Undisturbed Natural Soils Research Articles

Effectiveness Of Portland Cement Type 1 In Stabilizing Soft Clay Soil As Subgrade For Road Construction

Sawah Lunto – Talawi road segment (STA 139 + 700 m) in Sawah Lunto city, West Sumatera province has sustained major damages and been the scene of several accidents since the past few years. The degression of soft clay subgrade, which has a limited bearing capacity and makes it structurally impractical to sustain road construction, was discovered to be the source of these damages. As a recent option for enhancing soil qualities, soil stabilization by employing a variety of pozzolanic and industrial materials has gained popularity. The objective of this study is to investigate the effectiveness of Portland cement type 1 as stabilizing material in improving the soil properties and carrying capacity requirements for soft clay soil used as subgrade in road construction. To accomplish the objectives of this study, a laboratory testing procedure was implemented. Unconfined Compressive Strength (USC) values on natural soil and treated soil with Portland cement type 1 admixture were measured and compared during laboratory experiments. Soft clay soils were stabilized with varying percentages of Portland cement type 1 with the proportions of approximately 1%, 2%, 3%, 4%, 5%, 6%, 7%, and 10% by dry weight of soil during a 7-days curing period. Laboratory testing were performed in compliance with Indonesian National Standard (SNI): SNI 3420-2008 for testing Unconfined Compressive Strength. According to the results of laboratory testing, the UCS values increased roughly from 0.634 kg/cm2 (undisturbed natural soil) to 2.832 kg/cm2 (treated soil) by adding 3% of Portland cement type 1, and up to 8,024 kg/cm2 (treated soil) by adding 10% of Portland cement type 1. Based on the findings, it can be demonstrated that Portland cement type 1 can enhance clay soil's properties used as a subgrade for road construction, can create more stable road conditions, and can ultimately meet the technical feasibility requirements for the subgrade carrying capacity, particularly at the Sawah Lunto - Talawi road segment (STA 139 + 700 m).

Characterization of aggregate-stabilized dissolved organic matter release - A novel approach to determine soil health advances of conservation farming systems

PurposeSince principles of conservation agriculture mimic the soil conditions of undisturbed natural soils, linking aggregation and dissolved organic matter (DOM) occlusion would therefore provide a targeted descriptor for soil health advances of innovative farming systems. This study aimed to assess structure-related DOM patterns of conservation farming systems and underlying bio-chemical drivers by using a novel method for the combined analysis of aggregate breakdown and DOM release.MethodsSoil samples were collected from conventional farming, conservation farming and natural reference soil systems over a wide range of soil types. Ultrasonication aggregate breakdown combined with continuous UV–Vis measurement was used to characterize DOM release from soil. Measures of breakdown dynamics were related to soil physical and chemical properties to determine the strongest predictors of DOM release.ResultsThe quantity of DOM released and aggregate stabilization showed a steady continuum starting from standard farming through conservation agriculture towards reference soil systems. DOM released from reference soils however was less complex and occluded in more stable soil aggregates than arable soils. The overall DOM release dynamics are shaped by agricultural management with site-specific modifiers driving aggregation and mineral-organic interactions in soils.ConclusionsThe simultaneous quantification of aggregate breakdown and DOM release captures key biophysical effects in structure-related DOM stabilization and revealed significant differences between land-use and agricultural management systems. The linkage of physical with functional soil organic matter descriptors provides an improved approach to monitor soil health advances in arable cropping systems.

Assessment of the Potential of Umbrella Thorn [Vachellia tortilis (Forssk.) Galasso & Banfi] for the Rehabilitation of Sub-Sahelian Mining Sites at Essakane, North-Eastern Burkina Faso

