Effects of biochar additions on the mechanical stability of soil aggregates and their role in the dynamic renewal of aggregates in slope ecological restoration.

Mechanical stability of soil aggregates is important for resisting external disturbances in slope soils. Biochar (BC) is widely used in slope remediation. However, biochar application may not be conducive to the formation of mechanical-stable soil aggregates, and the effects of biochar additions on the mechanical stability of soil aggregates in slope restoration remain largely unclear. In this context, an incubation experiment was conducted in this study with four biochar levels added to artificial soil, namely 0 % (BC0), 1.5 % (BC1), 3 % (BC2), and 4.5 % (BC3), corresponding approximately to 0, 0.77, 1.53 and 2.30 M ha-1, respectively. The contributions of different soil aggregate fractions to maintaining the mechanical stability of aggregates, as well as the main influencing factors and pathways of biochar additions on soil aggregate stability in a dynamic renewal process of aggregates, were investigated in this study. The results showed a decreasing trend in the mean weight diameter (MWD) with increasing biochar levels and BC1 has no significant difference with BC0, showing MWD values of 2.74 and 2.75, respectively. In contrast, BC3 is significantly lower MWD value of 2.18. The BC3 exhibited negative impact on the mechanical stability of the aggregates. Redundancy analysis (RDA) showed that large macroaggregates (>5 mm) exhibited a stronger contribution on the aggregate mechanical stability between all soil aggregate fractions. The random forest (RF) algorithm and structural equation modeling (SEM) indicated that microaggregate-associated soil organic carbon (SOC) contents and soil pH values were the main factors driving the changes in the aggregate mechanical stability caused by biochar applications. Indeed, the biochar level of 1.5 % maintained the stability of macroaggregates and increased the microaggregate-associated SOC content by 35.7 %, which was conducive to the formation of microaggregates within macroaggregates. Our study suggests that the application of biochar at a level of 1.5 % is more beneficial for maintaining the mechanical stability of artificial soil aggregates.

A simulated ecological restoration of bare cut slope reveals the dosage and temporal effects of cement on ecosystem multifunctionality in a mountain ecosystem.

Cement is a critical building material used in the restorations of bare cut slopes. Yet, how cement affects ecosystem's functions and their undertakers remains elusive. Here, we revealed the dosage and temporal effects of cement on plant and soil traits, extracellular enzymes, greenhouse gas fluxes and microbiome using simulation experiments. The results showed that soil pH increased with the cement content at 1st day but relatively constant values around 7 to 7.5 were detected in the flowing days. The ß-1,4-glucosidase, phenol oxidase, leucine aminopeptidase and acid phosphatase showed high activities under high cement content, and they generally increased with the cultivations except for acid phosphatase. CH4 fluxes at 16th day were less than zero, and they increased to peak around at 37th to 44th days followed by decreasing until reaching to relatively stable fluctuations around 0. Despite of decrease patterns, N2O fluxes stayed around zero across the temporal gradient except for the maximum around at 30th day in 2%, 5% and 8% cement treatment. Microbial diversity decreased with the cement content, in which there were a recovery trend for bacteria. By integrating above- and belowground ecosystem traits into a multifunctionality index, we identified a potential optimum cement content (11%). PLSPM showed that multifunctionality was affected by the shifts in soil bacterial community, enzyme activity and greenhouse gases while these components were effected by other environmental changes resulted from cement. Our results demonstrate that cement determines multifunctionality through mediating microbial community and activity, providing new insights for designing in situ experiments and ecological restoration strategies for bare cut slopes.

Effects of antimony contamination on bioaccumulation and gut bacterial community of earthworm Eisenia fetida.

Antimony (Sb) contamination has brought great environmental problems to the surrounding soils. However, few studies focused on the response of bacterial communities in earthworm gut to Sb. Eisenia fetida was cultured in four soils with Sb contents (5,25,50,100 mg•kg-1) to investigate the distribution of Sb species in earthworm gut and the response mechanism of bacterial communities to Sb contamination. The results showed that Sb accumulated in the gut and tissues of earthworms, and the mortality of earthworms showed a dose-response relationship with the increase of Sb content. Sb(III) and Sbexe were the major species in gut, whereas Sb(V) and Sbsrp were predominant in surrounding soil. There were significant differences in bacterial diversity between earthworm gut and soil, but there was no significant between the two with different Sb content. The network constructed by gut bacterial community of earthworm was less stable and more sensitive to Sb species than that in soil. Sb(III) had the greatest influence on the gut bacterial community of earthworm, which not only directly affected the community through Xanthomonadaceae, Rhodomicrobiaceae and Anaerolineaceae, but also indirectly influenced through Chthoniobacteraceae. This study fills a research gap on the effect of Sb contamination on the gut bacterial community of earthworm.

