Lateritic Soil Profile Research Articles

Rock Magnetic and Mineralogical Properties of Lateritic Soil Profiles Developed on Two Different Parent Rocks in Northern Kerala, South-Western India

The rock magnetic and mineralogical properties of two lateritic soil profiles developed on two different parent rocks (khondalite and granite) in northern Kerala, south-western India were investigated to better understand pedogenic processes under tropical climate. Field investigations reveal the presence of various horizons in the lateritic profiles, such as saprolite, mottled zone, pebble horizon and top soil. The particle size, rock magnetic, Vibrating Sample Magnetometer (VSM), Scanning Electron Microscopy (SEM)-Energy-Dispersive X-ray Spectrometer (EDS) and X-Ray Diffraction (XRD) analyses were performed on samples collected from different horizons of the two profiles. Magnetic susceptibility (χlf) values of the lateritic profiles vary from 9.97 to 1717.04 x 10-8 m3 kg-1, with the granitic profile exhibiting overall higher values. The percentage frequency-dependent susceptibility (χ %) ranges between 0 % and 13.9 %. The XRD data reveal the presence of kaolinite, gibbsite (except for top soil layer) and quartz along with magnetic minerals like magnetite, hematite and goethite. The upper horizons (top-soil and pebble horizon) exhibit high values for concentration dependent magnetic parameters like χlf and χfd%, whereas, the lower horizons (saprock, saprolite, pallid zone horizons) exhibit low values. The tropical soils in the region have undergone a higher degree of pedogenesis with increased magnetic mineral concentration compared to temperate soils. The magnetic enhancement in the topsoil may be due to the neoformation of ultra fine-grained SP magnetite/maghemite (with minor anti-ferro magnetic component), aided by sufficient Fe supply, alternate wetting and drying cycles, dehydration, oxidation and redox conditions. Keywords: Lateritic Soils; Soil Magnetism; XRD; SEM; Magnetic Enhancement; Pedogenesis; Southern India

Variability Analysis of the Behaviors of a Lateritic Soil Profile as a Structural Material

The desideratum of determining the behavior of the underlying soil on which the foundations will be laid is indisputable. This study evaluates the strength characteristics of lateritic soil material at a new construction site opposite College of Engineering and Engineering Technology (CEET), Michael Okpara University of Agriculture, Umudike (MOUAU). A trail pit was dug taking disturbed soil samples at a depth of 1m, 2m, and 3m for experimental analysis. Laboratory tests on specific gravity, grain size distribution, moisture content, atterberg limits, and triaxial tests were carried out on each sample by the procedure highlighted in BS1377 1990. Inspecting visually, the soil profile was observed to consist of three layers; light reddish, reddish, and whitish at the top, middle, and bottom respectively. The natural water content of the soil samples varied as 9.06+0.00 %, 7.98+0.00 %, and 9.32+0.03 %, while the specific gravity obtained from the test results was 2. 630+0.00 %, 2.634+0.00 % and 2.647+0.00 % at depths 1m, 2m, and 3m respectively. Using the unified soil classification system (USCS), the top, middle and bottom layers were classified as cloud sand (SC). The soil samples have a liquid limit (LL) of 24.5%, 28.8%, 31.0%; plastic limit (PL) of 19.4%, 17.2%, 18.5%; and plasticity index (PI) of 5.1%, 11.6%, and 12.5% at depths 1m, 2m, and 3m respectively. It was observed that the soil index properties vary and are enhanced as the depth of the excavation increases. Furthermore, the value of the cohesion property of the soil is 74.62 kN/m2, 29.70 KN/m2, and 24.65 KN/m2 for samples at 2m, 3m, and 3m depth respectively. The greatest and least cohesion value was noted to be 74.62 kN/m2 and 24.65 kN/m2 for samples at 2m and 3m depth respectively; the maximum and minimum angles of internal friction were 25.52o and 13.67o at depths 1m and 2m respectively. The outcome of this paper showed that the analyzed soil samples are suitable for civil engineering works.

