of soil elements on the north and south banks of Xiaoqing River, there are the following rules, as shown in Figure 3-32. The background values of mercury, phosphorus, lead, nitrogen, silica and Na2 O in the south bank soil are slightly higher than those in the north bank soil, and mercury is 1.2 times that in the north bank soil. As, B, Cd, Cr, F, Mn, Ni, Pb, Zn, Se and other elements and oxides are all lower than the background values of soil elements in the north shore, among which As, S and CaO are 0.86, 0.88 and 0.8 1 times of the background values of soil in the north shore respectively.

Figure 3-32 Background values of soil elements in the south and north banks of Xiaoqing River

(2) Element profile characteristics

1. Distribution characteristics of elements in horizontal soil profile along Xiaoqing River

Three horizontal profiles are arranged in Licheng District, Boxing County and Wangdao, perpendicular to Xiaoqing River. According to the statistics of the data of three profiles, the distribution of element content in different soil profiles is quite different, and there are also significant differences on both sides of Xiaoqing River in the same soil profile, as shown in Table 3- 18.

Table 3- 18 Statistical Table of Element Contents in Soil Horizontal Profile along Xiaoqing River

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1) Licheng section starts from Wangsheren Town in the south and ends at Liujiaji in the north, with dense settlements. The soil on the south bank of this profile is mainly distributed in tidal cinnamon soil, and the soil on the north bank is mainly tidal soil and salinized tidal soil. Statistics show that the contents of soil elements As, Cr, F, Hg and Ni in the south bank are obviously higher than those in the north bank, while the contents of Cd, Cu, se and P are lower than those in the north bank, and the contents of other elements are similar. However, the content of heavy metal elements is higher than the background value of Xiaoqing River soil, which may cause some pollution to the soil environment, which is related to the influence of human activities.

2) In the south of Boxing section, from the north of Qifeng Town to Xifu Village in the west of Boxing County, the soil on the south bank is mainly wet fluvo-aquic soil, while the soil on the north bank is mainly fluvo-aquic soil. Statistics show that the distribution of heavy metal elements As, Cd, Cr, Cu, Hg, Pb and Zn in the soil on the north bank is obviously higher than that on the south bank, while the contents of B, Mo, Se, N, S and CaO in beneficial elements on the south bank are obviously higher than that on the north bank.

3) The Wangdao section starts from Woche Town in the south and ends at Guang Bei Farm in the north. The soil type is saline fluvo-aquic soil. The content of soil elements in the north bank is obviously lower than that in the south bank, and the content of heavy metal elements As, Cd, Cr, Cu, Hg, Ni, Pb and Zn is obviously lower than the background value of Xiaoqing River, while the content in the south bank is slightly higher.

2. Distribution characteristics of elements in vertical profile of soil along Xiaoqing River.

Distribution of 1) element in vertical profile of Licheng soil. Field investigation shows that the soil texture in the middle and upper layers of the profile is basically sandy clay, and clay is below 60 cm. There is rust in the depths. With the increase of depth, the organic matter content decreases, and the soil elements also show regular changes (Figure 3-33). The main components of soil, such as SiO2 _ 2, MgO, K2 O, CaO and Na2 O, have little change with depth, so it is inferred that the original sediment components are relatively stable and the sedimentary rhythm stratification is not obvious. The content of nitrogen, phosphorus, chromium, mercury, sulfur, selenium, cadmium and lead in topsoil is extremely high, and it drops sharply from the surface to the depth of 80( 100)cm, especially nitrogen, phosphorus, selenium, sulfur and mercury. It is considered that human production activities have great influence on soil, and the estimated depth of influence is 100 cm. The contents of TFe2 O3, Al2 O3, Mn, B, V, Co and other elements increase with the depth and are enriched in deep soil. The reason is that the top of the soil may be acidic, and the elements migrate to the bottom of the soil in the form of ionic compounds under the supergene action, resulting in the enrichment of elements at the bottom. The contents of arsenic, fluorine, nickel, copper, zinc, molybdenum and other elements do not change obviously with the increase of depth.

