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Entre 13 000 et 7000 BP, le territoire du sud du Brésil a été occupé de manière stable et diversifiée et le matériel lithique taillé constitue sa principale trace anthropique. Les recherches archéologiques révèlent de plus en plus la présence d'occupations dans différents environnements ainsi que les différents processus de formation stratigraphique à partir de la fin du Pléistocène. Ainsi, cet article propose d'analyser l'histoire des premiers témoignages d'occupation précoloniale dans le sud du Brésil d'un point de vue géoarchéologique, en se concentrant sur les données stratigraphiques et chronologiques et sur les processus de formation des niveaux archéologiques. Au total, 33 sections stratigraphiques ont été analysées sur 31 sites archéologiques répartis le long des bassins du Paraná, de l'Uruguay et du versant atlantique. Des témoins de niveaux archéologiques ont été trouvés dans différents contextes géomorphologiques : plateaux, versants, fonds de vallée, plaines alluviales et abris-sous-roche. Les résultats indiquent que les niveaux archéologiques les plus anciens de la région se sont formés au Pléistocène supérieur, associés à des périodes d'incisions fluviales qui signalent des changements importants dans les systèmes fluviaux du sud, marqués par la formation de terrasses alluviales et colluvio-alluviales dans les fonds de vallée. Par la suite, à l'Holocène inférieur, on observe des processus colluviaux généralisés dans les vallées encaissées, des alluvions dans les cours fluviaux moyens et des dépôts anthropiques dans les abris-sous-roche qui ont permis la formation des principaux niveaux anciens. Au début de l'Holocène moyen, les dépôts sédimentaires contenant du matériel archéologique diminuent considérablement, marquant des changements régionaux dans les industries lithiques. Les données indiquent un seuil de dépôt et d'archéologie à l'Holocène inférieur, marqué par une haute résolution d'enregistrement, où les séquences stratigraphiques présentent une plus grande épaisseur et une densité accrue de niveaux archéologiques. Enfin, la diversité des assemblages lithiques interrégionaux est clairement mise en évidence, marquée par la prédominance des industries sur galets et sur blocs, le débitage d'éclats et de lames comme supports de divers outils dans les bassins intérieurs et le façonnage de petites pointes sur le versant atlantique. Between ≈13,000 and 7000 BP, the territory of southern Brazil was occupied in a stable and diverse manner, with the main anthropic trace being in lithic material. Archaeological research has provided more consistent evidence of occupation in different environments and associated with different stratigraphic formation processes since the Late Pleistocene. Therefore, this paper proposes to analyse the history of the earliest evidence of pre-colonial occupation in southern Brazil from a geoarchaeological point of view, focusing on stratigraphic and chronological data and the process of formation of archaeological layers. Thirty-three stratigraphic sections were analysed from 31 archaeological sites distributed along the Paraná, Uruguay and Atlantic basins. Evidence of archaeological levels was found in different geomorphological contexts: plateau, slopes, valley bottom, alluvial plains and rockshelters. The results indicate that the oldest archaeological levels in the region were formed in the Late Pleistocene, associated with periods of fluvial incision that signal important changes in the southern river systems, characterized by the formation of alluvial and colluvial-alluvial terraces in the valley bottoms. This is followed in the Lower Holocene by widespread colluvial processes in the incised valleys, alluvium in the middle river courses and anthropogenic deposits in the rockshelters that formed the main ancient levels. In the early Middle Holocene, sedimentary deposits containing archaeological material decrease significantly, marking regional changes in lithic industries. The data indicate that there appears to be a threshold between deposition and archaeology in the Early Holocene, characterized by high stratigraphic resolution, where stratigraphic sequences show greater thickness and density of archaeological levels. Finally, the diversity of inter-regional lithic assemblages is clearly highlighted, marked by the predominance of industries on pebbles and blocks, the debitage of flakes and blades as a support for various tools in the interior basins and the shaping of small projectile points on the Atlantic slope. [ABSTRACT FROM AUTHOR]

To verification of quali-quantitative it has been accomplished collected of bivalve molluscs during the period of twelve months, together with analysis of some abiotic variables in the middle care of Uruguay river, situated in São Marcos, Uruguaiana municipality. The place where the collects has been accomplished, were divided in three distinct spots, considerating the substract type predominant; sand, rock and mud. The individuals were collected using hands and with. The selection screen aid, of 0.8mm size net and were conserved in a dry environment. They had been collected a total of 1,022 units of bivalves, wich belong to 12 taxa, being that of these only specimens Cyanocyclas limosa and Diplodon parallelopipedon had been captured alive (tanatocenosis). It had great quantitative predominance of Corbicula fluminea and Diplodon uruguayensis. With exception of bivalves invading, the too much species had been collected only in the slimy substratum. Other species occurrence were Mycetopoda siliquosa and Anodontites trigonus, there two species a vulnerable to extinction in Rio Grande do Sul.

