An archaeopedological and phytolitarian study of the “Dark Earth” on the site of Rue de Dinant (Brussels, Belgium)

During the excavations of the site of Rue de Dinant in the historic centre of Brussels (Belgium), remains of the first city wall dating from the 13th century have been discovered. Intra muros thick dark sediment units predating this wall are observed. These dark units are among the oldest occupation traces so far encountered in this higher, eastern, part of the historic centre of Brussels. In order to characterise them, and to understand the human activities and natural processes behind their formation, an interdisciplinary research, integrating archaeopedology and phytolith study, has been undertaken. This approach permitted us to identify a range of natural and cultural processes leading to the formation of these dark layers, and to characterise different activities. Remains of a hearth, old plough land (cropfields) and grassland have been identified, all activities referring to a rural landscape organisation. Later on, the area changes into an enormous silt extraction area, whereby Dark Earth is thrown into the dug pits. Finally, the construction of the first city wall marks the area as becoming part of the city. The study of Dark Earth shows to be a potentially valuable tool to shed light on the development and spatial organisation of pre-urban Brussels, a historically very poorly documented period.     

Rhizosphere effect of three plant species of environment under periglacial conditions (Majella Massif,central Italy)

The chemical, physical and biological processes occurring in the rhizosphere can influence plant growth by modifying root associated microorganisms and nutrient cycles. Although rhizosphere has been widely investigated, little is known about the rhizosphere effect of pioneer plants in soils of periglacial environments. The knowledge of the processes controlling soil–plant relationships in these severe environments may help understanding the ecological evolution of newly deglaciated surfaces. We selected three plants [Helianthemum nummularium (L.) Mill. subsp. grandiflorum (Scop.), Dryas octopetala (L.), and Silene acaulis (L.) Jacq. subsp. cenisia (Vierh.) P. Fourn.] that sparsely occupy deglaciated areas of central Apennines (Italy), with the aim to assess changes between rhizosphere and bulk soil in terms of physical, chemical, and biological properties. The three plants considered showed to have different rhizosphere effect. Helianthemum induced a strong rhizosphere effect through a synergistic effect between root activity and a well adapted rhizosphere microbial community. Dryas did not foster a microbial community structure specifically designed for its rhizosphere, but consumes most of the energetic resources supplied by the plant to make nutrients available. Conversely to the other two species, Silene produced slight soil changes in the rhizosphere, where the microbial community had a structure, abundance and activity similar to those of the bulk soil. The ability to colonize harsh environments of Silene is probably linked to the shape and functions of its canopy rather than to a functional rhizosphere effect.This study showed that the rhizosphere effect differed by species also under high environmental pressure (periglacial conditions, poorly developed soil), and the activity of roots and associated microbial community is decisive in modifying the soil properties, so to create a suitable environment where plants are able to grow.     

Characterization of the organic matter in sediments of the Great War Island (Belgrade,Serbia)

Journal of Soils and Sediments - The Great War Island (GWI) is a landform of exceptional features and a protected area located in the center of Belgrade at the Sava and Danube River’s...     

A soil chronosequence in the semi-arid environment of Patagonia (Argentina)

