Improved imaging of a karst aquifer using focused source electromagnetic and differentially normalized method: a qualitative analysis

Geophysical investigations using conventional techniques applied to groundwater exploration can often present strong limitations involving high financial costs, complex acquisition logistics and high ambiguity in results. Dispersion of the electric current flow, induced polarization) effects, cultural noises and shallow lateral heterogeneities represent the main problems faced by geoelectric methods in these types of surveys. Moreover, elements such as intrusions and mineralization at different depths may be responsible for signal attenuation as well as high resistivity in unsaturated zones and complex three-dimensional formations or clayey zones cause variations in the electric current. The focused source electromagnetic and differentially normalized method approaches can help to solve some these issues. Aiming at a higher signal-to-noise ratio, the focused source electromagnetic method and approaches of the differentially normalized method, first applied to petroleum exploration, are tested on a groundwater target, in a karst environment sectioned by a diabase dyke. We performed the processing and analysis on real IP resistivity profiling data acquired with two-way dipole-dipole array, guided by magnetic data acquired on the same profile, mapping a diabase dyke. The inversion of focused source electromagnetic method/differentially normalized method was not performed, instead that we converted the induced polarization–resistivity data to a differential signal to qualitatively prove the presence of aquifer. Joint interpretation of focused source electromagnetic method curves and inverted two-dimensional induced polarization–resistivity sections allowed for precise delineation of a conductive zone associated with the karst aquifer, le magnetics allowed for the definition of a neighbour dyke. The techniques have great potential in the aid of groundwater exploration, contributing substantially to the reduction of interpretation ambiguity. Focused source electromagnetic method/differentially normalized method/ approaches show that a simple linear combination of the conventional geoelectric data is able to remove the geological noise and provide the vertical focusing of the electric current.     

Wave observations from an array of directional buoys over the southern Brazilian coast

It is well known that the majority of buoy measurements are located around the US coast and along some Europeans countries. The lack of long-term and densely spaced in situ measurements in the Southern Hemisphere in general, and the South Atlantic in particular, hinders several investigations due to the lack of detailed metocean information. Here, we present an effort to overcome this limitation, with a dense network of buoys along the Brazilian coast, equipped with several meteorological and oceanographic sensors. Out of ten currently operational buoys, three are employed to present the main characteristics of waves in the Southern part of the network. For the first time, sensor characteristics and settings are described, as well as the methods applied to the raw wave data. Statistics and distributions of wave parameters, swell propagating events, comparison with a numerical model and altimeters and a discussion about the occurrence of freak waves are presented.     

Automated watershed subdivision for simulations using multi-objective optimization

A qualitative trial-and-error approach is commonly used to define watershed subdivisions through varying a single topographic threshold value. A methodology has been developed to quantitatively determine spatially variable threshold values using topography and a user-defined landscape reference layer. Optimization and topographic parameterization algorithms were integrated to create solutions that minimize the number of sub-watersheds and maximize the agreement between the discretized watershed and the reference layer. The system was evaluated using different reference datasets such as soil type, land management, and landscape form. Comparison of simulated results indicated that the scenario using land management as the reference layer yielded results closer to the scenario subdivided using a constant topographic threshold but with approximately 10 times more sub-catchments and therefore indicating customization of the watershed subdivision to the user-defined reference layer. The proposed optimization technology could be used in adequately applying watershed modeling technology in developing conservation practice implementation plans.     

Groundwater Level Prediction/Forecasting and Assessment of Uncertainty Using SGS and ARIMA Models: A Case Study in the Bauru Aquifer System (Brazil)

Natural Resources Research - Best water management practices should involve the prediction of the availability of groundwater resources. To predict/forecast and consequently manage these water...     

Morphological Variation of the Sea Silverside Odontesthes regia in Regions with Dissimilar Upwelling Intensity along the Humboldt Current System

Ocean Science Journal - We evaluated the influence of areas with dissimilar upwelling intensity along the Humboldt Current System on the morphological variation of the economically important sea...     