Geotechnical characterization of the lateritic soil profile. Moa, Cuba

This paper presents the results of the study of the physical and geotechnical properties of the vertical profile of lateritic soils. The study analyses the different zones of the profile. The study of the physical-mechanical properties is carried out according to the unified soil classification system. The mineralogical composition is determined by DRx and the chemical composition by ICP-AES. Among the physical properties analysed are particle size distribution, specific weight of solid particles, dry density and porosity, pore index, moisture and degree of saturation, plasticity, angle of internal friction and cohesion. The upper ferricretic layer is characterized by a sandy-gravelly grain size, whilst in the limonitic, transition and saprolitic zones the silt-clay fraction predominates.

Jurassic and Cretaceous clastic petroleum reservoirs of the West Siberian sedimentary basin: Mineralogy of clays and influence on poro-perm properties

• Kaolinite is a predominant clay for Jurassic while chlorite for Cretaceous reservoirs. • Secondary chloritization might not have affected the coarse-grained lithic clasts . • A lowland relief predominated in Jurassic and volcanic upland relief in Cretaceous. The West Siberian Sedimentary Basin (WSSB) is the main commercial and the biggest sedimentary basin of Russia and plays a huge role in the Russian oil and gas industry. Three deep wells intersecting full sections of the basin main Jurassic and Cretaceous reservoirs have been studied. This basin consists of two major petroliferous sedimentary sequences: uppermost is of Lower Cretaceous (the Neocomian Sedimentary Sequence) and the oldest petroliferous sandstones of Jurassic age (the Urman-Togur-Tyumen sequence). All the main oilfields of the WSSB are found in sandstone reservoirs, and this paper describes their petrography and mineralogy, emphasizing on the nature and origin of the clay fraction (<2 µm). Each section was characterized by granulometry and mineral composition using optical microscopy, X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) techniques. The uppermost Lower Cretaceous sequence, that appears to be related to volcanogenic debris of high iron content, is characterized by abundant chlorite of similarly high iron content. The clay mineralogy of the petroliferous sandstones in the lowermost Jurassic sequence is not so chloritic but is more kaolinitic, a feature believed to be inherited from weathering of lateritic type soil profiles in the source area, as well as post-sedimentary authigenic conversion of feldspars.

Original

A proper geomorphic study of a region can be useful in understanding past and present environmental circumstances and analyzing potential environmental risks. Careful analysis of morphodynamic processes and existing diagnostic landforms reveal several aspects about the origin, characteristics and possible pattern of morpho-climatic interactions on the landscape over temporal scale, which helps significantly in proper terrain evaluation from societal welfare and integrated management point of view, including environmental risk assessment and disaster management. This paper has made a thorough geomorphic investigation based on intensive fieldwork and multi-sourced remote sensing data to characterize the lateritic soil profile and landforms of the study area in respect to their morphology and Physico-chemical properties at the different sites of land degradation to understand the outcome of morphoclimatic interactions on the landscape over time, and to evaluate the severity of operation with pedo-geomorphic constraints in the lateritic environment for sustainable management purposes. It is found that the region is highly sensitive to weathering, mass movement and denudational activities, mainly caused by rainwater erosion which has resulted into varied landforms including well-developed rills and gullies, lateritic ridges, isolated residual hills etc and generated a unique identity to this part of the lateritic region. The study also suggested a model for the development of geomorphic landforms in a lateritic terrain based on past and present morphoclimatic interactions, nature of physiography, lithology, soil characteristics and other biotic and abiotic elements. The region is also found to be a subject to moderate to severe land degradation due to the active geomorphic processes in operation in tropical regions and inherently poor physical and chemical formation of the existing soil profile and radical conversion of land uses as observed at cadastral level leading towards irresistible desertification. Annual topsoil loss amount has been calculated using the Universal Soil Loss Equation method. Three sample Mouzas namely Ballavpur, Shyambati and Chawpahari jungle have been assessed to be having 36.98%, 71.42% and 61.73% of degraded land in respect to their total village area. Various conservative measures like stabilization of gully heads and beds through reforestation and afforestation with cutting earth plug, brush fills and check dams; improvement of the irrigation network, suitable dryland farming etc. have been recommended to arrest the desertification process.

