Influence of metal oxides in the colorimetric determination of acid volatile sulfide in sediments

The sediment of Lagoa dos Patos‐MS, Brazil, was investigated to verify the influence of metal sulfides and oxyhydroxides of Mn and Fe on the heavy metal availability. The spectrophotometric method of methylene blue was used, with 8 interlinked tubes containing the samples with SnCl₂, where N₂ was introduced to release the H₂S extracted with 6.0 mol L^–1 HCl, and trapped in 0.05 M NaOH solution. The influence of SO₄^2–, Mn(IV) and Fe(III) oxyhydroxides was investigated with samples constituted by a mixture of MnO₂; Na₂SO₄; FeCl₃, and sediments. The presence of SnCl₂ was very important to avoid the interferences of iron and manganese oxyhydroxides. The method of standard addition was applied and the efficiency was (100.8 ± 9.4)%. The ratio among the quantities of metals potentially available and the acid volatile sulfide (AVS) indicate that the system presents small metals availability to the benthic community, by the existence of sulfide capable to immobilize the metal as insoluble sulfide.     

Geochemical Control of Heavy Metal Concentrations and Distribution Within Bahia Blanca Estuary (Argentina)

Chromium and lead concentrations and distribution have been fully studied within Bahía Blanca estuary inner area, which is strongly influenced by urban and industrial stress. Not only metals dissolved in estuarine water but also those included in sediments and suspended particulate matters (SPM) were measured. In all cases, internationally standardized protocols were applied to metal measurements, including analytical quality check test through analysis of certified reference materials. Total metal contents from surface sediments and SPM were compared with those from a historical database of the area, as well as with values representing the natural geochemical baseline within the system. Results showed that heavy metal pollution is mainly localized in the areas close to both industrial effluents discharge system and urban sewage outfall discharge. Data from sequential extractions indicate that metals from anthropogenic sources (i.e., Pb) are potentially more mobile than those inherited from geological parent material (i.e., Cr). The influences of other potential sources of metals (i.e., streams, runoff) were also considered. SPM was clearly identified as the main carrier of the studied heavy metals within the system, and its significance to metals input into sediments and/or biota was verified. Finally, the normalization of measured metal concentrations against background reference elements (i.e., Al or Fe) has allowed to identify that most of the measured Cr was lithogenic, while a significant percentage of Pb was from anthropogenic origin within Bahía Blanca estuary.     

Geological risk assessment by a fracture measurement procedure in an urban area of Zacatecas,Mexico

Natural Hazards - Geological hazards represent medium- and long-term risks, when they affect urban infrastructure and residential areas as they become a source of danger for the population. In...     

Generalized extreme wind speed distributions in South America over the Atlantic Ocean region

Statistical analysis of extreme values is applied to wind data from National Centers for Environmental Prediction and National Center for Atmospheric Research reanalysis grid points over the ocean region bounded at 23°S and 40°W and 42°W towards the south and southeastern Brazilian coast. The period of analysis goes from 1975 to 2006. The generalized extreme value and generalized Pareto distributions are employed for annual and daily maxima, respectively. The Pareto?CPoisson point process characterization is also used to analyze peaks over threshold. Return levels for 10, 25, 50, and 100?years are calculated at each grid point. However, most of the reanalysis data fall within 1?C10-year return periods, suggesting that hazardous wind speed with low probability (return periods of 50?C100) have rarely measured in this period. Wide confidence intervals on these levels show that there is not enough information to make predictions with any degree of certainty to return periods over 100?years. Low extremal index (??) values are found for excess wind speeds over a high threshold, indicating the occurrence of consecutively high peaks. In order to obtain realistic uncertainty information concerning inferences associated with threshold excesses, a declustering method is performed, which separates the excesses into clusters, thereby rendering the extreme values more independent.     

