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Riparian areas of riverine plains develop extensive floodable areas named riverine wetlands, which are essential to the water cycle balance and ecosystem dynamics. In this study, we contrasted the hydrological and physicochemical variables of riverine wetlands of both peri-urban areas impacted by intensive farming and those of rural areas with the indicators of the biotic structure (taxonomic richness, Shannon diversity and total density) of benthic diatoms, phytoplankton, zooplankton, macroinvertebrates, chironomids, fishes, turtles, and birds. The study was performed on riverine waters of the Pampean plain, Argentina, with four seasonal samplings conducted in 2017–2018. Our results showed that the significant deepening of the groundwater level caused by aquifer overexploitation in peri-urban areas, as well as the declining surface water quality with higher phosphorus and total nitrogen concentrations, affected the taxonomic richness, diversity, and total density of the biotic assemblages of riverine wetlands. The taxonomic richness of birds, turtles, phytoplankton, chironomids, and fishes was the most sensitive to land use. Phytoplankton, chironomid, and fish diversity showed the greatest differences between rural and peri-urban riverine waters, while the total density of chironomids and birds showed the greatest differences according to land use. The results suggest that the socioeconomic development in those riverine wetlands that still maintain conditions close to the natural ones needs to be subject to guidelines derived from integrated basin management and sustainable urban planning.

The aim of this study was to investigate the effects of agricultural land use and periods of hydrological variability on the environmental variables, as well as macrophyte and macroinvertebrate assemblages in lowland riverine wetlands. We compared two wetlands with intensive agricultural land use against two others with extensive livestock considered references for the region during a normal and a dry flow period. Nutrient concentrations were significantly higher in agricultural riverine wetlands. These wetlands exhibited higher relative coverage of floating anchored macrophytes and the absence of submerged vegetation. They showed significantly lower taxonomic richness and density of macroinvertebrates and a higher relative abundance of scrapers and predators. Wetlands of both land uses had a lower total density of macroinvertebrates and a higher proportion of tolerant desiccation taxa in the dry period. Particular differences between land uses, such as lower dissolved oxygen concentrations and lower macroinvertebrate diversity in agricultural wetlands, were found during the dry period. These findings indicate that the differences between land uses increased during the aforementioned period. This study provides evidence of the effects of the surrounding landscape and hydrologic periods in the environmental characteristics as well as the macrophyte and macroinvertebrate assemblages of the riverine wetlands studied.

Knowing the interactions between exotic and native species is essential to establish possible threats to the local fauna. In this study, we assessed the use of food resources and diet overlap between a recently introduced snail, Sinotaia quadrata, and a native species, Pomacea canaliculata. We analyzed the gut content and stable isotope of snails and resources in a lowland stream where both species coexist. Both Schoener’s and isotope dietary overlap indexes supported dietary overlap. Conversely, gut content analysis showed differences in consumption: S. quadrata consumed more detritus and diatoms than P. canaliculata, whose diet was characterized by detritus and macrophyte remains. Macrophytes were the resource that most contributed to the diet of both species, as shown by stable isotope mixing models. The combination of both techniques, gut content and stable isotope analysis, indicated that S. quadrata consumed macrophyte detritus while P. canaliculata ate fresh macrophytes. This difference indicates differential use of food resources between the studied species coexisting in a lowland stream. Although no negative trophic interaction was found, we highlight the importance of continuing to monitor interactions for other resources and studying possible risks to the local fauna., Instituto de Limnología "Dr. Raúl A. Ringuelet", Facultad de Ciencias Naturales y Museo

Lowland streams are usually affected by river engineering works that produce the loss of habitat heterogeneity. Our aim was to assess the transplantation of macrophytes with different complexity into a lowland stream which was dredged and widened. Stuckenia pectinata and Hydrocleys nymphoides were collected at an extraction site and installed at a transplant site. The growth and coverage of macrophytes beds were quantified. Taxonomic richness, Shannon-Wiener diversity, abundance, composition and proportion of functional feeding groups of the macroinvertebrate assemblage presented in macrophyte beds were assessed between sites and species. The growth of both macrophytes did not differ significantly between sites and the coverage of transplanted beds increased, therefore they established at the transplant site within a short period. Regarding to macroinvertebrate assemblage, only the functional feeding groups did not show differences between sites. Moreover, the proportion of predators presented differences between macrophytes at the same site, with H. nymphoides having a higher proportion. Our study showed that this technique is suitable for reintroducing these species and is applicable in rehabilitation projects that promote the restoration of habitat heterogeneity deteriorated by river engineering works. Also, we highlight the importance of incorporate macroinvertebrate functional traits to assess the ecological status after rehabilitation. Fil: Altieri, Paula Daniela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; Argentina Fil: Paz, Laura Estefania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; Argentina Fil: Jensen, Roberto Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; Argentina Fil: Donadelli, Jorge Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; Argentina Fil: Abaigar, Alberto Guillermo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; Argentina

En este estudio se caracteriza el ensamble de macroinvertebrados en bañados de desborde fluvial de cuatro arroyos pampeanos bonaerenses con diferentes actividades en el uso del suelo (intensa horticultura y ganadería extensiva) desde un punto de vista estructural y funcional. Se aplicaron índices bióticos, ecológicos, análisis multivariados y se analizaron los ensambles de oligoquetos y quironómidos. Los mayores valores diversidad y riqueza taxonómica de macroinvertebrados correspondieron al bañado de Chubichaminí (H´= 1,9; S=19,25). Este arroyo presentó aguas ligeramente poluídas, siendo aceptable en términos de calidad del agua. El análisis multivariado ordenó a los sitios de los bañados Del Gato y Carnaval con la mayor carga de nutrientes vinculados a los taxa más tolerantes como los dípteros Stratiomyidae, Ephydridae y nematodes, oligoquetos y gasterópodos Physidae. La mayor diversidad y riqueza de oligoquetos se registró en los bañados del Cajaravillas y Chubichaminí en los meses cálidos y las diferencias encontradas se debieron principalmente a Limnodrilus hoffmeisteri Claparède, 1862. El ensamble de quironómidos estuvo conformado por 24 taxones pertenecientes a Chironominae, Orthocladiinae y Tanypodinae. El género Chironomus Meigen fue más abundante en el A° Del Gato, correspondiendo principalmente a C. calligraphus Goeldi, asociado a ambientes con evidente impacto antrópico. Los sitios estudiados mostraron diferentes patrones en la proporción de grupos funcionales alimentarios sin una clara relación con el uso del suelo. Los índices aplicados en el ensamble de macroinvertebrados resultaron efectivos para evaluar el estado ecológico de los bañados analizados., In this study, the assemblage of aquatic macroinvertebrates in the riverine wetlands (RW) of four streams in the Pampean region of Buenos Aires with different activities in land use (intensive horticulture and extensive livestock) is characterized from a structural and functional point of view. Biotic and ecological indices and multivariate analyses were applied, and the assemblages of oligochaetes and chironomids were analyzed. The highest values of diversity and taxonomic richness of macroinvertebrates corresponded to the Chubichaminí RW (H´= 1.9; S = 19.25). This RW showed slightly polluted waters, being acceptable in terms of water quality. The multivariate analysis ordered the sites of Del Gato and Carnaval RWs with the highest nutrient load associated with more tolerant taxa such as the dipterans Stratiomyidae, Ephydridae, nematodes, oligochaetes and Physidae gastropods. The greatest diversity and richness of oligochaetes were recorded in the Cajaravillas and Chubichaminí RW in the warm months being the differences mainly due to Limnodrilus hoffmeisteri Claparède, 1862. The chironomid assemblage consisted of 24 taxa belonging to Chironominae, Orthocladiinae and Tanypodinae. The genus Chironomus Meigen was more abundant in Del Gato RW, corresponding mainly to C. calligraphus Goeldi, associated with environments with evident anthropic impact. The RWs studied showed different patterns in the proportion of functional feeding groups without a clear relation with land use. The indexes applied to the macroinvertebrate assemblage were effective in evaluating the ecological status of the analysed RWs, Instituto de Limnología "Dr. Raúl A. Ringuelet"