El objetivo de este trabajo es realizar una estimación cuantitativa de la cantidad de agua aportada por la precipitación diaria al caudal del río Uruguay y del tiempo de retardo de la onda de crecida en sus diferentes subregiones. Se escogió como área de trabajo a la región superior de la cuenca del río Uruguay comprendida entre 26ºS-32ºS y 48.5ºW- 60.5ºW donde el dominio fue dividido en tres subcuencas (alta, media y baja). El análisis fue realizado para el período 1970-2001. Se empleó la triangulación de Delaunay como variante del método de Polígonos de Thiessen en el cálculo de la precipitación areal. Asimismo se estimó la onda de crecida para cada subregión en función de tormentas seleccionadas. Se determinó que una precipitación importante en la subcuenca alta o media, demoraría alrededor de 8 días en ser detectada en los registros de caudal de Paso de los Libres y 10 días en Salto Grande. A su vez, una lluvia intensa en la subcuenca baja tardaría alrededor de 2 días en ser detectada en los registros de caudal de Salto Grande.The main objective of the present work is the quantitative estimation of the discharge contributed by the daily rainfall to the Uruguay River discharge and the determination of the lag of the flood wave of the precipitation in each region. Due to its characteristics, the upper region of the basin of the Uruguay River comprised between 26ºS- 2ºS and 48.5ºW-60.5ºW was selected for this study where the domain was divided in three different sub-basins: upper, central and lower. The period considered for the present analysis was 1970-2001. A triangulation of Delaunay as a variant of the method of Thiessen Polygons was used in the calculation of the areal rainfall. Then, the flood wave for each sub-basin was calculated based on selected storms. Results show that an intense precipitation event in the upper or central sub-basins has an 8-days lag before its detection in the Paso de los Libres discharge and a 10- days lag in the case of Salto Grande discharge. Likewise, an intense rainfall over the lower sub-basin has a 2-days lag before being noticed in the Salto Grande discharge.

Multivariate floristic analyses of Butia yatay palm groves and gallery forest associated with the Uruguay River basin of Entre Rios Province (Argentina) were performed, including vegetation stands of Rio Grande do Sul State (Brazil). Several new phytosociological associations were identified. These include Eugenio myrcianthis-Butietum yatay association, which represents palm groves on sandy soils evolved from ancient river deposits, and Bignonio callistegioidis-Terminalietum australis association, which represents some gallery forests on regular floodplains of the Uruguay River. Both are placed in the new Pampean alliance Guettardo uruguensis-Bution yatay, which is part of the Dyckio brevifoliae-Terminalietalia australis order and Sebastianio schottiae-Terminalietea australis class, which has been described for Brazil. [ABSTRACT FROM AUTHOR]

In this note, the first record in Argentina of the harvestman Parampheres bimaculatus, a species from the Pampas of Brazil and Uruguay, is presented. The nearest known records come from north Uruguay, 180 km away in a straight line from Salto Grande. Some brief commentaries about the faunistic differences between both sides of the Uruguay River and the environmental changes of the collecting site are included. If the label data are correct, this is the first record of the species from Argentina, although the possibility of a labeling error is discussed. [ABSTRACT FROM AUTHOR]

A new species of Astyanax belonging to the Astyanax scabripinnis complex is described from dos Touros River, tributary of the Pelotas River, Uruguay River basin. Astyanax taurorum sp. nov. is distinguished from other species of the Astyanax scabripinnis species complex by having two humeral spots, the first vertically elongated; teeth of inner row of premaxilla with three to five cusps; 2-3 (modes 2 or 3) maxillary teeth; 20-23 (mode 22) branched anal-fin rays; 13-15 (mode 14) gill rakers on lower branch of the first branchial arch; 20-23 (mode 21) total gill rakers in first branchial arch; 33-36 (mode 35) perforated lateral line scales. Astyanax taurorum sp. nov. is similar to Astyanax paris; nevertheless, it can be readily distinguished from it by having a smaller head depth (73.6-83.1% vs. 86.4-95.6%) and smaller interorbital width (24.1-28.0% vs. 30.8-32.8%). In addition, it differs from A. paris by the presence a posttemporal hook-shaped posterodorsal margin. [ABSTRACT FROM AUTHOR]