Soil development with time was investigated on beach ridges with ages ranging from about 1380 to 6240 ¹⁴C-years BP at the eastern coast of central Patagonia. The main pedogenic processes are accumulation of organic matter and carbonate leaching and accumulation within the upper part of the soils. Soil formation is strongly influenced by incorporation of eolian sediments into the interstitial spaces between the gravel of which the beach ridges are composed. Different amounts of eolian material in the soils lead to differentiation into Leptosols (containing ≤ 10% fine earth in the upper 75 cm) and Regosols (containing > 10% fine earth). Soil depth functions and chronofunctions of organic carbon, calcium carbonate, pH, Ca:Zr, Mg:Zr, K:Zr, Na:Zr, Fe:Zr, Mn:Zr, and Si:Al (obtained from X-ray fluorescence analysis) were evaluated. To establish soil chronofunctions mean values of the horizon data of 0–10 cm below the desert pavement were used, which were weighted according to the horizon thicknesses. The depth function of pH shows a decrease towards the surface, indicating leaching of bases from the upper centimeters. Chronofunctions of pH show that within 6000 radiocarbon years of soil development pH drops from 7.0 to 6.6 in the Leptosols and from 8.1 to 7.5 in the Regosols. The higher pH of the Regosols is due to input of additional bases from the eolian sediments. Chronofunctions of Ca:Zr and K:Zr indicate progressive leaching of Ca and K in the Regosols, showing close relationships to time (R² = 0.972 and 0.995). Na leaching as indicated by decreasing Na:Zr ratios shows a strong correlation to time only in the Leptosols (R² = 0.999). Both, Leptosols and Regosols show close relationships to time for Fe:Zr (R² = 0.817 and 0.824), Mn:Zr (R² = 0.940 and 0.803), and Si:Al (0.971 and 0.977), indicating enrichment of Fe and Mn and leaching of Si. Leaching of mobile elements takes place on a higher level in the Regosols than in the Leptosols from the beginning of soil formation. Hence, a significant part of the eolian sediments must have been incorporated into the beach ridges very soon after their formation.     

Micromorphology of a Mousterian paleosol in aeolianites at the site Habonim, Israel

A paleosol with Mousterian tools in aeolianites at the Habonim site (Carmel Coastal plain, Israel) is a complex pedosedimentary sequence which records a succession of soil-forming episodes and stages of coastal dune instability. We identified three strong soils and one accretionary soil within Mousterian pedocomplex via micromorphological techniques, coupled with FTIR and SEM/EDAX. In the lowermost, red sandy soil (hamra) in Unit IV, decalcification led to the formation of micritic coatings, disrupted by faunal churning, while rubefication resulted in red ferric segregations. Illuviation of ferruginious clay in the form of clay coatings is lacking, probably due to its strong incorporation into the matrix. Redox features were intensified in the pseudogley of the next stage (Unit III). Polyphase calcitic features here indicate that illuviation of clay pre-dates illuviation of micrite and its later recrystallization into sparitic calcite. Further deterioration of drainage conditions and increased accumulation of fine particles led to the formation of vertisol (Unit II). Paleovertisol is characterized by a maximum of clay, stress-originated microfabric, abundant Mn precipitates and calcitic pseudomorphs. The peak of landscape instability occurred later and is recorded in the upper Unit I, in which micromorphological signs of colluvial and aeolian processes are juxtaposed with various ferric accumulations, associated with gleying. The final episode occurred at a time of climatic instability, devegetation, and probably, a simultaneous groundwater rise in the littoral zone.     

PaleoVertisols of the northwest Caucasus: (Micro)morphological,physical, chemical,and isotopic constraints on early to late Pleistocene climate

Physical and chemical properties, macro‐ and micromorphology, clay mineralogy, and stable‐isotope compositions of paleosols within a pedostratigraphic column (PSC) of early to late Pleistocene age, interstratified paleosols, and loess (NW Caucasus, S Russia) were examined to better understand the evolution of the pedogenic environment over this time period, separating the effects of postpedogenic diagenesis. The column includes eight paleosols and six intercalated loessic horizons. Most of paleosols represent Vertisols or vertic intergrades. Vertic features increase in the middle of the PSC, where the paleosols are more clayey in texture and reddish in color. The morphology of carbonate nodules and soft masses, morphology‐ and depth(age)‐related changes in stable C and O isotope compositions, soil color, redoximorphic features, clay mineralogy, and illuviated clay indicate periods of wetter pedoenvironment in the past and suggest the Pleistocene paleosols are polygenetic and were formed with several wet/dry stages under a climate generally similar to the modern environment in the N Caucasus (mean annual temperature approx. 9°C–12°C). Interpretation of the time sequence of climate/environmental change requires careful separation of pedogenic mineral phases from phases altered by later diagenesis. The early Pleistocene period of paleosol formation appeared to be wetter or more humid, resulting in more significant development of vertic features. The terrestrial ecosystem remained dominated by C3 vegetation throughout the formation of the PSC, with four small periods of change towards a greater proportion of C4 plants or increased moisture stress.     