La estructura y función de las comunidades bióticas expresan la integración de factores que acontecen durante cierta escala de tiempo y espacio. Respuestas estructurales, fisiológicas, morfológicas, entre otras, a nivel individuo, población o comunidad, pueden indicar cambios en los ecosistemas acuáticos debido el impacto que el hombre es capaz de infringirles. Un sistema biológico puede se considerado sano cuando su potencial intrínseco es realizado, su condición es estable, su capacidad de autorecuperación es preservada y un mínimo suministro externo es requerido para su manejo. Por lo tanto la biota resulta un preciado indicador para el conocimiento del estado ecológico reduciendo la información ambiental a un conjunto de variables relevantes que evidencian los cambios del ecosistema. En tal sentido nos permiten evaluar condiciones actuales y pasadas, comparar situaciones en el tiempo y espacio, anticipar tendencias y condiciones futuras entre otros aspectos.

Continuando con uno de los objetivos fundacionales del Instituto de Limnología los autores de esta contribución la dedicamos a la memoria de su fundador, el Dr. Raúl A. Ringuelet, quien siempre apoyó las iniciativas vinculadas a los estudios hidrobiológicos rioplatenses.

Fil: Blettler, Martin Cesar Maria. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Santa Fe. Instituto Nacional de Limnologia. Universidad Nacional del Litoral. Instituto Nacional de Limnologia; Argentina

The objective of the present study was to investigate the responses of the chironomid communities (Diptera: Chironomidae) to environmental variables in four moderately and highly disturbed rivers located in one of the most degraded watersheds in South America. Sampling campaigns were carried out during 2014–2016 in four sites of the Matanza-Riachuelo basin. The physical-chemical and hydrological variables were measured and, the ecological indices were calculated and evaluated by ANOVA. The responses of Chironomidae to the environmental variables were evaluated by redundancy analysis (RDA), and the sampling sites were grouped according to the populations of chironomids and the main environmental variables. Finally, the Spearman correlation was made to determine which of these variables were significant. In total, 13 chironomid taxa were found in 36 samples during the study period. The greatest density registered belongs to Rheotanytarsus and Cricotopus. The ANOVA detected the greatest Chironomidae density and taxonomic richness in the sites with agricultural-urban impact. The changes in the distribution of Rheotanytarsus, Thienemanniella, and Polypedilum were mainly explained by the increase in current velocity, organic matter, and hardness, and the decrease of NH3 and BOD. On the other hand, Goeldichironomus, Chironomus, Parachironomus, Dicrotendipes, and Cricotopus were explained by the increase in conductivity, dissolved oxygen, and temperature, and the decrease of the variables NO3, BOD, and Cu. In addition to this, the sites with urban-agricultural impact were clearly separated from sites with urban-industrial impact. The last one was more related to the increase in BOD, Cu, and NO3 that indicates moderate to poor water quality. In conclusion, we can infer that the physical and chemical variables are correlated with changes in the structure and distribution of the chironomid community and there are genera that respond differently at high and intermediate situations of disturbances. This knowledge contributes to the execution of strategies for the conservation and restoration of the lotic ecosystems. Fil: Cortese, Bianca. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; Argentina Fil: Zanotto Arpellino, Juan Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; Argentina Fil: Paggi, Analia Constancia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; Argentina Fil: Rodrigues Capitulo, Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; Argentina

We assessed the effects of nutrient enrichment on three stream ecosystems running through distinct biomes (Mediterranean, Pampean and Andean). We increased the concentrations of N and P in the stream water 1.6–4-fold following a before–after control–impact paired series (BACIPS) design in each stream, and evaluated changes in the biomass of bacteria, primary producers, invertebrates and fish in the enriched (E) versus control (C) reaches after nutrient addition through a predictive-BACIPS approach. The treatment produced variable biomass responses (2–77% of explained variance) among biological communities and streams. The greatest biomass response was observed for algae in the Andean stream (77% of the variance), although fish also showed important biomass responses (about 9–48%). The strongest biomass response to enrichment (77% in all biological compartments) was found in the Andean stream. The magnitude and seasonality of biomass responses to enrichment were highly site specific, often depending on the basal nutrient concentration and on windows of ecological opportunity (periods when environmental constraints other than nutrients do not limit biomass growth). The Pampean stream, with high basal nutrient concentrations, showed a weak response to enrichment (except for invertebrates), whereas the greater responses of Andean stream communities were presumably favored by wider windows of ecological opportunity in comparison to those from the Mediterranean stream. Despite variation among sites, enrichment globally stimulated the algal-based food webs (algae and invertebrate grazers) but not the detritus-based food webs (bacteria and invertebrate shredders). This study shows that nutrient enrichment tends to globally enhance the biomass of stream biological assemblages, but that its magnitude and extent within the food web are complex and are strongly determined by environmental factors and ecosystem structure

With the purpose of collecting macroinvertebrates for benthic studies of hill streams of the Argentinean Pampean ecoregion, a sampling program was performed in different seasons during 2015. The ingolfiellid crustaceans described in this paper were found only in May 2015 in a sector of the rithron of the Ventana Stream located below the point of the upwelling of hyporheic water, 50 m upstream where the stream is covered by larger conglomerates. The specimens (5 females and 4 males) were measured and photographed, and some were dissected and mounted in Euparal. Appendages of head, pereion and pleon were illustrated. The analysis of the examined material allowed us to conclude that it constitutes a new taxon, Yacana ventania n. gen. n. sp., enlarging the distribution of the family Ingolfiellidae in South America. Characteristics: body long and thin; without eyes; short antennae; inner seta of the outer lobe of maxilla1 is bi-dentate, vestigial molar process and serrations on one side, three spine row elements decreasing in size and the last one toothed; labium present; gnathopod 1 and 2 with a notch on the inner side of the carpus, the carpus of gnathopod 1 has three spines, the proximal one is on the top of a finger-shaped process, while the carpus of gnathopod 2 presents just two spines, propodus in both gnathopods with finger-shaped process at its distal end, a tiny spine and a seta; pereiopods dissimilar, with seta and terminal claw; pereiopod 7 differs from the others in size, number and arrangement of its setae. Uropod 2 longer than uropod 1, uropod 3 small and uniramous; sexual dimorphism clearly present in pleopods and uropod 2 because the females present more rows of setae than males, and probably in the setation of pereiopod 7. Sizes of specimens varied between 3– 8.8 mm. The cladistic analysis (TNT) demonstrates that Yacana ventania n. gen. n. sp. is closely related to South African genera because of the vestigial mandibular palp, also the new taxon here described shared the sexual dimorphism with Stygobarnardia and Trogloleleupia, its discovery gaining relevance on biogeographical aspects and providing new evidence to the theory of continental drift. Type specimens are deposited in the Carcinology Collection of the División Zoología Invertebrados, Museo de La Plata, Argentina., Instituto de Limnología "Dr. Raúl A. Ringuelet"