We evaluated the passage of early-stage fishes through the Salto Grande Dam using high-frequency downstream ichthyoplankton monitoring and five surveys involving samples taken upstream and downstream of the dam. Eggs and larvae of migratory fishes were captured downstream of the dam, usually during high discharges. Upstream and downstream larvae were frequently unyolked, which corresponds to individuals aged 4+ days, and represents a time significantly longer than that required for the displacement of the water mass from the dam to the sampling location. In low flow rate surveys, fish larvae of the same species and degree of development were captured immediately upstream and at 1, 10, 24 and 40 km downstream of the dam. The densities and percentage of Pimelodinae larvae captured alive by short time and low speed tows were similar upstream and downstream of the dam, indicating that larval mortality was a result of sampling and not to the passage through the turbines. The results show that the larvae of fish that spawn in the middle section are partly transported to the lower section, and suggest that both spillway and turbine discharge should be considered part of the passage. We also found evidence that the passage of small and fragile Pimelodinae larvae through the Salto Grande Kaplan turbines does not significantly affect survival rates. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Even though wetlands are very valuable environments, they suffer heavy exploitation and transformation processes that affect their biodiversity. The main goal of this study was to characterize the herbaceous plant communities associated with the southern Uruguay River flood plain. We focused on lowlands of two farms, one of which is surrounded by an embankment to prevent flooding. A random stratified sampling was performed in 72 plots. To detect distribution patterns and plant species associations we performed a Detrended Correspondence Analysis (DCA) and a Two-Way indicator species analysis (TWINSPAN). We could identify six groups of plots whose ordination patterns are related to the flooding preferences of dominant species. Herbaceous plant groups that develop in anthropically modified environments showed the highest overall richness and diversity with the ingression of invasive species but, they formed a homogeneous patch at a landscape scale. Plant associations with minor anthropic modifications showed lower richness and diversity values but, from a floristic point of view, they formed a heterogeneous mosaic. [ABSTRACT FROM AUTHOR]

The source and potential risks of trace metals in settling material collected with sediment traps in the Uruguay River were evaluated utilizing enrichment factors (EF), sediment quality guidelines (SQG) and speciation using a 4-step sequential extraction procedure. The total organic carbon content of the settling material was relatively high and homogeneous (2.5 ± 0.3 %) and showed no correlation with the metal concentrations. Total trace metal concentrations decrease from Fe (48,969 ± 7380 µg g), Mn (1859 ± 233 µg g), Zn (84 ± 7.6 µg g), Cu (56 ± 6.9 µg g), Cr (19 ± 2.7 µg g), Ni (16 ± 2.0 µg g) and Pb (13 ± 1.2 µg g). The average EF of Zn, Cr, Ni and Pb are below 1.5 indicating natural sources, whereas those of Cu and Mn are consistently higher (EF > 2) insinuating some anthropogenic influence. Consistently, Cu concentrations duplicated the SQG (35.7 μg g) suggesting that adverse biological effects may be observed occasionally. However, speciation results revealed that most metals are associated with the residual fraction, strongly linked to the mineral matrix, and therefore unavailable to aquatic organisms. The sole exception is Mn which is mainly found in the non-residual fractions (∑F1 − F3 = 82 %). Trace metal mobility/bioavailability decreased from Mn (82 %) ≫ Pb (37 %) > Cr (26 %) ~ Ni (25 %) > Zn (20 %) > Cu (14 %) > Fe (10 %). These results demonstrate the utility of metal speciation studies to assess the real risk for aquatic organisms of high Cu concentrations, but associated to relatively immobile fractions of reduced bioavailability. [ABSTRACT FROM AUTHOR]

The recruitment period of Locariichthys platymetopon (Isbrucker & Nijssen, 1979) was investigated. It has been found out, through the data analysis, that the gonadal condition factor is a good indicator of the reproductive period and that the hepatossomatic index is probably related to the storage of reservation for the winter period. The recruitment occurred in November coinciding with the reproductive activity of May.

The recruitment period of Locariichthys platymetopon (Isbrucker & Nijssen, 1979) was investigated. It has been found out, through the data analysis, that the gonadal condition factor is a good indicator of the reproductive period and that the hepatossomatic index is probably related to the storage of reservation for the winter period. The recruitment occurred in November coinciding with the reproductive activity of May.