Mineralogical and geochemical aspects of Miocene laterite, Sharm Lollia area, South Eastern Desert, Egypt

A lateritic soil profile formed on the top of the middle Miocene was identified in the south of the Eastern Desert of Egypt. It is located about 55 km south of Marsa Alam and far about 3 km from the Red Sea coast. The mineral identification of samples was carried out using X-ray diffraction (XRD) and scanning electron microscope (SEM). The study revealed the relative predominance of kaolinite and gibbsite beside iron minerals (hematite and goethite), evaporates (halite and anhydrite), carbonate (dolomite and calcite), quartz, and cryptomelane. Accessory minerals are represented by columbite, tapiolite, thorite, monazite, zircon, barite, atacamite, anarkite, romanchite, hemimorphite, cerussite, garnet, ilmenite, nickel, and flurorichterite. The geochemical data of the bulk samples reflect enrichment in SiO2, Al2O3, Fe2O3, Zn, Pb, Ba, Sr, As, Nb, Cu, and Zr. This lateritic soil shows high Uc/Th ratio indicating addition of uranium under suboxic to anoxic condition. The LREE predominance was over the HREE due to the presence of monazite mineral. Negative Eu anomaly confirms the saturated source rocks of these laterites.

Rock magnetic properties of lateritic soil profiles from southern India: Evidence for pedogenic processes

We report here data on the pH, electrical conductivity (EC) and environmental magnetic properties (χlf, χfd, χARM, IRMs at different field strengths) of modern tropical lateritic soils from Aribail, Miyapadavu and Uliyathadka, all in the Kasaragod District of Kerala, southern India. This study aims to characterize the rock magnetic properties of lateritic soils that formed under tropical high-rainfall conditions and determine the effects of pedogenesis on soil magnetic properties in comparison with temperate soils. The profiles may be divided into two or three zones based on differences in magnetic mineral concentration, grain size and mineralogy. There is no magnetic enhancement of topsoil in any of the profiles studied. As the lateritic rocks in the region are ferruginous, the lateritic soils developed over them contain significant amounts of coarse grained lithogenic magnetite as well as hematite. Because of the presence of this ‘laterite-derived’ magnetite and hematite, the lateritic soils have much higher susceptibility values when compared to temperate soils. The upper zone is characterized by a higher proportion of lithogenic grains and the lower zone by superparamagnetic (SP) grains. This is probably because of iron reduction and dissolution of fine magnetic grains at the profile-top because of the excessively high rainfall (average=~3500mm/year) in the region. The slight increase in χlf and SIRM values toward the top of the Aribail and Miyapadavu profiles is due to the presence of coarse magnetic grains. This characteristic is common to all the three profiles irrespective of the topography. Compared to pre-monsoon samples, post-monsoon samples exhibit an increase in the proportion of SP grains. However, the magnetic grain size of lateritic soils from the three locations is similar to that of temperate soils.

Aspects of Mechanical Behavior and Modeling of a Tropical Unsaturated Soil

The research studies the applicability of two elastoplastic models for the collapse prediction of the lateritic soil profile from Southeastern Brazil. These tropical soils have peculiar geotechnical behavior, due to their mineralogical composition and porous structure coming from intense process of formation. Two elastoplastic models were analyzed: the Barcelona Basic Model (BBM) and another one based on BBM, however developed for tropical soils. Oedometric tests with suction control were performed at three distinct depths of the soil profile. The BBM was not suitable for the upper layer of the soil profile, because BBM considers the compressible behavior of the soil in function of the reduction of the elastoplastic compressibility index with the increase of the matric suction. The model developed for tropical soils showed better suited to the compressible behavior of the soil profile, resulting in good prediction of the collapse potential, mainly by accepting increasing values of the elastoplastic compressibility index of the soil profile with the matric suction rise.