The city of La Plata, Argentina, is situated in a low alluvial zone, with streams having insufficient drainage into the Río de la Plata estuary. In April 2013, a prodigious storm front caused unprecedented flooding in the city and environs that resulted in extensive loss of life and property, especially in the Del Gato stream basin. Through an analysis of water quality and the conditions of the habitat on the basis of the macroinvertebrates present as bioindicators of environmental quality, this work aims to contribute to a reevaluation of the role of the marshes adjacent to the stream as flood-alleviation elements, and then propose alternatives for flooding management in the basin. Consequently, quantitative seasonal samples of vegetation, sediments, and benthic organic matter were taken and limnologic parameters measured in three sectors of the basin having different land uses: rural, periurban, and urban-industrial. The macroinvertebrate assemblages, as analyzed through the application of ecological indices, exhibited a marked decline in richness and in the Pampean Biotic Index towards the low-lying basin. Principalcomponents analysis associated Site 1 with the dissolved-oxygen concentration, Site 2 with high nitrate values, and Site 3 with oxygen demands. Redundancy analysis indicated a positive relationship between Baetidae and Aeolosomatidae with the dissolved-oxygen concentration and between Enchytraeidae and Stratiomyidae with the conductivity. These marshes are fundamental in maintaining good environmental conditions and attenuating the effects of the flooding that is predicted to become increasingly catastrophic in this region as the climate changes., La ville de La Plata, en Argentine, est située dans une zone alluvionnaire, avec des cours d’eau ayant un écoulement insuffisant dans l’estuaire du Río de la Plata. En avril 2013, un front de tempête exceptionnel a causé des inondations sans précédent dans la ville et dans les environs, qui a entraîné des pertes en vie humaine et en propriétés, en particulier dans le bassin de Del Gato. Grâce à une analyse de la qualité de l’eau et des conditions de l’habitat sur la base des macroinvertébrés présents en tant que bioindicateurs de la qualité de l’environnement, ce travail vise à contribuer à une réévaluation du rôle des marais adjacents à la rivière en tant qu’éléments d’atténuation des inondations et propose ensuite des solutions alternatives pour la gestion des inondations dans le bassin. Simultanément des échantillons saisonniers quantitatifs de végétation, de sédiments et de matières organiques benthiques ont été pris et des paramètres limnologiques mesurés dans trois secteurs du bassin ayant des utilisations de terres différentes : rurales, périurbaines et urbaines-industrielles. Les différences de macroinvertébrés, analysées par l’application d’indices écologiques, ont montré un déclin marqué de la richesse et de l’indice biotique Pampean vers l’aval. L’analyse en composantes principales associe le site 1 avec la concentration en oxygène dissous, le site 2 avec des valeurs élevées de nitrate et le site 3 avec des demandes en oxygène. L’analyse de redondance a indiqué une relation positive des Baetidae et Aeolosomatidae avec la concentration en oxygène dissous et des Enchytraeidae et Stratiomyidae avec la conductivité. Ces marais sont fondamentaux pour maintenir de bonnes conditions environnementales et atténuer les effets des inondations qui devraient devenir de plus en plus catastrophiques dans cette région à mesure que le climat change., Facultad de Ciencias Naturales y Museo

Sinotaia quadrata is a snail native from Asia recorded for the first time in South America in 2009 in central Argentina. In 2015, this species was also found in a lowland stream with different water qualities. Our aims were to contribute to the knowledge of its population ecology and to compare the individuals from the two locations anatomically. Snails were searched at 6 sites, where physicochemical and hydraulic parameters were measured. Biological samples were also taken at two sites (S3 and S4) to study the population traits of S. cf quadrata (density, size structure, fecundity and sex ratio) and to assess the water quality through macroinvertebrates’ biological indices (richness, diversity and IBPamp). Physicochemical and biological parameters allowed us classifying sites as “moderately polluted” (S3) and “heavily polluted” (S4). At S4, the population showed a lower density, larger individuals, higher fecundity and a scarce representation of young snails. The differences observed in the radula and mantle border of snails from the two geographical regions might be attributed to environmental differences. We conclude that this species is tolerant to a wide range of environmental variables which, along with its high fecundity and morphological plasticity, could allow this species to colonize neighbor streams., Facultad de Ciencias Naturales y Museo

Pomacea canaliculata is an apple snail that has become an invasive species in several countries. In this research, through two simultaneous experiments, we assessed the effects of different land uses (urban, agriculture, cattle grazing, farms and recreation) on the growth and survival of snails from native populations. The survival was not affected by the water quality of the three streams studied, whereas the growth of snails exposed to the water of the urban stream was impaired. Therefore, our results suggest that the growth rate of P. canaliculata could be useful for the assessment of a moderate urban impact., Instituto de Limnología "Dr. Raúl A. Ringuelet"

The Puna de Atacama plateau (South America; altitude 3800 m)dwith its endorheic basins and containing one of the principal deposits of lithium worldwidedis one of the most extensive tablelands on the planet. Information on the invertebrates of those internal catchment areas, however, is scarce and fragmentary. We describe here for the first time the structure and composition of the invertebrate assemblage of the Olaroz Salar (Argentina), analyze the spatial-temporal changes, and examine the relationships between the organisms and their environment. Samplings of the sediment and aquatic vegetation were carried out in three affluent streams of the salar during the wet season and the limnologic variables were measured in situ. Of the 26 taxa collected, the most highly represented were Nematoda, Harpacticoida, Paranais litoralis, and Limnocythere sp.; while Heterocypris incongruens registered the highest abundance. The total density was correlated with the sediment organic matter and differed among the streams. The abundance, richness, and diversity decreased upon proximity to the salar. The invertebrate assemblage varied spatially, with the conductivity gradient being one of the principal conditions influencing the distribution. Redundancy-detrended analysis demonstrated that within these environments the conductivity, amount of organic matter, and vegetation were the principal determinants of benthic development. The insularity, fragility, and low resilience of these wetlands necessitate adequate administration policies for their long-term management and utilization, particularly in view of the growing demand for mineral exploitation in the region. Fil: Rodrigues Capitulo, Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; Argentina Fil: Spaccesi, Fernando Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; Argentina Fil: Armendáriz, Laura Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; Argentina

Temporal variability in river morphology, sedimentology and flow are a fundamental control on instream habitat structure and riverine ecosystem biodiversity. However, long-term riverine ecological time-series in a wider temporal context are particularly rare. The present research involves long-term data series of riverine physical habitat and benthic macroinvertebrate ecology in the Correntoso River (secondary channel of the Paraná River floodplain).An anthropogenic morphological alteration was identified at the river inlet. As a consequence, a large sedimentation area was originated at the river inlet, preventing the inflow of suspended sand to the Correntoso. However, the natural morphological evolution during the last decades, probably led by three large floodings (1983, 1992 and 1997?8), reconfigured the inlet morphology, allowing the inflow of suspended sand into the channel. These phenomena allowed the sandy sedimentation a few kilometers downstream, redefining its bottom sediment condition over the years. This long-term process prompted great changes on benthic invertebrate ecology, causing a significant fauna depletion. This research demonstrates the value of long-term data series in ecological studies as well as the importance of an interdisciplinary point of view. Linking physical processes to ecology is particularly useful to aid understanding of the ecological legacy of anthropogenic modification and natural evolution on river systems. Fil: Blettler, Martin Cesar Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnologia; Argentina Fil: Amsler, Mario Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnologia; Argentina Fil: Ezcurra de Drago, Inés. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnologia; Argentina Fil: Bullo, Juan M.. Universidad Nacional del Litoral; Argentina Fil: Paira, Aldo Raul. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnologia; Argentina Fil: Drago, Edmundo Carlos E.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnologia; Argentina Fil: Espínola, Luis Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnologia; Argentina Fil: Fontana, Livia O.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnologia; Argentina Fil: Eberle Folmer, Eliana Gisel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnologia; Argentina Fil: Rodrigues Capitulo, Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - la Plata. Instituto de Limnología "dr. Raul A. Ringuelet". Universidad Nacional de la Plata. Facultad de Cs.naturales y Museo. Instituto de Limnología ; Argentina

