Analysis of the spatial variation of heavy metals in the Guadiana Estuary sediments (SW Iberian Peninsula) based on GIS-mapping techniques

This work reveals the usefulness of the GIS (Geographic Information Systems) mapping techniques to show the distribution of pollutants along an estuarine environment, as the final stage of a thorough study. In the case of study, the environmental quality of the sediments in the Guadiana river estuary was determined by means of a complete geochemical characterization consisting on the calculation of enrichment factors for the most important metals and metalloids (compared with the local background of non-contaminated sediments). The obtained results were depicted in “enrichment distribution maps” which evidenced a distribution of the elements in two groups: Group-I, elements with natural origin (Al, Fe, Mn, Co, and Cr) distributed homogeneously along the basin, and Group-II, elements associated to anthropic origin (As, Cd, Cu, Pb, Ni and Zn) with clear punctual sources besides a high concentration all over the estuary. The enrichment factors for the elements of Group-II are indicative of the existence of a noticeable diffuse historical mining pollution associated with the acid mine drainage generated in the internal zones of the basin, which could overlap minor pollution inputs from other human activities. The obtained results lead us to a reconsideration of the traditionally thought “unpolluted” environment when it was compared to nearby estuaries.     

Nd and Sr isotopic constraints on the origin of igneous rocks resulting from the opening of the Japan Sea, southwestern Japan

Strontium and Nd isotopic compositions and trace element abundances were determined for Cretaceous to late Cenozoic igneous rocks from the Japan Sea side of Southwest Japan in order to investigate the effect of the opening of the Japan Sea on igneous activity. The ⁸⁷Sr/⁸⁶Sr ratios for both high and low silica rocks decrease with decreasing age since the middle Miocene, when the opening occurred. Similarly, ¹⁴³Nd/¹⁴⁴Nd values for these rocks increase with decreasing age, and are negatively correlated with ⁸⁷Sr/⁸⁶Sr ratios. A two-component mixing process can best account for these isotopic and chemical characteristics. One end-member is likely the subcontinental lithospheric mantle (SCLM) and its derivative mafic to intermediate materials which had ɛ_Nd values of around +3. The other endmember consists of mafic to intermediate rocks with low ɛ_Nd values (e.g., −8), probably located in the lower crust. The mantle upwelling associated with the opening of the Japan Sea did not supply typical MORB or MORB-source materials to the crust, but did provide the heat that caused the melting of lithospheric mantle and lower crust. Received: 29 August 1996 / Accepted: 6 May 1997     

Frequency of Boundary-Layer-Top Fluctuations in Convective and Stable Conditions Using Laser Remote Sensing

The planetary boundary-layer (PBL) height is determined with high temporal and altitude resolution from lidar backscatter profiles. Then, the frequencies of daytime thermal updrafts and downdrafts and of nighttime gravity waves are obtained applying a fast Fourier transform on the temporal fluctuation of the PBL height. The principal frequency components of each spectrum are related to the dominant processes occurring at the daytime and nighttime PBL top. Two groups of cases are selected for the study: one group combines daytime cases, measured in weak horizontal wind conditions and dominated by convection. The cases show higher updraft and downdraft frequencies for the shallow, convective boundary layer and lower frequencies for a deep PBL. For cases characterized by strong horizontal winds, the frequencies directly depend on the wind speed. The temporal variation of the PBL height is determined also in the likely presence of lee waves. For nighttime cases, the main frequency components in the spectra do not show a real correlation with the nocturnal PBL height. Altitude fluctuations of the top of the nocturnal boundary layer are observed even though the boundary layer is statically stable. These oscillations are associated with the wind shear effect and with buoyancy waves at the PBL top.     

Seasonal variation of horizontal material transport through the eastern channel of the Tsushima Straits

We conducted hydrographic observations ten times in the Tsushima Strait to reveal seasonal variations of horizontal material transports such as of heat, freshwater, chlorophyll a, and dissolved inorganic nitrogen (DIN) and phosphorus (DIP) through the eastern channel of the Tsushima Strait (ECTS). The volume, freshwater, and heat transport results are of nearly the same order as results reported in previous studies. The annual mean DIN and DIP transports of 3.59 kmol/s and 0.29 kmol/s are large relative to those of the Changjiang and the Taiwan Strait and are horizontally transported through the ECTS. Nutrient transports are high in July–August and October and low in April and November. Increased nutrient transports in July–August and October are due to the appearance of a cold saline water mass in the bottom layer of the ECTS. Changes in DIN transports in summer and autumn, which account for two-thirds of the total annual DIN transport, would have a large effect on the nitrogen budget and biological productivity in the Tsushima Warm Current region.     

Crop residue effects on surface radiation and energy balance — review

Summary Crop residues alter the surface properties of soils. Both shortwave albedo and longwave emissivity are affected. These are linked to an effect of residue on surface evaporation and water content. Water content influences soil physical properties and surface energy partitioning. In summary, crop residue acts to soil as clothing acts to skin. Compared to bare soil, crop residues can reduce extremes of heat and mass fluxes at the soil surface. Managing crop residues can result in more favorable agronomic soil conditions. This paper reviews research results of the quantity, quality, architecture, and surface distribution of crop residues on soil surface radiation and energy balances, soil water content, and soil temperature.With 6 Figures     

A simple approach to evaluating leakage through thin impervious element of high embankment dams