Soil N availability drives the shifts of enzyme activity and microbial phosphorus limitation in the artificial soil on cut slope in southwestern China.

The construction of highways in the subalpine mountains generates many cut slopes. Currently, the restoration of cut slope mainly focuses on the aboveground landscapes and slope stability. Yet, it remains elusive about the belowground ecosystem functions at the early stage of restoration. In this study, we evaluated the belowground ecosystem functions of cut slopes that had been restored approximately 3 years using soil enzymatic activities, microbial biomass, and stoichiometry as the proxies. The results indicated that the phenol oxidase activity was higher in cut slopes, while the activities of ß-1,4-glucosidase, ß-1,4-N-acetylglucosaminidase, leucine aminopeptidase, and acid phosphatase were lower in cut slope soils compared with natural soils. Soil nitrogen availabilities (total and/or ammonium nitrogen) showed high negative correlations with the phenol oxidase activity and positive correlations with the activities of almost all other enzymes. These results suggested that soil nitrogen was the key factor in driving the shifts of enzymatic activities across two types of soils. Moreover, we found the imbalance of soil nutrients in cut slope soils, especially the carbon vs. nitrogen and the nitrogen vs. phosphorus. By applying the vector analysis, we found that the vector A values were more than 45° in all samples, suggesting that microbial phosphorus limitation occurred in both cut slope and natural soils. These findings suggested that maintaining the balance of soil nutrient supplies is important to the recovery of the below-ground ecosystem functions at the early restoration stage of cut slopes. This study provided new insights into designing the ecological restoration strategies for cut slopes by considering the belowground ecosystem functions.

Artificial soil nutrient, aggregate stability and soil quality index of restored cut slopes along altitude gradient in southwest China.

In the subalpine mountainous region of southwest China, the artificial soil properties of restored cut slopes along the altitude gradient were studied, including available nitrogen (AN), available phosphorus (AP), available potassium (AK), urease (UR), sucrase (SC), protease (PR), catalase (CAT), texture, and aggregate stability of soil. Soil aggregatet stability by mean weight diameter (MWD), geometric mean diameter (GMD), structure failure rate (P), index of unstable aggregates (IUA) and area difference of dry and wet sieve cumulative distribution curve (ΔS) were measured and analyzed. It was found that available soil nutrients, UR, and CAT activities increased initially and then decreased, but the texture of soil was finer, and aggregate structure tended to be more stable along with an increase in the altitude gradient. The soil aggregate stability index that MWD, GMD, P, IUA, and ΔS indicated that the higher the altitude, the stability of soil aggregates was better. Principal component analysis (PCA) was used to determine the soil quality index (SQI). The obtained results from this study showed that the artificial soil quality of the cut slopes was better at a higher altitude compared to a lower altitude. These results provide a reference for the improvement of artificial soil properties of cut slopes and their quality in the future. It is necessary to pay attention to the soil quality management at a low-altitude area and reform the soil nutrients, enzyme activities, and soil structure for the restored cut slopes in the mountainous subalpine highway of southwest China.

The life span and influencing factors of metal mesh in artificial soil on railway rock-cut slopes in humid areas.