The diet and trophic relationships between the macroinvertebrates Phyllogomphoides joaquini Rodrigues Capítulo, 1992 and Coenagrionidae (Odonata), Chironomidae (Diptera), Diplodon delodontus (Lamarck, 1919) (Bivalvia: Hyriidae), and Pomacea canaliculata (Lamarck, 1822) (Gastropoda: Ampulariidae) and the fishes Pimelodella laticeps Eigenmann, 1917 (Heptapteridae) and Bryconamericus iheringii (Boulenger, 1887) (Characidae) in a temperate lowland lotic system in Argentina were assessed on the basis of gut contents and stable-isotope analyses. The feeding strategies were analyzed by the AMUNDSEN method. Relative food items contribution for the taxa studied indicated a generalist-type trophic strategy. In macroinvertebrates, in general, the values of stable isotope confirmed the result of the analysis of gut contents. With the fish, stable-isotope analysis demonstrated that both species are predators, although B. iheringii exhibited a more omnivorous behaviour. These feeding studies allowed us to determine the trophic relationships among taxa studied. Detritus and diatoms were a principal source of food for all the macroinvertebrates studied. In La Choza stream the particulate organic matter is a major no limited food resource, has a significant influence upon the community.Se evaluó la dieta y las relaciones tróficas entre los macroinvertebrados Phyllogomphoides joaquini Rodrigues Capítulo, 1992 y Coenagrionidae (Odonata), Chironomidae (Diptera), Diplodon delodontus (Lamarck, 1919) (Bivalvia: Hyriidae), Pomacea canaliculata (Lamarck, 1822) (Gastropoda: Ampulariidae) y los peces Pimelodella laticeps Eigenmann, 1917 (Heptapteridae) y Bryconamericus iheringii (Boulenger, 1887) (Characidae) en un ecosistema lótico pampásico, sobre la base del contenido estomacal y el análisis de isótopos estables. La estrategia alimentaria fue analizada mediante el método de AMUNDSEN. La contribución relativa de cada categoría alimenticia para los taxa estudiados indicó que la estrategia predominante fue de tipo generalista. En general, en los macroinvertebrados, los valores de los isótopos estables confirmaron los resultados obtenidos por el análisis del contenido estomacal. En los peces, los isótopos estables demostraron que ambas especies son depredadores, aunque B. iheringii tiene un comportamiento más omnívoro. Además, el estudio de la alimentación, nos permitió establecer las conexiones tróficas entre los taxa estudiados. La principal fuente de alimento para los macroinvertebrados estudiados fueron el detritus y las diatomeas. En el arroyo La Choza la materia orgánica particulada es una fuente de recursos ilimitada con influencia significativa en toda la comunidad.

The objective of this work was assessing the sensitivity of leeches to several water quality attributes in lowlands streams.Weused occupancymodelling that account explicitly for detectability, to estimate the influence of four variables (dissolved oxygen, 5-days biochemicals oxygen demand, conductivity, and dissolved inorganic nitrogen) affecting nine species. We described the sensitivity as a change in the occupancy along the range of water quality attributes.We found at least one species of Helobdella in 81% of sites and Helobdella, as genus, was detected along the entire gradient of each attribute. However, differences in the sensitivitywere observed between species. For example, if we analyse the sensitivity of the genus Helobdella to dissolved oxygen, we can say that it is very tolerant. However, if we analyse the response to dissolved oxygen of each one of the species of Helobdella,wewill realize that H. michaelseni, and H. simplex showed a high occupancy at high levels of dissolved oxygen; while H. hyalina and H. triserialis lineata showed high occupancy at low levels. Describe the sensitivity of the species in terms of occupancy, offers a new methodology to understand how the species behave along a stressor gradient., Instituto de Limnología "Dr. Raúl A. Ringuelet", Facultad de Ciencias Naturales y Museo

The present continuous anthropogenic pressure has resulted in an enhancement of nutrient inputs into rivers and streams. This situation has worsened, mainly in agricultural areas, causing an accelerated eutrophication. Macroinvertebrate feeding strategies reflect the species’ adaptations to environments. For a characterization of the macroinvertebrate trophic response to eutrophication, we added nitrogen and phosphorus into the La Choza stream and examined the gut contents of those taxa in order to analyze dietary alterations and assign each macroinvertebrate to a functional feeding group (FFG). Complementary C and N stable isotopes analysis was carried out. The gut contents of all taxa studied contained principally detritus, but statistical analyses indicated significant differences before and after fertilization in some taxa. At the control site, and the treatment site before fertilization, the FFGs maintained constant proportions, the gathering-collector species being dominant in all samples. After fertilization the composition of the taxa at the treatment site varied. The δ13C isotopes values showed that most taxa used detritus as a basal resource. δ15N values were generally coincident with gut content analyses. These results provide a prediction of the functional responses of macroinvertebrates to the environmental consequences expected from accelerated land use. The functional responses constitute a powerful tool to assess eutrophication and its consequences in temperate plain streams. Fil: Ocon, Carolina Silvia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; Argentina Fil: López Van Oosterom, Maria Vanesa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; Argentina Fil: Muñoz, Isabel. Universidad de Barcelona. Facultad de Biología; España Fil: Rodrigues Capitulo, Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; Argentina

Pomacea canaliculata es una especie nativa de la Cuenca del Rio de la Plata, actualmente considerada invasora en el Sur y Este de Asia donde fue introducida con fines comerciales y se ha convertido en la principal plaga de los cultivos de arroz de la region. Realizar mas investigaciones en el habitat natural de este organismo es necesario debido a que caracteristicas fundamentales de su ecologia trofica permanecen aun desconocidas. El objetivo de este trabajo fue estudiar la dieta de P. canaliculata en su habitat natural mediante los analisis de contenidos digestivos e isotopos estables de 13C y 15N. Las muestras biologicas fueron tomadas desde noviembre de 2009 hasta diciembre de 2010 en el arroyo Carnaval, un arroyo pampeano caracteristico. Las muestras para analisis de isotopos estables y posterior aplicacion de modelos de mezcla fueron colectadas en noviembre de 2011. La aplicacion de un diagrama de estrategia trofica permitio establecer una dieta generalista con elevado consumo de detritos, seguidos por plantas vasculares y algas. Los resultados del modelo de mezcla, sin embargo, indicaron que la contribucion relativa a la dieta de todos los recursos basales evaluados (materia organica particulada fina y gruesa, epipelon y macrofitas acuaticas) fue similar (aproximadamente 40 %). Estos resultados evidenciaron una fuerte plasticidad dietaria para la especie.

