Significance,mechanisms and environmental implications of microbial biomineralization

Microorganisms can mediate the formation of minerals by a process called biomineralization. This process offers an efficient way to sequester inorganic pollutants within relatively stable solid phases. Here we review some of the main mechanisms involved in the mediation of mineral precipitation by microorganisms. This includes supersaturation caused by metabolic activity, the triggering of nucleation by production of more or less specific organic molecules, and the impact of mineral growth. While these processes have been widely studied in the laboratory, assessment of their importance in the environment is more difficult. We illustrate this difficulty using a case study on an As-contaminated acid mine drainage located in the South of France (Carnoulès, Gard). In particular, we explore the potential relationships that might exist between microbial diversity and mineral precipitation. The present review, far from being exhaustive, highlights some recent advances in the field of biomineralogy and provides non-specialists an introduction to some of the main approaches and some questions that remain unanswered.     

Simulation of long‐term consolidation behavior of soft sensitive clay using an elasto‐viscoplastic constitutive model

The phenomenon of excess pore water pressure increase or stagnation and continuing large ground deformation in soft sensitive clay following the completion of construction of embankment is simulated for a case study at Saint Alban, Quebec, Canada. The present model employs an updated Lagrangian finite element framework and is combined with an automatic time increment selection scheme. The simulation based on an elasto‐viscoplastic constitutive model considers soil‐structure degradation effect. It is shown that without consideration for the microstructural degradation effect, it is not possible to reproduce the field responses of soft sensitive clay even during the construction of the embankment. When the soil‐structure degradation effect is considered, the present model can offer reasonably accurate prediction for the consolidation behavior of soft sensitive clay, including the so‐called anomalous pore water pressure generation and continuing large deformation even after the end of construction, which has been posing numerous uncertainties on the long‐term performance of earth structures. Copyright © 2013 John Wiley & Sons, Ltd.     

Estimation of catchment yield and associated uncertainties due to climate change in a mountainous catchment in Australia

This paper examines the impacts of climate change on future water yield with associated uncertainties in a mountainous catchment in Australia using a multi‐model approach based on four global climate models (GCMs), 200 realisations (50 realisations from each GCM) of downscaled rainfalls, 2 hydrological models and 6 sets of model parameters. The ensemble projections by the GCMs showed that the mean annual rainfall is likely to reduce in the future decades by 2–5% in comparison with the current climate (1987–2012). The results of ensemble runoff projections indicated that the mean annual runoff would reduce in future decades by 35%. However, considerable uncertainty in the runoff estimates was found as the ensemble results project changes of the 5^th (dry scenario) and 95^th (wet scenario) percentiles by ?73% to +27%, ?73% to +12%, ?77% to +21% and ?80% to +24% in the decades of 2021–2030, 2031–2040, 2061–2070 and 2071–2080, respectively. Results of uncertainty estimation demonstrated that the choice of GCMs dominates overall uncertainty. Realisation uncertainty (arising from repetitive simulations for a given time step during downscaling of the GCM data to catchment scale) of the downscaled rainfall data was also found to be remarkably high. Uncertainty linked to the choice of hydrological models was found to be quite small in comparison with the GCM and realisation uncertainty. The hydrological model parameter uncertainty was found to be lowest among the sources of uncertainties considered in this study. Copyright © 2015 John Wiley & Sons, Ltd.     

Effect of isolation on fragility curves of highway bridges based on simplified approach

The trend of isolating highway bridges is on the rise after the recent large earthquakes in Japan, the United States, and other countries. Recent investigation shows that isolated systems perform well against seismic forces as the substructures of such systems experience less lateral forces due to energy dissipation of the isolation device. Hence, it is anticipated that there might be an effect on fragility curves of highway bridges due to isolation. In this study, 30 isolated bridge models were considered (and they were designed according to the seismic design code of highway bridges in Japan) to have a wider range of the variation of structural parameters, e.g. pier heights, weights, and over-strength ratio of structures. Then, fragility curves were developed by following a simplified procedure using 250 strong motion records, which were selected from 5 earthquake events that occurred in Japan, the USA, and Taiwan. It is observed that the level of damage probability for the isolated system is less than that of the non-isolated one for a lower level of pier height. However, having the same over-strength ratio of the structures, the level of damage probability for the isolated system is found to be higher for a higher level of pier height compared to the one of the non-isolated system. The proposed simple approach may conveniently be used in constructing fragility curves for a class of isolated bridge structures in Japan that have similar characteristics.     

