Las aguas brillantes de Corrientes

Fil: Orfeo, Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Centro de Ecología Aplicada del Litoral. Universidad Nacional del Nordeste. Centro de Ecología Aplicada del Litoral; Argentin

Estudio sedimentológico de ambientes fluviales del Chaco Oriental

Some sedimentological aspects of fluvial environments situated in the flood-plain of the Paraguay-Paraná river system (Northeastern of Argentina) were analized. The concentrations of suspended sediments, and the granulometric and textural characteristics of the bottom materials, were compared. The suspended load had an inverse relation with the hydrometric levels with exception of the highly saline streams (conductivity values between 4300 and 11000 uS.cm-1) showing the drastic succession of wet and dry seasons which periodically affected the region. The mean concentration of suspended sediments was 63,1 mg.l-1 and 206,3 mg.l-1 in flood and low water periods, respectively. Bed sediments were relatively homogeneous along all the hidrological eyele. Silt-sandy bottoms were the predominant, followed then by sand-silty and silt-clayey bottom types. Sediment transport was mainly carried out in acelerated flow suspensión, overcoming the erosion critical velocity. In flood period, some morphometric parameters overcome the 70% in relation with the values recorded in low water. Besides, different elements of diagnostic value for the evaluation of natural or antropical erosión, are also discussed.Some sedimentological aspects of fluvial environments situated in the flood-plain of the Paraguay-Paraná river system (Northeastern of Argentina) were analized. The concentrations of suspended sediments, and the granulometric and textural characteristics of the bottom materials, were compared. The suspended load had an inverse relation with the hydrometric levels with exception of the highly saline streams (conductivity values between 4300 and 11000 uS.cm-1) showing the drastic succession of wet and dry seasons which periodically affected the region. The mean concentration of suspended sediments was 63,1 mg.l-1 and 206,3 mg.l-1 in flood and low water periods, respectively. Bed sediments were relatively homogeneous along all the hidrological eyele. Silt-sandy bottoms were the predominant, followed then by sand-silty and silt-clayey bottom types. Sediment transport was mainly carried out in acelerated flow suspensión, overcoming the erosion critical velocity. In flood period, some morphometric parameters overcome the 70% in relation with the values recorded in low water. Besides, different elements of diagnostic value for the evaluation of natural or antropical erosión, are also discussed

Aproximación al conocimiento del proceso de erosión del suelo en el Chaco Oriental

Preliminar data obtained through periodical gauging Controls of the main rivers coming from the hydrographic basins inserted in the subregión of the Eastern Chaco, are reported. Physical and Chemical characteristics of the water quality were quantified and then correlated with the available data, related in the edaphic conditions to estimate, approximately, the interrelations existing between the soil tipology and the elements being moved by the hydric erosión. They were evaluated according with their role played in the water composition, in accordance with the different hydrologic situation and soil management. The hypothesis which preconizes that the effluent from a basin represents the landscape heterogenity and dinamism, is assumed to be valid.Preliminar data obtained through periodical gauging Controls of the main rivers coming from the hydrographic basins inserted in the subregión of the Eastern Chaco, are reported. Physical and Chemical characteristics of the water quality were quantified and then correlated with the available data, related in the edaphic conditions to estimate, approximately, the interrelations existing between the soil tipology and the elements being moved by the hydric erosión. They were evaluated according with their role played in the water composition, in accordance with the different hydrologic situation and soil management. The hypothesis which preconizes that the effluent from a basin represents the landscape heterogenity and dinamism, is assumed to be valid

Erosión fluvial en la cuenca del río Bermejito (Prov. del Chaco, Argentina)