One of the possible consequences of climatic change for streams and rivers in the pampean region of South America is an increment in nutrient loads. To analyze this possible perturbation on a biological scale, the response of oligochaetes to an experimental eutrophication of the La Choza Stream, Argentina was studied. We proposed that the addition of nutrients could increase the abundance, biomass, and species composition of the stream. Two stretches (Control and Treatment sites) were selected, with bimonthly samples being taken (March 2007 through February 2009) in two habitat types: the sediments and the aquatic vegetation. On each sampling occasion the environmental variables were measured. The nutrient addition consisted in the continuous dissolution of a commercial fertilizer. The oligochaete mean density and total biomass, the taxonomic richness, the Shannon diversity (H'), and the evenness (E) were calculated and the BACI ANOVA design used to compare the differences between the sites. Thirty-three species of the families Naididae (Naidinae, Pristininae, Tubificinae, and Rhyacodrilinae), Opistocystidae, Enchytraeidae plus Aphanoneura Aeolosomatidae were collected. The oligochaete abundance and biomass increased significantly in the sediments and on the aquatic vegetation, especially among the Naidinae and Pristininae during their asexual reproductive phase. The diversity and evenness varied significantly in the sediments with the nutrient addition. Significant differences in the species richness and diversity were found on the aquatic vegetation, with both increasing at the treatment site after the fertilization. A significant correlation (Spearman) was observed between the oligochaete density in the sediments and the NO 3-N and NH 4-N concentration in the water. The increment in the naidines resistant to the fertilizer throughout the experiment could be explained by the greater nutrient availability, their mode of reproduction, and their short life cycles. The results of our study suggested that the incorporation of nutrients modified the composition of the oligochaete assemblage in favor of herbivores and detrivores. The usefulness of these indicator organisms in monitoring freshwater systems is subsequently discussed., Instituto de Limnología "Dr. Raul A. Ringuelet", Facultad de Ciencias Naturales y Museo

The oligochaete assemblage on the Argentine coast of the Rio de la Plata estuary was sampled seasonally within environments having different types of disturbances. Three habitats were sampled: sediments free of vegetation, sediments within bullrush stands and substrates with Limnoperna fortunei. The species richness, evenness and Shannon–Wiener diversity values were different among those habitats. The only dominant species (according to the Kownacki index) was Nais variabilis. Mean density values varied between 400 and 199,500 ind./m2. Organic matter, ammonium and phosphates correlated positively with the mean oligochaete abundance, but not with the granulometry. Physicochemical variables and nutrient levels were measured and their relation to the sampling sites assessed through a principal component analysis (41.8% cumulative variance). The canonical correspondence analysis (41.2% cumulative variance) indicated that the oligochaetes distributed along both a eutrophication–pollution gradient and a turbidi...

The objectives of the present study were to describe the species composition, diversity and distribution of the zoobenthic assemblages, to estimate the abundance and biomass of the dominant species, and to identify the main environmental factors determining the distribution patterns of the invertebrates from a freshwater to an estuarine zone in a temperate estuary of South America. The Río de la Plata estuary is a microtidal system characterized by a high concentration of suspended solids. Fifty-three taxa of meso- and macro-invertebrates were identified in the samples collected during November and December 2001. Molluscs, annelids, crustaceans and nematodes were found at 90% of the sampling sites. Molluscs comprised up to about 90% of the total zoobenthos biomass: the remaining percentage corresponded mainly to annelids and less to nematodes and crustaceans. An ecocline along the salinity gradient could be observed for the benthic assemblages from the freshwater to the estuarine zone in Rio de la Plata. A Canonical Correspondence Analysis shows that results from sampling sites in the outer zone were strongly related to salinity, depth and pH and less to oxygen and percentage of clay. The results from stations in the inner zone, and part of the middle zone, were mainly related to the occurrence of sand and contents of NH4+–N, NO3−–N, and PO43−–P. Fil: Cortelezzi, Agustina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología ; Argentina Fil: Rodrigues Capitulo, Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología ; Argentina Fil: Boccardi, Lucía. Universidad de la República. Facultad de Ciencias; Uruguay Fil: Arocena, Rafael. Universidad de la República. Facultad de Ciencias; Uruguay

Sinelobus stanfordi is a tanaidacean of worldwide distribution of considerable significance within coastal ecosystems. The aim of this research was to provide essential information on the poorlyknown population biology of this species. Benthic samples were taken seasonally from winter 2005 through summer 2007 along 155 km of shoreline within the Río de la Plata Estuary, Argentina. The density of this tanaidacean was higher in vegetated than in bare sediments. The smaller individuals flourished in spring and summer, whereas the larger mature members prevailed in the cooler seasons. Females were always twice as abundant as males. Copulatory females, with 18 ± 8 eggs each, were collected during all the seasons. Five cohorts were distinguished by the von Bertalanffy growth function. This research represents a baseline investigation for future studies on the population dynamics of S. stanfordi both in this estuary and in other places where this species is found., Instituto de Limnología "Dr. Raúl A. Ringuelet"

One of the most important effects derived from the intensive land use is the increase of nutrient concentration in the aquatic systems due to superficial drainage. Besides, the increment of precipitations in South America connected to the global climate change could intensify these anthropic impacts due to the changes in the runoff pattern and a greater discharge of water in the streams and rivers. The pampean streams are singular environments with high natural nutrient concentrations which could be increased even more if the predictions of global climate change for the area are met. In this context, the effect of experimental nutrient addition on macroinvertebrates in a lowland stream is studied. Samplings were carried out from March 2007 to February 2009 in two reaches (fertilized and unfertilized), upstream and downstream from the input of nutrients. The addition of nutrients caused an increase in the phosphorus concentration in the fertilized reach which was not observed for nitrogen concentration. From all macroinvertebrates studied only two taxa had significant differences in their abundance after fertilization: Corbicula fluminea and Ostracoda. Our results reveal that the disturbance caused by the increase of nutrients on the benthic community depends on basal nutrients concentration. The weak response of macroinvertebrates to fertilization in the pampean streams could be due to their tolerance to high concentrations of nutrients in relation to their evolutionary history in streams naturally enriched with nutrients. Further research concerning the thresholds of nutrients affecting macroinvertebrates and about the adaptive advantages of taxa in naturally eutrophic environments is still needed. This information will allow for a better understanding of the processes of nutrient cycling and for the construction of restoration measures in natural eutrophic ecosystems., Uno de los efectos más importantes derivados del uso intensivo de la tierra es el aumento de la concentración de nutrientes en los sistemas acuáticos debido al escurrimiento superficial. Además, el incremento de las precipitaciones en América del Sur vinculado al cambio climático global podría intensificar estos impactos antrópicos debido a los cambios en los patrones de escurrimiento y una mayor descarga de agua en los arroyos y ríos. Los arroyos pampeanos son ambientes particulares, con altas concentraciones basales de nutrientes, que podrían incrementarse aún más si las predicciones del cambio climático global se cumplen. En este contexto, se estudió el efecto de la adición experimental de nutrientes en un arroyo pampeano sobre los macroinvertebrados. Los muestreos se llevaron a cabo entre marzo de 2007 y febrero de 2009 en dos tramos seleccionados, aguas arriba y aguas abajo de la entrada de nutrientes. La adición de nutrientes causó un aumento en la concentración de fósforo en el tramo fertilizado, lo que no se observó para la concentración de nitrógeno. De todos los macroinvertebrados estudiados sólo dos taxa tuvieron diferencias significativas en su abundancia después de la fertilización: Corbicula fluminea y ostrácodos. Nuestros resultados revelaron que la perturbación causada por el aumento de nutrientes en una comunidad bentónica depende de la concentración basal de nutrientes. La respuesta débil de macroinvertebrados a la fertilización en las corrientes pampeanas podría ser debido a su tolerancia a altas concentraciones de nutrientes de acuerdo a su historia evolutiva en arroyos enriquecidos naturalmente con nutrientes. Se necesitan nuevas investigaciones sobre los umbrales a partir de los cuales los macroinvertebrados podrían verse afectados y sobre las ventajas adaptativas de los taxones en ambientes eutróficos naturales. Esta información nos permitirá comprender mejor los procesos de reciclaje de nutrientes y así poder pensar medidas de restauración de ecosistemas eutróficos naturales., Facultad de Ciencias Naturales y Museo, Instituto de Limnología "Dr. Raul A. Ringuelet"

