Sensitivity of the active fracture model parameter to fracture network orientation and injection scenarios

Active fractures refer to the portions of unsaturated, connected fractures that actively conduct water. The active fracture model parameter accounts for the reduction in the number of fractures carrying water and in the fracture–matrix interface area in field-scale simulations of flow and transport in unsaturated fractured rocks. One example includes the numerical analyses of the fault test results at the Yucca Mountain site, Nevada (USA). In such applications, the active fracture model parameter is commonly used as a calibration parameter without relating it to fracture network orientations and infiltration rates. A two-dimensional, multiphase lattice-Boltzmann model was used in this study to investigate the sensitivity of the active fracture model parameter to fracture network orientation and injection scenarios for an unsaturated, variable dipping, and geometrically simple fracture network. The active fracture model parameter differed by as much as 0.11–0.44 when the effects of fracture network orientation, injection rate, and injection mode were included in the simulations. Hence, the numerical results suggest that the sensitivity of the active fracture model parameter to fracture network orientation, injection rates, and injection modes should be explored at the field-scale to strengthen the technical basis and range of applicability of the active fracture model.     

A Quaternary Timeline: a teaching tool for interpreting palaeoenvironmental, palaeoclimatic and archaeological change over the last 500,000 years

This short paper presents a case study for teaching elements of Quaternary Science to a non-specialist audience. A guided hands-on practical exercise in sedimentology and stratigraphy, palaeoenvironmental analysis and Palaeolithic archaeology was supported by the development of a ‘Quaternary Timeline’ chart, which introduces the concepts of changing climates and environments and characterises the broad expression of these changes in the terrestrial and fossil records. Using information from the practical exercises, the figure allows a step-by-step interpretation to be built up of past landscapes, including an understanding of the nature of fluvial responses to Quaternary climate change, a reconstruction of the contemporary flora and mammalian fauna and an analysis of the activities of early human populations.     

Investigations into a small fraction of volatile hydrocarbons: III. Two diatom cultures produce ectocarpene, a pheromone of brown algae

Ectocarpene was extracted from cultures of Skeletonema costatum and probably in traces from cultures of Lithodesmium undulatum shortly after a change in the light regime which is known to induce formation of gametes.     

Raman microprobe study of synthetic diaplectic plagioclase feldspars

Raman microprobe spectra were made on three post shock, diaplectic plagioclase feldspars. Optical and X-ray diffraction studies indicated that feldspars maintained a partially or totally crystalline state after having passed through the mixed phase zone of Hugoniot response to shock waves (15–38 GPa). The appearance of uniquely glass-type spectra occurs at different shock pressures for each specimen according to its atomic structural arrangement, below 38 GPa for mosaic structured labradorite, near 40 GPa for anorthite and above 50 GPa for the highly ordered low albite. The diaplectic anorthite and labradorite glasses give spectra which indicate the presence of two glass types. Shifts in the band envelope frequencies compared to spectra of fused glass and statically pressure densified glass suggest that these glasses have specific structural arrangements. These differences suggest that the shock and fusion glass-forming processes are not exactly identical. The results from material shocked in the mixed phase region of Hugoniot response show that the phase transitions are effected at different pressures depending upon the feldspar structural type.     

Clinopyroxene composition as a method of identification of the magmatic affinities of paleo-volcanic series

Uranium contents and²³⁴U/²³⁸U activity ratios have been determined for groundwaters from the Lincolnshire Limestone artesian aquifer in eastern England. Changes in the quantitative and isotopic chemistry of the dissolved uranium are explained in terms of a mixing model involving the rapidly moving fissure water and much older water stored in the pore system of this oolitic limestone. The western part of the aquifer, closest to recharge, is dominated by oxidising groundwaters which then enter a reducing zone towards the east, where there is an abrupt decrease in Eh and the chlorinity of the groundwaters begins to increase. Uranium contents in the oxidising zone range from 0.7 to 3.4 μg kg^?1 and²³⁴U/²³⁸U activity ratio of this dissolved uranium is close to unity, the equilibrium value. The uranium content decreases abruptly when the grounwaaters enter the reducing zone, averaging 0.04 μg kg^?1 east of the oxidation/reduction barrier. Simultaneously with the decrease in uranium content, there is an increase in²³⁴U/²³⁸U activity ratio and this ratio increases to a maximum within 7 km of the oxidation/reduction barrier. This increase in activity ratio is attributed to enhanced²³⁴U solution due to²³⁴Th recoil from uraniferous fissure surfaces east of the oxidising zone. The activity ratio of dissolved uranium in the ancient pore waters could in principle reach high values due to²³⁴Th recoil from the oolith surfaces. However, the activity ratio actually declines further east and this can only be explained as a consequence of mixing with pore waters in which the uranium activity ratio is closer to equilibrium.²³⁴Th recoil from the oolith surfaces has probably been inhibited by sealing of the uranium-bearing surfaces in the process of oolith cementation.     

Far infrared spectra of hydrous layer silicates

Observation of major bands seen in infrared spectra of 26 phyllosilicates (23 of which were produced in the laboratory) are reported for wave numbers from 50 to 280 cm^?1. Substitutions in the various structural sites (interlayer, tetrahedral and octahedral) permit one to identify the ions which contribute to the vibrations which give rise to bands in the infrared spectra. No attempt is made to assign vibrational modes or specific vibrational types. Using the following ion substitutions, OH-OD; Na-K-Sr-Mg-Ca; Si-Ge; Al-Ga; Mg-Co-Ni-Fe, it is apparent that in the 7 Å chlorite (amesite and chrysotile), kaolinite, pyrophyllite, aluminous dioctahedral mica, aluminous smectites and trioctahedral micas it is not possible to attribute any low frequency bands as being dominated by interlayer ion stretch vibrations (alkali ions). The cations which participate in the vibrators responsible for the dominant modes observed then seem to be Si and Al. This does not exclude the existence of interlayer ion stretch modes in these spectral regions, however they could not be identified. In the materials studied only a few bands can be attributed to hydroxyl-related vibrations and little influence is seen for octahedrally coordinated ions in dioctahedral minerals. It is important to note that the lowest frequency bands (80–140 cm^?1) are apparently dominated by vibrations in the network and especially to the Si-O part of the structure. Low frequency bands are however most apparent in charged layer structures, i.e. micas and smectites.     

Ecosystem responses in the Rhine-Meuse delta during two decades after enclosure and steps toward estuary restoration

Changes in hydrology, and developments in morphology, water quality, and ecology of the Rhine-Meuse estuary after its enclosure in 1970 are analyzed on the basis of existing monitoring data. Annual averages of ammonium, nitrate plus nitrite, total phosphate, total lead, and chlorophyll-a concentrations as well as transparency of the water are presented. Abundances of some water bird species are given for the period 1970–1993, and the relative fish biomass for the period 1971–1988 is discussed. The gradual evolution led toward the dominance of bream. The area has developed toward a system with generally low natural ecological values. Ecological impacts of present sluice management are discussed and include the accumulation of contaminated sediments, disappearance of intertidal areas and nursery grounds for fish, disturbance of fish migration, and less mixing of river and seawater. Recent policy developments have brought the present management of the Haringvliet sluices back in to discussion. A recent policy document has presented several management alternatives, including partial and complete reopening of the sluices to permit saltwater intrusion. Three management options are compared in terms of costs and ecological benefits. It is concluded that a complete reopening, and thus a partial restoration of the estuarine characteristics, is most beneficial for the ecosystems of the area itselt, for the upstream Rhine and Meuse rivers, and for the adjacent North Sea, but costs amount to about 600 million US $.