Bombs behaving badly: unexpected trajectories and cooling of volcanic projectiles

We collected thermal infrared video of two explosive eruptions at Stromboli in June 2008 and manually traced the trajectories of 95 particles launched during two eruptions. We found that 10–15?% of the analyzed trajectories deviated from predicted curves due to collisions, causing one particle to travel horizontally more than twice as far as expected. Furthermore, we observed an oscillatory cooling behavior for the airborne pyroclasts, with a median period of 0.46?s. Measured cooling was typically much faster than model-predicted cooling with discrepancies of up to 40?% between measured cooling and theoretical modeling. We interpret the measured cooling curves as resulting from the spinning and twisting and tearing of particles during travel: the periodic re-exposing of the hotter core of the pyroclasts to the atmosphere may cause the observed oscillations, and the spinning may accelerate cooling by enhancing convective heat transfer. Current volcanic trajectory and cooling models do not account for projectile collisions, spinning, or tearing and can thus severely underestimate the maximum landing distance and cooling rates of large pyroclasts.     

Runout of the Socompa volcanic debris avalanche, Chile: a mechanical explanation for low basal shear resistance

We propose a mechanical explanation for the low basal shear resistance (about 50 kPa) previously used to simulate successfully the complex, well-documented deposit morphology and lithological distribution produced by emplacement of the 25 km³ Socompa volcanic debris avalanche deposit, Chile. Stratigraphic evidence for intense basal comminution indicates the occurrence of dynamic rock fragmentation in the basal region of this large granular mass flow, and we show that such fragmentation generates a basal shear stress, retarding motion of the avalanche, that is a function of the flow thickness and intact rock strength. The topography of the Socompa deposit is realistically simulated using this fragmentation-derived resistance function. Basal fragmentation is also compatible with the evidence from the deposit that reflection of the avalanche from topography caused a secondary wave that interacted with the primary flow.     

Tracing water resources flows by complementary use of hydrological and water accounting models

Historically, there has been a dispute over water allocation between users and policymakers in Iran's Zayandeh-Roud Basin (ZRB). In this study, we used the “System of Environmental-Economic Accounting for Water” (SEEAW) framework in combination with the hydrologic model “Soil and Water Assessment Tool” (SWAT) to achieve the water balance in ZRB. We used SEEAW to combine a wide range of water-related statistics across stakeholders and SWAT to evaluate the unknown agricultural water use. The SWAT model is calibrated based on the stream flows and crop yields in the basin. The model assess the renewable water of the basin into two components, about 363 and 70 mm as green and blue water, respectively. Also results from the physical water supply and water use tables demonstrates that the agricultural sector uses 78% of the total renewable freshwater, followed by the residential, 16%, and the industrial sector, 6%. The flows of water from source to services in ZRB are traced based on the water supply and water use tables. The flow diagram shows that 8 MCM of industrial reused water was transferred to the agricultural sector, and 137 MCM and 18 MCM of water from the wastewater treatment plants to the agricultural and industrial sectors, respectively. Furthermore, the results show that the index of the basin dependence on groundwater resources is high (61%), the value of water stress is high (0.88) and the dependence of the basin on transboundary water resources is 30%. Therefore, this method is highly beneficial for achieving a conceptual water balance in disputed basins without enough agricultural water uses data.     