We investigated the responses of the assemblage of Oligochaeta and Aeolosomatidae to organic pollution; comparing taxonomic richness, diversity, abundance, and diet of the individuals inhabiting two lowland streams with different degrees of anthropic impact (the Rodríguez and the Carnaval) belonging to the Río de la Plata basin, Argentina. The physicochemical parameters in the Rodríguez Stream indicated a strong deterioration of the water quality compared to that of the Carnaval. A canonical-correlation analysis indicated that the Tubificinae, Megadrili, Enchytraeidae, and Rhyacodrilinae were more closely associated with the Rodríguez Stream; whereas the Naidinae, Pristininae, and Opystocystidae were more highly represented in the Carnaval. The diversity and taxonomic richness in the Rodríguez Stream exhibited significant differences from those of the Carnaval (P, Facultad de Ciencias Naturales y Museo, Instituto de Limnología "Dr. Raul A. Ringuelet"

Fil: Paggi, Analia Constancia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; Argentina Fil: Rodrigues Capitulo, Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; Argentina

The theory of ecological stoichiometry holds that heterotrophs are mostly homeostatic and exhibit less variation in body stoichiometry than do autotrophs. Most studies of stream foodweb stoichiometry have been done in low-nutrient environments. Little is known about foodweb stoichiometry in nutrient-rich streams, in which a higher level of stoichiometric homeostasis should be expected, mainly because imbalances between resources and consumers are low and nutrient availability may meet biotic requirements. We analyzed elemental content (C, N, P) and stoichiometric ratios (C:N, C:P, N:P) of basal resources, macroinvertebrates, and fishes in a nutrient-rich Pampean stream and compared these values to those from other studies. We manipulated P and N in a 1-y fertilization experiment to analyze biotic stoichiometric responses to additional nutrient input to this naturally enriched system. Soluble reactive P concentration in the treatment reach was doubled relative to the background concentration. Consumers had lower C:P and N:P than those in other lotic systems, whereas P content and C:P and N:P of basal resources were within the ranges observed for other systems. Most components of the trophic web were not affected by fertilization, and only epiphyton, fine benthic organic matter, and macroinvertebrate species (Palaemonetes argentinus and Pomacea canaliculata) changed their nutrient content or stoichiometric ratios. Imbalances in C:N and C:P occurred between primary consumers and their resources, particularly among macroinvertebrate collectors and detritivorous fishes feeding on FBOM. Most basal resources and consumers were strictly homeostatic for P content and the stoichiometric ratios, but a lower degree of homeostasis occurred in the epiphyton, P. canaliculata, and collectors feeding on epiphyton. A high degree of stoichiometric homeostasis exists across the various components of the food web in this nutrient rich stream, regardless of their trophic position. Fil: Feijoó, Claudia Silvina. Universidad Nacional de Lujan. Departamento de Cs.basicas. Laboratorio de Ecologia; Argentina Fil: Leggieri, Leonardo Ramón. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Patagonia Norte. Instituto de Investigación En Biodiversidad y Medioambiente; Argentina. Universidad Nacional de Luján; Argentina Fil: Ocon, Carolina Silvia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Limnología "dr. Raul A. Ringuelet"; Argentina Fil: Muñoz, Isabel. Universidad de Barcelona. Facultad de Biologia. Departamento de Ecologia; España Fil: Rodrigues Capitulo, Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Limnología "dr. Raul A. Ringuelet"; Argentina Fil: Giorgi, Adonis David Nazareno. Universidad Nacional de Lujan. Departamento de Cs.basicas. Programa Ecologia de Protistas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Colautti, Dario César. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Limnología "dr. Raul A. Ringuelet"; Argentina. Instituto de Investigaciones Biotecnológicas - Instituto Tecnológico Chascomús (San Martin); Argentina Fil: Ferreiro, Nicolas Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Patagonia Norte. Instituto de Investigación En Biodiversidad y Medioambiente; Argentina. Universidad Nacional de Luján; Argentina Fil: Licursi, Magdalena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Limnología "dr. Raul A. Ringuelet"; Argentina Fil: Gomez, Nora. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Limnología "dr. Raul A. Ringuelet"; Argentina Fil: Sabater Cortés, Sergi. Universidad de Barcelona. Facultad de Biologia. Departamento de Ecologia; España. Institut Català de Recerca de l; España. Universidad de Girona; España

Macro-invertebrate communities and environmental variables were assessed seasonally for two years in seven streams in North-Eastern of Buenos Aires province (Argentina) in order to analyse changes in their structure and composition in relation with the quality of the water. The study includes pristine streams and others affected by urban and industrial effluents with high conductivity, nitrates, nitrites, phosphates and low oxygen content. Organisms with well-known pollution tolerance were identified to assess biological water quality, using a new Biotic Index (IBPAMP: Biotic Index for PAMPean rivers and streams) in comparison with other existing biotic indices. The usefulness of principal component analysis (PCA) and correlation matrices were examined to evaluate the efficiency of the method to assess disturbances. In general IBPAMP did well correlate with several classical measures of biological water quality (taxon richness, diversity and several biotic indices). The El Gato stream was the most disturbed ecosystem among all studied sites. It was characterised by low dissolved oxygen levels, high turbidity in the middle course, high BOD5 (>30 mg l−1) and COD (>40 mg l−1) values. The Bunirigo stream has a bad quality in the industrial area, but varying according to the dry and wet periods. In general, in the mountainous areas the water quality of streams was good with the exception of the stations located downstream of cities like Ayacucho on the Tandileofu stream.

We assessed the effects of nutrient enrichment on three stream ecosystems running through distinct biomes (Mediterranean, Pampean and Andean). We increased the concentrations of N and P in the stream water 1.6–4-fold following a before–after control–impact paired series (BACIPS) design in each stream, and evaluated changes in the biomass of bacteria, primary producers, invertebrates and fish in the enriched (E) versus control (C) reaches after nutrient addition through a predictive-BACIPS approach. The treatment produced variable biomass responses (2–77% of explained variance) among biological communities and streams. The greatest biomass response was observed for algae in the Andean stream (77% of the variance), although fish also showed important biomass responses (about 9–48%). The strongest biomass response to enrichment (77% in all biological compartments) was found in the Andean stream. The magnitude and seasonality of biomass responses to enrichment were highly site specific, often depending on the basal nutrient concentration and on windows of ecological opportunity (periods when environmental constraints other than nutrients do not limit biomass growth). The Pampean stream, with high basal nutrient concentrations, showed a weak response to enrichment (except for invertebrates), whereas the greater responses of Andean stream communities were presumably favored by wider windows of ecological opportunity in comparison to those from the Mediterranean stream. Despite variation among sites, enrichment globally stimulated the algal-based food webs (algae and invertebrate grazers) but not the detritus-based food webs (bacteria and invertebrate shredders). This study shows that nutrient enrichment tends to globally enhance the biomass of stream biological assemblages, but that its magnitude and extent within the food web are complex and are strongly determined by environmental factors and ecosystem structure., Instituto de Limnología "Dr. Raúl A. Ringuelet"

