Composition Of Surface Soils Research Articles

High-precision estimation of pan-Arctic soil surface temperature from MODIS LST by incorporating multiple environment factors and monthly-based modeling

Global warming has shown an “Arctic amplification effect” in recent decades, leading to pronounced changes in pan-Arctic soil surface temperature (SST). SST plays a direct role in energy exchange between soil and atmosphere and serves as an indicator of the land–atmosphere energy balance. Remote sensing land surface temperature (LST) data is able to indicate near-surface temperature, but influences from environment factors, such as vegetation and snow, can introduce biases between LST and SST. In this study, the importances of five environment factors (vegetation, snow, surface soil composition, topography, and solar radiation) to monthly mean SST estimation from MODIS LST in pan-Arctic were analyzed. Then a method for pan-Arctic monthly mean SST estimation from MODIS LST by incorporating these environment factors and monthly-based modeling based on random forest (RF) algorithm was proposed. The results reveal that all the selected environment factors contribute to monthly-based modeling, with vegetation exerting the greatest importance from May to October and snow in March and April. The root mean square error (RMSE) of pan-Arctic monthly SST estimated by the proposed method from 2003 to 2022 ranges from 0.89 to 1.88 °C, which is a 42.95–––53.35 % reduction compared to the widely used season-based multivariate linear regression (MLR) models based solely on LST (RMSE between 1.56 and 4.03 °C). The accuracy is notably improved in areas with lower and no vegetation (grassy woodlands, grasslands, permanent wetlands, and barrens) in the cold season (September to the following April), and in higher vegetation (forests) areas in the warm season (May to August). The proposed method can contribute to producing high-precision monthly mean SST data from LST, estimating permafrost extent and active layer thickness, and understanding the land–atmosphere energy balance in pan-Arctic.

Влияние горных факторов на избыточность солей и токсичность почвы в горных условиях

Introduction. The study of soil composition in mountainous areas is important for assessing its suitability for agriculture, land use planning and mining, influencing environmental policy and socio-economic development. Exploration of the composition of surface soil in these conditions is necessary to understand the specific factors affecting the formation and properties of soils. The study allows us to determine the physical-chemical properties of the soil, identify toxicity and problems with salt, which is important for preserving the quality of the soil and the environment in the mining industry. Research methods and materials. In the study of soil composition in mountainous areas, methods were used: sample collection taking into account geological features, physical-chemical analysis, measurement of mountain factors and data analysis using machine learning methods. This made it possible to identify the influence of mountain conditions on soil properties, to identify factors associated with salt excess and toxicity, and to develop approaches to preserve soil quality, important for environmental sustainability and socio-economic development of mountain Research results. Studies of salt redundancy and toxicity in the soil in mountainous areas, especially in the context of the mining industry, are extremely important. These studies help to assess soil pollution, identify sources of harmful substances and develop measures to prevent negative consequences, such as deterioration of soil quality and a threat to human health. The analysis of mountain factors plays a key role in risk assessment and the development of strategies to minimize the negative impact on the environment and preserve biological diversity in mountain ecosystems. Discussion of research results. The most important factor from the entire data set is the «Nutrient Availability Indicator in the soil», which has a significant impact on salt excess and soil toxicity. However, when only mountain factors are taken into account, «Slope 2» becomes the key for salt redundancy, and «Aspect B» and «Slope 2» for soil toxicity, simplifying modeling and allowing more accurate analysis of chemical properties associated with mountain features. Conclusion. Mountain conditions significantly affect the composition and properties of the soil, which can lead to excess salts and toxicity of substances, having a serious impact on the ecosystem and human health. Soil slope plays an important role in this context and can be key in determining risk and developing strategies for managing soil conditions in mountainous conditions. Risk assessment and environmental impact forecasting allow mining companies to create effective measures to reduce harm and increase the sustainability of production. Conclusions on the article. The article presents the results of research demonstrating that mountain conditions have a significant impact on the composition and properties of the soil. It was found that the features of the mountain relief can lead to the accumulation of toxic substances and excess salts, which have serious consequences for the ecosystem and human health. It has been established that the slope of the soil plays a key role in the formation of these phenomena, which can be useful for strategies for managing the soil condition in mountainous areas and reducing the negative impact on the environment. Suggestions for practical application and direction of future research. Research can be aimed at developing more sustainable management strategies for mountainous regions, taking into account the influence of geological factors on soil composition and possible environmental consequences. As well as the development of models that will allow to anticipate and assess potential risks to ecosystems and human health associated with the accumulation of toxic substances in mountain conditions, may be a direction for future research.