Impact of climate and hydrology on juvenile fish recruitment towards estuarine nursery grounds in the context of climate change

Larvae of various coastal fish undergo immigration from spawning grounds towards estuarine nurseries. Several environmental factors can have an important impact on survival at this stage making it crucial for recruitment. Generalized linear models were applied in order to investigate the relation between river drainage, sea surface temperature (SST), NAO index and the North-South wind component intensity, over the two months prior to the estuarine colonization peak, and the densities of Platichthys flesus, Dicentrarchus labrax, Diplodus vulgaris and Diplodus bellottii in the nursery grounds based on a discontinuous historical dataset (from 1978 to 2006), for the Tagus estuary. The relation between SST over the 12 months prior to the estuarine colonization peak and fish densities in the nurseries was also investigated, as it integrates the periods of spawning stock maturation, spawning and larval immigration. While SST over the prior 12 months was negatively correlated with the abundance of P. flesus, it was positively correlated with the abundance of D. bellottii. Abundance of D. vulgaris was positively correlated with SST in the two months prior to the estuarine colonization peak, while the abundance of D. labrax was positively correlated with river drainage. The relations between SST and the abundance of P. flesus, a cold-water species with declining densities, and the subtropical species D. bellottii and D. vulgaris, which are increasing in abundance, are indicative of species abundance alterations related to climate warming. Dicentrarchus labrax will probably also be affected by climate change because of lowered precipitation and consequently river drainage.     

How Does Large Flaring Activity from the Same Active Region Produce Oppositely Directed Magnetic Clouds?

We describe the interplanetary coronal mass ejections (ICMEs) that occurred as a result of a series of solar flares and eruptions from 4 to 8 November 2004. Two ICMEs/magnetic clouds occurring from these events had opposite magnetic orientations. This was despite the fact that the major flares related to these events occurred within the same active region that maintained the same magnetic configuration. The solar events include a wide array of activities: flares, trans-equatorial coronal loop disappearance and reformation, trans-equatorial filament eruption, and coronal hole interaction. The first major ICME/magnetic cloud was predominantly related to the active region 10696 eruption. The second major ICME/magnetic cloud was found to be consistent with the magnetic orientation of an erupting trans-equatorial filament or else a rotation of 160° of a flux rope in the active region. We discuss these possibilities and emphasize the importance of understanding the magnetic evolution of the solar source region before we can begin to predict geoeffective events with any accuracy.     

Volcanic-sedimentary features in the Serra Geral Fm., Paraná Basin,southern Brazil: Examples of dynamic lava-sediment interactions in an arid setting

The formation of volcanic–sedimentary interaction features in extreme arid environments is not a commonly described process. Specifically the occurrence of dynamically mixed sediments and juvenile igneous clasts as peperites, for water has been considered one major important factor in the processes of magma dismantling and mingling with unconsolidated sediment to form such deposits. The study area, located in south Brazil, shows a sequence of lava flows and intertrapic sandstone layers from the Paraná Basin, associated with the formation of clastic dykes, flow striations, peperite and ‘peperite-like’ breccias. Four processes are suggested for the genesis of the peperites: (a) fragmentation of the flow front and base; (b) sand injection; (c) dune collapse; (d) magma cascade downhill. The continued flow of a lava, while its outer crust is already cooling, causes it to break, especially in the front and base, fragments falling in the sand and getting mixed with it, generating the flow front ‘peperite-like’ breccia. The weight of the lava flow associated to shear stress at the base cause sand to be injected inwards the flow, forming injection clastic dykes in the cooled parts and injection peperite in the more plastic portions. The lava flow may partially erode the dune, causing the dune to collapse and forming the collapse ‘peperite-like’ breccia. The shear stress at the base of a flowing lava striates the unconsolidated sand, forming the flow striations. The sand that migrates over a cooled, jointed lava flow may get caught in the cavities and joints, forming the filling clastic dykes. These deposits are analogous to those found in the Etendeka, NW Namibia, and show that sediment–lava interactions in arid settings are widespread throughout the Paraná-Etendeka province during the onset of flood volcanism.