The external ultrastructure of Manayunkia speciosa Leidy, 1858 from specimens collected at the lower Uruguay River, South America is described using scanning-electron-microscopy. The branchial crown has a pair of semicircular lateral lobes, a pair of mediodorsal radioles and a pair of medioventral ones. Radiolar surfaces are ciliated. The faecal groove is observed on peristomium middorsally. The anterior margin of the anterior peristomial ring formed a rectangular lobe, with a ciliated band. Chaetal shape exemplifies the basic type of tapering cylinder. Two types of thoracic notochaetae: one wider distally, with a smooth handle, and covered on the surface by denticles, and other are significantly finer at the base and covered by thin structures with a free distal end. These structures were not previously recorded in Fabriciidae. Rows of 3 aligned uncini anteriorly projected are found in the thorax. Each uncinus presents a long manubrium which connects with the crest, extending to a main fang. The teeth of the crest are equal in size. The abdomen present 4 types of neurochaetae: one of small size than the other 3. In the abdomen 10-14 uncini form dense dorsal-transverse-lines. Each uncinus presents a short manubrium. The crest is covered with teeth of similar size., Se describe la ultraestructura externa mediante el uso de SEM de especímenes de Manayunkia speciosa Leidy, 1858, colectados en el Río Uruguay, Sudamérica. La corona branquial presenta un par de lóbulos laterales semicirculares, un par de radiolos en posición mediodorsal y otro medioventral. La superficie de las pínulas es ciliada. Sobre el peristomio se observa un surco fecal mediodorsal. El margen anterior del anillo peristomial anterior está formado por un lóbulo rectangular con una banda ciliada. Las setas son de tipo cilíndrico ahusado. Existen 2 tipos de notosetas torácicas: unas anchas distalmente con mango liso, cubiertas por dentículos sobre su superficie; y otras significativamente más delgadas en la base, cubiertas por extensiones delgadas con extremo distal libre. Estas estructuras son registradas por primera vez en Fabriciidae. El tórax presenta grupos de 3 uncinos alineados, proyectados anteriormente, cada uno presenta un manubrio largo, cresta y diente principal. Los dientes de la cresta son similares en tamaño. En el abdomen se registraron 4 tipos de neurosetas: una pequeña y 3 de mayor tamaño. El abdomen presenta de 10 a 14 uncinos agrupados en una línea transversal dorsal. Cada uncino posee un manubrio corto. La cresta está cubierta por dientes de tamaño similar., Facultad de Ciencias Naturales y Museo, Instituto de Limnología "Dr. Raul A. Ringuelet"

The diet and trophic relationships between the macroinvertebrates Phyllogomphoides joaquini Rodrigues Capítulo, 1992 and Coenagrionidae (Odonata), Chironomidae (Diptera), Diplodon delodontus (Lamarck, 1919) (Bivalvia: Hyriidae), and Pomacea canaliculata (Lamarck, 1822) (Gastropoda: Ampulariidae) and the fishes Pimelodella laticeps Eigenmann, 1917 (Heptapteridae) and Bryconamericus iheringii (Boulenger, 1887) (Characidae) in a temperate lowland lotic system in Argentina were assessed on the basis of gut contents and stable-isotope analyses. The feeding strategies were analyzed by the Amundsen method. Relative food items contribution for the taxa studied indicated a generalist-type trophic strategy. In macroinvertebrates, in general, the values of stable isotope confirmed the result of the analysis of gut contents. With the fish, stable-isotope analysis demonstrated that both species are predators, although B. iheringii exhibited a more omnivorous behaviour. These feeding studies allowed us to determine the trophic relationships among taxa studied. Detritus and diatoms were a principal source of food for all the macroinvertebrates studied. In La Choza stream the particulate organic matter is a major no limited food resource, has a significant influence upon the community., Instituto de Limnología "Dr. Raul A. Ringuelet"

Our objective was to assess the effect of the physical habitat degradation in three lowland streams of Argentina that are subject to different land uses. To address this matter, we looked into some physical habitat alterations, mainly the water quality and channel changes, the impact on macrophytes’ community, and the structural and functional descriptors of the epipelic biofilm and invertebrate assemblages. As a consequence of physical and chemical perturbations, we differentiated sampling sites with different degradation levels. The low degraded sites were affected mainly for the suburban land use, the moderately degraded sites for the rural land use, and the highly degraded sites for the urban land use. The data shows that the biotic descriptors that best reflected the environmental degradation were vegetation cover and macrophytes richness, the dominance of tolerant species (epipelic biofilm and invertebrates), algal biomass, O₂ consumption by the epipelic biofilm, and invertebrates’ richness and diversity. Furthermore, the results obtained highlight the importance of the macrophytes in the lowland streams, where there is a poor diversification of abiotic substrates and where the macrophytes not only provide shelter but also a food source for invertebrates and other trophic levels such as fish. We also noted that both in benthic communities, invertebrates and epipelic biofilm supplied different information: the habitat’s physical structure provided by the macrophytes influenced mainly the invertebrate descriptors; meanwhile, the water quality mainly influenced most of the epipelic biofilm descriptors., Facultad de Ciencias Naturales y Museo, Instituto de Limnología "Dr. Raúl A. Ringuelet"

The structure and composition of benthic communities on hard substrates covered by the nonindigenous bivalve Limnoperna fortunei Dunker, the golden mussel, were quantified in the middle zone of the Río de la Plata Estuary (Argentina) from April 2001 through March 2002. A total of 26 taxa were recorded. L. fortunei and Nematoda were the central and dominant groups, with a prodigious abundance of over 80%. The prevalence of L. fortunei, rather than the environmental variables, regulated the dynamics of the associated invertebrate fauna. The golden mussel alters both the structure and function of benthic native communities on hard substrates, allows a higher surface available for colonization and refuge, and provides food source to deposit-feeding organisms in the form of organic or residual material. The mussel also increases the abundance and diversity of taxa on hard substrata - such as Oligochaeta, Hirudinea, Tardigrada, Chironomidae, Copepoda, Tanaidacea, and Hydrachnidia. Similarities and nonparametric multidimensional-scaling analyses indicated that the benthic composition had a seasonal variation. L. fortunei has an environmental impact, an ability to invade new freshwater ambiences worldwide and ecological characteristic comparable to those of Dreissena polymorpha Pallas (the zebra mussel) of North America and Europe., Facultad de Ciencias Naturales y Museo