2) Vertical profile distribution characteristics of soil elements in Boxing County. On-the-spot investigation shows that the soil texture on the profile has not changed obviously, and it is all clay. With the increase of depth, various elements show regular changes (Figure 3-34). The main components of soil, SiO2 _ 2 and Na2O, have little change with the increase of depth, and are relatively stable in the depth range of 0 ~ 100 cm, but increase with the increase of depth from 100 cm. On the contrary, elements such as TFe2 O3, Al2 O3, MgO, K2 O, V, Co, Mn (very significantly related to TFe2 O3 and Al2 O3) decrease with the increase of depth at 100 cm. Although pedogenesis can cause clay formation and vertical change of mineral composition in topsoil, this sharp change of mineral composition is obviously more closely related to the original sedimentary composition. As, Cd, Cr, Hg, Ni, F, Cu, Pb, Zn, N, P, S, Se and other elements decrease with the increase of depth, and are abnormally enriched in the surface layer of soil, and drop sharply from the surface to the depth of 60 cm, especially N, P and Hg. This distribution is not only related to the stratification of original sedimentary components, but also to the surface migration and redistribution of adsorbed precipitation under the constraints of soil texture and organic matter content. Among them, N, P, Hg and S have strong characteristics of surface soil enrichment, which is obviously related to pollution. C, B, Mo and other elements do not change obviously with the increase of depth.

Figure 3-33 Element Distribution Map of Soil Mileage Profile along Xiaoqing River

3) Distribution characteristics of soil elements in Wangdao in vertical section. The soil type is mainly salinized fluvo-aquic soil. Field investigation shows that the soil quality on the profile is mainly clay and sandy clay, and the soil quality is loose. The content of elements shows obvious regularity with the depth (Figure 3-35): the contents of main components of soil, such as SiO2 _ 2 and Na2O, increase with the depth, while TFE _ 2O _ 3, Al2O3, K2O and MgO are enriched in the surface layer of soil, and then drop sharply from 60cm to the background value, which may be related to the changes of clay/sand composition and organic matter. As, Cd, Cr, F, Hg, Ni, Cu, Pb, Zn, Mn, N, P, Se, S and other elements are deeply enriched from the surface to 60cm, and then sharply decreased from 60cm to the background, especially N, P, S, Cu, Pb, Zn. On the one hand, this distribution is related to the original sedimentary composition of soil, on the other hand, the strong enrichment characteristics of N, P, S, Cu, Pb, Zn and other elements caused by supergene are obviously affected by pollution. After dropping sharply from the surface to 130cm, As element increased obviously, which may be related to the downward migration of As after dripping. CaO gradually increased from the surface layer to 60cm, enriched in the middle and decreased sharply from 60cm to the deep layer, which may be related to the use of mineral phosphate fertilizer. Elements such as B and Mo have no obvious changes from the surface to the deep.

Figure 3-34 Element Distribution Map of Soil Profile along Xiaoqing River

Figure 3-35 Distribution Map of Elements in Soil Profile along Xiaoqing River

(C) the combination characteristics of soil elements

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Cluster analysis is a multivariate statistical method, which is mainly used to identify similar things and cluster them according to their different characteristics, so that similar things have a high degree of similarity. Clustering analysis can be used to classify the background values, which can naturally and objectively describe the differences and relations between the background values of multiple sample elements. The principle of cluster analysis method is to classify elements (or samples) according to the similarity between multiple samples, so that all elements in a class have close relationships, while the relationships between types are relatively far. Usually, some indicators are used to express the similarity of soil geochemical characteristics of multiple samples, and the correlation coefficient between geochemical characteristics is the main basis. Select the cluster analysis results that conform to the agricultural geological interpretation. Through the cluster analysis of the pedigree map (correlation coefficient, Euclidean distance) of surface soil elements along Xiaoqing River, as shown in Figure 3-36, 25 elements have the following element combinations:

Figure 3-36 Pedigree diagram of correlation coefficient of cluster analysis of surface soil elements along Xiaoqing River.