Despite wide knowledge of environment-community relationships in inland waters, the relative effects of niche conditions (environment) and dispersal (space) on microorganism communities remain controversial. In lotic waters, nondirectional processes (i.e. overland dispersal) and the unidirectional connectivity among sites control species distributions along a gradient. We aimed to detect phytoplankton biogeographical patterns in a large subtropical river (Uruguay River, 1150 km, Brazil) and to isolate the contributions of the environment (limnology, climate and topography) and space in shaping community structure. Phytoplankton (total and functional groups) and abiotic variables were sampled from a hydroplane in motion. To detect biogeographical patterns, we used Mantel's correlation test, and to evaluate the relative roles of environment and space, we used partial redundancy analysis with non-directional symmetrical and directional asymmetrical approaches. Similarity in phytoplankton composition decreased with distance, but only environment significantly explained this pattern. Space was not significant, considering non-directional and directional processes. Phytoplankton communities considering both individual species and their functional groups were more similar between closer sites, because niche conditions play the main role in shaping phytoplankton, not because dispersal is favored among nearby communities. The species-sorting model, based mostly on niche theory, was the main metacommunity mechanism for phytoplankton communities in this river basin. [ABSTRACT FROM AUTHOR]

Copyright of Neotropical Biology & Conservation is the property of Pensoft Publishers and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Water quality of the Uruguay River was evaluated with multi-parametric (temperature, turbidity, conductivity, pH, dissolved oxygen) and sediment trap data (particle flux, total organic carbon and nitrogen contents) and correlated to precipitation, river discharge and El Niño Southern Oscillation (ENSO) indices for the period 2006–2011. Hydro-meteorological parameters averaged 24–85% variability with coincident precipitation (200–400 mm month-1), discharge (7000–28 000 m3 s-1) and turbidity peaks (50–80 NTU) in the austral spring, and absolute maxima during the El Niño 2009 episode. Spectral analysis of discharge and sea-surface temperature anomaly (SSTA) showed consistent variance maxima at approx. 3 and 1.5 years. Deseasonalized discharge was significantly correlated to SSTA. During river floods, pH decreased (from 7.5 to 6.6) and particle dynamics peaked (turbidity: 15–80 NTU; vertical fluxes: 20–200 g m-2d-1; total solid load: <1000 to 100 000 t d-1),whereas TOC remained stable (3.2 ± 0.8%) and C/N ratios increased (10–12) due to the higher contribution of terrestrial detritus. [ABSTRACT FROM AUTHOR]

Copyright of Prohistoria is the property of Prohistoria Ediciones and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Studies for location of breeding sites and early development areas of freshwater fish in subtropical basins are still incipient. Most of the existing knowledge is based on sampling in environments impacted by dams of hydroelectric power plants and studies in areas with characteristics similar to the original are lacking. In this way, this study evaluated the spatial distribution of the ichthyoplankton in a Conservation Unit (Turvo State Park, Rio Grande do Sul State, Brazil) on the subtropical basin of the Uruguay River, in a stretch with no hydroelectric power plants and at best preservation condition. The density distribution of fish eggs and larvae was evaluated quantitatively through plankton nets samples, while the analysis of the species composition of larvae was assessed qualitatively through plankton nets and light traps sampling. There were significant differences in two stretches situated inside the park separated by a waterfall, both in the distribution of eggs and larvae and in species composition of the larval assemblage. Our results indicate that periods without the total flood of Yucumã Falls influences the composition of the ichthyoplankton and the existence of two distinct reproductive environments over an approximate length of 50 km. This result supports the hypothesis that in subtropical basins the alternation of flood and dry periods can influence the structure of fish community and evidences the importance of maintenance of hydrological conditions to fish reproduction in this river section, because showed the importance of the habitat diversity in the river channel to fish recruitment. [ABSTRACT FROM AUTHOR]

Sediment constitutes an important sink of endocrine disruptor compounds; however, the potential of sediments to act as a source of endocrine disruptors should be more extensively investigated. The main objective of this study was to determine whether exposure of immature common carp to Uruguay River sediments undergo physiological and endocrine alterations. The lower Uruguay River watershed supports intensive agricultural and forest production, receives municipal sewage discharge and industrial effluent, and a new large pulp mill was constructed in 2006. A 30-day semi-static assay was performed using sediments from four sites along the Uruguay River and compared with an unexposed group in dechlorinated water as a negative control. We focused on two upstream and two downstream sites of a new elemental chlorine free pulp mill. The results showed that plasma vitellogenin levels increased in fish along the river and significant differences were found between the exposed and unexposed groups. Condition factor and gonadosomatic index were not different; however, a significant difference in hepatosomatic index was observed in fish exposed to sediment from an industrial site. A significant reduction in primary spermatocyte accumulation was observed in the exposed group compared with that in the control group, and some individuals exposed to sediments from industrial sites presented with testis-ova. Our results suggest that Uruguay River sediments act as an important source of estrogenic compounds that could be responsible for the alterations observed. Future studies are needed to identify the causal agents and determine exposure routes. [ABSTRACT FROM AUTHOR]

