Apparent discrepancy in contamination history of a sub-tropical estuary evaluated through 210Pb profile and chronostratigraphical markers

Zn and Cd concentrations, stable lead isotopes and ²¹⁰Pb-derived chronology were determined in a sediment core sampled at Sepetiba Bay (South-eastern Brazil). During the last decades, the bay’s watershed has been modified by the increase of industrial activities and human interventions. In particular, Zn and Cd ore treatment plants were built near the coast in 1960 and 1970, respectively, and water has been diverted from the adjacent Paraíba do Sul River watershed since 1950. The core collected at shallow depth near the industrial area exhibits four successive events: (i) at 50 cm depth, a change in the ²⁰⁶Pb/²⁰⁷Pb ratio from about 1.162 to more than 1.18 might be the result of the São Francisco Channel opening and water diversion from Paraíba do Sul river; (ii) at 40 cm depth, Zn concentration starts to increase (up to 0.8 mg g⁻¹) (iii) above 30 cm depth, relatively high Cd concentrations (up to 1.6 μg g⁻¹) are observed and (iv) at 16 cm depth, change in unsupported ²¹⁰Pb slope is probably related to a waste dam built to prevent strong metal contamination in the bay. Sediment accumulation rates evaluated by Zn and Cd profiles used as time-markers are higher than those calculated from ²¹⁰Pb-based chronology models. Using the constant initial concentration (CIC) model both events are supposed to date back to about 1884 and 1902, respectively, while using the constant rate of supply (CRS) model it shifts to about 1925 and 1935. Such discrepancies are probably assigned to the fact that these models do not take into account site-specific local sedimentation dynamics. In the study area, particles deposition seems to be controlled by enrichment with unsupported ²¹⁰Pb transported by runoff from a mangrove flat bank. Chronology derived from a model that assumes an exponential increase of the initial ²¹⁰Pb activity fits well with the estimated rates obtained from historical events.     

Integration of GIS and remote sensing for estimation of soil loss and prioritization of critical sub-catchments: a case study of Tapacurá catchment

Mapping of erosion risk areas is an important tool for the planning of natural resources management, allowing researchers to propose the modification of land use properly and implement more sustainable long-term management strategies. The objective of this study was to assess and identify critical sub-catchments for soil conservation management using the USLE, GIS, and remote sensing techniques. The Tapacurá catchment is one of the planning units for water resource management of the Recife Metropolitan Region. Maps of the erosivity (R), erodibility (K), slope (LS), cover-management (C), and support practice (P) factors were derived from the climate database, digital elevation model, and soil and land-use maps. In order to validate the simulation process, total sediment delivery ratio was estimated. The results showed a mean sediment delivery ratio (SDR) of around 11.5?% and a calculated mean sediment yield of 0.108?t?ha^?1?year^?1, which is close to the observed one, 0.169?t?ha^?1?year^?1. The obtained soil loss map could be considered as a useful tool for environmental monitoring and water resources management. The methodology applied showed acceptable precision and allowed the identification of the most susceptible areas to soil erosion by water, constituting an important predictive tool for soil and environmental management in this region, which is highly relevant for the prediction of varying development scenarios for Tapacurá catchment. This approach can be applied to other areas for simple and reliable identification of critical areas of soil erosion in catchments.     

Environmental issues in urban groundwater systems: a multidisciplinary study of the Paranhos and Salgueiros spring waters,Porto (NW Portugal)

This study presents the results of a multidisciplinary approach, using hydrogeochemical, isotopic and ecotoxicological analyses, performed to assess the nature and suitability for use of Paranhos and Salgueiros spring waters (Porto city, NW Portugal). Based on the surface activities located along the course of the springs, 23 water samples were collected. All the samples were analysed for major element concentrations. The isotopic techniques employed included δ²H, δ¹⁸O and ³H. Standard acute bioassays with Daphnia magna were also performed. The hydrogeochemical analyses showed a nitrate and sulphate-enriched composition for these groundwaters, resulting mainly from urban drainage and sewer leakage. In the ecotoxicological analyses, no significant mortality was observed in any of the tests performed. The results obtained in this study suggest that Porto urban groundwater could be suitable for irrigation uses.     

Changes in coronal condensations emission after solar bursts at microwaves

The amount of circular polarization of the total solar radio emission at 7 GHz present permanent changes after the occurrence of certain radio bursts associated with larger flares. For isolated S-components, associated with such flares the changes of the polarization degree _sranges between 0.004 to 0.1, and appears to be a function of the flare importance. A semi-qualitative interpretation associates _swith magnetic field reductions at the S-component, agreeing fairly well with a flare mechanism based on collisionless dissipation of magnetic energy, corresponding to energies in the range of 10³⁰ to 10³² ergs, assuming an average model for the coronal condensations.     