Size, distribution and longitudinal changes of suspended load was analized in Bermejito River, located in the Chaco subtropical plain. Temporal variability was compared with hydrometric levels and rainfalls in selectionated areas of the drainage basin. Field activities were carried out in three sections with free runoff and one section with reduced velocity for natural causes. Sampies were taken with an instantaneous point-sampler placed at 20X, 60X and 80X of depth, through equally spaced verticals across the sections. Laboratory procedures ineludes filtering through 62 a open sieve and subsequently through filters with 4 a and 0,45a por es, for retention sand, sllt and clay fractions, respectively. Mean textural composition in the free-runoff sections comprised silts (95X) and clays (5X). Concentration had an homogeneous distribuíiuon in the flow, owing to the turbulence effect. Longitudinal changes were related with the transport capacity of the water course. Rainfall determined a quick increment of the suspended sediment concentration by wash-load incorporationowing to the scarce vegetal protection. The restrict runoff section had fewer suspended sediment concentration and a greater clay fraction proportion. Sediment yield was estimated in 12.4 tn/km'/yr and the present erosión rate was calculated in about 5 mm for each 1000 years.Size, distribution and longitudinal changes of suspended load was analized in Bermejito River, located in the Chaco subtropical plain. Temporal variability was compared with hydrometric levels and rainfalls in selectionated areas of the drainage basin. Field activities were carried out in three sections with free runoff and one section with reduced velocity for natural causes. Sampies were taken with an instantaneous point-sampler placed at 20X, 60X and 80X of depth, through equally spaced verticals across the sections. Laboratory procedures ineludes filtering through 62 a open sieve and subsequently through filters with 4 a and 0,45a por es, for retention sand, sllt and clay fractions, respectively. Mean textural composition in the free-runoff sections comprised silts (95X) and clays (5X). Concentration had an homogeneous distribuíiuon in the flow, owing to the turbulence effect. Longitudinal changes were related with the transport capacity of the water course. Rainfall determined a quick increment of the suspended sediment concentration by wash-load incorporationowing to the scarce vegetal protection. The restrict runoff section had fewer suspended sediment concentration and a greater clay fraction proportion. Sediment yield was estimated in 12.4 tn/km'/yr and the present erosión rate was calculated in about 5 mm for each 1000 years

Introducción al estudio de sedimentos fluviales de llanura

Con la finalidad de conservar los ambientes fluviales en sus condiciones prístinas, diversas variables deben ser analizadas. Los sedimentos son unas de las variables más importantes dado que influye potencialmente la morfología del paisaje, la química de las aguas y la dinámica biológica de los cursos de agua. El presente trabajo presenta una introducción de fácil interpretación sobre las características de mayor relevancia ambiental de los sedimentos, sus interacciones y su dinámica en áreas de llanura, de tal modo que los científicos que trabajen en ambientes fluviales de llanura puedan tener una primera aproximación para una correcta interpretación ambiental del rol de los sedimentos. Las características aquí mencionadas incluyen clasificación granulométrica, transporte y mineralogía. En las últimas décadas aumentaron las investigaciones sobre estudios orientados a la evaluación de ambientes fluviales con el objeto de mejorar el conocimiento de su estructura y dinámica, para así poder trabajar en mantenerlos lo más cercano posible a sus condiciones prístinas, mediante una correcta gestión de los recursos involucrados.En el presente trabajo se realiza una breve introducción a los fundamentos que rigen el estudio de los sedimentos en ambientes fluviales de llanura, una de las variablesa tener en cuenta, junto a las características físicas y químicas de las aguas, así como de los suelos, cuando se pretende realizar un estudio del estado y evolución de un ambiente. Una correcta interpretación de los ambientes de llanura resulta indispensable para los científicos que trabajan en la región, dado que la Llanura Chacopampeana y la región Mesopotámica, son áreas caracterizadas por la baja pendiente.

Atenuación del escurrimiento fluvial por bosques de Tessaria

The flow interference effect of the Tessaria integrifolia forest intwo islands of the Paraná River, located dounstream of the Paraná-Paraguay rivers confluence, was studied. Current velocity, suspended sediments, channel depth, water transparency, tree density, tallness and coverage, were measured in cross sections of the stream. The atenuation of the running water by trees can be assumed as a "biological roughness" of the vegetation. It produce a strong decrease in the grain-size distribution of the islands superficial sediments as concequence of the flow interference. In central areas of the islands occuped by forest with 20-30 ind/m*, current velocity was 10 times lower than similar (depth, slope) Coastal sites without vegetation, while the suspended load resulted lesser than the half. The erodability coefficient decrease proportionally to the square of the current velocity diminishing. Owing to the forest extensión and coverage in rivers of the De la Plata basin, it is advisable to consider their effect during flood periods.The flow interference effect of the Tessaria integrifolia forest intwo islands of the Paraná River, located dounstream of the Paraná-Paraguay rivers confluence, was studied. Current velocity, suspended sediments, channel depth, water transparency, tree density, tallness and coverage, were measured in cross sections of the stream. The atenuation of the running water by trees can be assumed as a "biological roughness" of the vegetation. It produce a strong decrease in the grain-size distribution of the islands superficial sediments as concequence of the flow interference. In central areas of the islands occuped by forest with 20-30 ind/m*, current velocity was 10 times lower than similar (depth, slope) Coastal sites without vegetation, while the suspended load resulted lesser than the half. The erodability coefficient decrease proportionally to the square of the current velocity diminishing. Owing to the forest extensión and coverage in rivers of the De la Plata basin, it is advisable to consider their effect during flood periods

“Sedimentological characteristics of fluvial environments in the subtropical Chaco plain (Argentina)”.

