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Santiago Yepez
Departamento de Manejo de Bosques y Medio Ambiente, Universidad de Concepción, Concepción, Chile

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Journal article
Published: 30 November 2020 in Journal of South American Earth Sciences
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Satellite images have been widely used to characterize mineral alteration zones in surface rocks affected by hydrocarbons' upward seepage. Likewise, magnetic surveys over oil fields have been employed for similar purposes. This work integrates satellite image spectral analyses with rock magnetic and geochemical data (i.e., mass-specific magnetic susceptibility χ, saturation isothermal remanent magnetization SIRM, analysis of SIRM acquisition curves, absorption spectro-radiometry, and X-ray diffraction analyses). The target area was an oil-prospective region in northwestern Venezuela (Falcon Basin) swarmed by hydrocarbon seeps. The study's main goal was to depict the spatial extension and vertical reach of the hydrocarbon-mediated alteration produced by these seeps and gain some knowledge about the processes involved in the subsequent mineral changes. Multispectral and hyperspectral satellite images showed three hydrocarbon-induced diagenetic anomalies (HIDAs) associated with undifferentiated clays and kaolinite, and low dolomite content. A simple weathering model was suggested combining the likely effects of the ascending seepage of oil and gas with the seasonal alternation of leaching and evaporation of meteoric waters. This model explains the magnetic enhancement with depth due to Fe oxides and sulfides' formation by reducing and oxidizing events. A non-supervised Two-Step Cluster Analysis (TSCA) was applied to integrate geochemical and rock magnetic properties with satellite images. The input variables were log SIRM and proxies of undifferentiated clays and dolomite concentrations obtained from the band-ratio ASTER images. The TSCA yields three clusters associated with different alteration levels in the top and low (0.3–1 m) soils and sediments. By mapping the class membership of each sampling site, for both depth levels, it was possible to obtain a broad view of the synergistic change of these combined properties, not only over the whole extent of the study area but also from top to bottom of the weathered sequence. This case study illustrates the potential of such an integrated method as an oil exploration tool, and a means to assess the level and scope of the environmental impact produced by hydrocarbon seepage on terrestrial ecosystems.

ACS Style

Roberto De la Rosa; Milagrosa Aldana; Vincenzo Costanzo-Alvarez; Santiago Yepez; Cristina Amon. The surface expression of hydrocarbon seeps characterized by satellite image spectral analysis and rock magnetic data (Falcon basin, western Venezuela). Journal of South American Earth Sciences 2020, 106, 103036 .

AMA Style

Roberto De la Rosa, Milagrosa Aldana, Vincenzo Costanzo-Alvarez, Santiago Yepez, Cristina Amon. The surface expression of hydrocarbon seeps characterized by satellite image spectral analysis and rock magnetic data (Falcon basin, western Venezuela). Journal of South American Earth Sciences. 2020; 106 ():103036.

Chicago/Turabian Style

Roberto De la Rosa; Milagrosa Aldana; Vincenzo Costanzo-Alvarez; Santiago Yepez; Cristina Amon. 2020. "The surface expression of hydrocarbon seeps characterized by satellite image spectral analysis and rock magnetic data (Falcon basin, western Venezuela)." Journal of South American Earth Sciences 106, no. : 103036.

Journal article
Published: 12 October 2020 in Water
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This paper proposes a systematic procedure to identify river reaches from a geomorphic point of view. Their identification traditionally relies on a subjective synthesis of multi-dimensional information (e.g., changes of slope, changes of width of valley bottom). We point out that some of the attributes adopted to describe geomorphic characters of a river (in particular sinuosity and confinement) depend on the length of reaches, while these latter are not yet identified; this is a source of ambiguity and introduces, at least conceptually, an unpleasant, implicit, iterative procedure. We introduce a new method which avoids this difficulty. Furthermore, it is simple, objective, and explicitly defined, and as such, it is automatable. The method requires to define and determine a set of intensive attributes, i.e., attributes that are independent of the segment length. The reaches are then identified by the intersection of the segmentations induced by such attributes. We applied the proposed procedure in two case studies, the Magdalena River (Colombia) and the Baker River (Chile), and investigated whether the adoption of the traditional approach for the definition of reaches would lead to a different result. We conclude that there would be no detectable differences. As such, the method can be considered an improvement in geomorphic river characterization.