The stability of slope is strengthened by the metal mesh. The studies of the life span and influencing factors of metal mesh in the artificial soil in humid areas will guide ecological restoration of rock-cut slopes in Southwest China. Due to metal corrosion, the fixation function of the metal mesh could last for 10 years. The factors of soil contents, soil electrochemical properties and soil bacteria not only changed with the vegetation succession but also weakened the effect of the metal mesh on soil fixation for slope protection. The potential gradient, chloride ion content, sulfate ion content and water content were the main influencing factors for metal mesh corrosion during the vegetation restoration stage from 0 to 5 years, while the corrosion potential, potential gradient, chloride ion content, and water content were the main influential factors for metal mesh corrosion during the vegetation restoration stage after 11 years. At different vegetation restoration stages, the soil bacteria contained different dominant species, which had spatial heterogeneity, and the heterogeneity of the soil bacteria was another factor influencing the corrosion of the buried metal mesh. Meanwhile, the plant root as a soil fixation function strengthened with time, and 8 years later, the local woody plants gradually migrated to form a community dominated by multiple woody species. It is the first time that the life span of a metal mesh under the artificial soil of rock-cut slopes and factors affecting the different corrosion stages of the metal mesh in a humid area have been judged. The fixation function of plant root gradually replaces metal mesh, and main factors affecting the process include soil contents, soil electrochemical properties and soil bacteria. The research on corrosion factors of metal mesh under artificial soil for rock-cut slopes will contribute towards reducing the environmental risk of ecological restoration.

How backfill soil type influencing on Cd and Pb migration in artificial soil on railway rock-cut slopes.

Cadmium (Cd) and lead (Pb) that accumulates in the surface soil of railway rock-cut slopes may migrate to nearby croplands. It is important to determine whether backfill soil type influences the transportation of Cd and Pb in the surface soil. Representative rock-cut slopes, backfill soil of 100% rock fragments, 100% agricultural soil, and 50% agricultural soil and 50% rock fragments (n = 2 for each type) were selected. The pollution and migration levels of Cd and Pb and the soil quality and erodibility were investigated. The soil concentrations of Cd and Pb on the rock-cut slopes were much higher than those of China soil quality standard. Soil erosion was the most important factor that influences the migration of Cd and Pb in the slopes. Increasing the percentage of agricultural soil in the backfill soil resulted in decreasing the diffusion of Cd and Pb by reducing soil erosion. The backfill soil affected the soil quality and erosion durability, which, in turn, affected the transportation of Cd and Pb in the runoff. The soil quality index (SQI) accurately reflects the soil quality and can serve as an indicator of the migration of Cd and Pb on the surface soil of the slopes. Therefore, agricultural soil was more appropriate to use as a backfill soil in slope revegetation practice than was the rock fragment, which was helpful for decreasing the environmental risk of Cd and Pb on the slopes.

Vegetation and soil nutrient restoration of cut slopes using outside soil spray seeding in the plateau region of southwestern China.

Outside soil spray seeding (OSSS) is used widely for road cut revegetation, and the artificial soil used in OSSS can improve slope soil conditions and nutrients, and help promote plant growth and succession. Three different slopes was investigated to evaluate the effectiveness of OSSS for restoration, including a natural slope (NS), a cut slope without any artificial recovery treatment (CSW) and a cut slope treated with OSSS (CSO). The recovery of cut slopes was determined by evaluating a number of factors, including indices associated with plants on the slopes, soil enzyme activities (urease and sucrase), and soil nutrient content (soil organic matter (SOM), total phosphorous (TP), total potassium (TK), available nitrogen (AN), available phosphorous (AP), available potassium (AK), potassium (K+), calcium (Ca2+), magnesium (Mg2+), and sulphate (SO42-)). The results indicated that the vegetation and soil conditions differed between the three slopes. The Shannon-Wiener index (H), the Simpson index (D), and the Margalef index (R) values from the CSO and NS were lower than those of the CSW, whilst the Pielou index (E) value and vegetation canopy cover were higher for the CSO and NS than for the CSW. The content of SOM and AN in soil from the CSO was lower than in soil from the NS and CSW, and content of many nutrients were higher in soil from the CSO than in soil from the NS and CSW. This suggests that the restoration of vegetation and soil nutrients on the CSO was relatively successful. Our results indicated that the use of OSSS to restore cut slopes is effective in plateau areas. However, despite improvements in soil nutrient levels, there were still nutritional imbalances. Therefore, more attention should be paid to balancing nutrients in the later stage of OSSS implementation for the recovery of cut slopes at high altitudes.

Topographic aspect affects the vegetation restoration and artificial soil quality of rock-cut slopes restored by external-soil spray seeding.