El sector oriental de la llanura chaqueña se encuentra drenado por cursos fluviales autóctonos, regulados por baja pendiente y clima subtropical. La geomorfología regional la determina el mega-abanico aluvial perteneciente al río Bermejo. Algunos paleocauces que se desprenden de ésta unidad, dan lugar a ríos cuyas características químicas se encuentran bajo influencia de los particulares suelos salinos locales. Enmarcados en ambientes de humedales con interés regional e internacional, estos ríos revisten gran importancia ambiental. El presente trabajo logra una aproximación al conocimiento de la dinámica hidrosedimentológica local a través del estudio de dos sistemas fluviales, propios de la región. Con ésta finalidad se tomaron muestras de la fase líquida, así como de sedimentos de fondo y sólidos suspendidos, en períodos hidrológicos diferentes. El material fue sometido a técnicas estándares de análisis de laboratorio. Los resultados granulométricos, de materia orgánica y los caracteres hidroquímicos revelaron identidad propia en cada sistema. No obstante en ambos ríos se observó homogeneidad granulométrica, con un valor de más del 50% de abundancia de materiales finos. Del mismo modo la carga suspendida tuvo un comportamiento análogo en los ríos estudiados, según el cual siguen una correlación inversa con el caudal y con el contenido de sales disueltas.The Eastern sector of the Chaco plain is drained by autochthonous rivers, regulated by the low slope and the subtropical climate. The regional geomorphology is determined by the mega-alluvial fan, belonging to the Bermejo River. Some of the paleochannels that flow from this unit result into rivers whose chemical characteristics are under the influence of particular local saline soils. These rivers framed into wetland environment, with regional and international interest, have a great environmental importance. The present contribution is an approach to the understanding of the local hydrosedimentologic dynamics, through the study of two typical river systems of the region. According to this purpose, samples were taken from the liquid phase, as well as bed and suspended load, in different hydrological periods. The material was analyzed in laboratory by standard techniques; the results of grain size, organic matter and hydrochemical features revealed own identity in each water system. However, in both rivers was obser ved particle size uniformity, with a value of over 50% in abundance of fine materials. Similarly, the suspended load had an analogous behavior in the two rivers, according to which are inversely correlated with the flow and content of dissolved salts.Fil: Suárez, Paola Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Centro de Ecología Aplicada del Litoral. Universidad Nacional del Nordeste. Centro de Ecología Aplicada del Litoral; ArgentinaFil: Sartirana, Marta Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Centro de Ecología Aplicada del Litoral. Universidad Nacional del Nordeste. Centro de Ecología Aplicada del Litoral; ArgentinaFil: Orfeo, Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Centro de Ecología Aplicada del Litoral. Universidad Nacional del Nordeste. Centro de Ecología Aplicada del Litoral; Argentin