1)TFe2 O3、Al2 O3、Co、Ni、V；

2) Cadmium, zinc, molybdenum, lead and selenium;

3) fluorine, manganese and arsenic;

4) silica and Na2O；;

5) Nitrogen and phosphorus;

6) Mercury, phosphorus and chromium;

7) South.

2. Factor analysis

Factor analysis is a multivariate statistical analysis method to analyze and reasonably explain a large number of geological observation data, which can reflect the intricate relationship between many variables through data methods. Twenty-five elements reflecting the characteristics of agricultural geological background were selected for factor analysis of soil along Xiaoqing River. According to the characteristic root percentage (variance contribution) and cumulative percentage. The calculation results show that the variance contribution percentage of the first four eigenvalues reaches 765,438+0.1.87%, and taking the first four eigenvalues can extract more than 70% information of the original data change, which is enough to explain the problem.

The initial factor load matrix is calculated, and the structure of the factor load matrix is simplified by using the maximum variance of orthogonal rotation. Table 3- 19 shows the load matrix of the rotation factor. As can be seen from the table, As, Co, F, Mn, Ni, V, Al2 O3, TFe2 O3 and K2 O are positively correlated with the first principal factor, while Na2 O is negatively correlated. The elements positively related to the second principal factor are cadmium, copper, mercury, molybdenum, lead, zinc and selenium. The elements positively related to the third main oscillator are S and CaO, and the negatively related elements are SiO _ 2. The elements positively related to the fourth principal factor are N and P, and the elements negatively related are Cr.

Table 3- 19 Load Matrix of Surface Soil Factors along Xiaoqing River after Rotation

According to the score chart of principal factor (Figure 3-37), the combination characteristics of metal elements represented by principal factor 1 stand out in the middle of Xiaoqing River, belonging to Boxing and gaoqing county, and there are also high-value areas around Jinan. The elements of Cd, Cu, Hg, Mo, Pb, Zn and Se represented by principal factor 2 are important indexes to judge the quality of topsoil, which is outstanding in Jinan, indicating that urban man-made pollution has a great influence on the enrichment of these ions in soil. Factor 3 shows that the combination of S, SiO2 _ 2 and CaO can be used as a characterization of soil geological factors, and its distribution is consistent with the distribution of soil types along Xiaoqing River. Principal factor 4 represents the combination of N and P elements, which is outstanding in the agricultural developed areas in the middle reaches of Xiaoqing River, indicating that agricultural activities have certain influence on the distribution of these elements.

Figure 3-37 Scores of Main Factors along Xiaoqing River

Second, the Xiaoqing River Basin environmental pollution status

Xiaoqing River Basin is an important industrial concentration area in Shandong Province, including Jinan, Jining and Zibo. The main pollution sources are fertilizer plants, plastics plants, steel mills, oil refineries, heavy machinery plants, pharmaceutical factories and power plants. In recent years, with the rapid rise of township enterprises, there have been many small factories and mines all over the major counties and towns. Due to the poor treatment of industrial waste discharge, it has brought serious pollution and harm to the environment.

Pollution sources in this area include sewage and wastewater, solid waste, municipal waste and medical waste, as well as fertilizers and pesticides. There are dozens of large enterprises such as Shandong Chemical Plant, Jinan Yuxing Chemical General Factory, Jinan Fuhou Knitting Company, the Second Affiliated Hospital of Shanda, Qilu Pharmaceutical Factory, Huangtai Power Plant, Jinan Dayi Paper Factory No.3 and Jinan Chemical Fiber Corporation.