A simplified method of constructing fragility curves for highway bridges

Fragility curves are found to be useful tools for predicting the extent of probable damage. They show the probability of highway structure damage as a function of strong motion parameters, and they allow the estimation of a level of damage probability for a known ground motion index. In this study, an analytical approach was adopted to develop the fragility curves for highway bridges based on numerical simulation. Four typical RC bridge piers and two RC bridge structures were considered, of which one was a non‐isolated system and the other was an isolated system, and they were designed according to the seismic design code in Japan. From a total of 250 strong motion records, selected from Japan, the United States, and Taiwan, non‐linear time history analyses were performed, and the damage indices for the bridge structures were obtained. Using the damage indices and ground motion parameters, fragility curves for the four bridge piers and the two bridge structures were constructed assuming a lognormal distribution. It was found that there was a significant effect on the fragility curves due to the variation of structural parameters. The relationship between the fragility curve parameters and the over‐strength ratio of the structures was also obtained by performing a linear regression analysis. It was observed that the fragility curve parameters showed a strong correlation with the over‐strength ratio of the structures. Based on the observed correlation between the fragility curve parameters and the over‐strength ratio of the structures, a simplified method was developed to construct the fragility curves for highway bridges using 30 non‐isolated bridge models. The simplified method may be a very useful tool to construct the fragility curves for non‐isolated highway bridges in Japan, which fall within the same group and have similar characteristics. Copyright © 2003 John Wiley & Sons, Ltd.     

Undrained shear strength response under monotonic loading of Chlef (Algeria) sandy soil

During the last mid-century, the Chlef area was strongly affected by two earthquakes. From the geological context, there were numerous ejections onto the ground level of great masses of sandy soils and large displacements of various forms of some building foundations. These damages are due to soil liquefaction problem. This loss of shear strength can be attributed to many factors. History of recent cases indicates that sand deposited with silt content is much more liquefiable than clean sand. Therefore, a deep understanding of silty sand behavior is needed for the liquefaction assessment of silty sandy soils. Moreover, during seismic shaking, the post-liquefaction behavior of silty sand and, consequently, the stability of structures founded on liquefied soil depend on the steady-state shear strength of soil. The objective of this laboratory investigation is to show the effect of silt contents and the relative density on the mechanical behavior of such soils in monotonic loading. In this context, a series of undrained triaxial tests were performed on reconstituted saturated silty sand samples with different fines content ranging from 0% to 40%. In all tests, the confining pressure was held constant to 100 kPa. The fines content and the global void ratio are expressed by means of the equivalent void ratio. Linear correlations relating the undrained residual shear strength of loose, medium dense, and dense (D _r?=?12%, 50%, and 90% before consolidation) sand–silt mixtures to the equivalent void ratio are obtained. The concept of the equivalent void ratio will then be used as a key parameter to express the dilatancy behavior of both clean and silty sand soils. Moreover, from the experimental results obtained, it is clear that the global void ratio cannot be used as a state parameter and may not represent the actual behavior of the soil as well.     

Syncline contribution to mountain peak building: examples from Western Zagros,Kurdistan Region,Northeastern Iraq

The current study focuses on roles of the synclines in building mountains of the Zagros Fold-Thrust Belt from Northeastern Iraq, Kurdistan Region. The studied area is located in the Imbricated Zone, which is a continuation of Simply Folded Zone of Iran. In some parts of this zone, the synclines contribute to building nearly half of the mountains and increase the relief contrast of the landscapes. The role of syncline in building mountains is opposite to its apparent intrinsic shape which is located in low land and normally forms synclinal valleys. In studied area, this phenomenon is observable in the areas that are complexly deformed, deeply exhumed, and predominately composed of the carbonate rocks. In these areas, exhumation and stream erosion have removed high thickness of overburden rocks and the tectonic stresses have crenulated carbonate rocks in the synclines. Due to these processes, these synclines are observable on the peak of the mountains now. The contribution of synclines in mountain building is related to three properties: the first is folding of synclines in confined condition (relative to anticlines) by which they have transformed to highly compact and stiff rocks. The second is accumulation of hydrothermal or meteoric water in the synclines due to its downward bending which aids precipitation of minerals and heals the possible tectonically and lithostatically induced fractures. The third is ductile deformation of synclines in confined and deeper level as compared to brittle deformation of anticlines in relatively shallower level and unconfined condition during deformation. Consequently, these factors result in an inversion of topography by which synclines are remained as mountains (high topography) above surface during exhumation while erosion removes anticlines. The result of this study is applicable for geological, geomorphological, and structural mapping in highly deformed and deeply exhumed terrains. The possible prediction of geomorphological position of synclines and anticlines on the mountain peaks and valley bottoms respectively is the applicable result in the above terrains.