A proposal of structural models for colluvial and lateritic soil profile from southwestern Brazil on the basis of their collapsible behavior

This paper aims to propose structural models for understanding the collapsibility of a colluvial and lateritic soil by conducting oedometric tests with controlled suction executed in laboratory. The undisturbed soil samples submitted to experiments were collected by opening a trial pit in Experimental Field for Soil Mechanics and Foundations situated at the State University of Campinas, São Paulo, Brazil. The soil samples were characterized by means of standard geotechnical tests, chemical and mineralogical tests and mercury intrusion porosimetry. Oedometric tests with controlled suction showed the influence of matric suction on the compressibility of the soil samples. It was also observed that the higher the values of matric suction, the higher the Laboratory Collapse Potential — CP. The mineralogical chemical tests indicated the presence of oxides and hydroxides of iron in the samples, compounds usually associated with cementation. The presence of mineral, such as kaolinite, gibbsite, hematite and goethite, was also observed. The impregnated thin-layer plates of the soil samples, as well as the grain-size distribution curves and mercury intrusion porosimetry, indicated the presence of a structure formed by microaggregates. Structural models for soil collapse were proposed basing on the results obtained. There were behavioral differences in each soil sample collected at different depths. The behavior of the sample collected at a 1.5m depth was basically influenced by matric suction. As for the samples collected at 4.5m and 6.5m, besides being both influenced by matric suction they were also influenced by the presence of cementing agents (samples collected at 4.5m) and by the presence of more angular grains of quartz (samples collected at 6.5m).

Soil–Water Characteristic Curves Obtained for a Colluvial and Lateritic Soil Profile Considering the Macro and Micro Porosity

This study aims to determine and to model the relationship of matric suction versus water content, known as soil–water characteristic curve (SWCC), for a tropical soil profile at the southeastern Brazil. This soil profile consists of a colluvial, lateritic silty clay, with thickness of about 6.5 m. The filter paper and pressure plate techniques were used to determine the SWCC. Specimens were trimmed from the undisturbed soil samples collected along soil profile depth and submitted to drying paths. Impregnated thin-layer plates and a petrographic microscope were used to examine the structure and mineralogical composition of the soil samples. Mercury intrusion porosimetry tests were performed on some soil samples to obtain the frequency histogram of the pores. SWCC with bimodal pore-size distribution were obtained by the filter paper technique and SWCC with unimodal pore-size distribution were obtained by the pressure plate technique. The SWCC showed values of air-entry ranging from 1 to 3 kPa, depending on the technique used, resembling soils with macroporosity, as the lateritic soils. Combining both techniques, the SWCC could be fitted by a model that takes into consideration soils with macro and microporosity.

Degraded lateritic soils cape and land uses in Birbhum district, West Bengal, India

Degradation of lateritic environment as found in the south western and eastern Birbhum district can be considered as irresistible. Inherently poor physical and chemical status of existing lateritic soil profile and radical conversion of land uses as observed at cadastral level are the key factors of land degradation. Lateritic soilscapes are mostly affected by water erosion induced, vegetal and anthropogenic degradation attaining severe and very severe degradation status. Degraded lands in sample mouzas like Ballabhpur, Shyambati, Chawpahari Jungle, Bodakuri and Pachami account for 60.33%, 71.42%, 72.99%, 87.31% and 79.66% respectively out of their total lateritic exposures. In other words about 36.98%, 71.42%, 61.73%, 56.70% and 76.02% out of their total village areas and mostly non agricultural land use are affected by it. Four degraded villages get the higher priority for friendly landscape conservation actions.