The sewage and wastewater in this area mainly come from urban domestic sewage and industrial wastewater. The main pollutants in wastewater are chloride, sulfate, chemical oxygen demand, fluoride, volatile phenol, ammonia nitrogen, cyanide, arsenic, lead, chromium, cadmium and mercury. According to the existing data, the COD (chemical oxygen demand) emission statistics of several key industrial pollution sources in the work area are shown in Table 3-20.

Table 3-20 Statistics of COD Emission of Regional Key Industrial Pollution Sources

Note: The information source is Jinan Water Pollution Prevention and Control Plan of Jinan Environmental Protection Bureau.

At present, the pollutants that produce the most slag in the study area are mainly smelting slag, fly ash, slag, coal gangue and tailings. Taking Jinan as an example, solid waste disposal is a weak link in solid waste management. At present, the main disposal methods are incineration and landfill. The storage methods of solid waste in Jinan are various, and the storage points are scattered. The main solid wastes stored are coal gangue and fly ash. Coal gangue is mainly stored in major coal companies; Fly ash is mainly stored in Xiaoqing River and Dasi dry ash yard. Because most solid wastes are well managed, they are not discharged into the environment.

According to the distribution of industries that produce solid waste, the industries that produce solid waste are smelting, thermoelectric, mining and chemical industry, accounting for more than 90% of the total, of which Jigang is the largest source of solid waste, with an average annual output of 155.6× 104 t.

Chromium-containing waste in Jinan is mainly produced by Jinan Yuxing Chemical Plant, including chromium slag and aluminum sludge. Chromium slag contains toxic component Cr6++, which is harmful to the surrounding environment. The production of fly ash is relatively concentrated, mainly distributed in Huangtai Power Plant in Licheng District. 1998, Huangtai Power Plant produced 57.5× 104 t of fly ash. The production of steel slag is relatively concentrated, mainly distributed in the factory area and the west side of Jigang General Factory in Licheng District (Table 3-2 1).

Table 3-2 1 Statistical Table of Output of Key Sources of Solid Waste

Note: The information source is Jinan Water Pollution Prevention and Control Plan of Jinan Environmental Protection Bureau.

Urban garbage is mainly composed of domestic garbage, road cleaning garbage, wheeled garbage bins and domestic garbage of enterprises and institutions. According to the survey, the annual output of domestic waste in Jinan in 1998 is about 55× 104 t, and the domestic waste in the work area accounts for nearly 1/6 of the domestic waste in Jinan. The removal rate of domestic garbage, treatment and disposal rate 100%, and harmless treatment reached 92. 14%. Although the removal rate has reached 1.000%, not all of them have been treated harmlessly, and some of them are still piled up in various simple garbage dumps without any treatment, or discharged into suburban villages, causing environmental pollution.

Medical waste is toxic, contains bacteria and is harmful, which is one of the main pollution sources that cause social cross-infection. The daily output of medical waste in Jinan is 4269kg. The pathogenic bacteria of medical waste are much higher than domestic waste and industrial waste. The main treatment methods of medical waste are incineration and landfill, which will pollute the local atmospheric environment, increase the probability of disease transmission and diffusion, and aggravate the groundwater pollution of landfill. Therefore, it is necessary to strengthen the management, collection and treatment of medical waste.

In addition, the agriculture in the upper reaches of Xiaoqing River is mainly wheat, rice and corn. Agricultural fertilization is mainly chemical fertilizer, supplemented by farmyard manure. In addition, the spraying of pesticides and the use of plastic films have also caused certain pollution to the environment. Farmhouse manure, chemical fertilizers and pesticides are widely used, most of which are absorbed by crops, and some of them infiltrate into the ground with precipitation and irrigation, polluting underground water bodies.

Three. Evaluation of soil environmental quality

(A) evaluation factors and standards

The evaluation standard of soil environmental quality is the national standard (GB15618-1995) (Table 3-22). The standard only stipulates the standards of eight components or indicators, namely, the upper limit contents of eight elements such as cadmium, mercury, arsenic, copper, lead, chromium, zinc and nickel in different grades. So the evaluation factor chooses these eight elements.

