Isotope measurements and ground water flow modeling using MODFLOW for understanding environmental changes caused by a well field in semiarid Brazil

Measurements of the environmental isotopes carbon-14 and oxygen-18 and of the electrical conductivity in ground water, together with MODFLOW-88 (DOS) simulations of pumping tests, were used to achieve a detailed understanding of the functioning of an aquifer in the area of a well field. The methodology was applied in the sedimentary basin of the Cariri region, in the south of Ceará State in Brazil. Localized hydraulic connections between adjacent aquifer units could be detected, and mixing ratios for the contributions from the units involved were determined. Cone of depression simulations for a three-year drought period revealed well interference and a drastic lowering of the piezometric level, thereby explaining the hydrogeologic changes and transformations in vegetation that were observed in the area of the well field. The combined use of the modeling tools and the geochemical field observations is shown to provide more detailed insight into the conceptual model of the groundwater flow system.     

Spatial and temporal variations in soil chemistry on the Amazon floodplain

Soil samples were collected on the floodplains of the Amazon River and its principal Brazilian tributaries during dry, early rising water, and early falling water periods. The concentrations of basic cations and pH in these alluvial soils were always higher than those in the more common terra firme soils while the concentrations of aluminum were generally lower. Among the alluvial soils, those from the main channel floodplain were generally higher in basic cations and pH, and lower in aluminum than those from the tribuary floodplains. The concentrations of basic cations in soils along the main channel floodplain decreased downstream. No significant difference was found in the levels of basic cations, pH, or aluminum between sampling periods.     

The use of GPR for characterizing underground weathered profiles in the sub-humid tropics

Ground penetrating radar (GPR) has been used as a tool to access information about ground subsurface features. Such information is very important for different types of studies, varying from those related to archeological research to those studying geological elements of bedrock. More recently, however, GPR has been increasingly applied to environmental studies, especially for soil research. This paper presents the results of an application of GPR for the study of weathered profiles. GPR was used to discover the degree of trustworthiness of the information on the ground subsurface through the interpretation of the results of the radar sections as well as the data collected from boreholes, which reached until 21 m. The results show a relatively high degree of details obtained by GPR, indicating the possibility of speeding up ground subsurface surveys related to geomorphological, geological, and pedological studies.     

Source Parameters of Old Earthquakes: Semi-Automatic Digitization of Analog Records and Seismic Moment Assessment

Recovering seismic information contained in old analog records could increase our knowledge of seismic source characteristics and the seismicity of a region. This is particularly important in zones with low to moderate seismicity.To extract the available information, it is necessary to digitize the seismic records. This is not an easy task especially owing to the generally poor quality of the original records, with illegible or missing parts. However some exceptions were found in the records of a few seismological stations in Germany, Sweden and France.This paper presents an example of the recovering of source parameters and can be divided in two parts: the first one presents a simple semi-automatic technique for digitization of old analog seismic records, developed using commercial software on a PC; the second part describes the methodology of assessing the seismic moment, using empirical and theoretical relations, as well as the seismic source dimensions.The earthquake selected to illustrate this procedure is the 23 April 1909 Benavente (Portugal) earthquake. This earthquake occurred in the Lower Tagus Valley region and caused great destruction in the meizoseismal area. It is the biggest earthquake that occurred during this century in the central part of the country and its magnitude has been estimated between 6.6 and 7.6.The digitization procedure allowed the recovery of seismic information contained in old analog records, in particular, the seismic moment estimation. The results obtained indicated that 7.6 was a very high value for the magnitude of the 23 April 1909 earthquake, suggesting that the magnitude reported in the Portuguese catalogue is overestimated. The estimated moment magnitude is 6.0.     

A Possible Mechanism to Form Low Mass Objects at Low Redshifts

We develop a quantitative criterion for the collapse of matter within a region where a global texture just collapsed and a non-zero peculiar velocity field is produced. We also describe the evolution of the density contrast in this region according to the non-linear spherical collapse model. In particular, we find that the overdensity needed to virialisation is reached at z ≤ 2.2, covering a mass range of about 10⁴–10⁷ M_⊙ in the context of an Einstein-de Sitter universe.     

HT-fabrics in a garnet-bearing quartzite from Western Portugal: geodynamic implications for the Iberian Variscan Belt

ABSTRACT The study of a garnet-bearing quartzite from a major suture zone in Iberia reports an unusual high-T fabric. Quartz c -axis patterns were plotted using shaped garnet as reference axis for the finite stretch ( X -axis). The pole figures are characterized by a dominant single maximum around X together with other point maxima along the XY plane (mylonitic foliation). These patterns suggest that dominant < c > prism slip and subordinated < a > prism slip operated during quartz plastic deformation in agreement with P–T conditions for syntectonic garnet growth (4–5 kbar and 700 ± 50 °C) and, pre-dating the well-known (late) Variscan D1 event (<6 kb and 600 ± 30 °C). The geotectonic framework suggests that the fabrics were formed along the western shear margin of the Ossa-Morena Zone during the early stages of the Variscan orogeny.     