Establishment of plant communities at mine sites with significant disturbance depends upon factors such as the presence of efficient mycorrhizal fungi and rhizobia. Field and greenhouse experiments were conducted to assess growth performance of umbrella thorn as a potential tree species for reforestation of mine sites in arid areas. In the first experiment, seedlings were transplanted onto waste rock stockpile (WR) and tailings (TLG) with high arsenic (As) content on sites at the Essakane gold mine. Trees were assessed for growth and survival 3 years after planting. In experiment 2, soil was sampled on four sites across a disturbance gradient from mining waste (WR and TLG) and artisanal gold mining to undisturbed natural soil (NS). Each soil was planted with two separate leguminous trap crops (cowpea and umbrella thorn) in pots to check for microsymbionts. At 3 years, trees grew better on TLG soils with greater arsenic contamination than WRs in the field. Although tree establishment was moderate, with <50% survival, overall results suggest the ability of umbrella thorn to tolerate As contamination levels up to 1,300 ppm and, therefore, its potential for reforestation. Soil pH has shown strong effects on soil nutrient content. In particular, ammonium was the dominant form of mineral nitrogen (N) in the more neutral pH NS soils, while nitrate was present in the more alkaline WRs. Denitrification likely resulted in high N loss where nitrate dominates, reflecting the poor performance of N-deficient trees on WRs compared to TLG soils. Growth trends of umbrella thorn in potted-soils were consistent with those reported on TLG and WR soils in plantations.

Chemical and microbial properties of post-mining and post-fire soils afforested with different tree species

The effect of tree species on properties of soils revegetated after serious disturbance may depend on the properties of the soil substrate and type of disturbance. We compared the microbial properties of reclaimed mine soils differing in texture (RMS Sands and RMS Loams, respectively), post-fire (Postfire) soils, and undisturbed natural soils (NAT) under three different tree species (black alder, silver birch and Scots pine). The uppermost mineral soil (depth 0–5 cm) samples were measured for the contents of organic carbon (Corg), total nitrogen (Nt) and phosphorus (Pt), dissolved organic carbon (DOC) and nitrogen (DON), pH in H2O and texture. Microbial analyses of the samples included determination of microbial biomass carbon (Cmic), basal respiration rate (RESP), as well as the activities of acid and alkaline phosphatase and urease. Enzyme activities were expressed per soil dry (AcdPho, AlkPho, URE for acid phosphatase, alkaline phosphatase and urease, respectively) and per unit of Cmic as specific enzyme activities (SP AcdPho, SP AlkPho and SP URE for acid and alkaline phosphatase and urease, respectively). The studied tree species differently affected the microbial properties of RMS, Postfire and NAT soils. Silver birch stimulated the development of large microbial biomass with high RESP and URE activity in RMS and Postfire soils. Black alder distinctly stimulated the activity of phosphatases – in particular AcdPho. High activity of phosphatases in the restored soils under black alder resulted from higher N content under this species and the competition for P between the tree species and soil microorganisms. This competition caused lower Cmic in the restored soils under alder despite their high Corg and Nt content. Scots pine had the weakest effect on the microbial properties of the soils restored after disturbance as the values of Cmic, RESP and the enzyme activities were the lowest under this species. Our results suggest that P availability may be limiting factor for the soil restoration under black alder. Therefore, additional P fertilization should be considered when using this tree species in restoration of degraded areas.

Antagonism and Resistance to Antibiotics of Actinomycetes from Soils of Three Specially Protected Natural Territories

The relevance of the study of antibiotic resistance of microorganisms in specially protected natural areas is due to the need to control the spread of resistance among human, animal, and plant pathogens. According to the concept of resistome, microorganisms of natural microbial communities, including soil microbial cenoses, contain many antibiotic-resistant genes and actively exchange them. Information on the spread of antibiotic resistance among microorganisms in the habitats undisturbed by economic activity is currently insufficient. Forty-eight strains of streptomycetes were isolated from soils of different geneses: soddy alluvial soil (Fluvisol) in the Nurgush State Nature Reserve (Kirov oblast), mountainous cinnamonic soil (Cambisol) in the Novyi Svet Nature Reserve (Crimea), and brown forest soils (Cambisols) in the Belovezhskaya Pushcha National Park (Belarus). Their antagonistic activity against micromycetes and bacteria was examined. It was shown that the potential of antagonistic action of the isolates from acid soddy alluvial soil exceeds that of the cultures isolated from other two soils. The assessment of resistance of natural isolates to eight antibiotics of different classes and with different mechanisms of action (the inhibitors of synthesis of cell walls, nucleic acid, protein, and metabolic pathways) has revealed specific features that distinguish the resistance spectra of streptomycetes isolated from undisturbed natural soils of different geneses from one another. The findings expand existing concepts of the spread of antibiotic resistance to undisturbed biotopes and are of great interest for assessing the risk of resistance gene transfer from the environment to pathogens.