Horizontal Bearing Capacity of Piles in a Lateritic Soil

The behavior of pile foundations subjected to horizontal loading is typically evaluated using horizontal load tests. Although load tests are valuable to understand site-specific soil-structure interaction phenomena, validated predictive methods are also useful during the design phase. In this study, the results from horizontal load tests are compared with methods which predict the horizontal bearing capacity of piles using in situ measurements of soil behavior. Specifically, several horizontal load tests were performed in order to evaluate the behavior of two 12-m long Strauss piles and four bored piles with similar length, all installed in a lateritic soil profile. Two prediction methods were evaluated using p-y curves computed from the results of Marchetti's dilatometer test DMT results. The predictive methods using the p-y curves from the DMT showed good agreement with the behavior observed in the pile loading test.

Genesis of High-Grade Iron Ores of the Archean Iron Ore Group around Noamundi, India

High-grade hematite ores of the Iron Ore Group in the Noamundi area, Jharkhand state, India, are hosted by a laterally extensive, 220-m-thick banded iron formation (BIF) in a folded greenstone belt succession of Paleoarchean age. Single orebodies, which are up to 3 km long along strike and several hundred meters wide, depending on dip of the beds, are strata bound and composed of two major ore types—namely, hard hematite ore that is of ancient geologic origin and ores related to recent weathering along a lateritized Cretaceous-Cenozoic land surface. The ancient hard hematite orebodies comprise laminated hematite ores in which microplaty hematite is dominant, and massive ores composed almost entirely of martite. Supergene ores, in contrast, are comprised of goethite-rich duricrust and soft saprolitic hematite ores representing the leached zone of the Cretaceous-Cenozoic laterite profile. Hard hematite-martite ores formed by hydrothermal replacement of BIF protolith, not only through leaching of silica but possibly also through introduction of iron by hydrothermal fluids of meteoric origin. Hematite iron ore pebbles in a conglomerate at the base of the Meso- to Neoproterozoic Kolhan Group near Noamundi attest to the antiquity of the hard hematite orebodies. Soft saprolitic iron ores formed as a product of lateritic weathering processes in Cretaceous-Cenozoic times. Supergene alteration took place under the influence of reducing and acidic meteoric water, which is typical for lateritic soil profiles developed under humid tropical climatic conditions with lush plant cover. Goethitic duri-crusts capping the laterite profile suggest alternating wet and dry seasons in this environment.

IN-SITU CHARACTERIZATION OF UNSATURATED SOIL HYDRAULIC PROPERTIES OF A LATERITE SOIL PROFILE IN COASTAL KARNATAKA

ABSTRACT Unsaturated laterite soil formations play an important hydrologic role in the West Coast region of India. However, very little information on the hydraulic/hydrologic properties of lateritic soils exists in literature. The present study was taken up to characterize the unsaturated soil water retention curves and hydraulic conductivity function of a sandy lateritic soil profile located in the coastal district of Dakshina Kannada, Karnataka State. This was achieved by conducting a field internal drainage test involving measurements of soil moisture contents and soil water pressures at various depths within a 1.5 m deep soil profile over a period of 39 days. Soil moisture contents were measured using a sophisticated Time Domain Reflectrometry (TDR) probe and soil water suction pressures were measured using tensiometers. The water retention curve for each depth layer was characterized by fitting the popular van Genucthen model to observed moisture contents and suction pressures. Depth-wise differences in the shapes of the water retention curves were evident. Observed temporal variations in moisture content and suction pressures during internal drainage were analyzed using well-established procedures to calculate unsaturated hydraulic conductivity values. Results indicated more or less homogeneous depth-wise drainage behaviour and a single relationship based on van Genucthen's model was sufficient to describe the hydraulic conductivity variations with moisture content for the entire profile. Computed hydraulic conductivities showed extreme sensitivity to soil moisture contents and varied from a low value of 0.47 cm/d at moisture content of 0.208 cm3/cm3 to as high as 134.82 cm/d at 0.261 cm3/cm13. Results of this study can provide useful inputs in applications of mathematical models to describe water flow and solute transport in unsaturated lateritic soil media. This may lead to better understanding of the role of the unsaturated soil zone in the hydrologic cycle in the West Coast region and thereby lead to more efficient designs of water conservation structures.