ACS Style

Andrea Nardini; Santiago Yépez; Bruno Mazzorana; Héctor Ulloa; María Bejarano; Alain Laraque. A Systematic, Automated Approach for River Segmentation Tested on the Magdalena River (Colombia) and the Baker River (Chile). Water 2020, 12, 2827 .

AMA Style

Andrea Nardini, Santiago Yépez, Bruno Mazzorana, Héctor Ulloa, María Bejarano, Alain Laraque. A Systematic, Automated Approach for River Segmentation Tested on the Magdalena River (Colombia) and the Baker River (Chile). Water. 2020; 12 (10):2827.

Chicago/Turabian Style

Andrea Nardini; Santiago Yépez; Bruno Mazzorana; Héctor Ulloa; María Bejarano; Alain Laraque. 2020. "A Systematic, Automated Approach for River Segmentation Tested on the Magdalena River (Colombia) and the Baker River (Chile)." Water 12, no. 10: 2827.

Review
Published: 18 September 2020 in Water
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Although the Congo Basin is still one of the least studied river basins in the world, this paper attempts to provide a multidisciplinary but non-exhaustive synthesis on the general hydrology of the Congo River by highlighting some points of interest and some particular results obtained over a century of surveys and scientific studies. The Congo River is especially marked by its hydrological regularity only interrupted by the wet decade of 1960, which is its major anomaly over nearly 120 years of daily observations. Its interannual flow is 40,500 m3 s−1. This great flow regularity should not hide important spatial variations. As an example, we can cite the Ubangi basin, which is the most northern and the most affected by a reduction in flow, which has been a cause for concern since 1970 and constitutes a serious hindrance for river navigation. With regard to material fluxes, nearly 88 × 106 tonnes of material are exported annually from the Congo Basin to the Atlantic Ocean, composed of 33.6 × 106 tonnes of TSS, 38.1 × 106 tonnes of TDS and 16.2 × 106 tonnes of DOC. In this ancient flat basin, the absence of mountains chains and the extent of its coverage by dense rainforest explains that chemical weathering (10.6 t km−2 year−1 of TDS) slightly predominates physical erosion (9.3 t km−2 year−1 of TSS), followed by organic production (4.5 t km−2 year−1 of DOC). As the interannual mean discharges are similar, it can be assumed that these interannual averages of material fluxes, calculated over the longest period (2006–2017) of monthly monitoring of its sedimentology and bio-physical-chemistry, are therefore representative of the flow record available since 1902 (with the exception of the wet decade of 1960). Spatial heterogeneity within the Congo Basin has made it possible to establish an original hydrological classification of right bank tributaries, which takes into account vegetation cover and lithology to explain their hydrological regimes. Those of the Batéké plateau present a hydroclimatic paradox with hydrological regimes that are among the most stable on the planet, but also with some of the most pristine waters as a result of the intense drainage of an immense sandy-sandstone aquifer. This aquifer contributes to the regularity of the Congo River flows, as does the buffer role of the mysterious “Cuvette Centrale”. As the study of this last one sector can only be done indirectly, this paper presents its first hydrological regime calculated by inter-gauging station water balance. Without neglecting the indispensable in situ work, the contributions of remote sensing and numerical modelling should be increasingly used to try to circumvent the dramatic lack of field data that persists in this basin.

ACS Style

Alain Laraque; Guy D. Moukandi N’Kaya; Didier Orange; Raphael Tshimanga; Jean Marie Tshitenge; Gil Mahé; Cyriaque R. Nguimalet; Mark A. Trigg; Santiago Yepez; Georges Gulemvuga. Recent Budget of Hydroclimatology and Hydrosedimentology of the Congo River in Central Africa. Water 2020, 12, 2613 .