Downscaling the non-stationary effect of climate forcing on local-scale dynamics: the importance of environmental filters

Large-scale climatic variability exerts a strong influence on local-scale environmental patterns and processes. However, disentangling the effects of global climate forcing from observed patterns in local processes requires robust understanding of the underlying patterns of temporal variability and consideration of the specific setting in which these processes take place. Here, we examine the influence of intermediate-scale environmental factors in modulating the effects of the North Atlantic Oscillation (NAO) on long-term water level dynamics in natural lakes. Lakes are ideal systems to study these relationships because of their acute sensitivity to environmental change and their linkages with multi-scale processes through the hydrological cycle. Using a novel combination of analytical tools, we show that the coupling between the NAO and water level dynamics is markedly nonstationary (i.e., time-frequency variant) and strongly lake-specific, filtered through the particular weather and environmental settings of lakes and their catchments. We conclude that to fully understand the nonstationary interplay between climate and ecology, we need first to disentangle the intermediate links between climate and different embedded environmental factors related to the process of interest. This knowledge should enhance significantly our ability to produce adequate long-term water resource management strategies, to preserve biological diversity and to achieve sustainable development under a globally changing climate.     

Wind wave climate change: Impacts on the littoral processes at the Northern Buenos Aires Province Coast, Argentina

Several works reported wind-wave climate changes at Buenos Aires Province continental shelf. The aim of this work is to investigate the impact of these changes in the coastal processes of the region. This study is carried out by means of visual wave parameters gathered at the surf zone of Pinamar and by a conveniently implemented and validated numerical wave model (SWAN). Numerical results corresponding to a grid point located 30 km off Pinamar show a significant increase of wave heights from the S and SSE directions and in the frequency of occurrence of waves coming from the S, SSE and E. It is shown that these slight offshore appreciated trends would not have significant effects on the breaker heights observed at the surf zone at Pinamar. On the contrary, the slight positive trend observed offshore in the frequency of occurrence could be affecting the incidence of waves onshore, producing an increase in the number of cases of normal incidence at the surf zone and, consequently, a significant decrease in the alongshore wave energy flux assessed at Pinamar. This reduction in the alongshore wave energy flux could be responsible for some coastal changes detected in the region as, for instance, the remarkable shortening of Punta Rasa spit located 70 km northward Pinamar.     

Spatio-temporal trends of precipitation,its aggressiveness and concentration,along the Pacific coast of South America (36–49°S)

ABSTRACT

Precipitation is the most critical climatic element that directly affects the availability of water resources. The objective of this study was to describe and discuss spatio-temporal patterns of annual precipitation, its aggressiveness, and its concentration along the southwest coast of South America (36°–49°S) from 1930 to 2006. An annual and multi-decadal analysis was applied to 107 sampling stations distributed throughout this region, using the Mann-Kendall test (MK), and the Sampling Uncertainty Analysis (SUA) coupled with Gumbel probability density function (SUA-Gumbel). The analysis revealed positive but not significant trends in annual precipitation and aggressiveness for the region between 36° and 44°S, at least during the last 50 years of the analysed period. However, a significant decrease in annual precipitation and aggressiveness was observed between 44° and 49°S during the same period. The annual concentration of precipitation became slightly more seasonal in the last 50 years within the entire study area.     

Advances in automated detection of sand dunes on Mars

This paper describes advances in an automatic approach for the detection of sand dunes of Mars, based on supervised learning techniques. A set of features (gradient histogram) is extracted from the remotely sensed images and two classifiers (Support Vector Machine and Random Forests) are trained from this data. The evaluation is conducted on 230 MOC‐NA images (spatial resolution between 1·45 and 6·80 m/pixel) leading to about 89% of correct detections. A detailed analysis of the detection results (dune/non‐dune) is performed by dune type or bulk shape, confirming high performances independently of the way the dataset is analysed. This demonstrates the robustness and adequacy of the automated approach to deal with the large variety of aeolian structures present on the surface of Mars. Copyright © 2012 John Wiley & Sons, Ltd.