Determination of iodine mobility in the soil vadose zone using long-term column experiments

129I is emitted continuously in large amounts by reprocessing plants in La Hague and Sellafield. For determination of mobility in soil, we provide results of column experiments with undisturbed natural soils. Directly after short-term (28 days) contact with water from the bottom, iodine shows high upwards mobility only due to capillary forces. Furthermore, desiccation of the contaminated tracer reservoir led to an even stronger migration effect, which indicates remobilization of iodine from the drying soil layers. Chemical speciation proves difficult, as either gaseous iodine or organically bound iodine attached to dissolved organic matter are possible for the upward migration processes.

Novel rapid measurement system of undisturbed soils water characteristics curve utilizing the continuous pressurization method

Through this paper, a sampling methodology and a novel full automatic system adopting the continuous pressurization method which is capable of determining the Soil Water Characteristics Curve (SWCC) for both remoulded and undisturbed samples in a very short time were developed. The proposed system was validated by comparing the SWCCs of standard testing soils obtained using the developed system to the SWCCs obtained using a conventional method. Remoulded and undisturbed natural soil samples were tested, where the degree of disturbance influence on the obtained SWCC was discussed. In addition, the undisturbed samples containing moulds material influence on the obtained SWCC was investigated. It was found that remoulded samples do not properly represent the in-situ conditions with significant error that should be carefully considered when conducting analysis and proposing countermeasures against unsaturated soils related Geo-disasters. In addition, the material which the containing mould is made from has minor influence on the obtained SWCC which can be neglected. Finally, it can be concluded that the developed undisturbed soil water characteristics curve obtaining system is direct, rapid, reliable and simple. In addition, the proposed undisturbed sampling and testing methodology can be used to accurately evaluate the spatial variations of the SWCC regardless the heterogeneity of the soil profile.

Corrosion Rate Estimation in Steel Sheet Pile Walls - Comparison between Empirical Models and Eurocode 3, Part 5

Steel sheet pile wall corrosion in soils and water is a complex phenomenon. The deterioration of these structures is costly and difficult to predict. The aim of this paper was to deal some empirical corrosion models which are analyzed and compared to Eurocode 3, Part 5 to estimate corrosion rate and the loss of thickness of anchored steel sheet pile wall. The results show that care should be taken to ensure that the maximum bending moments do not occur at the same level as the main corrosion zones. Furthermore, it is possible to define an upper and a lower bound, corresponding respectively to the presence of sea water in low water and the undisturbed natural soils, in order to predict the loss of thickness due to corrosion.

Protection of extractable lipid and lignin: Differences in undisturbed and cultivated soils detected by molecular markers

Understanding formation of organo-mineral association is crucial for soil organic matter (SOM) stabilization. To remove reactive minerals from un-disturbed natural soil (NS) and two cultivated soils (dry-farming soil, TD, and terrace paddy soil, TP), a 10% HF/1M HCl treatment was applied. The mineral protection of different molecular SOM structures before and after cultivation was compared by using markers for lipid and lignin. The removal of reactive mineral increased the lipid extractability in TD and NS similarly, indicating that the cultivation did not reduce the mineral protection; this is attributable to fertilizer application and amorphous Fe oxide enrichment. In TP, the extent of lipid protection was lower than in TD, demonstrating that the protection depends on the type of cultivation. In contrast to lipids, lignin-derived phenols decreased over 80% after acid treatment. Furthermore, the ratios of acid to aldehyde in vanillyl ((Ad/Al)V) of TD and TP were much higher than in NS, indicating an increased oxidation of lignin in cultivated soils. During acid treatment, two distinct layers of soil particles were identified: an organic matter (OM)-enriched layer (LOM), and a non-reactive mineral-enriched layer (LNR) with hardly detectable OC content. However, up to 50% of lipids were detected in LNR, indicating that lipids did not selectively interact with reactive mineral particles. In TD and TP, (Ad/Al)V values were higher in LOM than in LNR, indicating a strong interaction of oxidized lignin in LOM. Therefore, the protection of lignin, especially highly oxidized lignin, can depend more on reactive minerals than lipid. Promoting the formation of organo-mineral complexes is the primary strategy for soil management, especially for highly oxidized OM.