External-soil spray seeding (ESSS), a technique of spraying artificial soil materials onto bare slopes for vegetation cover construction, has been widely used to restore rock-cut slopes. However, studies on the effect of the practical application of this technique on different topographic aspects have been rarely performed. In this study, two topographic aspects, namely, north-facing versus south-facing, were investigated under two railway lines, and two local natural slopes (north-facing versus south-facing) were selected as references. Vegetation and soil conditions, which are paramount aspects of ecological restoration assessment, were characterized in terms of the richness and diversity indices, vegetation canopy cover, basic soil physico-chemical properties, and structural characteristics of these slopes. Results showed that (1) the topographic aspect significantly affected the vegetation restoration and artificial soil quality of rock-cut slopes restored by ESSS; (2) the ecological restoration effect of north-facing slopes were better than that of south-facing slopes; and (3) the vegetation and soil conditions of natural slopes were better than those of rock-cut slopes. Therefore, additional scientific management measures should be implemented to promote the ecological restoration of rock-cut slopes, especially for south-facing slopes.

Effects of heavy metal pollution on enzyme activities in railway cut slope soils.

Railway transportation is an important transportation mode. However, railway transportation causes heavy metal pollution in surrounding soils. Heavy metal pollution has a serious negative impact on the natural environment, including a decrease of enzyme activities in soil and degradation of sensitive ecosystems. Some studies investigated the heavy metal pollution at railway stations or certain transportation hubs. However, the pollution accumulated in artificial cut slope soil all along the rails is still questioned. The interest on non-point source pollution from railways is increasing in an effort to protect the soil quality along the line. In this study, we studied spatial distributions of heavy metals and five enzyme activities, i.e., urease (UA), saccharase (SAC), protease (PRO), catalase (CAT), and polyphenol oxidase (POA) in the soil, and the correlation among them beside three different railways in Sichuan Province, China, as well. Soil samples were respectively collected from 5, 10, 25, 50, 100, and 150 m away from the rails (depth of 0-8 cm). Results showed that Mn, Cd, Cu, and Zn were influenced by railway transportation in different degrees while Pb was not. Heavy metal pollution was due to the abrasion of the gravel bed as well as the tracks and freight transportation which caused more heavy metal pollution than passenger transportation. Enzymatic activities were significantly negatively correlated with heavy metals in soils, especially Zn and Cu. Finally, it is proposed that combined use of PRO and POA activities could be an indicator of the heavy metal pollution in cut slope soils. The protective measures aimed at heavy metal pollution caused by railway transportation in cut slope soils are urgent.

Enzyme activity and microbial biomass availability in artificial soils on rock-cut slopes restored with outside soil spray seeding (OSSS): Influence of topography and season.

Large-scale railway construction has resulted in large areas of bare-cut-slope, and outside soil spray seeding (OSSS), a frequently used technique, has been adopted for slope restoration for many years. However, compared with natural slope soils, the quality of artificial soils on rock-cut slopes is low. Enzyme activity and microbial biomass are the main indices used for estimating soil quality; thus, our objective was to explore the influence of slope position, slope aspect, and season on two important factors that positively influence the plant growth capability in artificial soil. Further, we suggest modifications of the proportions of OSSS ingredients, not only to manage cut slopes more economically but also to provide a new framework for managing desertification. We chose a bare-cut-slope that had been restored five years ago near the Suiyu Railway (Chongqing-Suining), in Sichuan Province, China, as our study plot. Soil samples were collected at a depth of 10 cm. We conclude that natural slopes exhibited higher urease, sucrase, and catalase activity and higher microbial biomass than cut slopes. The protease and polyphenoloxidase enzyme activities and the microbial biomass were higher on the cut slopes in the months of October and January, with the highest protease activity in October, and the highest polyphenoloxidase activity in January. The enzyme activity and microbial biomass were always lower on lower slopes, with the exception of polyphenoloxidase activity. The slope aspect influenced soil enzyme activity, resulting in higher activity on north-facing slopes than on south-facing slopes. These results provided scientific support for artificial revegetation methods in an ecological context.

Effects and mechanisms of revegetation modes on cadmium and lead pollution in artificial soil on railway rock-cut slopes.