AMA Style

Alain Laraque, Guy D. Moukandi N’Kaya, Didier Orange, Raphael Tshimanga, Jean Marie Tshitenge, Gil Mahé, Cyriaque R. Nguimalet, Mark A. Trigg, Santiago Yepez, Georges Gulemvuga. Recent Budget of Hydroclimatology and Hydrosedimentology of the Congo River in Central Africa. Water. 2020; 12 (9):2613.

Chicago/Turabian Style

Alain Laraque; Guy D. Moukandi N’Kaya; Didier Orange; Raphael Tshimanga; Jean Marie Tshitenge; Gil Mahé; Cyriaque R. Nguimalet; Mark A. Trigg; Santiago Yepez; Georges Gulemvuga. 2020. "Recent Budget of Hydroclimatology and Hydrosedimentology of the Congo River in Central Africa." Water 12, no. 9: 2613.

Journal article
Published: 15 June 2020 in Geosciences
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This paper presents a systematic procedure for developing a characterization and classification of river reaches inspired by the River Styles Framework, through which insight can be gained about the understanding of river behavior. Our procedure takes advantage of several computer based “tools", i.e., algorithms implemented in software packages of various types, from "simple" Excel sheets to sophisticated algorithms in Python language, in general all supported by Geographic Information Systems (GIS). The main potentially useful, existing tools for this specific aim are discussed here, revealing their strengths and weaknesses. New, complementary or alternative tools that have been developed in the project feeding this paper are presented, which can contribute to the scientific community and stakeholders of the topic. The main result of our research is a structured and practical guide (a ToolBox Manual) that can support practitioners and researchers wishing to characterize and classify large rivers, based on the River Styles Framework. The main contribution is that this set of ideas, solutions, and tools, makes this type of exercise significantly more transparent and at the same time much less subjective. Moreover, the procedure is applicable to large systems and does not require more information than that generally available also in developing or emerging countries.

ACS Style

Andrea Nardini; Santiago Yépez; Maria Bejarano. A Computer Aided Approach for River Styles—Inspired Characterization of Large Basins: A Structured Procedure and Support Tools. Geosciences 2020, 10, 231 .

AMA Style

Andrea Nardini, Santiago Yépez, Maria Bejarano. A Computer Aided Approach for River Styles—Inspired Characterization of Large Basins: A Structured Procedure and Support Tools. Geosciences. 2020; 10 (6):231.

Chicago/Turabian Style

Andrea Nardini; Santiago Yépez; Maria Bejarano. 2020. "A Computer Aided Approach for River Styles—Inspired Characterization of Large Basins: A Structured Procedure and Support Tools." Geosciences 10, no. 6: 231.

Journal article
Published: 17 April 2020 in Water
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This paper addresses the geomorphic characterization and classification of large rivers in a framework of scarce information. This is inspired by the River Styles Framework with some modifications that make the process more straightforward and accessible to practitioners and more applicable to large basins, while reducing the subjective, expert-based inputs, as the process is now more systematic. To this aim, it utilizes innovative criteria and some computer-aided procedures and tools based on GIS, Excel and Python. This approach sheds light on the character and the behavior of rivers, which is key to informing planning, management and restoration. The application to the Magdalena River (Colombia) illustrates the characterization and classification process and the type of results, which ultimately highlight the great geomorphic diversity of that river. The process is applicable to many other rivers worldwide.

ACS Style

Andrea Nardini; Santiago Yepez; Lislie Zuniga; Carlo Gualtieri; Maria Dolores Bejarano. A Computer Aided Approach for River Styles—Inspired Characterization of Large Basins: The Magdalena River (Colombia). Water 2020, 12, 1147 .

AMA Style

Andrea Nardini, Santiago Yepez, Lislie Zuniga, Carlo Gualtieri, Maria Dolores Bejarano. A Computer Aided Approach for River Styles—Inspired Characterization of Large Basins: The Magdalena River (Colombia). Water. 2020; 12 (4):1147.