Internal erosion is the most common reason which induces failure of embankment dams besides overtopping. Relatively large leakage is frequently concentrated at defects of impervious element, and this will lead to eventual failure. The amount of leakage depends not only on integrity of impervious element, but also on dam height, shape of valley, shape of impervious element and water level in reservoir. The integrity of impervious element, which represents the relative level of seepage safety, is not easy to be determined quantitatively. A simple method for generalization of steady seepage state of embankment dams with thin impervious element is proposed in this paper. The apparent overall value of permeability coefficient for impervious element can be obtained by this method with reasonable accuracy and efficiency. A defect parameter of impervious element is defined as an index to characterize seepage safety of embankment dams. It equals the ratio of the apparent overall value of permeability coefficient to the measured value in laboratory for intact materials. Subsequently, seepage safety of three dams is evaluated and the evolution of defect level of impervious element of dams is investigated. It is proved that the newly proposed method in this paper is feasible in the evaluation of relative seepage safety level of embankment dams with thin impervious element.     

Environmental hydrogeology of the southern sector of the Samborombon Bay wetland,Argentina

The Samborombon Bay wetland is located on the west margin of the Rio de la Plata estuary, in the Province of Buenos Aires, Argentina. This paper analyses the geological, geomorphologic, soil and vegetation characteristics of the southernmost sector of this wetland and their influence on surface water and groundwater. The study area presents three hydrologic units: coastal dunes, sand sheets and coastal plain. Coastal dunes and sand sheets are recharge zones of high permeability with well-drained, non-saline soils, and a few surface water flows. Changes in the water table are related to rainfall. Groundwater in coastal dunes is Ca–Mg–HCO₃ to Na–HCO₃, and of low salinity (590 mg/l). Groundwater in sand sheets is mainly Na–HCO₃ with a salinity of about 1,020 mg/l. The coastal plain exhibits medium to low permeability sediments, with submerged saline soils poorly drained. Groundwater is Na–Cl with a mean salinity of 16,502 mg/l. A surface hydrological network develops in the coastal plain. Surface water levels near the shoreline are affected by tidal fluctuations; far from the shoreline water accumulates because of poor drainage. Both sectors have Na–Cl water, but the former is more saline. Human intervention and sea level rise may affect the wetland severely.     

Gravitational collapse, black holes and naked singularities

This article gives an elementary review of gravitational collapse and the cosmic censorship hypothesis. Known models of collapse resulting in the formation of black holes and naked singularities are summarized. These models, when taken together, suggest that the censorship hypothesis may not hold in classical general relativity. The nature of the quantum processes that take place near a naked singularity, and their possible implication for observations, is briefly discussed.     

Implications of channel flow analogue models for extrusion of the Higher Himalayan Shear Zone with special reference to the out-of-sequence thrusting

The Higher Himalayan Shear Zone (HHSZ) contains a ductile top-to-N/NE shear zone—the South Tibetan detachment system-lower (STDS_L) and an out-of-sequence thrust (OOST) as well as a top-to-N/NE normal shear at its northern boundary and ubiquitously distributed compressional top-to-S/SW shear throughout the shear zone. The OOST that was active between 22 Ma and the Holocene, varies in thickness from 50 m to 6 km and in throw from 1.4 to 20 km. Channel flow analogue models of this structural geology were performed in this work. A Newtonian viscous polymer (PDMS) was pushed through a horizontal channel leading to an inclined channel with parallel and upward-diverging boundaries analogous to the HHSZ and allowed to extrude to the free surface. A top-to-N/NE shear zone equivalent to the STDS_U developed spontaneously. This also indirectly connotes an independent flow confined to the southern part of the HHSZ gave rise to the STDS_L. The PDMS originally inside the horizontal channel extruded at a faster rate through the upper part of the inclined channel. The lower boundary of this faster PDMS defined the OOST. The model OOST originated at the corner and reached the vent at positions similar to the natural prototype some time after the channel flow began. The genesis of the OOST seems to be unrelated to any rheologic contrast or climatic effects. Profound variations in the flow parameters along the HHSZ and the extrusive force probably resulted in variations in the timing, location, thickness and slip parameters of the OOST. Variation in pressure gradient within the model horizontal channel, however, could not be matched with the natural prototype. Channel flow alone presumably did not result in southward propagation of deformation in the Himalaya.     

Multiscale characterization of a heterogeneous aquifer using an ASR operation

Heterogeneity in the physical properties of an aquifer can significantly affect the viability of aquifer storage and recovery (ASR) by reducing the recoverable proportion of low-salinity water where the ambient ground water is brackish or saline. This study investigated the relationship between knowledge of heterogeneity and predictions of solute transport and recovery efficiency by combining permeability and ASR-based tracer testing with modeling. Multiscale permeability testing of a sandy limestone aquifer at an ASR trial site showed that small-scale core data give lower-bound estimates of aquifer hydraulic conductivity (K), intermediate-scale downhole flowmeter data offer valuable information on variations in K with depth, and large-scale pumping test data provide an integrated measure of the effective K that is useful to constrain ground water models. Chloride breakthrough and thermal profiling data measured during two cycles of ASR showed that the movement of injected water is predominantly within two stratigraphic layers identified from the flowmeter data. The behavior of the injectant was reasonably well simulated with a four-layer numerical model that required minimal calibration. Verification in the second cycle achieved acceptable results given the model's simplicity. Without accounting for the aquifer's layered structure, high precision could be achieved on either piezometer breakthrough or recovered water quality, but not both. This study demonstrates the merit of an integrated approach to characterizing aquifers targeted for ASR.