Biological influences on the morphology and micromorphology of selected Podzols (Spodosols) and Cambisols (Inceptisols) from the eastern United States and north-east Scotland

Biological activities greatly influence the formation of many soils, especially forest soils under cool humid climates. The objective of this study was to investigate the effects of vegetation and soil biota on the formation of selected soils. Field morphology, micromorphology, and carbon and organic matter analysis were determined on six Podzols (Spodosols) and two Cambisols (Inceptisols) from the eastern United States and north-east Scotland. Humification of plant material by soil fauna and fungi occurs in all organic horizons. Thick organic coatings are observed on soil peds and rock fragments from the E1 to the Bs horizon in a Haplic Podzol from Clingmans Dome Mt., TN. Thin sections reveal large accumulations of root material in different stages of decomposition in the spodic horizons of a Haplic Podzol from Whiteface Mt., NY. Organic carbon ranges from 5.4 to 8.5% in the spodic B horizons of the Whiteface Mt. Podzol. Earthworms and enchytraeids have a great effect on the structure of the surface and subsurface horizons in the Dystric Cambisols from Huntly and Clashindarroch Forests, Scotland and a Cambic Podzol from the Corrie Burn Basin, Scotland. Podzols from Speymouth Forest, Scotland (Gleyic Podzol), Clingmans Dome Mt., and Whiteface Mt. have thick organic horizons. The Podzols from the Flatwoods in Georgia, the Pine Barrens in New Jersey, the Corrie Burn Basin, and the Cambisol from Huntly Forest have only A horizons at the surface. The Clashindarroch Forest soil has a very thin organic horizon. Warm and humid climates and sandy parent material are responsible for thick E horizons and lack of thick organic horizons in the Flatwoods (Carbic Podzol) and Pine Barrens (Ferric Podzol) soils. Earthworms and enchytraeids thrive in the Corrie Burn Basin and Huntly Forest soils due to the vegetation and the highly weathered basic parent material. The site at Clashindarroch once carried oak, and then birch forest, both of which produce a mild litter and also encourage earthworm and enchytraeids. This fauna is responsible for much mixing of the topsoil. The present conifer vegetation will eventually produce a deep litter and cause podzolization.     

The partitioning of mercury in the solid components of dry and flooded forest soils and sediments from a hydroelectric reservoir,Quebec (Canada)

Upon inundation, the soils in a hydroelectric reservoir are subjected to several years of physical, biological, and chemical changes as the transition from a terrestrial to an aquatic ecosystem is achieved. It is suspected that changes in soil Eh and pH alter the metal binding capacity of organic matter, reactive iron (Fe) oxides/oxyhydroxides, and clay minerals, and may cause the mercury associated with these phases to be remobilized. Four cores were collected along a transect from an unflooded forest soil to a pre-impoundment lake bottom sediment. They were subjected to a customized sequential extraction procedure to determine the distribution of Hg between three operationally-defined solid compartments: organic carbon, reactive Fe oxides/hydroxides, and the solid (clay and sulfide) residue. Results indicate that up to 80% of the Hg in the O-horizon of forest soils and flooded soils and up to 85% of the Hg in lake sediments is bound to the NaOH-extractable organic carbon fraction. Furthermore, it was observed that the highest Hg concentrations are associated with degraded organic matter. In the B-horizon of a podzol, 40–60% of the total Hg was found associated with reactive Fe minerals. In contrast, the flooded podzol contains almost no reactive Fe at any depth and associated Hg concentrations are low. We propose that upon inundation, Fe oxides are reduced and Hg released to the pore waters where it is rapidly bound to other available substrates. Analyses of the extractions residues suggest that there is an enrichment of Hg in this fraction immediately above the B-horizon in a flooded soil.     

Influence of clay mineralogy on the stability of a landslide in Plio-Pleistocene clay sediments near Grassano (Southern Italy)

Clayey silts involved in a landslide have been sampled to study the role of sediment composition in developing sliding surfaces. Five drillings enabled the collection of 46 samples and to define active slide surfaces and non-active surfaces (discontinuities).     