Ground calibration and validation of laser-induced breakdown spectroscopy for the Mars surface composition detector

<p indent=0mm>In the Tianwen-1 mission, China’s first Mars exploration, the lander/rover had safely landed in the south Utopian plain and conducted a series of scientific explorations. The Mars surface composition detector (MarSCoDe) equipped on the Zhurong rover uses remote laser-induced breakdown spectroscopy (LIBS) and short-wave infrared spectroscopy to perform the <italic>in situ</italic> detection of the elemental composition of surface soils, rocks, and minerals on Mars. In this paper, first, the basic components of this instrument suite are introduced. Second, the LIBS principle is described. Third, the spectral and radiation calibration of the LIBS spectrometer and its surveying distance and pointing angle calibration are described. Finally, the performance associated with the navigation and terrain cameras (NaTeCam) is presented. The results from the joint detection and analysis of the MarSCoDe and the NaTeCam show that the MarSCoDe can accurately fire the target and determine the elemental components.

Analysis of atmospheric emissions in Murmansk and their relationship with pollution of urban lakes

The main sources of anthropogenic emissions into the atmosphere of Murmansk are emissions from thermal power plants and boiler houses operating on fuel oil. As a result of the analysis of the dynamics of pollutant emissions from stationary anthropogenic sources for the period 1997-2019 it has been established that the level of air pollution is assessed as low; there is a tendency towards a decrease in gross emissions from stationary sources. The main pollutants from thermal power plants are sulfur dioxide, nitrogen oxides, carbon monoxide, formaldehyde, and benzo(a)pyrene. Together with gaseous and liquid substances, fuel oil ash and products of incomplete underburning of fuel, which include heavy metals V, Ni, Cr, Pb, Fe, Sn, enter the atmospheric air. Technogenic compounds of heavy metals and other pollutants from the enterprises of the power unit, falling out with dust or precipitation on the surface and catchment areas of lakes, affect the formation of the chemical composition of surface soils, waters and bottom sediments of water bodies. This is reflected in an increase in the concentration of heavy metals (in particular, V and Ni) in the water and bottom sediments of the lakes of Murmansk in comparison with the background values.

Elemental composition of surface soils in Nature Park Shumen Plateau and Shumen City, Bulgaria

Abstract Anthropogenic activities cause environmental pollution and alter biogeochemical cycles. Soils in cities and their vicinity are exposed to different pollutants. Nature Park Shumen Plateau is a protected area situated in the proximity of Shumen (Bulgaria). The aim of this research was to compare elemental composition of surface soil samples from Nature Park with two areas in Shumen city. Soil samples from seven sites on the territory of Nature Park and from two urban sites were collected. The elemental composition of the samples was determined using Energy Dispersive X-Ray Fluorescence technique. Principal component analysis and cluster analysis were performed to interpret the complex data. The content of 24 elements was determined: Br, Y, Zr, Mo, Ag, Cd, Sn, Sb, I, Cs, Ba, La, Ce Si, K, Ca, Ti, Mn, Fe, Cu, Zn, Rb, Sr, and Pb. Results presented here and previously showed that concentrations of heavy metals Cu, Zn, Cd and Pb are below the upper limit according to Bulgarian legislation. Concentrations of Mn and Fe in samples from Nature Park were comparable to the literature data reported for unpolluted areas. Principal component analysis and cluster analysis show similarity of the content of 24 elements between samples from Nature Park and from Shumen city. These findings are in accordance with our previous positive results from Allium-test: cytogenetic endpoints showed a presence of harmful compounds in Nature Park soils. The content of heavy metals in the surface soils studied show a lack of environmental risk for Nature Park. However, a similar distribution pattern of the investigated elements in the park and two anthropologically influenced areas in Shumen city indicated a potential hazard in Nature Park.