Martínez and Rojas (2013) published a paper about the relative sea level during the Holocene in Uruguay. The paper of Martínez and Rojas could be handled as an attempt to construct a sea-level curve from data collected from different sources: open-ocean coast, the Río de la Plata coastline and the outlet of Uruguay River. In this sense, several processes were involved: storm effects at open-ocean beaches, the Holocene enclosing of coastal lagoons, storms within the funnel-shaped estuary and the floods of the Uruguay River. However, they included a series of omissions, inaccuracies, errors and critics to our work, that need to be amended, rectified and argued. In response we present a historical background about the research on this issue in Uruguay. We refute the comments about the empirical framework used to construct the first sea-level curve for Uruguay (Bracco et al., 2008, 2011b). We point out that the assumptions on which the curve proposed by Martínez and Rojas (2013) is based are mistaken. In addition, there are limitations of the performed statistical techniques, and errors — mainly systematic — within their formulation. We present evidence that the decrease in sea level from middle Holocene would not have been constant. Instead, a rapid sea level decrease would have taken place by 4300yrBP. Finally, we not only compare our sea level curve with that proposed by Martínez and Rojas, but also we corrected the altimetry errors incurred in their formulation. We conclude that the similarity supports the validity of our curve. [ABSTRACT FROM AUTHOR]

Australoheros is represented by species of Cichlidae spread over different Brazilian river systems. Individuals of Australoheros angiru were collected in isolated lagoons at 950 m of altitude in a dividing plateau between the basins of the Iguassu River and the Uruguay River, located in the São Lourenço do Oeste region (Santa Catarina State), and subject to basic and molecular cytogenetic analyzes. Moreover, a review about the occurrence and collections sites of A. angiru was used to the clarification of biogeographical issues of Australoheros and other species of fish that are common between the basins of the Uruguay River and Iguassu River. The analysis by conventional staining with Giemsa found a diploid number of 48 chromosomes (18 submetacentric + 30 subtelocentric/acrocentric) for males and females, without sex chromosome differentiation. The nucleolar organizing regions identified by silver impregnation and by fluorescence in situ hybridization with 18S rDNA probes showed to be simple, located on the end of the short arm of subtelocentric chromosome pair 15. Heterochromatin was observed in the centromeric region of most of the chromosomes of the complement, in addition to coincide with the nucleolar organizing regions. The data presented in this study are the first reports on the location of sites of 5S rDNA for Australoheros, being located in interstitial position on the long arm of subtelocentric chromosome pair 11. The basic and molecular cytogenetic data presented here contribute to the better understanding of chromosomal evolution of Cichlidae, act as interesting tools for taxonomy and phylogeny of the group, in addition to help in understanding the dispersion of A. angiru between the two hydrographic basins. [ABSTRACT FROM AUTHOR]

This paper introduces the results obtained during archaeological prospection activities in the eastern Uruguay River littoral. Such a systematic archaeological survey had never been undertaken before. The research activities were executed considering different scales of analysis. Here we introduce the field and lab activities related to the archaeological prospection. The results highlight the location of 107 spots of interest within different landscape units. Some of them exhibit excellent features to undertake research on Holocene human occupations. The recovered cultural material indicate activities related to manufacturing lithic and ceramics tools, which together with other evidence, allow to postulate the presence of camp sites for multiple activities. [ABSTRACT FROM AUTHOR]

The observed multi-annual variability of streamflow for three rivers (Paraná River (PR), Uruguay River (UR) and Negro River (NR)) in La Plata Basin (LPB) during the twentieth century is analysed. Several spectral methods (singular spectrum analysis, maximum entropy method and multi-taper method) are applied to annual and seasonal run-off time series in order to capture low frequency variability (LFV) modes and pseudo-periodic patterns. Very robust quasi-periods in the three to six years band are detected for the three rivers, suggesting a strong link with El Niño-Southern Oscillation. Pseudo-cycles of eight to nine years appear in NR and UR. No quasi-periods above 10 years are obtained for any of the rivers. The three rivers exhibit significant LFV components associated with increasing trends that show a clear seasonality. For PR, LFV modes appear between May and December while for UR this occurs during December to April. Both periods cover the whole annual cycle, giving rise to complementary behaviours in the timing of trends of these two rivers. Remarkably, for the three rivers, the most intense increasing trend and the minimum streamflow occur at the same time of the annual cycle. Six global climate indices are selected in order to analyse the relationship between the multi-year streamflow variability modes in LPB and those of global climate: Niño 3.4 (N3.4), Pacific Decadal Oscillation (PDO), North Atlantic Oscillation (NAO), Atlantic Multidecadal Oscillation (AMO), Southern Annular Mode (SAM) and Global Temperature Trend (GTT). Similar to the rivers, almost all these indices present very robust modes of variability in the 3–4.5 years band. Except for N3.4 and PDO, the indices show significant LFV modes that exhibit a pronounced increase at the common end of their records. The NAO, AMO and SAM seem to behave in a nearly cyclic way with periods longer than 60 years while the GTT increases steadily along the whole register. [ABSTRACT FROM PUBLISHER]