Extremes in dune preservation: controls on the completeness of fluvial deposits

Understanding sedimentary preservation underpins our ability to interpret the ancient sedimentary record and reconstruct palaeoenvironments and palaeoclimates. Dune sets are ubiquitous in preserved river deposits and are typically interpreted based on a model that that describes the recurrence of erosion in a vertical sequence, but without consideringspatial variability. However, spatial variability in flow and sediment transport will change the recurrence of erosion, and therefore dune preservation. In order to better understand the limits of these Interpretations and outline the causes of potential variability in preservation potential, this paper reviews existing work and presents new observations of an extreme end-member of dune preservation: ?form-sets?, formed by dunes in which both stoss- and lee- slopes are preserved Intact. These form-sets do not conform to models that are based on the recurrence of erosion, since erosion does not recur in their case, and can therefore be used to evaluate the assumptions that underpin sedimentary preservation. New Ground Penetrating Radar data from the Río Paraná, Argentina, show dune fields that are buried intact within larger scale barforms. These trains of form-sets are up to 300 m in length, are restricted to unit-bar troughs in the upper 5 m of the channel deposits, occur in >5% of the mid-channel bar deposits, show reactivation surfaces, occur in multiple levels, and match the size of average-flow dunes. A review of published accounts of form-sets highlights a diversity of processes that can be envisaged for their formation: i) abandonment after extreme floods, ii) slow burial of abandoned dune forms by cohesive clay in sheltered bar troughs and meander-neck cut-offs, iii) fast burial by mass-movement processes, and iv)climbing of dune sets due to local dominance of deposition over dune migration.Analysis of these new and published accounts of form-sets and their burial processes highlights that form-sets need not be indicative of extreme floods. Instead, form-sets are closely associated with surrounding geomorphology such as river banks, meander-neck cutoffs,and bars because this larger-scale context controls the local sediment budget and the nature of recurrence of erosion. Locally enhanced preservation by the ?extreme? dominance of deposition is further promoted by finer grain sizes and prolonged changes in flow stage. Such conditions are characteristic, although not exclusive, of large lowland rivers such as the Río Paraná. The spatial control on dune preservation is critical: although at-a-point models adequately describe near-horizontal sets of freely migrating dunes in uniform flows, they are unsuitable for inclined dune co-sets and other cases where multiple scales of bedforms interact. Spatial and temporal variations in flow and sediment transport betweenthe thalweg and different positions on larger bar-forms can change the preservation potential of dunes within river channels. Therefore, dune set thickness distributions are likely grouped in larger-scale units that reflect both formative dune geometries and bar-scale variations inpreservation potential. The multi-scale dynamics of preservation highlighted herein also provides a useful comparison for other sedimentary systemsFil: Reesink, Arnold J.. University Of Binghamton; Estados UnidosFil: Van den Berg, J. H.. University of Utrecht; Países BajosFil: Parsons, Daniel R.. University Of Hull; Reino UnidoFil: Amsler, Mario Luis. Universidad Nacional del Litoral. Facultad de Ingeniería y Ciencias Hídricas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Best, James L.. University of Illinois. Urbana - Champaign; Estados UnidosFil: Hardy, Richard J.. University Of Durham; Reino UnidoFil: Orfeo, Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Centro de Ecología Aplicada del Litoral. Universidad Nacional del Nordeste. Centro de Ecología Aplicada del Litoral; ArgentinaFil: Szupiany, Ricardo Nicolas. Universidad Nacional del Litoral. Facultad de Ingeniería y Ciencias Hídricas; Argentin

The role of discharge variability in determining alluvial stratigraphy

We illustrate the potential for using physics-based modeling to link alluvial stratigraphy to large river morphology and dynamics. Model simulations, validated using ground penetrating radar data from the Río Paraná, Argentina, demonstrate a strong relationship between bar-scale set thickness and channel depth, which applies across a wide range of river patterns and bar types. We show that hydrologic regime, indexed by discharge variability and flood duration, exerts a first-order influence on morphodynamics and hence bar set thickness, and that planform morphology alone may be a misleading variable for interpreting deposits. Indeed, our results illustrate that rivers evolving under contrasting hydrologic regimes may have very similar morphology, yet be characterized by marked differences in stratigraphy. This realization represents an important limitation on the application of established theory that links river topography to alluvial deposits, and highlights the need to obtain field evidence of discharge variability when developing paleoenvironmental reconstructions. Model simulations demonstrate the potential for deriving such evidence using metrics of paleocurrent variance

Fluvial organic carbon cycling regulated by sediment transit time and mineral protection

Rivers transfer terrestrial organic carbon (OC) from mountains to ocean basins, playing a key role in the global carbon cycle. During fluvial transit, OC may be oxidized and emitted to the atmosphere as CO2 or preserved and transported to downstream depositional sinks. The balance between oxidation and preservation determines the amount of particulate OC (POC) that can be buried long term, but the factors regulating this balance are poorly constrained. Here, we quantify the effects of fluvial transit on POC fluxes along an ~1,300 km lowland channel with no tributaries. We show that sediment transit time and mineral protection regulate the magnitude and rate of POC oxidation, respectively. Using a simple turnover model, we estimate that annual POC oxidation is a small percentage of the POC delivered to the river. Modelling shows that lateral erosion into POC-rich floodplains can increase POC fluxes to downstream basins, thereby offsetting POC oxidation. Consequently, rivers with high channel mobility can enhance CO2 drawdown while management practices that stabilize river channels may reduce the potential for CO2 drawdown