Climatic significance of the stable carbon isotopic composition of surface soils in northern Iran and its application to an Early Pleistocene loess section

The stable carbon isotopic composition of bulk organic matter (δ13Corg) in paleosols has been widely used as a proxy indicator for reconstructing past vegetation and climate. Previous studies generally show a negative correlation between the δ13Corg values of modern C3 plants and surface soils under C3 plant-dominated ecosystems and mean annual precipitation (MAP). However, the relationship between δ13Corg and MAP varies among different climatic regimes, resulting in uncertainties in paleo-precipitation reconstructions. In this study, we analyzed the δ13Corg values of surface soil samples collected along a north-south climatic gradient in northern Iran, in the western part of arid central Asia (ACA). Our aims were to explore the relationship between surface soil δ13Corg values and climatic factors; to use it to develop a transfer function for ACA; and then to apply the transfer function to a well-dated loess-paleosol sequence (AB1) to reconstruct early Pleistocene (2.4–1.8 Ma) MAP in northern Iran. The results show that: (1) the δ13Corg values of 44 surface soil samples range from −27.56‰ to −23.61‰, with an average of −25.77‰, indicating that the modern natural ecosystem in northern Iran is dominated by C3 vegetation; (2) The δ13Corg values of the surface soil samples are strongly negatively correlated with MAP (y = −0.0079x − 22.8418, R2 = 0.4419, p < 0.001), with a coefficient of −0.79‰/100 mm. We infer that the effects of mean annual temperature (MAT) and elevation on the relationship are minimal; (3) Reconstructed early Pleistocene MAP in northern Iran was ∼649 mm, much wetter than the present day (∼331 mm); (4) The loess δ13Corg values from ACA exhibit similar trends to records from monsoonal Asia, suggesting a similar history of Quaternary climate change between ACA and monsoonal Asia, which is likely related to the growth and decay of Northern Hemisphere ice sheets.

Soil mercury accumulation, spatial distribution and its source identification in an industrial area of the Yangtze Delta, China

Understanding soil mercury (Hg) accumulation, spatial distribution, and its sources is crucial for effective regulation of Hg emissions. We chose a study area covering approximately 100 km2 representing one of the rapid growing industrial towns of the Yangtze River Delta (YRD), China, to explore soil Hg accumulation. In surface soil, total Hg ranged from 310 to 3760 μg/kg, and 53% samples exceeded the most generous Chinese soil critical value (1500 µg/kg). Hg concentration in rice ranged from 10 to 40 µg/kg, and 43% samples exceeded the regulatory critical value (20 µg/kg). Total Hg concentrations in soil profiles gradually decreased, reaching background levels up to 60 cm profile depth. Meanwhile, proportions of mobile, semi-mobile and non-mobile Hg to total Hg at every soil depth were similar, leading us to deduce that soil Hg has accumulated in this area over a long period. Total and bioavailable Hg in topsoil exhibited the highest concentrations in the center of the study area, and radially decreased towards the periphery, which might be explained by the distribution of industry and the prevailing wind. To trace the Hg sources, we selected soil and atmospheric dust samples for isotope analysis. Hg isotopic composition of surface soil (δ202Hg = −0.29 ± 0.10‰ and Δ199Hg = 0.03 ± 0.03‰) was close to that of atmospheric dust (δ202Hg = −0.54 ± 0.10‰ and Δ199Hg = 0.03 ± 0.05‰), but considerably different from Hg isotopic composition in subsoil (δ202Hg = −0.90 ± 0.09‰ and Δ199Hg = −0.04 ± 0.04‰). Thus, we speculated that atmospheric deposition could change Hg isotopic composition in topsoil. Our findings suggest that when Hg atmospheric dust deposition changes Hg levels in surface soil, soil remediation, and crop safety might be compromised.