Hydrological modelling with climate scenario data are used to develop projections of changes in frequency and duration of flood events in the margins of the lower sections of the Paraná and Uruguay Rivers in La Plata Basin for the twenty-first century. Discharges were simulated with the Variable Infiltration Capacity hydrologic model considering the statistically bias corrected daily maximum and minimum temperatures and rainfall outputs from five regional climate models and different emission scenarios. Results show that although it is expected that compared to the current conditions the temperature would rise and precipitation would have a slight increase in La Plata Basin during the present century, more frequent and lasting fluvial flooding events in the lower Paraná and Uruguay basins could be expected. However, the range of results derived from different climate models though consistent in sign, indicate that the uncertainty is large. [ABSTRACT FROM PUBLISHER]

We analyzed the diet of Pachyurus bonariensis, captured in the Mocoretá river, Uruguay River, in March 2012. The feeding regime of this perciform agreed with the carnivorous bentophagous type, and the dominant prey of both juveniles and adults, were chironomid larvae and Ephemeroptera nymphs. The adult specimens exhibited a more diverse diet than the juveniles. [ABSTRACT FROM AUTHOR]

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Characterization of food web structure may provide key insights into ecological function, community or population dynamics and evolutionary forces in aquatic ecosystems. We measured stable isotope ratios of 23 fish species from the Rio Cuareim, a fifth-order tributary of the Rio Uruguay basin, a major drainage of subtropical South America. Our goals were to (i) describe the food web structure, (ii) compare trophic segregation at trophic guild and taxonomic scales and (iii) estimate the relative importance of basal resources supporting fish biomass. Although community-level isotopic overlap was high, trophic guilds and taxonomic groups can be clearly differentiated using stable isotope ratios. Omnivore and herbivore guilds display a broader δ13C range than insectivore or piscivore guilds. The food chain consists of approximately three trophic levels, and most fishes are supported by algal carbon. Understanding food web structure may be important for future conservation programs in subtropical river systems by identifying top predators, taxa that may occupy unique trophic roles and taxa that directly engage basal resources. [ABSTRACT FROM AUTHOR]

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Surveys performed in streams from the sub-basins of the Canoas and Pelotas rivers, which jointly form the Uruguay River in southern Brazil, led to the discovering of three new species of Aeglidae: Aegla brevipalma, Aegla leachi, and A. oh/ala. Here we present their morphological descriptions coupled with phylogenetic analyses, to infer evolutionary relationships to other aeglids using DNA sequence data from the 16S rRNA and COLI gene regions of the mitochondrial genome. The presence of these new species increases the importance of the Upper Uruguay ecoregion for biodiversity richness of freshwater fauna in the Neotropical South America. [ABSTRACT FROM AUTHOR]

Studies that assess reproduction dynamics and ichthyoplankton distributions are scarce for the upper Uruguay River, especially in environments such as tributary mouths. Therefore, this study aimed to evaluate: (i) ichthyoplankton composition; (ii) spatial and temporal variation in ichthyoplankton abundance; and (iii) relationships between environmental variables and the abundance of ichthyoplankton during one annual cycle in this region. Monthly samples were collected from September 2001 to August 2002 in 48 h cycles at 6 h intervals between each sampling. Samples of eggs and larvae were collected from three of the main tributaries of the region (Ligeiro, Palomas and Chapecó rivers) and from three stretches of the Uruguay River near the confluence of these tributaries. Surface samples were collected with a 0.5 mm mesh cylindro-conical net. In general, reproductive seasonality was well-defined between October and February. It was most intense from November to January, when the photoperiod reached its highest values, flow was decreased, and the water temperature was increased. Based on egg and larval distributions, we found that spawning occurred mainly in the Ligeiro and Chapecó tributaries and in the Uruguay/Chapecó section. In contrast, fish spawning in the sites downstream of dams was more restricted. Finally, a difference was observed between the egg and larval distributions of the main river and its tributaries: the greatest reproductive activity in the tributaries occurred during periods of high flow and increased water temperature, while in the main river, more eggs and larvae were observed when the flow decreased and the water temperature increased. [ABSTRACT FROM AUTHOR]