Table 3-22 Standard Value Table of Soil Environmental Quality Unit: 10 -6

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Note: ① Heavy metals (Cr is mainly trivalent) and As are calculated according to the amount of elements, which is suitable for cation exchange capacity > 5cmol (+)/kg; if it is ≤ 5cmol (+)/kg, the standard value is half of the value in the table. (2) BHC is the total amount of four isomers and DDT is the total amount of four derivatives. ③ Soil environmental quality standard of paddy-upland rotation farmland, in which paddy field value is As and dry land value is Cr.

(B) Single factor evaluation

1. Single factor environmental quality classification statistics

See Table 3-23 for the statistical results of single factor environmental quality assessment of heavy metals in Xiaoqing River Basin. The results of single-factor soil environmental quality assessment such as mercury, arsenic, cadmium, lead, zinc, copper, chromium and nickel show that the surface soil quality in Xiaoqing River survey area is mainly Class I and Class II, and the soil samples of Class III and above account for a certain proportion, but the proportion is controlled within 3%. In the single factor index, Cu, Ni and Pb did not exceed the three types of soil, and the number of samples in type I soil reached more than 90%. There are four grades of Hg and Zn in the surface soil, among which the proportion of Class I soil is over 90%, and the proportion of super-Class III soil samples is only 1 ~ 2, and the proportion is not more than 1%. As and Cd both appear in the fourth grade. Although there are more than three kinds of soil, the proportion does not exceed 1%. Compared with mercury and zinc, the proportion of type I soil decreased and the proportion of type II soil increased. Among all the single-factor evaluation indexes, the proportion of Cd in grade one is the smallest, and that in grade three is the largest. In this investigation area, the number of soil samples with metal chromium exceeding Class III is the largest, accounting for 0.6% of all samples. Generally speaking, the soil quality grade in Xiaoqing River basin can still ensure the safety of agricultural production.

2. Graded distribution characteristics of single-factor environmental quality

The environmental quality grade of As index is mainly Class I soil, and Class II soil is mainly distributed in the middle reaches of Xiaoqing River, concentrated in Huashan Town, Sunzhen Town, Fanjialin, Dingjiazhuang, Boxing County and Dingzhuang Town, with island distribution, accounting for 5% of the total area. Although the overall quality is good, it is noted that Boxing County has a large distribution area and has a tendency to connect with surrounding towns and villages.

The environmental quality grade of Cd index is mainly Class I soil, Class II soil is distributed in Jinan, Boxing, Gaoqing, Zouping and other northeastern towns, and Class III soil is mainly concentrated in Jinan city and Beiyuan town in the upper reaches of Xiaoqing River.

The environmental quality grade of Cr index is mainly Class I soil, but there are also Class III and Super Class III soils. Class II soil is distributed near Jinan in the upper reaches of Xiaoqing River, between Fanjialin in the middle reaches, east of Gaocheng and west of Boxing County, and east of Boxing County. Class III soil is mainly distributed in the urban areas of Beiyuan Town and Zhaihao Town, Jinan City, while super-Class III soil is only distributed in the north of Beiyuan Town, Jinan City.

The soil with copper index grade II environmental quality is mainly distributed in the urban area of Jinan in the upper reaches of Xiaoqing River, the northeast area in the middle reaches and the eastern part of Boxing County, and it is only distributed in sporadic islands in Boxing County.

Table 3-23 Statistical Table of Single Factor Evaluation of Environmental Quality of Surface Soil Samples in Xiaoqing River Investigation Area

The environmental quality grade of Hg index is mainly Class I soil. Although Class II and Super Class III soils are also distributed, they are mainly concentrated in the urban area of Jinan. Judging from its distribution form, although Class III soil is only distributed in Jinan city, the distribution range of Class II soil around it tends to spread downstream, and its development needs to be closely monitored in future work.