History, origin and extent of soil erosion on Easter Island (Rapa Nui)

The isolated Easter Island (Rapa Nui) is an outstanding example of land degradation caused by land use in a sensitive ecosystem. The focus of the investigation was placed on Poike peninsula, the most eastern part of Rapa Nui. While Poike peninsula was once supplied with fertile soils, in large areas desertification takes place today. Detailed analysis of soil profiles allowed the reconstruction of the history and of causes and effects of soil erosion and gullying in the context of land use history and cultural evolution. The results of the stratigraphic analysis prove that from the beginning of human settlement around AD 300/600 until AD 1280 the agriculture on Poike peninsula was characterised by sustainable land use and a traditional type of agro-forestry. Soil erosion was not significant. At around AD 1280 the woodland on Poike, dominated by the endemic palm Jubaea sp., was cleared by slashing and burning. Intensive farming on the upper slopes of the volcanic peninsula resulted in sheet erosion lasting until the 20th century. Settlements and ceremonial places which were built around AD 1300 on downslope areas were buried soon by sediments. Agriculture ceased around AD 1400 on downslope areas as the fertile soils were completely eroded. From AD 1400 until the late 19th century sheet erosion and the accumulation of fine-layered sediments migrated upslope. On average 8.6 Mg of soil per hectare and per year were reworked by erosion (eroded and accumulated within the catchment). Gullying began on Rapa Nui with the sudden increase in the number of sheep during the early 20th century. Gullies are still developing on the island and their ongoing enlargement created extended badlands on Poike which pose a significant problem for ecological and archaeological conservation strategies. Gullying rates exceed 190 Mg ha^{− 1} y^{− 1}.     

Determination of Thallium and Other Elements (As,Cd, Cu,Mn, Pb,Se, Sb,and Zn) in Water and Sediment Samples from the Vicinity of the Zinc-Lead Smelter in Poland (3 pp)

Background, Goal and Scope   The aim of this study was to check the concentration of some elements in water samples collected near Pb-Zn mining and smelting works and comparison of the obtained data with results achieved for sediment samples originated from the same reservoirs. Objective   Here, 8 water samples and 3 bottom sediments collected from water reservoirs in the vicinity of 3 big Polish Pb-Zn smelters were analysed.Methods   Water analysis was performed after filtration through a 0.45 µm filter and pH adjustment to 2. For decomposition of dried sediment samples, microwave assisted digestion with total dissolution of silicate matrix was applied. The elements studied were determined using ICP-MS and ICP-OES methods. Results and Discussion   The concentrations of most studied elements in water samples were on the 0.X µg/L level, while only the contents of Tl, As, Mn, Cd, Pb and Sb in two water reservoirs were above the limits established for drinking water. The content of studied metals in sediments was in a wide range from X mg/kg (Se and Sb) to X000 mg/kg (Pb and Zn).Conclusions  and Recommendation. The study indicates that the impact of Tl, As, Cd, Cu, Mn, Pb, Zn, Se and Sb on bottom sediments is much more extensive than on the water in ponds located in the vicinity of a post-flotation waste heap. Monitoring of surface and underground waters, if limited only to the dissolved elements, can lead to faulty conclusions about environmental pollution. The bottom sediments mainly contain easily mobilised phases, and water-sediment equilibrium could be changed easily.     

The influence of surface volcaniclastic layers from Haleakala (Maui, Hawaii) on soil water conservation