Holocene boundary dynamics of a northern Australian monsoon rainforest patch inferred from isotopic analysis of carbon, (14C and δ13C) and nitrogen (δ15N) in soil organic matter

Abstract Soil organic matter (SOM) was sampled from lateritic soil profiles across an abrupt eucalypt savanna–monsoon rainforest boundary on the north coast of Croker Island, northern Australia. Accelerator mass spectrometry dating revealed that SOM that had accumulated at the base of these 1.5 m profiles had a radiocarbon age of about 5000 years. The mean carbon and nitrogen stable isotope composition of SOM from 10 cm deep layers from the surface, middle and base of three monsoon rainforest soil profiles was significantly different from the means for these layers in three adjacent savanna soil profiles, suggesting the isotopic ‘footprint’ of the vegetation boundary has been stable since the mid Holocene. Although there were no obvious environmental discontinuities associated with the boundary, the monsoon rainforest was found to occur on significantly more clay rich soils than the surrounding savanna. Tiny fragments of monsoon rainforest and abandoned ‘nests’ (large earthen mounds) of the orange‐footed scrubfowl, an obligate monsoon rainforest species, occurred in the savanna, signalling that the rainforest was once more extensive. Despite episodic disturbances, such as tropical storm damage and fires, the stability of the boundary is probably maintained because clay rich soils enable monsoon rainforest tree species to grow rapidly and achieve canopy closure, thereby excluding grass and reducing the risk of fire. Conversely, slower tree growth rates, grass competition and fire on the savanna soils would impede the expansion of the rainforest although high rainfall periods with shorter dry seasons may enable rainforest trees to grow sufficiently quickly to colonize the savanna successfully.

Behavior of Sm and Nd in a lateritic soil profile

A study of lateritic soils and samples of ground and river waters was carried out in the Nsimi-Zoetele, a tropical watershed in the southern Cameroon. The Nd isotopic compositions and concentrations of Nd and Sm were determined. It was found that the Nd isotopic composition of the river waters was much more radiogenic than the parent rocks, and that the Nd in the waters is not homogeneous but is carried by different dissolved and complexed components that are not isotopically homogenized. The soil profile shows a regular increase in ε Nd going from the parent rock (ε Nd = −36) to ε Nd = −18 near the top of the profile. The Nd transported in the river is thus not representative of the parent rock but reflects the results of differential weathering of constituent minerals and the redeposition of REE in phosphates and a significant contribution of radiogenic Nd from dust. The concentration of Nd in the river water is far above that found in temperate climate rivers and thus this type of tropical river may play a dominant role in the marine Nd and REE budget. It is suggested that the correlation of REE with DOC is related to DOC fixing some dissolved REE but that the REE in solution is governed by other mechanisms. No major shifts were found in Sm/Nd; however, a regular progression from the parent rock through the lateritic profile was found. The upper laterite profile shows large, almost uniform depletions in all REE below Tb and enrichment above. Complementary behavior was found in the lower part of the section. The concentration of Nd relative to the immobile elements Zr and Ti in the laterite is depleted by a factor of ∼10. Th, Nd and Sm are enriched in the lowest zone sampled and must reflect redeposition of REE from the upper part of the weathering section and is associated with phosphate formation. It is concluded that the soil evolution involves both differential dissolution of primary phases from the parent rock, significant to major input of REE from atmospheric dust from other regions, and the formation of diagenetic phases, particularly phosphates.