O Rio Uruguai é um rio sul-americano que nasce na Serra Geral e que forma-se pela junção dos rios Canoas e Pelotas, na divisa entre os estados do Rio Grande do Sul e Santa Catarina. A nascente mãe do rio é o Rio Pelotas, que nasce cerca de 65 km a oeste da costa do Atlântico. A foz do Rio Uruguai é a bacia hidrográfica do Prata e é formado pela junção dos rios Uruguai e Paraná. O rio Uruguai é um dos rios mais importantes na hidrografia do sul do Brasil e serve de fronteira entre o país e a Argentina e o Uruguai, tendo Uruguaiana como principal cidade gaúcha banhada por suas águas. O Rio Uruguai forma-se nas nascentes na Serra Geral em cotas aproximadas de 1800 m com o nome de Rio Pelotas. Somente após receber as águas do Rio Canoas passa a se chamar Rio Uruguai indo na direção geral leste-oeste, até receber, pela margem direita, as águas do Rio Peperi-Guaçu, quando começa a infletir para sudoeste, servindo de fronteira inicialmente entre Brasil e Argentina, até receber o rio Quaraí, afluente da margem esquerda e que atua como fronteira entre o Brasil e o Uruguai. Depois de receber as águas do rio Quaraí, o rio Uruguai continua para o sul até a localidade de Nueva Palmira, onde deságua no rio da Prata. Sua extensão total é de 1770 km. Note que desde a junção de seus formadores até a foz do Quaraí são um total de 1262 km, ficando os restantes 508 km do rio Uruguai correndo inteiramente entre terras uruguaias e argentinas. Se for considerado a extensão do Rio Pelotas, sua extensão chega aos 2150 Km. Seu desnível total é de 24 cm/km. [ABSTRACT FROM AUTHOR]

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Abstract: A hydrodynamic numerical study at the mouths of the Paraná and Uruguay rivers and the upper Río de la Plata is presented in this paper. Water Quality Mapping numerical model was implemented and realistic and very simple boundary conditions were specially developed for this complex estuarial system. A set of numerical experiments were carried out using different constant discharges for the Paraná and Uruguay rivers but unrealistic currents were generated. In order to obtain more realistic results, a set of numerical simulations were carried out imposing water level timeseries at the open boundaries. M2, S2, K1 and O1 harmonic constants were used to generate water levels at Zárate (Paraná river), Nueva Palmira (Uruguay river) and the eastern boundary of the domain (La Plata–Colonia). A mean water level equal to zero was set between La Plata and Colonia. Positive mean water levels (0.3–0.4m) were imposed at Zárate and Nueva Palmira to simulate the hydraulic slope of both rivers and, consequently, to generate realistic and unsteady discharges. These boundary conditions, built by means of the addition of a mean water level and the astronomical tide, significantly improve the simulated currents at the northernmost region of the RDP estuary. [Copyright &y& Elsevier]

The article presents information on the case Argentina v. Uruguay regarding the pulp mills on the Uruguay River under the International Court of Justice. The case was filed by Argentina against Uruguay due to the approval of a pulp mill and its potential of damaging the fishing industry of the country and polluting the river. Information on the statute regarding the case and reasons for the decision of the court in favor of the defendant is also presented.

The present study aimed to investigate the distribution and abundance of fish eggs and larvae in three important tributaries (Chapecó, Peixe, and Ligeiro rivers) of the Upper Uruguay River. The spatial and temporal distribution of fish eggs and larvae were studied as well as the correlation between environmental parameters and the abundance of ichthyoplankton species. The study was conducted between October 2005 and September 2006. Ichthyoplankton samples were collected at night with cylindroconical 0.5-mm mesh plankton nets every 5 days. Of the 591 samples collected, 170 contained ichthyoplankton organisms, resulting in the capture of 12,847 fish eggs and 962 fish larvae. Twenty-seven fish species were observed, of which 69% were Characiforms and 27% were Siluriforms. Among the fish species captured, the representatives were predominantly young forms of small and medium size fishes, with rheophilic species occurring infrequently. Eggs occurred exclusively between October and January, while the highest larvae occurrence was observed between November and December. Fish larvae assemblage structure was shown to be related to some environmental variables. There was a tendency of higher values of water temperature and velocity at the lower sampling sites than at the upper ones, as well an increase number of eggs and larvae. The study tributaries serve as reproduction sites and nursery areas for several fish species of the Upper Uruguay River; thus, the maintenance of their integrity is important for the preservation of diversity and enhancement of fisheries in the region. [ABSTRACT FROM AUTHOR]