Effects of topography on the curvature of fold-and-thrust belts during shortening of a 2-layer model of continental lithosphere

We have used analogue experiments to investigate the effects of surface topography on the curvature of fold-and-thrust belts, under conditions of (1) initial relief, but no erosion, and (2) no initial relief, but differential erosion, sedimentation and transport.In experiments where a 2-layer model lithosphere shortened and thickened in front of an advancing straight piston, the geometry of the developing thrust wedge was very sensitive to variations in surface topography. In models with an initially flat, horizontal surface, and in the absence of erosion and sedimentation, thrusts were straight, propagated forwards, and nucleated at buckle folds far in front of an advancing piston. Around an initial topographic high (plateau or cone), thrusts tended to be arcuate, forming salients towards the foreland. Initial plateaux and cones tended to behave rigidly, while arcuate thrust slices formed around them. To accommodate differential slip, transfer zones developed on both sides of initial highs. Fault blocks rotated about vertical axes and thrusts moved in oblique slip within transfer zones. In models with initially horizontal surfaces, which were subject to differential erosion, sedimentation and transport, thrusts initially were straight, but then progressively rotated around non-eroded, thickened and stronger areas. These worked as indenters, in front of which new thrusts nucleated at curved buckle folds. These thrusts were also curved, their apices being in front of the thickened, non-eroded areas.In nature, arcuate structural patterns are to be found around the Altiplano of the Central Andes and around the Tromen volcanic ridge in the Neuquén Basin of northern Patagonia. We infer that these areas behaved in quasi-rigid fashion, protected as they were by their high elevations, and that differential erosion at the scale of the entire Andes may have contributed to oroclinal bending.     

Physical models of rifting and transform faulting, due to ridge push in a wedge-shaped oceanic lithosphere

By scaled physical modelling, we have investigated the mechanical response to gravitational forces in an oceanic lithosphere, overlying a less dense asthenosphere. In the models, an upper wedge-shaped layer of sand represented an oceanic lithosphere (0–35 Ma old, with a half-spreading velocity of 3 cm/yr), and a lower layer of polydimethylsiloxane (PDMS), mixed with dense wolframite powder, represented the asthenosphere. In the models, as in nature, isostatic compensation resulted in uplift of ridges and subsidence on their flanks. The resulting relief was responsible for ridge push. We tested two main configurations: straight ridges and offset ridges. In all the models, ridge push was sufficient to cause plate motion, underlying advection, and symmetrical rifting at the ridge axis. There was no need to impose plate motions through external pistons and motors. In models of straight ridges, the style of normal faults in the axial rift zone depended on the local thickness of the brittle sand layer. For thick layers, normal faults rafted out from the active zone of rifting, creating a fossil topography of tilted blocks, between faults dipping toward the ridge. In a model of an offset ridge, with thin lithosphere at the ridge crest and no embedded weakness, ridge push was responsible for a short transform fault, linking en-échelon rifts. In a similar model, but with thick lithosphere, an oblique rift formed at about 20° to the offset trace. We conclude that ridge push was not adequate to create an ideal transform fault. In a model of an offset ridge, with an embedded thin vertical layer of pure PDMS at 90° to the ridge, transform motion concentrated along this weak layer, and the resulting structural style was very similar to that in nature. On the basis of these results, we infer that, in nature, (1) ridge push can indeed drive plate motion, and (2) ridge push can drive strike-slip motion on transform faults, provided that these are weaker than the adjacent oceanic lithosphere and that they form early in the history of spreading.     

2060 Chiron: Visual and thermal infrared observations

Five-color (λλ = 0.36?0.85 μm) and thermal infrared (λ = 22.5 μm) photometric observations of the unusual asteroid 2060 Chiron were made. Between 0.36 and 0.85 μm, Chiron's reflectance spectrum is similar to those of C-class asteroids as well as Saturn's satellite Phoebe. However, the thermal IR measurements imply an albedo≥0.05 (i.e., a diameter ≤250 kmat the level 2σ level) that is probably higher than those of C-class asteroids or Phoebe.     

Microwave observations of the 4 January, 1973 solar eclipse

The eclipse was observed at two microwave frequencies, 7 GHz and 22.2 GHz, and has shown the presence of polarized regions, suggesting also excess of left-handed polarized radiation from the solar northern hemisphere. Difference in eclipsing times at the two frequencies for an active center near the limb is discussed.     

Multi-criteria analysis for the identification of waste disposal areas

The municipality of Cachoeiro de Itapemirim (ES) is currently the largest domestic producer and exporter of marble and granite in Brazil. The processing of the rock, especially the sawing results in a large volume of waste, including the abrasives used during sawing and the off-cut pieces. Presently these waste products are disposed of without proper environmental protection and cause pollution to surface water and groundwater resources, including silting, an increase in hardness and increased aluminium values in the groundwater. In order to minimize the harmful effects of these practices on the environment, a research project was undertaken to identify potential disposal sites for the generated waste. A multi-criteria approach was followed during which a database was compiled of all the companies generating waste products and also including a baseline environmental study of the region, integrated analysis (multi-criteria analysis) of the restriction factors and the preliminary identification of possible disposal sites. This revised version was published online in July 2006 with corrections to the Cover Date.