Artificial soil on railway rock-cut slopes may be considerably contaminated with cadmium (Cd) and lead (Pb), which may migrate to nearby croplands and pose substantial risks to human and animal health. We investigate the influence of three types of revegetation modes - herbs (HS); herbs and shrubs (HSS); and herbs, shrubs, and trees (HSTS) - on the transportation of these heavy metals in soils. Six representative rock-cut slopes were chosen, and the vegetation, pollutant concentration, phytostabilization, and simulated rainfall were investigated. The results indicated that Cd posed a considerable ecological risk, while Pb posed a low ecological risk in the artificial soil. The erosion of artificial soil on the slopes played a primary role in the migration of Cd and Pb, because 87-91% of Cd and 85-89% of Pb was lost in sediments. Revegetation modes significantly affected the transportation of Cd and Pb. HSTS controlled a lot of Cd in their dominant plants among the three revegetation modes. HSTS not only decreased enrichment factor (EF) and ecological risk (Er) values of Cd in the soils, but also decreased runoff, sediment and cumulative migrated Cd and Pb. The relationships among multi-factors were analyzed by stepwise mediation effect test and the results indicated that root weight density, aboveground biomass and immobilization of dominant plants for Cd and Pb were important direct factors which influenced the transportation of Cd and Pb. Overall, HSTS has proven to be beneficial in controlling the migration of Cd and Pb to croplands near the slopes and reducing their environmental risk. These results can offer a tested and implementable solution for mitigating the risks posed by these pollutants around the quickly expanding railways in the study region.

The texture, structure and nutrient availability of artificial soil on cut slopes restored with OSSS - Influence of restoration time.

Outside soil spray seeding (OSSS) is widely used to restore cut slopes in southwest of China, and artificial soil is often sprayed onto cut slopes to establish a soil layer for revegetation. The stability of artificial soil layer and its supply of water and nutrients for plants is crucial for successful restoration. To evaluate the long-term effectiveness of OSSS, the texture, structure and nutrient availability of artificial soil were studied, various soil samples were obtained from three cut slopes with different restoration time (restored with OSSS in 1996, 2003 and 2007 respectively) and one natural developed slope (NS). The properties measured including soil particle size distribution (PSD), texture, fractal dimension of PSD (Dm), the bias (CS) and peak convex (CE) coefficients of aggregate size distribution, structure failure rate, bulk density, moisture, pH, soil organic carbon (SOC), calcium carbonate content, Available nitrogen (NA), Available phosphorus (PA), and Available potassium (KA). The results showed that different restoration time resulted in significant differences in soil PSD, Dm, CS, CE, structure failure rate, bulk density, moisture, pH, NA, and KA. And these properties improved with increasing restoration age. However, there is still a huge disparity in soil texture, structure, and the availability of nutrients and moisture between the cut slopes and NS over a restoration period of up to 17 years, and this is caused by the little fine particles and the lack of slow release fertilizers and organic fertilizers in the artificial soil, resulting in poorer soil structure stability, retention and availability of moisture and nutrients on the cut slopes. Overall, the OSSS technique shows a long-term effectiveness in southwest of China, but there is still room for improvement.

The physico-chemical properties and structural characteristics of artificial soil for cut slope restoration in Southwestern China.

Cut slopes are frequently generated by construction work in hilly areas, and artificial soil is often sprayed onto them to promote ecological rehabilitation. The artificial soil properties are very important for effective management of the slopes. This paper uses fractal and moment methods to characterize soil particle size distribution (PSD) and aggregates composition. The fractal dimension (D) showed linear relationships between clay, silt, and sand contents, with coefficients of determination from 0.843 to 0.875, suggesting that using of D to evaluate the PSD of artificial soils is reasonable. The bias (CS) and peak convex (CE) coefficients showed significant correlations with structure failure rate, moisture content, and total porosity, which validated the moment method to quantitatively describe soil structure. Railway slope (RS) soil has lower organic carbon and soil moisture, and higher pH than natural slope soil. Overall, RS exhibited poor soil structure and physicochemical properties, increasing the risk of soil erosion. Hence, more effective management measures should be adopted to promote the restoration of cut slopes.

Impact of Soil Composition and Electrochemistry on Corrosion of Rock-cut Slope Nets along Railway Lines in China.