Amorphous alumino-silicate materials in a Brazilian hydromorphic lateritic soil

Two ancient lateritic soil profiles from Brazil that are now experiencing hydromorphic conditions were investigated by chemical extractions, X-ray diffraction, differential thermal and thermogravimetric analysis, and analytical transmission electron microscopy (ATEM) to identify if the hydromorphic conditions had affected soil minerals. The soils are composed of gibbsite and kaolinite with less quartz, anatase, goethite, pedogenic chlorite, and amorphous alumino-silicate phases. These last 2 constituents occur in the middle and upper horizons of both soil profiles, together with considerable amounts of organic carbon. Analytical TEM showed that the amorphous phases enveloped corroded gibbsite and kaolinite crystals and may indicate the transformation of these minerals to amorphous phases. The amorphous phases have a similar microfabric to that of allophane and ATEM analyses of the amorphous phases gave an Al/Si atom ratio that was always &gt;2, and commonly about 10. These atom ratios are consistent with the bulk chemical results obtained using pyrophosphate, oxalate, and dithionite extractants, but not with the theoretical ratio for allophane. The Al/Si atom ratio of the amorphous phases was related to the Al content of the mineral enveloped by the amorphous phases, i.e. gibbsite or kaolinite. This association supports the interpretation that the amorphous phases formed from the crystalline minerals. The saturated condition of the profiles, together with the high concentration of organic matter in the upper horizons, favours dissolution of the original gibbsite and kaolinite in the laterite and their transformation to amorphous alumino-silicate phases with a high Al content.

Soils as an Important Sink for Mercury in the Amazon

This work focuses on the behaviour of mercury in lateritic soil profiles found in the Serra do Navio and Tartarugalzinhoareas of the State of Amapa in Northern Brazil. The Hg contents are high in the upper horizons of the soil profiles(100–300 μg kg-1), and decrease to less than 100 μg kg-1 at depths of 200 or 300 cm. The higher levels of Hg are associated with higher Fe concentrations, particularly in the ferruginous accumulations as mottles andnodules. For each horizon of the soil profile, balance calculations were used to distinguish the amount of mercury naturally accumulated from rocks through lateritic pedogenesis (lithogenic mercury) from the anthropogenic mercury introduced in the profile through atmospheric contamination. The results show that the anthropogenic contribution is significant in the upper horizons (up to 95%% of the total Hg), and decreases downward in the soil profile. Mercury burdens were calculated for soil profiles in both upslope (272 880 and 217 440 μg m-2 for the first 70 cm) and downslope positions (118 800 and 182 160 %μg m-2 for the first 70 cm). The loss of Hg in downslope profiles seems to be related to the natural evolution of iron duricrust into latossols, which has been brought about by climatic changes toward increasing humidityin the Amazon since the Tertiary.

Infiltration characteristics of a complex lateritic soil profile

AbstractLarge infiltration ponds (10–15 m2) were used, in conjunction with a ring infiltrometer and a well permeameter, to determine the infiltration characteristics of a complex lateritic soil profile in the jarrah (Eucalyptus marginata) forest of Western Australia. Simultaneous measurements of soil water content and soil water potential allowed a description of the infiltration and redistribution in the soil profile. The infiltration ponds effectively measured the conductivity of a subsurface lateritic duricrust which was found to have a relatively high saturated hydraulic conductivity (Ks) of 2.7 m d−1, despite its apparently massive and extensive nature. Removal of the topsoil identified large (≈1 m2) infilled holes penetrating the duricrust over about 6% by area. Measurements indicated that these large ‘holes’ had a high Ks value (≈ 10 m d−1), whereas the remaining duricrust had a lower Ks value (≈ 2m d−1). These results have implications for probable maximum flood design calculations and assessing the hydrological impact of extensive open‐cut bauxite mining.

Engineering properties of a lateritic soil profile

Engineering properties of a lateritic soil profile