This study focuses on the soils and surficial volcaniclastic layers of Haleakala's crater (Maui, Hawaii). The main objective is to assess the effects of covers with fragments of various sizes (ash, cinder, lapilli) on soil water conservation. Soil and gravel samples were collected in Haleakala National Park from a site at 2505 m where the Hawaiian silversword, a giant rosette-plant, grows densely on pyroclastic materials. An evaporation experiment lasting 22 days showed a gradual drop in seven pairs of soil samples initially at field capacity. One set of samples was left bare, the other was covered by gravel mulches (GM); these resulted in lengthening of T_100% (total desiccation time) by a factor of 2.3–5.2. Bare soils dried after 70–140 h, but drying time under gravel was 246–509 h. Mean grain size (M_z) and sorting (φ_σ) had the greatest influence on evaporation rates. Coarse lapilli (M_z: 13.8 mm) were less effective than fine ash (M_z: 2.9–3.8 mm) in preventing water losses, while medium-grained cinder (M_z: 4–5.2 mm) produced the greatest water savings. Lapilli (mean φ_σ: 0.48) and ash (φ_σ: 0.6) were moderately- to well-sorted; cinders, with a broader grain-size range (φ_σ: 1.13), were poorly sorted. This allowed infilling of large interstices between coarse fragments by smaller grains, effectively reducing pore size and therefore evaporation rates. A second experiment determined water storage and rates of water loss by mulches. Wetting occurred swiftly, within 3–4 min. All gravel types were dry within 26 h. This drying process is important for water conservation, as it effectively prevents further water loss from the mulch surface. Larger fragments stored less water. This is related to their ‘surface area/weight' ratio, which increases for smaller particles. Thus, fine ash or cinder grains, with a high total area, intercept more water than larger lapilli. A 5-cm thick layer of ash intercepted an average of 6.8 mm of rain, slightly more than the same depth of cinder (6.3 mm), but lapilli retained only 4.7 mm. Therefore, light rainfall events are more likely to contribute water to soil under lapilli than below finer pyroclastic material. Volcaniclastic covers serve an important ecological role in Haleakala by prolonging periods of water availability to plants, thus allowing Hawaiian silverswords to grow for longer time spans.     

Distribution of Trace Elements in Soils from the Sudbury Smelting Area (Ontario,Canada)

The sequential extraction procedure proposed by the European Commission Measurement and Testing Programme, combined with Scanning Electron Microscopy and Energy Dispersive X-ray Analysis(SEM/EDS), was applied to identify and quantify the chemical andmineralogical forms of Cu, Ni, Fe, Mn, Zn, Pb, Cr and Cd presentin the topsoil from a mining and smelting area near Sudbury (Ontario, Canada). The possible mobility of the chemical forms was also assessed. The metal fractions: (1) soluble and exchangeable, (2) occluded in manganese oxides and in easily reducible iron oxides, (3) organically bound and in form of sulphides, (4) residual mainly present in the mineral lattice structures were separated. Cu and Ni were the major metallic contaminants, occurring in soils in broad ranges of concentrations: Cu 11–1890 and Ni 23–2150 mg kg^-1. Cu was uniformly distributed among allthe extracted fractions. Ni was found associated mainly withthe residual forms, accounting for 17–92%, with an averageof 64%, of the total Ni present in the soils. Fe, Mn, Zn,Pb, Cr and Cd, while occurring in most analysed samples innormal soil concentrations, were primarily held in theresidual mineral fraction (on average >50%). The solubleand exchangeable forms made a small contribution (≤8.1%)to the total content of metals extracted. At least 14% ofthe total Cd, Mn and Pb was mobilised from the reducibleforms. The oxidizable fraction assumed mean values higher than10% only for Pb and Zn. Statistical treatment of the experimental data showed significant correlations between totalmetal content of the soils, some soil properties such as pH value, clay and organic matter content, and metal concentrationsin the various fractions. SEM/EDS analysis showed Fe in form ofoxides and sulphides in soils and Cu, Ni, Mn, Zn and Cr in association with iron oxides. Numerous black carbonaceous particles and precipitates of aluminium fluoride salts, observedin the solid residue left after `total’ digestion, were found tocontain Fe, Ni and Cr.     

