Laboratory Study on the Hydraulic Conductivity and Pore Pressure of Sand-Silt Mixtures

The hydraulic conductivity plays a major role on the excess pore pressure generation during monotonic and cyclic loading of granular soils with fines. This paper aims to determine how much the hydraulic conductivity and pore pressure response of the sand-silt mixtures are affected by the percentage of fines and void ratio of the soil. The results of flexible wall permeameter and undrained monotonic triaxial tests performed on samples reconstituted from Chlef River sand with 0, 10, 20, 30, 40, and 50% nonplastic silt at an effective confining stress of 100 kPa and two relative densities (D_r = 20, and 91%) are presented and discussed. It was found that the pore pressure increases linearly with the increase of the fines content and logarithmically with the increase of the intergranular void ratio. The results obtained from this study reveal that the saturated hydraulic conductivity (k) of the sand mixed with 50% low plastic fines can be, on average, four orders of magnitude smaller than that of the clean sand. The results show also that the hydraulic conductivity decreases hyperbolically with the increase of the fines content and the intergranular void ratio.     

A Mass Balance Approach to Resolving LNAPL Stability

This article explores the hypothesis that natural losses of light nonaqueous phase liquids (LNAPLs) through dissolution and evaporation can control the overall extent of LNAPL bodies and LNAPL fluxes observed within LNAPL bodies. First, a proof‐of‐concept sand tank experiment is presented. An LNAPL (methyl tert‐butyl ether) was injected into a sand tank at five constant injection rates that were increased stepwise. Initially, for each injection rate the LNAPL bodies expanded quickly. With time the rate of expansion of the LNAPL bodies slowed and at extended times the extent of the LNAPL became constant. Attainment of a stable LNAPL extent is attributed to rates of LNAPL addition being equal to rates of LNAPL losses through dissolution and evaporation. Secondly, analytical solutions are developed to extrapolate the processes observed in the proof‐of‐concept experiment to dimensions and time frames that are consistent with field‐scale LNAPL bodies. Three LNAPL body geometries that are representative of common field conditions are considered including one‐dimensional, circular, and oblong shapes. Using idealized conditions, the solutions describe volumetric LNAPL fluxes as a function of position in LNAPL bodies and the overall extent of LNAPL bodies as a function of time. Results from both the proof‐of‐concept experiment and the mathematical developments illustrate that natural losses of LNAPL can play an important role in governing LNAPL fluxes within LNAPL bodies and the overall extent of LNAPL bodies.     

Cladoceran community composition in tropical semi-arid highland reservoirs in Tigray (Northern Ethiopia): A metacommunity perspective applied to young reservoirs

A field survey of zooplankton communities was carried out in 32 recently established tropical semi-arid reservoirs in the highlands of Northern Ethiopia with the aim to identify to what extent environmental factors determine species composition of the cladoceran community in such isolated and young reservoirs. To address seasonal variation, the survey was carried out both at the beginning and the end of the dry season. A total of 15 species of cladocerans were identified. Daphnia was the most abundant cladoceran genus, and was present in all reservoirs. Using presence-absence data, no association between cladoceran community composition and geographic distance was found. RDA results indicate that the set of environmental variables that explained cladoceran community composition differed among seasons. Depth, altitude and fish biomass showed a significant association with cladoceran community composition during the wet season, whereas variation in cladoceran community structure was associated with phytoplankton biomass in the dry season. The relative abundance of Daphnia was much higher in the pelagic than in the littoral zone of our study systems. Two key groups of pelagic filter-feeding cladocerans, Diaphanosoma and Daphnia, showed a clear pattern, in which one or the other tended to strongly dominate the community. In addition, we observed a negative association between dominance of Daphnia in the zooplankton community and dominance of cyanobacteria in the phytoplankton community.     

Surface lowering of limestone pavement as determined by cosmogenic (36Cl) analysis

Determination of the rate and total amount of limestone pavement surface lowering is a critical issue in developing models of regional landscape change in limestone terrain. Erratic‐capped pedestals have frequently been used for this purpose but problems concerning definition and measurement of pedestal height, and the absence of a secure timeframe for erratic emplacement, have resulted in conflicting interpretations. We have used cosmogenic (³⁶Cl) to establish the emplacement age of erratic boulders and the total amount of pavement surface lowering at sites in northwest England. Since erratic emplacement at 17.9 ka the limestone pavement has been lowered by 22–45 cm (average: 33 ± 10 cm), assuming lowering was continuous. Although indicating some spatial heterogeneity, the results contrast with earlier reported values based on the measurement of pedestal heights and inferred age for deglaciation. We consider that changes in climate and the character and duration of regolith covers to have been important influences in promoting surface lowering. It is argued that nivation (chemical and mechanical snow‐related processes) associated with several cool/cold periods is likely to have played an important role in surface lowering. Complicating factors associated with surface lowering (thickness and longevity of snow and regolith covers) are identified but as yet cannot be quantified. Copyright © 2012 John Wiley & Sons, Ltd.     