The environmental quality grade of Ni index is mainly Class I, Class II soil is mainly distributed in the middle reaches of Xiaoqing River, and the distribution area of Niⅱ soil is relatively scattered, mainly distributed in Huashan Town, Dingjiazhuang, Zhaihao Town North-Longhe and other areas.

The environmental quality grade of Pb index is mainly Class I soil, and Class II soil is only distributed in Jinan city and some surrounding villages and towns. Class II soil is distributed in some residential areas such as Beiyuan Town, Yaojia Town, Wangsheren Town and Guodian Town.

The environmental quality grade of Zn index is mainly Class I soil, but Class II and III soils are also distributed in the upper reaches of Xiaoqing River. Type II soil is concentrated in Jinan urban area and Beiyuan Town-Luokou, Yaojia Town-Beitantou and Guodian Town. Class ⅲ soil is distributed on both sides of Xiaoqing River tributary in the northwest of Guodian Town, which is suspected to be point pollution caused by industrial wastewater discharged from local factories.

3. Single factor pollution index analysis

By calculating the single pollution index of each evaluation index, we can reflect the influence of each index on the evaluation of regional environmental quality and analyze the influence degree of regional environmental pollution. Commonly used pollution indicators include:

1) soil single pollution index. The single pollution index is small, the pollution is light, and the index is large, the pollution is heavy. Its calculation formula is

Single pollution index of soil = measured value of soil pollutants/quality standard of soil pollutants

2) Accumulation index of soil pollutants. Because of the great difference of soil regional background, sometimes the cumulative index of soil pollution can better reflect the degree of human pollution of soil. The calculation formula of soil pollution cumulative index is as follows:

Accumulation index of soil pollutants = measured value of soil pollutants/background value of pollutants

3) Sharing rate of soil pollutants. The sharing rate of soil pollutants can be used to evaluate and determine the main pollution projects of soil. The pollutant sharing rate is ranked from large to small, and so are primary pollutants and secondary pollutants.

Sharing rate of soil pollutants (%) = (sum of one pollution index/soil pollution indexes) × 100%.

4) Multiple of soil pollution exceeding the standard. The multiple of soil pollution exceeding the standard is a statistic that can reflect the soil environmental conditions.

Over-standard rate of soil pollution = (measured value of a pollutant in soil-quality standard of a pollutant)/quality standard of a pollutant.

5) Over-standard rate of soil samples. The over-standard rate of soil samples is also a statistic reflecting the soil environmental conditions.

Over-standard rate of soil contaminated samples (%) = (total number of over-standard soil samples/total number of tested samples) × 100%.

The pollution indexes of eight factors are calculated, and the calculation results are shown in Table 3-24. The results show that the soil index in the whole region is low and the pollution degree is very light. Soil pollutants along Xiaoqing River are mainly As, Cd, Cr and Ni, and the order of heavy metal pollution is Ni > CD > As > Cr > Zn > Cu > Hg > Pb. The multiple of each single pollutant exceeding the standard is less than 0, indicating that the soil environmental quality in the whole region is good and the pollution scale is small, which is not enough to affect the whole region.

Table 3-24 Statistical Table of Surface Soil Pollution Index and Excess Rate in Xiaoqing River Basin

Note: The comparison standard is the upper limit of secondary soil.

(3) Comprehensive evaluation

1. Fuzzy comprehensive evaluation

See Table 3-25 for the statistics of fuzzy evaluation results in each region. According to the data, the soil in Xiaoqing River area is mainly Class I and Class II, and there is no soil exceeding Class III. The number of Class III soil samples is 10, accounting for less than 0.5%. The overall environmental quality is good.

Table 3-25 Statistical Table of Fuzzy Comprehensive Evaluation of Environmental Quality of Surface Soil Samples in Various Investigation Areas

See Figure 3-38 for the grade distribution of soil comprehensive environmental quality. It can be seen that most soils belong to Class I and Class II grades. This result looks different from that of single factor evaluation, but after careful study, it can be concluded that when we choose the weight, it is based on the multiple of each factor exceeding the standard, and finally it is homogenized. Therefore, the fuzzy evaluation results show that the soil environmental background of each region is excellent, and even some polluted sections are only at a relatively low stage at present, and the surface soil environment of each region is generally excellent.