Characteristics of Color and Chemical Composition of Surface Soils Collected in Source Regions of Asian Dusts and Identification of the Source of Kosa Aerosols Transported to Japan

Characteristics of Color and Chemical Composition of Surface Soils Collected in Source Regions of Asian Dusts and Identification of the Source of Kosa Aerosols Transported to Japan

Heterogeneity and loss of soil nutrient elements under aeolian processes in the Otindag Desert, China

Abstract The heterogeneity of the composition of surface soils that are affected by aeolian processes plays important roles in ecological evolution and the occurrence of aeolian desertification in fragile ecological zones, but the associated mechanisms are poorly understood. Using field investigation, wind tunnel experiments, and particle size and element analyses, we discuss the variation in the nutrient elements of surface soils that forms in the presence of aeolian processes of four vegetation species (Caragana microphylla Lam, Artemisia frigida Willd. Sp. Pl., Leymus chinensis (Trin.) Tzvel. and Stipa grandis P. Smirn) growing in the Otindag Desert, China. These four vegetation communities correspond to increasing degrees of degradation. A total of 40 macro elements, trace elements, and oxides were measured in the surface soil and in wind-transported samples. The results showed that under the different degradation stages, the compositions and concentrations of nutrients in surface soils differed for the four vegetation species. Aeolian processes may cause higher heterogeneity and higher loss of soil nutrient elements for the communities of Artemisia frigida Willd. Sp. Pl., Leymus chinensis (Trin.) Tzvel, and Stipa grandis P. Smirn than for the Caragana microphylla Lam community. There was remarkable variation in the loss of nutrients under different aeolian transportation processes. Over the past several decades, the highest loss of soil elements occurred in the 1970s, whereas the loss from 2011 to the present was generally 4.0% of that in the 1970s. These results indicate that the evident decrease in nutrient loss has played an important role in the rehabilitation that has occurred in the region recently.

The relationship between intertidal soil composition and fiddler crab burrow depth

Fiddler crab burrow morphologies in tidal flat ecosystems depend largely on physical characteristics of the soil. Herein, we aimed to examine the relationship between soil texture profiles and the burrow depths and morphologies of four fiddler crab species: Tubuca arcuata, Gelasimus borealis, Xeruca formosensis, and Austruca lactea. We found that the burrow depths of T. arcuata, G. borealis, and A. lactea (range=8–50cm) were strongly affected by surface soil composition; only the burrow depth of X. formosensis (which reached 100cm in some cases) was influenced by the presence of deeper, clay-rich soils. Specifically, X. formosensis relied more heavily on fine soils, such as clay or silt, when they burrowed deeper into sand-covered mudflats. We hypothesize that deep burrowers, such as X. formosensis, may coat clay-rich soils on their burrow walls to impede flooding and to prevent burrow collapse, suggesting that surface soil composition does not necessarily determine the burrow depth and composition for all fiddler crab species.

Sediment generation on a volcanic island with arid tropical climate: A perspective based on geochemical maps of topsoils and stream sediments from Santiago Island, Cape Verde

The present research tests the application of geochemical atlas of soils and stream sediments in the investigation of weathering and erosion processes on volcanic islands. The composition of surface soils collected in six catchments from Santiago Island (Cape Verde) are compared with bedload stream deposits sourced by these catchment areas in order to evaluate the spatial variability of these exogenous processes. The geochemistry of bedload stream deposits is between that of the fresh rocks and the topsoils of their source areas. Relative to average soil composition, bedload deposits are depleted in most of less-mobile elements (e.g., Al, Fe, La, Sc) and strongly enriched in Na and, usually, Ca. When the topsoil weathering intensity in the catchment areas is highly variable and the composition of bedload deposits is substantially different from the average soil composition, bedload deposits should incorporate significant amounts of poorly-weathered rocks and sectors from erosion occur within the drainage basin. Ratios of non-mobile elements allow the identification of highly vulnerable and erosion-protected sectors within the catchments. It is proposed that the catchments of the rivers in the SW flanking side of Santiago Island include sectors where lava shields formed during the post-erosional eruptive phases are capable of an effective protection to erosion. Conversely, the NE-facing part of the island is highly dissected and any younger post-erosional cover was either completely eroded away, or never existed in the first place. Simple compositional parameters derived from the databases of geochemical maps of soil and stream sediments provide important information for the analyses of weathering, erosion and denudation processes at the catchment scale.