Chicago/Turabian Style

Andrea Nardini; Santiago Yepez; Lislie Zuniga; Carlo Gualtieri; Maria Dolores Bejarano. 2020. "A Computer Aided Approach for River Styles—Inspired Characterization of Large Basins: The Magdalena River (Colombia)." Water 12, no. 4: 1147.

Journal article
Published: 03 October 2019 in Water
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The Casiquiare River is a natural channel that connects two of the greatest rivers in the world, the Orinoco and the Amazon in the South American continent. The aim of this paper is to present a review and synthesis of the hydrological and sedimentological knowledge of the Casiquiare River, including the first hydro-sedimentary balance of the Casiquiare fluvial system conducted 9–12 September 2000 at the bifurcation and mouth during the expedition ‘Humboldt-Amazonia 2000’. Bathymetric flow discharge and physico-chemical measurements were made at the inlet and outlet of the Casiquiare Channel. The main conclusions of this study indicate that Casiquiare is taking a significant proportion of flow (20% to 30%) from the Upper Orinoco basin to the Amazon basin. Throughout its 356 km-course, this chameleon channel undergoes significant morphological, hydrological, and bio-geochemical variations between the inlet and outlet, whose most visible witnesses are the increase in its width (3 to 4 times), flow (7 to 9 times), and its change in water color (white to black water), under the influence of tributaries coming from vast forest plains.

ACS Style

Alain Laraque; Jose Luis Lopez; Santiago Yepez; Paul Georgescu. Water and Sediment Budget of Casiquiare Channel Linking Orinoco and Amazon Catchments, Venezuela. Water 2019, 11, 2068 .

AMA Style

Alain Laraque, Jose Luis Lopez, Santiago Yepez, Paul Georgescu. Water and Sediment Budget of Casiquiare Channel Linking Orinoco and Amazon Catchments, Venezuela. Water. 2019; 11 (10):2068.

Chicago/Turabian Style

Alain Laraque; Jose Luis Lopez; Santiago Yepez; Paul Georgescu. 2019. "Water and Sediment Budget of Casiquiare Channel Linking Orinoco and Amazon Catchments, Venezuela." Water 11, no. 10: 2068.

Preprint
Published: 26 September 2019
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The Casiquiare River is a natural channel that connects two of the greatest rivers in the world, the Orinoco and the Amazon in the South American Continent. The aim of this paper is to present a review and synthesis of the hydrological and sedimentological knowledge of the Casiquiare River, including the first hydro-sedimentary balance of the Casiquiare fluvial system conducted at the bifurcation and at the mouth on September 9-12, 2000, during the expedition ‘Humboldt-Amazonia 2000’. Bathymetric, flow discharge and physico-chemical measurements were made at the inlet and at the outlet of the Casiquiare Channel. The main conclusions of this study indicate that Casiquiare is taking a significant proportion of flow (20 to 30%) from the Upper Orinoco basin to the Amazon basin. Throughout its 356 km-course, this chameleon channel undergoes significant morphological, hydrological and bio-geochemical variations between the inlet and the outlet, whose most visible witnesses are the increase in its width (3 to 4 times), flow (7 to 9 times) and its change in water color (white to black water), under the influence of tributaries coming from vast forest plains.

ACS Style

Alain Laraque; Jose Luis Lopez; Santiago Yepez; Paul Georgescu. Water and Sediment Budget of Casiquiare Channel Linking Orinoco and Amazon Catchments, Venezuela. 2019, 1 .

AMA Style

Alain Laraque, Jose Luis Lopez, Santiago Yepez, Paul Georgescu. Water and Sediment Budget of Casiquiare Channel Linking Orinoco and Amazon Catchments, Venezuela. . 2019; ():1.

Chicago/Turabian Style

Alain Laraque; Jose Luis Lopez; Santiago Yepez; Paul Georgescu. 2019. "Water and Sediment Budget of Casiquiare Channel Linking Orinoco and Amazon Catchments, Venezuela." , no. : 1.