The first type of soil is mainly distributed in the areas of Yao Qiang-Gaoguanzhai Town-Weiqiao Town and West Qiao Liu-Sleeper-Yangkou on the north bank of Xiaoqing River, the second type of soil is mainly distributed in the surrounding area of Jinan, the soil on the south bank of the upper reaches of Xiaoqing River and the soil in the middle reaches, and the third type of soil is mainly distributed in the vicinity of Jinan urban area and individual township stations.

Figure 3-38 Distribution of Comprehensive Environmental Quality Grades of Surface Soils in Xiaoqing River Basin

2. Comprehensive index evaluation

The calculation of comprehensive index method is generally based on solving the weight of single factor pollution index and adopting different mathematical models. Nemerow index method is selected as the comprehensive index method. This index reflects the impact of various pollutants on soil, highlighting the impact of high-concentration pollutants on soil environmental quality. The calculation method is as follows:

Study on Geological and Geochemical Environment of Typical Ecological Zone in Northwest Shandong Plain

Where: P is the comprehensive pollution index; I = ci/si (measured value/background value), and the background value is the background value of this element in the soil along the Xiaoqing River.

Figure 3-39 Evaluation Diagram of Mero Index of Soil Environment in Xiaoqing River Basin

The comprehensive pollution distribution of heavy metals in Xiaoqing River soil is shown in Figure 3-39. The heavily polluted areas are mainly concentrated on the banks of Xiaoqing River from Beiyuan Town to Huashan Town in Jinan City, and are also scattered in residential areas such as Sihouzhang, Xixiang Village and Nankou. The polluted areas are mainly distributed in some township stations such as Luokou, Wangsheren Town and Zhaihao Town, while the lightly polluted areas are mainly concentrated in Qijia, Wangsheren Town-Jiazheng Wharf and Xinji-Qifeng Town.

From the above evaluation results, it can be seen that the soil in this area is relatively clean and the pollution degree is small, but at present, only one polluted soil in this area is unpolluted, and other areas are polluted to varying degrees. By analyzing the pollution distribution range and main pollution factors in the polluted area, the following conclusions can be drawn:

1) From the distribution form of pollution, pollution in all parts of the country is mainly distributed in the form of spots or islands. The pollution in Yutai area is concentrated in Changgou area in the northwest of Jining, Zhangqiu is concentrated in Baiyun Lake area in the north of Zhangqiu, and Shouguang is concentrated in Aric-Tian Jin Ryu. The pollution distribution in Xiaoqing River Basin has developed to a large extent, and the pollution is concentrated in Jinan City in the upstream and Boxing County in the middle reaches. Xiaoqing River basin has the largest pollution distribution area, and the distribution pattern has changed from point distribution to area distribution, showing a rapid expansion trend, which needs to be monitored in future investigations.

2) From the position of pollution distribution, the pollution distribution in different places presents a relatively unified feature, that is, the areas with high pollution index are overlapped by rivers or traffic roads to some extent. This phenomenon shows that if the pollution source is not found and treated in time, its diffusion speed will be faster, its scope of action will be easier to expand with the expansion of human activity area, and its influence will be stronger.

3) From the analysis of pollution indicators, pollution sources vary from place to place. The proportion of Cr pollution in Zhanhua area is large, and the contribution of Cd pollution in Yutai area is large. Zhangqiu, Shouguang and Xiaoqing River basins have the largest nickel pollution index.

To sum up, through pollution assessment, it is found that the soil pollution in the assessment area is relatively slight, which is suitable for developing agricultural production. But at the same time, due to the trend of further expansion of local pollution, the focus of pollution source investigation and prevention should be further carried out in the future work to ensure the healthy development of ecological agriculture.