The Energy Balance Experiment EBEX-2000. Part I: overview and energy balance

An overview of the Energy Balance Experiment (EBEX-2000) is given. This experiment studied the ability of state-of-the-art measurements to close the surface energy balance over a surface (a vegetative canopy with large evapotranspiration) where closure has been difficult to obtain. A flood-irrigated cotton field over uniform terrain was used, though aerial imagery and direct flux measurements showed that the surface still was inhomogeneous. All major terms of the surface energy balance were measured at nine sites to characterize the spatial variability across the field. Included in these observations was an estimate of heat storage in the plant canopy. The resultant imbalance still was 10%, which exceeds the estimated measurement error. We speculate that horizontal advection in the layer between the canopy top and our flux measurement height may cause this imbalance, though our estimates of this term using our measurements resulted in values less than what would be required to balance the budget. The National Center for Atmospheric Research is supported by the National Science Foundation     

Tephrochronology of recent events in the Andean Range (northern Patagonia): spatial distribution and provenance of lacustrine ash layers in the Nahuel Huapi National Park

Tephrochronology is a powerful tool for dating sedimentary sequences, especially in Patagonia, where a large number of active volcanoes have produced frequent historical eruptions. Short lacustrine sedimentary sequences were extracted from the lakes Moreno Oeste and Ton?ek (Nahuel Huapi National Park). Seventeen volcanic ash layers were identified in both cores, ²¹⁰Pb and ¹³⁷Cs were used for dating techniques, and historical volcanic records were employed for correlation. White pumice and glass shards from the tephras were characterised by measuring major and trace element contents by instrumental neutron activation analysis. Two volcanic sources – the Cordón Caulle and the Calbuco volcanoes – were recognised as the prevailing systems that impacted the area in the past 800–1000 a. The Calbuco volcano was mainly responsible for the nine tephras identified in the Lake Ton?ek sequence. Four of these nine tephras also contained material from the Cordón Caulle complex, and could be interpreted as composite tephras or possible reworked ones. The Calbuco volcano showed predominant influences in the Lake Moreno Oeste sequence. Six of the eight tephras identified in such a sequence were from the Calbuco volcano, and three of these six contained material from the Cordón Caulle complex. The other two were from the Cordón Caulle complex, with contributions from the Calbuco volcano in one of them. These findings show that the high frequency of volcanic events in the study region demands an accurate characterisation of the products generated by each source, as well as an evaluation of their spatial distribution, to obtain a consistent framework for dating recent environmental changes. Copyright © 2010 John Wiley & Sons, Ltd.     

Spatial concentration and variability of rainfall in the Iguaçu River Basin,State of Paraná−Brazil

The analysis of rainfall as an environmental factor that influences landscape dynamics is an important and ongoing topic of discussion. This discussion can be centred on the discovery of impacts caused by the increase or decrease in rainfall frequency and intensity. From this perspective, this study sought to analyse the rainfall variability in the Iguaçu River basin, located in the State of Paraná, southern Brazil. The main objective was focused on the temporal-spatial rainfall distribution in the study area and its interaction with landscape dynamics (different land uses). Precipitation data for the period 1988−2018 were obtained from the ‘Águas Paraná’ Institute. To calculate the Concentration Index−CI values of the study area, data analysis was performed using the ‘R’ software with Climatol and Precindicon subroutines of the software, and analysis of Landsat 8 satellite images through ArcGIS. The results indicated that there was a well-defined spatial variability in the study area, as the CIs defined higher rainfall concentrations upstream from the river basin and lower rainfall concentrations downstream—implying that these processes may be strongly associated with land use.     

An Environmental Threshold of Soil Test P and Degree of P Saturation of Brazilian Oxisols

To develop P management guidelines for poultry litter application in Oxisols of Brazil, the relationship between water soluble P (WSP), soil test P (STP), and degree of P saturation (DPS) needs to be established. The study examined this relationship in Oxisols of Brazil receiving poultry litter. Soils were analyzed for Mehlich‐1 P (M1‐P), WSP, P fractions, P sorption index (PSI), and P saturation based on Mehlich‐1 extractable P, Al, Fe (DPS_M1), and PSI (DPS_PSI). Surface water bodies in the catchment area were examined for inorganic and total P. All the surface water bodies in the catchment area of the sampled plots were highly enriched in inorganic and organic P. Enrichment of soil P fractions following poultry litter application followed the order HCl‐bound > NaOH‐bound > NaHCO₃‐bound fraction. M1‐P was correlated to labile (NaHCO₃‐P_i), and stable P pools (NaOH‐P and HCl‐P) and reflected the cumulative P accumulation in these soils. P saturation indices increased with cumulative P addition and increasing M1‐P. WSP increased with increasing DPS and a change point was noticed at 23% DPS_PSI (equivalent to DPS_M1 of 16.5%) corresponding to M1‐P of 44.5 mg P kg^?1, which could be regarded as threshold for P loss in these soils.