Soils of Different Land Use Categories in the City of Petrozavodsk

In the territory of the city of Petrozavodsk, the following categories of land use were distinguished: lands of common use, lands of urban and rural development, natural recreation zone, and reserved land. In each area, soil pits were made, and each full profile was analyzed for its morphological structure and physicochemical properties. Among soils, urbostratozems (Urbic Technosols) predominate, urbistratified natural soils (Plaggic Cambisols, Technic Podzols), and technogenic surface formations are spread to a lesser extent. The undisturbed natural soil cover is preserved in suburban forests and on lands of reserve and rural development. The urban soils differ in their physicochemical properties from the zonal natural soils by the elevated base saturation and high content of mineral nutrients. Heavy metal concentrations are mainly at the level of regional background characteristics. Maximum/tentatively permissible concentrations of lead, copper and zinc are exceeded on the lands of common use, building areas, and in the natural recreational zone of the city, which was influenced in the past by the activity of the city-forming plant.

Polycyclic aromatic hydrocarbons in atmospheric particulate depositions and urban soils of Moscow, Russia

The study was conducted to quantify the polycyclic aromatic hydrocarbons (PAHs) accumulation in urban soils from different functional areas via atmospheric inputs with particulate matter. PAH concentration and pattern were measured in the particulate matter of snow depositions, in the upper layers of artificial soils from densely built-up areas and in the undisturbed natural soils (Umbric Retisols) from green park area. Samples were collected in 2011–2013 at 58 sites with different traffic activities located at the territory of the Eastern Administrative Okrug of Moscow. The soil samples and filters with particulate matter were extracted by pressurized liquid extraction using Dionex ASE200. Clean-up analyses were performed on SPE cartridges filled with silica gel. Concentrations of PAHs were determined by high-performance liquid chromatography using an Agilent 1100 System equipped with fluorescent detector. Mean values of PAH input with snow particles were 45–57 μg/m2 for recreational and residential zones, and 140–264 μg/m2 for traffic zones. The samples of depositions from different functional areas showed a similar PAH pattern and consisted primarily of 3–4-ring PAHs. Total PAH concentrations in upper layers of artificial soils showed similar mean values of 1.43–2.21 μg/g for all functional zones. The PAH content in soils from the park area was twofold lower than that from the built-up area (0.34–0.63 μg/g), despite equal levels of atmosphere contamination on these territories. The upper layers of natural soils from recreational and traffic zones showed slight differences in PAH content, though PAH input with snow was fivefold higher in the traffic zone. Compared with airborne depositions, soils contained significant amounts of 5–6-ring PAHs. A high level of soil PAH contamination in urban areas of Moscow, several orders of magnitude higher than the current PAH input to them from the atmosphere, indicates a lack of direct connection of the PAH pool in soils with this source. The high PAH content in the upper layer of constructed soils can be the result of repeated use of materials subjected to a constant technogenic impact for the production of artificial soils.

Isolation of actinomycetes with antibacterial activity against multi-drug resistant bacteria

Aims: To isolate and characterise actinomycetes from various sources of soil samples (fruit orchard, dipterocarp forest and oil palm plantation) and to screen these isolates for antibacterial activity against multi-drug resistant bacteria. Methodology and results: A total of 158 fast-growing actinomycete isolates with different colony morphology were subjected to primary cross-streak and secondary well diffusion screening. Six isolates (OP1E, OP7A, OP2A-C, MG1A, UT9C1 and UT7E) were found to inhibit at least one of the seven multi-drug resistant (MDR) bacteria. MG1A exhibited the strongest and broadest spectrum of antibacterial activity against 6 MDR bacteria tested. These isolates were identified as Streptomyces species based on 16S rRNA gene sequence analysis. Further morphological and biochemical analysis revealed that MG1A was highly similar to S. griseocarneus (98.36%) whereas OP1E and OP2A-C were similar to S. parvulus (99.93% and 99.51% respectively). Preliminary identification using LCMS/MS and database search revealed that the major compound in the extract of OP2A-C could be dactinomycin (1255.4170 g/mol). Other antibacterial compounds in the extracts remain to be identified. Conclusion, significance and impact of study: Soil actinomycetes with antibacterial activity against MDR bacteria were isolated not only from undisturbed natural soils but cultivated soils. These isolates were characterised, identified and the antibacterial compounds were extracted for further study. The isolates could serve as a potential source for the development of new and sustainable compounds against MDR bacteria.

