A probabilistic approach for computing water retention of particulate systems from statistics of grain size and tessellated pore network

The paper offers an analytical determination of the hydraulic properties of an unsaturated soil with reference to its retention curve, which describes the relationship between the volumetric water content and capillarity through matric suction. The analysis combines a particulate approach focused on the physics at the pore scale, including microstructural aspects, with a probabilistic approach where the void space and grain size are considered as random variables. In the end, the soil water characteristic curve of an unsaturated granular medium along a drying path can be derived analytically based on the sole information of particle size distribution. The analysis hinges on the tessellation of a wet granular system into an assemblage of tetrahedral unit cells revealing a pore network upon which capillary physics are computed with respect to pore throat invasion by a non-wetting fluid with evolving pendular capillary bridges. The crux of the paper is to pass from particle size probability distribution to a matching void space distribution to eventually reveal key information such as void cell and solid volume statistics. Making reasonable statistically based assumptions to render calculations tractable, the water retention curve can be readily constructed. Model predictions compare quite favourably with experimental data available for actual soils, especially in the high saturation range. Having a sound scientific basis, the model can be made amenable to address a variety of soils with a wider range of particle sizes.     

Climate change and human impact in a sensitive ecosystem: the Holocene environment of the Northwest Icelandic highland margin

Complex interactions of climate and volcanic activity have shaped the environment of Iceland during the Holocene. Palaeoecological records from Iceland offer a unique look at a Holocene environment that was uninhabited by humans and free of mammal herbivores until about AD 870. We present a new reconstruction of Holocene vegetation and landscape dynamics from a small lake, Barðalækjartjörn, located near the highland margin in Northwest Iceland. A multi‐proxy approach was used to reconstruct vegetation based on pollen and plant macrofossil analysis and landscape stability based on lithological proxies. The record covers the period c. 10 300–200 cal. a BP. For the first two millennia aeolian processes probably played a part in vegetation development. This period is characterized by high input of minerogenic material into the lake and a vegetation assemblage in which plants tolerant of aeolian deposition are prominent. Betula pubescens woodland reached a maximum between c. 7400 and 6500 cal. a BP. Betula nana‐dominated dwarf shrub heath replaced woodland after c. 4000 cal. a BP, following the onset of Neoglaciation. Land use following human settlement caused an environmental shift at the highland margin. Betula pubescens probably disappeared from the vicinity of the lake soon thereafter. Large‐scale soil erosion began at c. 1000 cal. a BP in the wake of human activities, such as introduction of grazing livestock and woodcutting. This study offers an important long‐term perspective of the development of the highland ecosystem under both wholly natural and human‐influenced conditions.     

The ancient water system at the Upper city of Hasankeyf,Turkey

In this paper, the water distribution system at the Upper city of a well-preserved medieval town of Hasankeyf near the Tigris is questioned and its relation to the urban settlement pattern is assessed. The discussions are based on the cistern-intensive and available canal data collected within the residential borders of the Upper city in 2005. Being the third level features of the water system, the cisterns the majority of which are now attributable to the “conical, small and individual” typology, have shown that they were actively operated through the open rock-cut canals which were fed by the backbone of the distribution network—namely the siphon system, until recent times. Although a considerable number of converted cisterns hallmark shifts in the function of the water system and the changing conjectures over time, the blue prints of such a big “hydro-design” reveal the competence of semi-arid occupational environments in Upper Mesopotamia in showing how to cope with the topographical constraints and climatic disadvantages and turn these into an opportunity through the efficient use of terrain along with a carefully designed settlement area. That the Upper city now offers numerous water features makes this piece of land quite a representative of the regional works and shows the apex of the perception of ancient technology achieved with the siphon that could have been launched in the Roman era, and the state of art of planning ancient natural and man-made habitats.     

Impact-generated carbonate melts in the Talemzane impact structure (Laghouat,Algeria)

The 1750-m-diameter, bowl-shaped Talemzane impact structure in Algeria is emplaced in Senonian or Eocene flint-bearing limestones. Field studies reveal a thin layer of light-colored polymict breccia with rounded, dark inclusions beneath a limestone megablock zone located at the top of the crater rim. The matrix of the rounded, dark inclusions consists of Si-rich glass and microcrystalline calcite. The latter is characterized by high contents of Si and Al suggesting rapid crystallization of the calcite from a melt. Backscattered electron imagery shows textural evidence for liquid immiscibility between the CaCO₃-rich and Si-rich glass of the matrix in the form of intermingling of calcite with Si-rich glass, coalesced blebs within silicate glass, individual calcite blebs within Si-rich glass, carbonate spherical globules in fresh Si-rich-glass, and sharp menisci between silicate and calcite blebs. These features are interpreted as evidence of impact melting of limestone and flint. The low totals of the Si-Al-Mg-rich glasses suggest that they contain significant amounts of volatiles. X-ray diffraction analyses indicate partial alteration of the Si-Mg-Al-rich glass to phyllosilicates.     

Carcinogenic risk evaluation for human health risk assessment from soils contaminated with heavy metals

Human activities have progressively increased in recent years. Consequently, significant environment deterioration resulted. Soils have a particularly varied vulnerability to heavy metal pollution, especially in the vicinity of industrial areas. Heavy metal contamination of soil may induce risks and hazards to humans and the ecosystem, while toxic metals in soil can severely inhibit the biodegradation of organic contaminants. This paper is focused on human health risk assessment from extremely contaminated soil with heavy metals, mainly with carcinogenic elements. The study refers to an agricultural area in the vicinity of an old metallurgical processing industrial facility. The contaminants evaluated in the present paper are beryllium (Be), cadmium (Cd), chromium (Cr), nickel (Ni) and lead (Pb). Contamination level is pointed out through laboratory analysis results of soil samples taken from 0–0.2 m, 0.2–0.4 m soil layers and up to 2.1 m soil depth. Some heavy metal concentrations (Cd, Cr and Pb) exceed the intervention thresholds for sensitive areas, as they are stipulated in the national regulation in Romania. The identified average concentration levels of Cd, Cr^VI and Pb in the first layer of the investigated land are 23.83, 7.71 and 704.22 mg/kg_d.w, respectively. The results show that the potential risk of human health is relevant (higher than the acceptable one after World Health Organization) and a possible solution for the remediation should become a major concern for the investigated area.