基于最小数据集与LESA体系的县域耕地质量评价

建立科学合理的县域耕地质量评价体系对快速准确摸清耕地质量家底和建立耕地保护分区具有重要指导意义。该研究基于主成分分析法建立最小数据集精选指标,构建土地评价与立地条件分析（land evaluation and site assessment,LESA）体系,开展耕地质量综合评价,分析耕地质量区域分布特征及差异性特征并划定耕地保护分区。结果表明：1）自然质量指标最小数据集由砂粒、有机质、全钾、有效磷、pH值、综合污染指数、耕层质地、容重、阳离子交换量组成,立地环境指标最小数据集包括排水条件、连片度、生态兼容性、河流距离、路网密度、灌溉能力、农田林网化率、耕地利用类型。2）采用LESA评价模型计算耕地自然质量指数及立地环境指数,确定LESA体系为FLESA=0.5FLE+0.5FSA（FSA、FLE、FLESA分别为耕地立地环境条件、自然质量条件和综合分值）,采样点综合评分为51.517～81.838。综合比选各插值误差检验结果后采用普通克里金法进行耕地质量结果空间插值,评价单元耕地质量综合评分为52.148～79.624。3）铁岭县耕地资源可划分为5个等级区：1级区划分为永久基本农田核心保护区,占比20.52%;2级区划分为耕地自然地力条件重点治理区,占比36.79%;3级区和4级区耕地土壤和立地条件均存在多样性的限制因素,可划分为耕地综合整治区,占比36.33%;5级区划分为耕地生态自然保育区,占比6.36%。4）经计算基于最小数据集与LESA相结合的评价结果有效系数为0.615,相对偏差系数为0.009,说明该体系耕地质量评价结果准确,可信度较高。该研究成果简化了县域耕地质量评价指标体系,量化了自然质量与立地条件协同关系,为开展耕地质量提升和保护利用提供了理论和方法依据。     

Initial Soil Formation Processes of Volcanogenous Regosols (Scoriacious) from Miyake-jima Island, Japan

In the initial soil formation processes of the Volcanogenous Regosols (Scoriacious) from Miyake-jima Island, Japan, the soil profile morphology showed a distinct formation of the A horizon, about 10 cm thick, over C horizons during a period of 125 years. Along with these soil formation processes under the primary succession of vegetation from bare land to mixed forest, the following changes in the soil characteristics were observed of four study sites where soil formation had occurred over a period of 16, 38, 60 and 125 years in scoriacious volcanic materials ejected during each eruption. Whole soil samples of the surface horizon showed that the proportion of the > 2mm fraction decreased and the clay fraction increased. Electron microscopic observation revealed that pores on the scoria surface were newly formed and had expanded with advanced weathering, and that the formation of a weathering zone on the scoria surface (polygonal shape) was more recognized with the passage of time. Soil pH of the surface horizon decreased, and the amount of carbon in the surface samples showed a linear increase with the passage of time. The amounts of exchangeable bases and the CEC value of the surface samples showed comparable increase rates with time. Consequently, the base saturation percentage was kept at about 100% during the 125-year period. It was suggested that the increase in the amounts of exchangeable bases was controlled by the increase in the amounts of soil organic matter accumulated during the initial soil formation processes of Volcanogenous Regosols (Scoriacious).     

Repair of a compacted Oxisol by the earthworm Pontoscolex corethrurus (Glossoscolecidae, Oligochaeta)

The potential of Pontoscolex corethrurus to repair the physical degradation of a compacted Oxisol was studied. The Oxisol from Kingaroy, Queensland, Australia was uniformly packed to four treatments of different bulk densities (0.95, 1.15, 1.25, 1.35 Mg m^–3) in pots of 0.24 m diameter and 0.22 m deep. Each pot was inoculated with 12 earthworms (equivalent to 300 m^–2) and maintained close to field capacity water content for 3 months, after which selected soil physical (dry bulk density, penetration resistance, water infiltration), worm activity (cast production, worm weight) measurements and image analysis were carried out. Results showed that worm numbers were maintained at the initial levels in all the treatments except in the 1.35 Mg m^–3 treatment, where there was a 33% decrease. The weight of surface casts per surviving worm was the greatest in the 1.35 Mg m^–3 treatment compared to the lower density treatments. Final soil density was lessened in all treatments to a depth of 0.2 m. Surface cast production was positively correlated with the percentage reduction in bulk density. The greatest percentage reduction in bulk density was in the 1.35 Mg m^–3 treatment and was equivalent to a doubling of soil aeration (to 18.4%). Penetration resistance to the 0.2-m layer was also reduced and values were less than 2 MPa. Slumping of the surface soil was evident in both the lowest and the highest bulk densities resulting in low rates of water infiltration. Image analysis supported the soil physical properties showing an abundance of both fine pores and worm channels in the three lowest bulk densities, and lesser activity (concentrated in the immediate soil surface) in the 1.35 Mg m^–3 treatment. Received: 6 November 1996     