Distribution, fractions, and potential release of thallium in acidic soils nearby a waste copper mining site from southern China.

Although thallium (Tl) is a highly toxic element, little information is available on the environmental risks of Tl in agricultural soils with intensive practices, particularly nearby mining sites. Therefore, we investigated the potential release of Tl in acidic soils with intensive cultivation nearby a waste copper mining site from southern China based on its level and chemical fractions as well as simulated release under artificial acid rain. Results showed that the average Tl content was 1.31mg/kg in the studied area, which significantly exceeds the permissible thallium value of 1mg/kg for agricultural soil in China. Some vertical increases of soil Tl from different land uses indicate the potential transport of Tl downward to groundwater. High positive correlations between surficial soil Tl and rubidium (Rb) and copper (Cu) indicated that Tl has the lithophile and chalcophile behavior. Tl in soils is mainly entrapped in residual fraction. The exchangeable fraction of Tl in agricultural soils was less than undisturbed natural soils and copper mined soils. Additionally, the percentage of Tl release from undisturbed natural soils and soils of copper ore area was more than that from agricultural soils in simulated acid rain. Furthermore, the releases of Tl from the soils increased with the acidity of artificial acid rain. Thus, more attention must be paid to land management of this similar area to avoid the risk of Tl impact on human health.

The combination of quarry restoration strategies in semiarid climate induces different responses in biochemical and microbiological soil properties

Mining activities generate loss of environmental and landscape quality, especially in arid and semiarid Mediterranean regions. A precondition for ecosystem reclamation in such highly disturbed areas is the development of functional soils with sufficient amount of organic matter. In a restoration experiment in limestone quarries in the Sierra de Gádor (Almería), SE Spain, several combinations of organic amendments (sewage sludge and compost from domestic organic waste) and mulches (gravel and woodchip) were tested and native plants (Anthyllis cytisoides, A. terniflora and Macrochloa tenacissima) were planted. After five years, the effect of each treatment on the soil chemical properties, basal respiration, four enzyme activities (dehydrogenase, urease, β-glucosidase and alkaline phosphatase) and the microbial community composition was analysed. Analysis of phospholipid fatty acids (PLFAs) and polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) fingerprinting were used to analyse the microbial communities (bacteria and fungi). Undisturbed natural soils adjacent to the mining area were used as soil quality references. Organic amendments, particularly compost, improved soil chemical and biochemical properties as well as microbial biomass. However, the effects of mulch application did not show a clear trend with respect to soil functionality and did not increase the microbial biomass. Soils treated with sewage sludge and compost showed bacterial PLFA concentrations similar to those of reference soils, but compost treatments presented fungal PLFA concentrations that were much higher. Each combination of organic amendment and mulch was selective for a proper microbial community. Nevertheless, increases in soil functionality and microbial biomass were not related to changes in microbial diversity. After five years, the microbial properties of restored soils had not yet converged to values recorded in the reference soils. However, the combination of mulches and organic amendments, particularly compost treatment, is suggested to be beneficial for restoring degraded soils from quarrying areas because they stimulate microbial growth and activity, with positive implications for the increase in both soil fertility and quality.

An experimental study on the effects of physical, mechanical, and electrochemical properties of natural cohesive soils on critical shear stress and erosion rate

The field of cohesive sediment erosion is still not fully understood, in large part due to the many soil parameters that affect cohesive sediment erodibility. In this study several undisturbed natural soil samples were taken from different river banks in Manitoba, Canada. The samples mainly contained clay and silt with 24–94% clay content, thus the study covered a wide range of cohesive soil. For each sample 13 different physical, mechanical, and electrochemical properties were measured. Critical shear stress of erosion and erosion rate were quantified using an Erosion Measurement Device (EMD). Stepwise regression was used to find the variables most significantly correlated to critical shear stress and erosion rate, which led to the development of a new empirical equation to estimate the critical shear stress of cohesive soils. It was found that the critical shear stress is highly correlated with cohesion, while both cohesion and sodium adsorption ratio (SAR) had significant influence on the erosion rate.