Elemental and isotopic composition of surface soils from key Saharan dust sources

Saharan dust contains significant amount of P, an important macronutrient to all living organisms, which has been shown to exert large effects on nearby and remote ecosystems located across the dust transport pathways. The biological effect of Saharan dust depends on the amount and nature of the P speciation of the dust. However, thus far relatively small numbers of samples from potential source areas (PSA) has been analyzed. Here we report the P speciation (resin-P, HCl-P, Fe-bound-P and organic-P), the δ18OP values, the elemental composition, and the 87Sr/86Sr and 143Nd/144Nd of the fine fraction and bulk soil from 5 important PSAs across Northern Africa. We found the HCl-P concentrations between different source areas were relatively constrained but that these concentrations were higher in the fine fraction, which here is used a surrogate for dust. The δ18OP values for soils from sand dunes varied from 15.0 to 21.4‰, which is in the range of phosphate minerals from sedimentary origin. The δ18OP values of soils from dry lakes were significantly higher (24.0–28.5‰), probably since their P is derived from fossilized plankton that lived in the lake as it dried up. The 87Sr/86Sr and εNd values ranged from 0.7219 to 0.7276 and −12.7 to −14.0 in eastern samples and from 0.7146 to 0.7185 and −11.9 to −13.4 in western samples, suggesting a different source for the siliciclastic material of eastern and western samples. Our analysis indicates that the δ18OP values are decoupled from the Sr and Nd isotopic systems. Together, the new chemical and isotope data are specific for different PSAs and thus are used for source apportionment purposes. Such data can be used to provide more accurate estimates of the flux of potentially bioavailable P to marine and terrestrial ecosystems. These estimates can be used in global climate models to determine the magnitude and distribution of P control on carbon uptake.

Identification of environmental lead sources and pathways in a mining and smelting town: Mount Isa, Australia

Lead (Pb) concentrations and isotopic compositions from soils, dusts and aerosols from public land and residential lots adjacent to the copper and Pb mine and smelter at Mount Isa, Australia, were examined to understand the sources and risks of environmental Pb exposure. Urban soil samples contain elevated Pb concentrations (mean 1560 mg/kg), of which 45–85% of the Pb is bioaccessible. The Pb isotopic composition of surface soils (0–2 cm), aerosols and dusts (206Pb/207Pb, 208Pb/207Pb range: 1.049, 2.322–1.069, 2.345) are dominated by Pb derived from the Mount Isa Pb–zinc ore bodies. Underlying soil horizons (10–20 cm) have distinctly different Pb isotopic compositions (206Pb/207Pb, 208Pb/207Pb range: 1.093, 2.354–1.212, 2.495). Surface soil-, dust- and aerosol-Pb are derived predominantly from smelter emissions and fugitive mining sources and not from in situ weathered bedrock. Remediation strategies should target legacy and ongoing sources of environmental Pb to mitigate the problem of Pb exposure at Mount Isa.

Organic stable carbon isotopic composition reveals late Quaternary vegetation changes in the dune fields of northern China

Vegetation changes during the late Quaternary in the dune fields of northern China are not well understood. We investigated organic carbon stable isotopic composition of surface soils, related mainly to the ratio of C3and C4plants, across a range of arid to subhumid climates in this region. Isotopic composition is weakly related to both temperature and moisture (multiple R2= 0.53), with the highest δ13C (greatest C4abundance) in the warm, subhumid Horqin dune field. In late Quaternary, eolian stratigraphic sections of the Mu Us and Horqin dune fields, but not in the much colder Otindag dune field, δ13C is higher in organic carbon from paleosols than in eolian sands. This contrast, most evident for paleosols recording a major early to middle Holocene phase of dune stabilization, is interpreted as evidence for expansion of C4plants due to increased effective moisture, high temperature because of high insolation, and decreased disturbance related to eolian erosion and deposition.

