The Uruguay River: A Permeable Border in South America

The Uruguay River basin in South America has held a social, cultural, environmental, and economic relevance for many centuries. The river flows for about 2,000 km, linked to an important remnant of native forest, the Selva Misionera in Argentina, and to a Brazilian conservation unit for biodiversity, the Turvo State Park. The Uruguay River is fed by several other important rivers, forming a basin region in which thousands of people live and work. The history of the Uruguay River is intensively linked to the permeable borders between Brazil, Argentina, and Uruguay where different social groups circulated in diverse historical time periods. Forests along the river played a very important role with emphasis on the extraction and trade of yerba mate (Ilex paraguariensis, Saint-Hilaire), a forest product widely consumed in southern America, and also the timber extraction from native forests, during the nineteenth and twentieth centuries. As a result, a profound socio-environmental transformation took place with the reconstruction of regional landscapes shaped by the Uruguay River basin.

Daily variation feeding of Astyanax lacustris (Lütken 1875) in a subtropical river

This study aimed to know the daily variation of Astyanax lacustris (Lütken 1875) feeding in a lotic environment. Fish were caught with a net for three days every three hours in the summer to capture ten individuals per hour in a stretch of the Ijuí River, Middle Uruguay River, Brazil. The captured specimens had their stomachs removed and the content analyzed and separated into seven food categories with the aid of stereomicroscope. For the analysis of food items were used the frequency of occurrence methods, volumetric method and applied the Alimentary Index (IAi). Two hundred stomachs were analyzed, of which 95% had food content. The most abundant items were algae and autochthonous insects. Astyanax lacustris feeds throughout the day especially early in the morning (9 hours) and reduces its feeding at night (24 hours and 3 hours). It was also verified variation of AI of different food items throughout the day. It is concluded that A. lacustris feeds throughout the day, especially in the daytime and that throughout the 24 hours it varies its diet due to photoperiod and food availability.

Microplastic ingestion by Characidae in rural streams (Rio Grande do Sul, Brazil)

Microplastics (MP) have several negative effects on biodiversity, from the ecosystem to individual levels, and can be easily consumed by small invertebrates and fish. The increased production of plastic and absence of efficient management systems for these residues facilitate their presence in aquatic environments. In this study, we evaluated the presence of MP in the stomach contents of four species of Characidae in rural streams in the upper portion of the Uruguay River watershed (northern Rio Grande do Sul). Among the total of collected organisms (n=121), the presence of MP was observed in 72% of the analyzed stomach contents. Bryconamericus iheringii had the highest occurrence of MP (85.7%), followed by Astyanax lacustris (69.4%), Astyanax henseli (69.1%) and Oligosarchus breviostris (66.7%). Our results demonstrate the high occurrence of MP in freshwater aquatic environments, especially rural streams. The results observed in this study confirm the importance of conservation of streams, from the maintenance of riparian vegetation as a way to reduce the input of MP in these ecosystems.

A new freshwater fabriciid species (Sabellida, Fabriciidae) from the Uruguay River, Argentina, with some remarks on the relationships of Monroika Hartman, 1951, Manayunkia Bourne, 1884 and Brandtika Jones, 1974

Between the years 2007 and 2009 a hitherto unknown fabriciid species was found in the Lower Uruguay River, Argentina. Initially, it was assumed that this species could represent Manayunkia speciosa, a freshwater species originally described from North America. However, re-examinations have revealed that these specimens are clearly different from M. speciosa but they resemble Monroika africana. However, differences were also found that clearly distinguish this South American species from the African species so that it is described here as M. clarae sp. nov. The characters found in Monroika clarae sp. nov. make it also possible to compare and discuss these characters with those from the West African species Monroika africana, the Southeast Asian species Brandtika asiatica as well as Manayunkia species in terms of their systematic position. This mainly concerns the structure of the radiolar crown, the number of abdominal chaetigers, the presence of transitional chaetae as well as the structure of the thoracic and abdominal uncini. Potential origins of the freshwater Fabriciidae are also discussed.

Limnoperna fortunei - Updating the geographic distribution in the Brazilian watersheds and mapping the regional occurrence in the Upper Uruguay River basin

Limnoperna fortunei is an invasive alien species (IAS) that cause serious ecological and economic problems in Brazilian freshwater environments. Due to its high dispersion capacity and the lack of new records in peer-reviewed journals we carried out an extensive survey to update the distribution of L. fortunei in the Brazilian hydrographic basins. We also performed a detailed investigation of its distribution in the Upper Uruguay River basin using a molecular method. We presented new records, showing the invasion in new basins and a wide distribution in the basins previously infested. Additionally, we confirmed that the Upper Uruguay River is fully colonized by the golden mussel, being distributed in the lentic, lotic, and transitional lotic/lentic environments presented in this region. This update is an important tool for the implementation of guidelines and the development of safety protocols and sanitary barriers to avoid the dispersion of this IAS to new environments..

Flood mapping employing local, regional and global scale modeling methods for the Uruguay river

The delimitation of flooded areas is important information for natural disaster management, environmental impact prediction and for territorial planning. Flooding occurs when water levels overflow the limits of a river’s channel and seep into the floodplains. When they affect people, they are considered a natural disaster. The delimitation of a flooded area, in the occurrence of an extreme event, can be performed by using field techniques, such as mapping, surveying through the afflicted area or by taking aerial photographs. However, field survey is not a trivial task and not always does it allow for the attainment of the necessary data for a given project. For that purpose, there are various techniques that can be used to assess flood-spots. Some techniques are simpler, being based only on a Digital Elevation Model (DEM), and such is the case of the HAND model (Height Above Nearest Drainage), which has garnered plenty of fame recently in the process of applying delimitations to possibly flooded areas. Other techniques are more complex, like the use of hydrodynamic modeling. There are large-scale hydrologic-hydrodynamic models that simulate runoff generation and water transportation processes in the river basin from rainfall, basin, and meteorological data. This is the case of the large-scale distributed hydrological model called MGB (Modelo de Grandes Bacias), which has been developed and employed in these types of cases. However, there are no studies in the literature that compare the results produced by these multiple approaches using differing degrees of complexity and spatial scales. It was precisely to fill this gap in scientific literature that this work was developed. Featured here, for the first time, is the validation of the MGB model’s performance in two versions, one of regional scale and another of continental scale (MGB AS), in delimiting the flooded areas, compared to a satellite image of the inundation; and with two versions of the HAND model, one generated by a local study and the other by a global reference. The case study used in this validation was a major flood that occurred in the Uruguay River, near the town of Itaqui (Rio Grande do Sul), which borders Brazil and Argentina, in October 1997. The results show that the MGB model, both in the regional and the continental scales, could delimit the flooded area, with a few overestimations in the northern portion of the image. The HAND method at the local scale also allowed a mapping of the flooded area, with overestimates for more springhead-like areas in small tributaries. The HAND method at the global scale, on the other hand, proved to be inadequate for the purpose of delimiting flooded areas in this region. The leading cause is believed to be the small drainage area threshold linked to the utilized global HAND product. From the calculation of performance metrics, like hit rate, false alarm ratio and criticality index, Regional MGB was the one that most adequately expressed the extent of the flood observed in the Landsat 5 image when compared to the others, followed by MGB AS.