The marine and coastal access act—A hornets' nest?

The Marine and Coastal Access Act 2009 is now enacted into law. This paper looks at predictions made about new law by one of the authors, Peter Jones, in his paper The Marine Bill: Cornucopia or Pandora's Box [1] and assesses how successful the Act has been in turning aspirations into law. The paper focuses on the following areas: ecosystem protection, stakeholder engagement, marine spatial planning and the provision of a network of highly protected marine reserves, and raises concerns that the ecosystem approach has progressively been dropped in the drafting process of the legislation. Concerns are raised that the new Inshore Fisheries and Conservation Authorities have similar inherent conflicts of interest to those exhibited by Sea Fisheries Committees, which they sought to replace. The effectiveness of marine planning is questioned, as there appear to be inbuilt loopholes for public authorities to avoid complying with the marine plans. The draft marine policy statement (MPS), published in July 2010, includes appropriate environmental safeguards, but the MPS has not yet been formally adopted. The absence of a concrete target for highly protected marine reserves means there is a danger that designations under the Act may have little effect on the ground. In conclusion the Act provides some new mechanisms for marine protection, but arguably does not yet provide a framework for implementing the ecosystem approach and is not an end in itself.     

The accuracy of methods used to estimate the whole-lake accumulation rate of organic carbon, major cations, phosphorus and heavy metals in sediment

The accuracy of three methods used to estimate the whole-lake accumulation rate of chemicals in sediment, the simple mean accumulation rate, regression against water depth and the mean accumulation rate in sedimentation zones, was assessed. The concentrations and accumulation rates of organic carbon, four major cations, phosphorus and four heavy metals in the 1902 to 1988 sediment layer at 43 sites in Kassjön were used and the three methods gave identical results. The accuracy of the simple mean accumulation rate method using 5 or 10 sites was investigated using Monte Carlo simulation and both versions gave accurate results. If the method used the dry sediment accumulation rate at 5 or 10 sites, along with chemical concentration at one central site, then the errors were less than ±10% for five of the chemicals and larger for the others (?20 or 20–40%), although the direction of the bias was predictable. If chemical accumulation rate at the central site only was used to estimate the whole-lake value, the bias increased to 25% for the major cations, 50% for the heavy metals and P, and 85% for organic carbon. Having 43 sites in Kassjön meant that the true whole-lake chemical accumulation rate was known and so the accuracy of the methods and their variants could be assessed for the first time. These findings allow the particulars of the simple mean accumulation rate method to be chosen to suit the accuracy needed for a palaeolimnological investigation.     

Evolution of borate minerals from contact metamorphic to hydrothermal stages: Ludwigite-group minerals and szaibélyite from the Vysoká – Zlatno skarn,Slovakia

Mineralogy and Petrology - Borate minerals of the ludwigite group (LGM) and szaibélyite in association with hydroxylclinohumite, clinochlore, a serpentine mineral, magnesian magnetite, spinel,...     

Heat transfer coefficients of natural volcanic clasts

Heat transfer coefficients used in numerical simulations of volcanic eruptions are typically borrowed from industrial settings where the coefficients are well determined for non-permeable, machined (spherical) materials. Volcanic clasts, in contrast, are permeable and have irregular shapes. We performed a series of laboratory experiments to determine heat transfer coefficients for natural volcanic particles. We measured the surface and interior temperatures during cooling at wind speeds ranging from 0 to 10 m/s. We also measured the permeability and density of the particles. We find that the permeability of the particles has little effect on clast cooling. In the absence of any wind, heat loss occurs by free convection, and we find no relationship between the heat transfer coefficient and particle density. However, for non-zero Reynolds numbers (finite wind speed), the heat transfer coefficient decreases with increasing porosity. We obtain a correlation for the dimensionless heat loss, or Nusselt number, of the form Nu = 2 + aRe^1/2Pr^1/3 where a is a density dependent coefficient given by a = 0.00022ρ + 0.31, with ρ in kg/m³, and Re and Pr are the Reynolds number and Prandtl number, respectively. Compared with non-porous particles, heat transfer coefficients for natural pumice clasts are reduced by a factor of 2–3 for particles with similar Re. Numerical simulations show that this leads to an increase in depositional temperature by 50–90 °C.