Chemical Speciation of PM2.5 and PM10 in South Phoenix, AZ

ABSTRACT Phoenix, AZ, experiences high particulate matter (PM) episodes, especially in the wintertime. The spatial variation of the PM concentrations and resulting differences in exposure is of particular concern. In this study, PM2.5 (PM with aerodynamic diameter <2.5 μm) and PM10 (PM with aerodynamic diameter <10 μm) samples were collected simultaneously from the east and west sides of South Phoenix and at a control site in Tempe and analyzed for trace elements and bulk elemental and organic carbon. Measurements showed that although PM2.5 concentrations had similar trends in temporal scale across all sites, concentrations of PM10 did not. The difference in PM10 concentrations and fluctuation across the three sites suggest effects of a local soil source as evidenced by high concentrations of Al, Ca, and Fe in PM10. K and anthro pogenic elements (e.g., Cu, Pb, and Zn) in PM2.5 samples on January 1 were strikingly high, suggesting the influence of New Year's fireworks. Concentrations of toxic elements (e.g., Pb) in the study presented here are not different from similar studies in other U.S. cities. Application of principal component analysis indicated two broad categories of emission sources—soil and combustion—together accounting for 80 and 90% of variance, respectively, in PM2.5 and PM10. The soil and combustion components explained approximately 60 and 30% of the variance in PM10, respectively, whereas combustion sources dominated PM2.5 (>50% variance). Many elements associated with anthropogenic sources were highly enriched, with enrichment factors in PM2.5 an order of magnitude higher than in PM10 relative to surface soil composition in the study area. IMPLICATIONS This study investigates the variability of PM10 and PM2.5 mass concentrations and speciation between two sites in southern Phoenix, representative of a lower income part of the city, and a comparison site in nearby Tempe, with a higher income lower minority population. The results indicate similar temporal trends in PM2.5 concentrations and sources, although lower overall concentrations in Tempe. For PM10, the highest concentrations and a unique temporal variability at one South Phoenix site suggest a particular influence of local dust sources.

Online Terrain Parameter Estimation for Wheeled Mobile Robots With Application to Planetary Rovers

Future planetary exploration missions will require wheeled mobile robots (rovers) to traverse very rough terrain with limited human supervision. Wheel-terrain interaction plays a critical role in rough-terrain mobility. In this paper, an online estimation method that identifies key terrain parameters using on-board robot sensors is presented. These parameters can be used for traversability prediction or in a traction control algorithm to improve robot mobility and to plan safe action plans for autonomous systems. Terrain parameters are also valuable indicators of planetary surface soil composition. The algorithm relies on a simplified form of classical terramechanics equations and uses a linear-least squares method to compute terrain parameters in real time. Simulation and experimental results show that the terrain estimation algorithm can accurately and efficiently identify key terrain parameters for various soil types.

Potential terrain controls on soil color, texture contrast and grain-size deposition for the original catena landscape in Uganda

Inspired by the catena concept, we returned to the landscape of origin for this idea in central Uganda and applied quantitative soil–landscape-modeling techniques to the study of soil formation. In particular, we employed Generalized Least Squares (GLS) regression to identify potential terrain (and other) controls on surface texture with the goal of explaining texture contrast formation for well-drained red soils, and fluvial deposition for yellow–gray lowland soils. Well-drained red soils and poorly drained yellow–gray soils were identified using a high-resolution spectroradiometer and soil redness was highly correlated with a measure of elevation above the valley floor. For the yellow–gray soils, sand content and sand grain size increased with greater slope gradient and in converging areas—evidence supporting fluvial control of surface soil composition. For red soils, texture contrast increased on lower backslopes, decreased over ferricrete-rich parent material, and had no significant association with either infiltration- or runoff-influenced locations. Surprisingly, texture contrast was also reduced or even inverted on fine scale convexities (<18 m in diameter). These findings were consistent with the following theoretical processes: (1) sand deposition on lower-backslopes, increasing texture contrast; (2) ferricrete weathering at the soil surface, reducing texture contrast; and (3) texture contrast inversion through termite turbation. A number of techniques proved useful in this study: (a) the use of GLS regression supported the interpretation of model coefficients in an explicitly spatial context; (b) thin-plate splines provided a flexible means of controlling the spatial scale of terrain index computation; and (c) the development of a new downslope-looking Elevation Above Stream (EASy) terrain index provided a powerful tool for the identification of poorly drained soils—a tool that could have applications in a variety of landscapes and environments. Overall, we found that the catena concept as a soil–terrain-modeling approach worked best on lower, less well-drained, depositional landscape components. For the well-drained portion of this landscape, there was little evidence to suggest that soil formation was controlled by hillslope hydrology as proposed by the catena concept. The catena concept interpreted in a broad sense challenges pedologists to explicitly link soil geographic patterns with specific soil forming processes and environmental controls—an approach that proved valuable in this study.