The role of tephra covers on soil moisture conservation at Haleakala's crater (Maui, Hawai'i)

The influence of tephra covers on soil water was studied in Haleakala (Maui, Hawai'i) during two summers; eight sites with tephra layers and silverswords (Argyroxiphium sandwicense DC.) were sampled at 2415–2755 m. At each site, eight paired-sample sets were obtained in bare soils and under adjacent tephra, at three depths. Tephra were sharply separated from underlying soils and showed prominent vertical stratification. Tephra clast size-distribution was assessed by photosieving and on interstitial-gravel samples; stones included 45.6% cobbles, 29.4% pebbles, and 25% blocks.Moisture content increased with depth in both positions, but soils below tephra had more water at all depths than exposed areas. Surface soils beneath tephra contained 83% more water than bare ground. Soils at 5–10 cm had  106% greater moisture under rocks, but only  70% at 10–15 cm. Differences between plots were statistically significant ( p < 0.001) for surface soils, but less pronounced for subsoils. Soils above 2650 m had greater water content than at lower elevations, and moisture disparity between sample pairs increased with altitude.All soils were coarse, with  20% gravel and  94% sand; most fine material (≤ 0.063 mm) was silt, as clay content was negligible. Organic-matter percentage was low (1.65%). Bulk density and porosity were associated with moisture variation both in tephra-insulated and bare soils; 80% of field moisture was statistically (p < 0.001) accounted for by pore space. Air and soil temperatures were recorded at three sites during  one-week periods prior to moisture sampling. Tephra substantially decreased soil maxima and daily thermal amplitude in underlying soils, but did not noticeably affect nightly minima. Thin (5–6 cm) tephra layers were nearly as effective as thicker (9–15 cm) deposits in depressing soil maxima. Possible water-conservation mechanisms under tephra include: decreased evaporation due to ground shielding and lower maxima; reduced capillary flow; greater infiltration depth; nocturnal dew condensation; and fog interception by blocks.     

Composition,distribution and sources of polycyclic aromatic hydrocarbons in sediments of the western harbour of alexandria,egypt

Aim and Background  Little data are available on the levels of polycyclic aromatic hydrocarbons (PAHs) in the sediments of the Mediterranean Sea Coast of Egypt in general and the Alexandria coastal zone in particular. It was therefore deemed necessary to set up a monitoring programme to determine the current concentrations of PAHs in bottom sediments, and to identify any area where high concentrations of these potential hazardous contaminants were present in the Western Harbour of Alexandria. Methods  The composition, distribution and the source of PAHs in surficial sediments of the harbour were investigated. To document the spatial PAH input, surficial sediment samples from 23 locations throughout the harbour were analysed. as]Results and Discussion The total PAH load determined in the surficial sediment samples ranged from 8 to 131150 ng g¹ dry wt, generally with most of the samples having total concentrations of PAHs greater than 5000 ng g¹ dry weight. The highest concentration of total PAHs was recorded in sediments of the inner harbour. Ratio values of specific compounds such as phenanthrene to anthracene, fluoranthrene to pyrene, methyl-phen-anthrene to phenanthrene, methyl-dibenzothiophenes to dibenzothiophenes, alkylated to non-alkylated and high molecular weight to low molecular weight PAH, were calculated to evaluate the possible source of PAH contamination in the harbour sediments. Conclusions  Two main sources of PAH in the study area have been found: pyrolytic and petrogenic. Interferences of rather petrogenic and pyrolytic PAH contaminations were noticed for most samples. The dominant sources of PAH appear to be the combustion processes through run-off, industrial and sewage discharges, and atmospheric input. The concentrations of PAHs were generally above levels expected to cause adverse biological effects. Recommendations and outlook  Information from this study and any other relevant studies should be useful in designing future strategies for environmental protection and management of the harbour.