Role of macropore flow in the transport of Escherichia coli cells in undisturbed cores of a brown leached soil.

The objective of this work was to evaluate the transport of Escherichia coli cells in undisturbed cores of a brown leached soil collected at La Côte St André (France). Two undisturbed soil cores subjected to repeated injections of bacterial cells and/or bromide tracer were used to investigate the effect of soil hydrodynamics and ionic strength on cell mobility. Under the tested experimental conditions, E. coli cells were shown to be transported at the water velocity (retardation factor close to 1) and their retention appeared almost insensitive to water flow and ionic strength variations, both factors being known to control bacterial transport in model saturated porous media. In contrast, E. coli breakthrough curves evolved significantly along with the repetition of the cell injections in each soil core, with a progressive acceleration of their transport. The evolution of E. coli cells BTCs was shown to be due to the evolution of the structure of soil hydraulic pathways caused by the repeated water infiltrations and drainage as may occur in the field. This evolution was demonstrated through mercury intrusion porosimetry (MIP) performed on soil aggregates before and after the repeated infiltrations of bacteria. MIP revealed a progressive and important reduction of the soil aggregate porosity, n, that decreased from approximately 0.5 to 0.3, along with a decrease of the soil percolating step from 27 to 2 μm. From this result a clear compaction of soil aggregates was evidenced that concerned preferentially the pores larger than 2 μm equivalent diameter, i.e. those allowing bacterial cell passage. Since no significant reduction of the global soil volume was observed at the core scale, this aggregate compaction was accompanied by macropore formation that became progressively the preferential hydraulic pathway in the soil cores, leading to transiently bi-modal bacterial BTCs. The evolution of the soil pore structure induced a modification of the main hydrodynamic processes, evolving from a matrix-dominant transfer of water and bacteria to a macropore-dominant transfer. This work points out the importance of using undisturbed natural soils to evaluate the mobility of bacteria in the field, since the evolving hydrodynamic properties of soils appeared to dominate most physicochemical factors.

Effect of ethanol on the biodegradation of gasoline in an unsaturated tropical soil

Leaking underground storage tanks are a worldwide problem nowadays, therefore gasoline degradation and distribution in the subsurface have been widely studied. Brazil is the only country to currently use ethanol as fuel and as an oxygenate additive to gasoline, in amounts varying from 20 to 26% v/v. Consequently, both gasoline and ethanol may contaminate the environment when spills and leaks occur. Some authors suggest that despite the high degradability of gasoline, its degradation in the aquifer is hindered by the preferential biodegradation of ethanol, which would delay gasoline degradation; however, processes in the unsaturated zone are far less understood. The present study concentrates on degradation and distribution processes of ethanol-amended gasoline in tropical soil under unsaturated conditions. A multi-parametrical approach was adopted to assess the effects of ethanol on the fate of gasoline. Undisturbed natural soil was used to evaluate biodegradation processes while tank experiments determined differences in infiltration, distribution and retention of gasoline in unsaturated artificial porous medium. Physical, chemical and microbiological results suggest that ethanol enhances BTEX retention in soil, boosts microbial activity but delays BTEX biodegradation.

Environmental concerns related to high thallium levels in soils and thallium uptake by plants in southwest Guizhou, China