Application of multivariate statistical analysis to superficial soils around a coal burning power plant

The Thermoelectric Complex Jorge Lacerda (TCJL), located in the Santa Catarina State, Brazil, is the largest coal burning thermoelectric complex of Latin America and consists of seven power plants with a total capacity of 832 MWe. In order to estimate the contribution of the atmospheric releases from the TCJL to the elemental composition of surface soils around it, forty-five samples were collected at up to a distance of 8 km. Forty-two elements were determined by ICP-MS and ICP-AES after total acid dissolution. The technique of principal component analysis was employed to identify the major sources that contribute to surface soil composition. Additionally, a source apportioning using multiple regression on absolute principal component scores was performed in order to obtain quantitative information about the contribution of the different identified sources on the soil composition. Based on the results obtained, four sources were identified as the main contributors to the surface soil elemental composition. One of them was related to TCJL because it retains volatile elements enriched on fly ash and released from powerhouse stacks.

VARIABILITY OF SELECTED SOIL PROPERTIES IN WINTER WHEAT AND NATI VE GRASS WATERSHEDS

The spatial and temporal transferability of saturated infiltration, surface bulk density, and surface soil composition on a field scale was investigated by a comprehensive analysis of a large data set from eight research watersheds at the ARS Grazinglands Research Station near El Reno, Oklahoma. The watersheds represented two land uses: dryland winter wheat and native warm season grasses. Variability was compared on adjacent watersheds with different land uses and on adjacent watersheds with similar land uses. Regression analysis indicated no direct relationship among the soil properties. From analysis of variance tests, grass watersheds exhibited greater saturated infiltration, lower surface bulk density, and different surface soil composition than the dryland winter wheat watersheds. Within watersheds of the two land uses, the soil properties are equivalent on all watersheds for some properties, while other properties are equivalent on only two or three of four watersheds. Saturated infiltration and surface bulk density were found to be independent of hillslope position, whereas surface soil composition was correlated with hillslope position. A limited study also indicated that saturated infiltration does not vary significantly through the growing season on the wheat watersheds. Overall, the results indicate that caution should be exercised when treating the watersheds within a single land use as equivalent units or replicates. Ultimately, this decision should be based on the specific use of the data to be collected. Study objectives that focus on the finer details of runoff production or soil–water processes may require treating each field scale watershed as a separate unit. However, if study objectives focus on seasonal water balance issues or comparisons between land uses, the field scale watersheds within each land use can be considered equivalent units.

AQUA REGIA EXTRACTABLE TRACE ELEMENTS IN SURFACE SOILS OF VENEZUELA

Surface soils (0–15 cm) were sampled at 10–20 km intervals along two transects in Venezuela. One (1162 km, 70 samples) ran west to east parallel with the Caribbean coastline, the other (920 km, 92 samples) ran south to north from the frontier with Brazil to the Caribbean shore. Sampling took place in both a wet and a dry season. Trace metals were extracted from dried, sieved (<2 mm) soil with boiling aqua regia followed by analysis by ICP or flame AAS. Metal values did not differ significantly between the two seasons and dates were averaged. Geometric mean values for the west–east transect were: Cr = 41.5, Cu 17.9, Cs 3.6, Li = 13.9, Mn = 294, Ni = 21.3, Pb = 17.4, Sr = 39.4, V = 60.4 and Zn = 83.7 μg g−1, respectively. Similarly, for the south–north transect Cr = 21.3, Cu = 4.3, Cs = 1.1, Li = 2.0, Mn = 55.7, Ni = 4.4, Pb = 6.1, Sr = 13.3, V = 28.2 and Zn = 16.7 μg g−1, respectively. A classification of samples by lithology showed surface soil composition to be related to rock composition. Metal values were low in the soils in the south of the country, in the Guyana highlands (Gran Sabana). Low Zn contents were prevalent. Lead contents were affected by roadside fallout from vehicles using leaded petrol except that high Pb contents of soils in the Gran Sabana were of more complex origin.