We report the migration of Manayunkia speciosa from its distribution in North America into the Neotropical Region (Argentina). We collected specimens from November 2007 to March 2009 in the lower Uruguay River-at 33° 5.01′S 58° 12′W, 33° 5.9′S 58°25.2′W from sediments reaching densities of 2,890 ind. m, at a mean abundance of 350 ind. m. Introductions of nonindigenous species, resulting intentionally or accidentally from anthropic activities, cause significant changes in ecosystems. In aquatic environments, polychaetes are a key invasive group that increases the geographical range of several species through human activities. M. speciosa may have reached the Río de la Plata Basin through a shipping vector and thereafter the Uruguay River by self-navigation. [ABSTRACT FROM AUTHOR]

Based on National Collections records, this article presents the first report of eight freshwater fish species for Uruguay in the middle and lower Uruguay River basin, extending their current distribution: Cyanocharax alegretensis Malabarba and Weitzman, 2003; Leporinus lacustris Amaral Campos, 1945; Microglanis aff. eurystoma Malabarba and Mahler, 1998; Tatia boemia Koch and Reis, 1996; Lepthoplosternum pectorale (Boulenger, 1895); Crenicichla missioneira Lucena and Kullander, 1992; C. minuano Lucena and Kullander, 1992; Apistogramma borellii Regan, 1906. These species were previously recorded either for upper Uruguay River or Parana River. [ABSTRACT FROM AUTHOR]

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This article analyzes how news management strategies coupled with journalistic conventions affect news coverage of the Asamblea Ciudadana Ambiental de Gualeguaychú in Argentina, a social movement against the establishment of two paper mill plants on the Rio Uruguay. Since 2003, the Asamblea has received wide attention in local and national news. Media advocacy has been central to the Asamblea's political goals. This case offers an opportunity to examine the role of the news media in the definition of environmental risk in a country with weak environmental policies and a weak tradition of environmental reporting. News coverage of the Asamblea confirms the media's penchant for sensational and dramatic events. Also, it suggests that the mainstream media does not necessarily portray social movements negatively. Because the media largely relies on official sources in setting news frames, shifting views about the movement among political elites on news events take attention away from structural processes and environmental policies. [ABSTRACT FROM AUTHOR]

The Variable Infiltration Capacity (VIC) land surface hydrology model forced by gridded observed precipitation and temperature for the period 1979–99 is used to simulate the land surface water balance of the La Plata basin (LPB). The modeled water balance is evaluated with streamflow observations from the major tributaries of the LPB. The spatiotemporal variability of the water balance terms of the LPB are then evaluated using offline VIC model simulations, the 40-yr European Centre for Medium-Range Weather Forecasts Re-Analysis (ERA-40), and inferences obtained from a combination of these two. The seasonality and interannual variability of the water balance terms vary across the basin. Over the Uruguay River basin and the entire LPB, precipitation (P) exceeds evapotranspiration (E) and the basins act as a moisture sink. However, the Paraguay River basin acts as a net source of moisture in dry seasons (strong negative P - E). The annual means and monthly time series of ERA-40 P are in good agreement with gauge observations over the entire LPB and its subbasins, except for the Uruguay basin. The E estimates from VIC and inferred from the ERA-40 atmospheric moisture budget are consistent in both seasonal and interannual variations over the entire LPB, but large discrepancies exist between the two E estimates over the subbasins. The long-term mean of atmospheric moisture convergence P - E agrees well with observed runoff R for the upper Paraná River basin, whereas the imbalance is large (28%) for the Uruguay basin—possibly because of its small size. Major problems appear over the Paraguay basin with negative long-term mean of atmospheric moisture convergence P - E, which is not physically realistic. The computed precipitation recycling in the LPB (for L = 500 km) exhibits strong seasonal and spatial variations with ratios of 0%–3% during the cold season and 5%–7% during the warm season. [ABSTRACT FROM AUTHOR]

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Rineloricaria isaaci is described from tributaries of the Uruguay River basin in Argentina, Brazil and Uruguay. The new species is distinguished by having a long and wide area of naked skin at the snout tip, surpassing the anteriormost pore of the infraorbital ramus of the sensory canal, approximately in the middle of the third postrostral plate, and by its particular sexual dimorphism characterized by the long pectoral and pelvic fins of mature males. [ABSTRACT FROM AUTHOR]