Taking the slope of Suiyu Railway to study, the research separately studied soil resistivity, soil electrochemistry (corrosion potential, oxidization reduction potential, electric potential gradient and pH), soil anions (total soluble salt, Cl(-), SO4(2-) and ), and soil nutrition (moisture content, organic matter, total nitrogen, alkali-hydrolysable nitrogen, available phosphorus, and available potassium) at different slope levels, and conducted corrosion grade evaluation on artificial soil according to its single index and comprehensive indexes. Compared with other factors, water has the biggest impact on the corrosion of slope protection net, followed by anion content. Total soluble salt has the moderate impact on the corrosion of slope protection net, and stray current has the moderate impact on the corrosion of mid-slope protection net. Comprehensive evaluation on the corrosive degree of soil samples indicates that the corrosion of upper slope is moderate, and the corrosion of mid-slope and lower slope is strong. Organic matter in soil is remarkably relevant to electric potential gradient. Available nitrogen, available potassium and available phosphorus are remarkably relevant to anions. The distribution of soil nutrient is indirectly relevant to slope type.

Distribution and phytoavailability of heavy metal chemical fractions in artificial soil on rock cut slopes alongside railways.

Artificial soil is often sprayed onto cut slopes alongside railroad tracks to promote revegetation. This study evaluated the heavy metal content and the distribution of heavy metal chemical fractions in the soil, as well as the uptake of heavy metals by plants. The soil at four sites was determined to be considerably contaminated with Cd and Pb. The concentrations of Cd and Pb increased with the length of time the railway had been in use and decreased further away from the railway tracks. Pb primarily existed in reducible form but as residual fractions, whereas Cd was predominantly in exchangeable form. A correlation analysis indicated that pH, organic matter, and total phosphorus levels were important factors affecting the distribution of the heavy metal chemical fractions. The amounts of exchangeable Pb and Cd in the soil were highly correlated with their amounts in the plants sampled, indicating that the exchangeable fraction is a better indication of heavy metal phytoavailability than the total amount of heavy metals in the soil. Bioaccumulation and translocation factors indicated that Indigofera amblyantha had moderate tolerance and bioaccumulation capability for Pb, as did Leucaena leucocephala for Cd. These two plant species can serve as ideal slope remediation plants.

[Determination of heavy metals in artificial soil on railway rock-cut slopes by microwave digestion-AAS].

The purpose of this paper is as follows: (1) Optimizing the parameters of microwave digestion-atomic absorption spectroscopy (AAS) and establishing method for the determination of heavy metals in artificial soils. (2) Evaluating heavy metal pollution conditions in artificial soil samples from railway rock-cut slopes. The results showed that the mixture of HNO3-H2O2-HF was found to have the best digestion efficiency; under the optimized conditions, the recoveries of the method ranged from 95% to 105%; the measurement precision and the relative deviation were less than 4% and 5%, respectively; the concentrations of Cd, Pb and Zn were significantly higher in the artificial soil on railway rock-cut slope than in the control soil, and they were 4.7, 1.3 and 1.2 times as much as the control soil, respectively; compared to the contents of Cr, Cu and Fe in control soils, there was no significant difference. This research will provide a reliable method for determining metal elements in artificial soils on rock-cut slopes and a theoretical basis for the management of the railway rock-cut slopes.

[Determination of heavy metal by AAS in railway rock-cut slope soil].

Heavy metal contents in railway rock-cut slope soil have directly influenced ecosystem on rock-cut slope and eco-envi- ronment safety of farmland nearby. In the study heavy metal Pb, Cd, Zn, Cu and Mn was determined by AAS in railway rock-cut slope and control soil samples on Cheng-Da Railway crossing purple soil in Sichuan province. The results showed that Pb and Mn were significantly higher in rock-cut soil than in control soil, that is 29.7%-35.4%, while Cd, Zn and Cu were similar in both soils.

[Application of AAS to detecting the influence of railway on the soil of navel orange garden].

Railway transportation has boosted the economy of railway road area, meanwhile it brings some undesirable impacts on the environment of the railway road area. The quality of the fruits is directly related with the elements of the soil, so understanding the element contents of soil in navel oranges garden in the vicinity of railway is meaningful to the security of agriculture products and ecological conditions in the areas surrounding the railways. As a favorite fruit, navel orange is widely planted around the railway in the south China, especially in Sichuan, Chongqing, Hubei, Jiangxi and Guizhou. The present paper studied the contents of Pb, Cd, Mn, Cu, Zn etc in the soil planting navel orange in the vicinity of Chengdu-Dazhou railway by AAS. The railway was built in 1997 and the research area was sited in Jintang county, Sichuan. The results showed that the contents of Pb and Mn in soil planting navel orange were significantly higher than those in the control soil, but the contents of Cd, Cu and Zn showed no significant difference.