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Santa Fe de la Vera Cruz, Argentina

Kopprio G.A.,CONICET | Kopprio G.A.,Leibniz Center for Tropical Marine Ecology | Kattner G.,Alfred Wegener Institute for Polar and Marine Research | Freije R.H.,National University of the South | And 3 more authors.
Environmental Monitoring and Assessment | Year: 2014

The seasonal variability of inorganic and organic nutrients and stable isotopes and their relations with plankton and environmental conditions were monitored in Lake Chasicó. Principal component analysis evidenced the strong influence of the river runoff on several biogeochemical variables. Silicate concentrations were controlled by diatom biomass and river discharge. Higher values of nitrate and soluble reactive phosphorus (SRP) indicated agricultural uses in the river basin. Elevated pH values (∼9) inhibiting nitrification in the lake explained partially the dominance of ammonium: ∼83 % of dissolved inorganic nitrogen (DIN). The low DIN/SRP ratio inferred nitrogen limitation, although the hypotheses of iron and CO2 limitation are relevant in alkaline lakes. Particulate organic matter (POM) and dissolved organic matter (DOM) were mainly of autochthonous origin. The main allochthonous input was imported by the river as POM owning to the arid conditions. Dissolved organic carbon was likely top-down regulated by the bacterioplankton grazer Brachionus plicatilis. The δ13C signature was a good indicator of primary production and its values were influenced probably by CO2 limitation. The δ15N did not evidence nitrogen fixation and suggested the effects of anthropogenic activities. The preservation of a good water quality in the lake is crucial for resource management. © 2014 Springer Science+Business Media Dordrecht.

De Domitrovic Y.Z.,Northeast National University | Devercelli M.,Instituto Nacional Of Limnologia | Forastier M.E.,Northeast National University
Advances in Limnology | Year: 2014

This article summarizes the characteristics of phytoplankton of the Chaco-Pampean Plain between the Pilcomayo River (25°15′S; 57°45′W) and the Lower Salado River (31°39′S; 60°45′W) towards the Paraguay-Paraná system. This subtropical area has a climate gradient from east (wet) to west (arid). Rivers and streams have a seasonal regime, with floods in autumn and dry periods at the end of winter. These hydrological fluctuations appear to be the driving forces of the phytoplankton community. During low waters (flow reduction and increase in salinity), diversity is reduced and density of euryhaline species is increased. The highest algal development in this area was observed during the extraordinary low water period of La Niña. In occasions of environmental stability and high temperatures, water blooms of Anabaenopsis arnoldii. A. nadsonii and Nodularia harveyana have been recorded. The lenitic environments of the western region (arid) show marked fluctuations in extension and depth and may dry during periods of scarce precipitations. Phytoplankton density is low and represented by small Chlorococcales and Euglenophyceae. Water blooms of Dolichospermum spp. and Cylindro-spermopsis raciborskii are frequent. Shallow lakes and wetlands of the eastern region (wet), which have presence of macrophytes and high organic matter, are dominated by Cryptophyceae, Chlorococcales and a wide variety of species of Euglenophyceae and diatoms. The Ramsar Site called 'Humedales Chaco' has the greatest diversity of species in this region. © 2014 E. Schweizerbart'sche Verlagsbuchhandlung, 70176 Stuttgart, Germany.

Sirombra M.G.,National University of Tucuman | Mesa L.M.,Instituto Nacional Of Limnologia
Ecological Indicators | Year: 2012

A modified QBR index adapted to examine the riparian quality of streams included in the Yungas biome is presented. The index, named QBRy, included modifications of the original index in three of the four sections in order to be useful for the studied region. The assessment of QBRy included trials in three subtropical sub-basins of Tucumán province (Argentina). Thirty-seven sampling sites were assessed. The composition of riparian forest varied in relation to a geographical pattern, and this was related with the climatic differences existing within the same ecoregion. The quality of riparian vegetation was poor near population centers and in sites impacted by livestock, while good quality conditions were related with areas adjacent to a protected region and in physiographical inaccessible zones. The introduction of exotic species represents a real problem to the integrity of Yungas riparian vegetation. The protection of the few well preserved zones and the necessity of restoration of highly altered ones becomes an essential priority for biodiversity conservation. © 2012 Elsevier Ltd.

Szupiany R.N.,National University of Litoral | Amsler M.L.,National University of Litoral | Amsler M.L.,Instituto Nacional Of Limnologia | Hernandez J.,University of Illinois at Urbana - Champaign | And 4 more authors.
Water Resources Research | Year: 2012

Channel bifurcations associated with bars and islands are important nodes in braided rivers and may control flow partitioning and thus affect downstream confluences, as well as the formation and dynamics of bars. However, the morphodynamic processes associated with bar formation are poorly understood, and previous studies have largely concerned laboratory experiments, small natural streams, or numerical analyses with large Froude numbers, high slopes, and low Shields stresses. In these cases, the morphologic changes at bifurcations are relatively rapid, with predominant bed load transport and the suspended load playing a minor role. In this paper, the evolution of the flow structure and suspended bed sediment transport along four expansion-diffluence units in the Rio Paran, Argentina, are described. The Rio Paran is a large multichannel river with a bed composed of medium and fine sands and possesses low Froude numbers and high suspended bed material transport. Primary and secondary flow velocity components were measured with an acoustic Doppler current profiler (ADCP) along the expansion-diffluence units, and the backscatter signal of the ADCP was calibrated to allow simultaneous measurements of suspended bed sediment concentrations. The interactions between these variables show that the cores of primary flow velocity and suspended bed sediment concentration do not necessarily follow the thalweg at the bifurcation and that inertial effects on the suspended bed sediment may influence the morphodynamics of bar formation. It is suggested that changes in flow stage, as well as the presence of vegetation, may further increase the deposition of suspended bed sediment at the bar head. This study suggests that the ratio of suspended bed material to bed load is an important factor controlling the morphodynamics of bifurcations in large sand bed braided rivers. © 2012 American Geophysical Union. All Rights Reserved.

Latosinski F.G.,National University of Costa Rica | Szupiany R.N.,National University of Santa | Guerrero M.,University of Bologna | Amsler M.L.,Instituto Nacional Of Limnologia
Journal of Hydraulic Engineering | Year: 2014

The standard experimental methods used for sampling suspended loads in large rivers are usually time consuming, unsafe, rather expensive, and have a limited spatial resolution. Acoustic Doppler current profilers (ADCPs), usually applied to measure the flow discharge, may also be used to assess the suspended sediment concentration by analyzing the backscattering acoustic strength. Though important efforts have been dedicated to test this method, results are not as reliable as engineering practices require, especially in large fluvial systems. In this paper, the correlation between the corrected backscatter from a 1,200kHz ADCP and the suspended concentration from a depthintegrated sampler is presented and discussed. Despite the assumptions required to utilize this method (i.e., monosized grain and homogeneous vertical concentration), the results showed acceptable differences when they were compared with traditional methods. An evaluation of the backscatter and attenuation of sound produced by fine and coarse material is presented. Finally, the total suspended load of bed sediment is assessed using moving-boat ADCP measurements and compared with results from the corresponding standard method. Differences are at most 46%. © 2014 American Society of Civil Engineers.

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