Thallium (Tl) contamination in soils poses a significant threat to human health due to the high toxicity of Tl and its ready assimilation by crops. This study is focused on high concentrations of Tl in soils in the Lanmuchang area of southwest Guizhou, China, which is related to natural processes of Tl-rich sulfide mineralization. Thallium contents range from 40 to 124 mg/kg in soils originating from the mining area, from 20 to 28 mg/kg in slope wash materials, from 14 to 62 mg/kg in alluvial deposits downstream, from 1.5 to 6.9 mg/kg in undisturbed natural soils and <0.2 to 0.5 mg/kg Tl in soils from the background area. These values indicate that both the erosion of natural soils from the Tl mineralized area and the mining activity are responsible for the distribution of high Tl concentrations in soils. Two other important toxic metals of interest, mercury and arsenic, also show high contents in soils, and are generally higher than Tl concentrations. Thallium concentration in plants exhibit species-dependent preferences. Thus, the enrichment of Tl in the edible parts of crop species decreases in the following order: green cabbage>carrot>chili>Chinese cabbage>rice>corn. The highest level of Tl in green cabbage is up to 500 mg/kg as dry wt., surpassing the values of Tl in the soils in which the green cabbages grow. In contrast, Hg and As are relatively less concentrated in local plants. The average daily uptake of Tl by the villagers of the Lanmuchang area through consumption of locally planted crops has been estimated to be 1.9 mg/person, which is 50 times the daily ingestion of individuals from the Tl-free background area. The daily ingestion of As and Hg from the study area are 0.03 and 0.01 mg, respectively. This indicates that Tl in the contaminated soils related to the natural Tl mineralization is being readily transferred to the human body through the food chain, and poses a significant threat to the health of the local villagers. Arsenic may pose a lesser health hazard, but mercury has an insignificant health risk. This study illustrates a real environmental concern related to land use and human health in areas containing high contents of Tl in soils associated with the natural occurrence of Tl-rich sulfides and coals, with or without mining activities. Thallium contamination in soils should be a critical parameter for proper land use and health related environmental planning and regulations.

PHYSICAL RECONSTRUCTION OF MINE TAILINGS AFTER SURFACE MINING MINERAL SANDS FROM PRIME AGRICULTURAL LAND

Minable quantities of heavy minerals occur in prime agricultural lands of the Atlantic Coastal Plain. We evaluated the use of yard waste compost to reclaim tailings mined from these lands. A 30 × 60-m area was excavated to a depth of 5 m to establish a reclamation study site. Soils were removed, treated in a manner simulating the separation of the mineral sands, and returned in a slurry form. Undisturbed natural soils, Hapludults and Paleudults, have sand and loamy sand surface horizons. Mining these soils and redistributing the tailings as a slurry resulted in sandy loam and sandy clay loam textures. Treatments established in the tailings were: unamended tailings; tailings amended with 23 to 270 t/ha compost; and tailings capped with 45 cm of topsoil. Selected treatments were sampled and analyzed to test for differences in the physical properties related to treatment. Gravimetric water contents of tailings amended with 135 t/ha compost were significantly higher (at the 0.05 level) than unamended tailings, tailings capped with top soil, or the natural soil. Mechanical resistance values recorded in the Fall for tailings amended with 135 t/ha of compost were lower than the unamended tailings and tailings capped with topsoil. Mean hydraulic conductivity (Ksat) and porosity values for tailings amended with 135 t/ha compost were higher than the natural soil surface horizons. Tailings amended with as little as 45 t/ha compost had higher porosity (48%) and lower bulk density (1.38 g/cm3) values than the natural soil surface (45% and 1.43 g/cm3). Tailings capped with topsoil had the highest bulk density (1.64 g/cm3) and lowest porosity (38%) and Ksat (0.13 cm/hr), suggesting that this reclamation approach may not be the best way to try to reclaim the tailings. Average corn yields for tailings amended with compost were higher than those for tailings capped with topsoil or unamended tailings. Results suggest that mine soils can be constructed with excellent physical properties with regard to plant growth by amending tailings with yardwaste compost.

THE EFFECT OF SOIL STRUCTURE ON THE BANK EROSION RATE

Estimation of erosive resistance of natural bank is important subject of river course design. Erosion process is found to be composed of three stages: erosion of lower non-cohesive layer of bank, collapse of overhanging upper cohesive layer in tension and the breakup and transport of the collapsed soil mass by the flow. And there are many attempts to understand erosion rate of bank soil by field experiments. But it is not enough to explain erosion mechanism and generalize erosion rate and so on. Because the field experiments were in the limited hydraulics and soil conditions. In this study, the direct relationship between soil characteristics, soil structure and erosion mechanism was examined by the erosion experiments using an open channel with 3 kinds of undisturbed natural soils. Finally prospect of bank erosion is discussed and summarized.