Aim: This study evaluated the use of oligochaetes at different levels of taxonomic resolution as environmental indicators in Argentine lowland streams affected by different land uses. Methods: Sampling sites were grouped based on the physicochemical and habitat characteristics (low-, moderate-, and high-impact disturbance). Collection of the oligochaetes samples was carried out seasonally in sediment and vegetation habitats. Results: The increases in nutrients and organic matter produced elevated densities of the Oligochaeta, but when the disturbance also involved changes in the physical habitat or enhancements in toxic substances, the abundance decreased significantly to values even lower than those of non-impacted environments. The responses of Naidinae and Tubificinae were similar. The density of the Pristininae decreased with increasing impact, but those of the Enchytraeidae and Rhyacodrilinae increased at the most highly impacted sites. The Opistocystidae were not recorded in high-impact sites. Species richness and diversity (H’) were lower in high-impact sites and even lower in sediments. Some species presented no restrictions in the habitat type or with the contamination level: Limnodrilus hoffmeisteri, Dero furcatus, D. digitata, D. pectinata, Pristina longiseta, and P. aequiseta. Moreover, Trieminentia corderoi, Slavina appendiculata, and Aulodrilus pigueti exhibited the highest abundances at low-impact sites and were not registered in high‑impact sites. Conclusions: The Oligochaeta show a relatively wide ecological valence through their extensive number of species. Although lower taxonomic levels can give information about environmental status, test-species’ sensitivities to different types and degrees of contamination will be of utmost relevance to the evaluation of ecological quality., Objetivo: Este estudo analisou as uso de oligoquetos em diferentes níveis de resolução taxonômica como indicadores ambientais em rios de planície Argentina afetadas por diferentes usos da terra. Métodos: Os sítios de amostragem foram agrupados com base nas características físico-químicas e habitat (perturbação baixa, moderada ou alta). Amostras de oligoquetos foram coletadas sazonalmente em habitats de sedimentos e vegetação. Resultados: Os aumentos de nutrientes e matéria orgânica resultaram em densidades elevadas de Oligochaeta, mas quando a perturbação também envolveu mudanças no habitat físico ou incrementos em substâncias tóxicas, a abundância diminuiu de forma significativa para valores ainda mais baixos que os de ambientes naõ perturbados. As respostas dos Naidinae e Tubificinae foram semelhantes. A densidade de Pristininae diminuiu com o aumento da perturbação, mas as densidades de Enchytraeidae e Rhyacodrilinae aumentaram nos locais mais altamente perturbados. Os Opistocystidae não ocorreram em locais de alta perturbação. A riqueza de espécies e a diversidade (H’) foram menores em locais de perturbação elevada e ainda mais baixos nos sedimentos. Algumas espécies não apresentaram restrições no tipo de habitat ou com o nível de contaminação: Limnodrilus hoffmeisteri, Dero furcatus, D. digitata, D. pectinata, Pristina longiseta e P. aequiseta. Além disso, Trieminentia corderoi, Slavina appendiculata e Aulodrilus pigueti exibiram uma maior abundância em locais de baixa perturbação e não foram registrados em locais com elevadas perturbações. Conclusões: Os Oligochaeta apresentaram uma valência ecológica relativamente ampla, através de seu extensivo número de espécies. Embora os níveis taxonômicos mais baixos podem dar informações sobre o status ambiental, testes com espécies com diferentes sesibilidades para diferentes tipos e graus de contaminação serão da maior relevância para a avaliação da qualidade ecológica., Instituto de Limnología "Dr. Raúl A. Ringuelet"

The rivers and streams in the pampean plains are characterized by a low flow rate due to the low slope of the surrounding terrain, high levels of suspended solids, silty sediment in the benthos, and reduced rithron; the riparian forest of this region has been replaced by low-altitude grasslands. Many of these environments contain a wide coverage of aquatic reeds, both submerged and floating, making the pampas limologically extraordinary. These terrains have undergone a gradual transformation in response to the progress of urbanization and agricultural activity in recent years with a resulting loss of biodiversity, leaving only few sites that continue to reflect the original characteristics of the region. Because of human activities in combination with the global climate change, variations have occurred in biological communities that are reflected in the structure and function of populations and assemblages of algae, macrophytes, and invertebrate fauna or in the eutrophication of affected ecosystems. The objective of this article is to describe the principal limnologic characteristics of the streams that traverse the Buenos Aires Province and relate these features with the predicted future global changes for the area under study. Considering the future climate-change scenarios proposed for the pampean region, the projected increment in rainfall will affect the biological communities. Higher rainfall may enhance the erosion and generate floodings; increasing the transport of sediments, nutrients, and contaminants to the ocean and affecting the degree of water mineralization. Changes in discharge and turbidity may affect light penetration in the water column as well as its residence time. The modifications in the use of the soil will probably favor the input of nutrients. This latter effect will favor autotrophy, particularly by those species capable of generating strategies for surviving in more turbid and enriched environments. An accelerated eutrophication will change the composition of the consumers in preference to herbivores and detritivores. The increase in global population projected for the next years will demand more food, and this situation coupled with the new scenarios of climate change will lead to profound socioeconomic changes in the pampean area, implying an increase in demand for water resources and land uses. Fil: Rodrigues Capitulo, Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología ; Argentina Fil: Gomez, Nora. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología ; Argentina Fil: Giorgi, Adonis David Nazareno. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Luján. Departamento de Ciencias Básicas. Programa Ecología de Protistas; Argentina Fil: Feijoó, Claudia Silvina. Universidad Nacional de Luján; Argentina

The use of benthic invertebrates is considerate and recognized at present as one of the better methodological alternative to detect early modifications or contamination from diffuse origin. The objective of this work was to evaluate the biological quality of two regional pampean plain streams by means of taxonomic and functional indicators of the whole of invertebrates assemblages and to compare the utility of the different applied indicators. The selected streams belong to the Rio de La Plata basin, with different anthropogenic impact. Over a period of two years, the physicochemical parameters and the benthic invertebrates and those present in the vegetation, of these lotic systems were assessed in samplings sites located upstream and downstream. Taxonomic and functional feeding groups, of the invertebrate assemblages were analyzed. The estimated taxonomic indicators reflected seasonal differences and the valuation of the quality of the sites were different and variable depending on the parameter and the taxonomical level used. Even so, the density of the most abundant family, the abundance of Ephemeroptera-Trichoptera (ET), the ET/total and ET/Oligochaeta relations resulted useful to establish differences between sites and streams. The collectors appeared as the dominant functional feeding group in all the sites. No significant differences were observed in the composition of the functional feeding groups of the invertebrate assemblages from headwaters to the mouth of both streams. Then these indicators would not be efficient to evaluate the environmental quality of these systems., Instituto de Limnología "Raúl A. Ringuelet"

The spatial and temporal differences in the structure and composition of benthic invertebrates were studied at three sites of the Samborombón River, which is an important tributary of the Río de la Plata Estuary (Argentina), having a low slope and brackish drainage. Biological samples were taken during each season. Physico-chemical variables were measured to determine their association in the benthic fauna distribution. Site 1, in the headstream, was characterized by freshwater Pampean organisms; site 2 showed the highest density, taxa diversity, and richness; brackish species, e.g., Laeonereis culveri, were found here. Site 3, close to the Samborombón Bay, was characterized by an unstable taxonomic composition that is strongly influenced by the estuary. The lowest density and taxonomic diversity of organisms were registered and distinguished by estuarine species. The multivariate method (redundancy analysis) showed the benthic groups having an important spatial variability, superimposed on the temporal variability, associated with the salinity gradient of the river. Fil: Spaccesi, Fernando Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; Argentina Fil: Rodrigues Capitulo, Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; Argentina

The ingress of an urban stream carrying high contaminant loads into a large coastal river originates a “dispersion plume” subject to the hydrological conditions of a river affected by tidal influences. In the present study 21 sites within the “contaminant plume” of the Riachuelo River in the Rio de la Plata were analysed on the same date in order to evaluate the biological status of the area which receives this strong environmental impact, and to examine its effect on the zoobenthic communities. Diversity, taxonomic richness, abundance, physico-chemical parameters and a biological index (IMRP) were used to assess the responses of the macroinvertebrates. The correlation between exposure and effect was calculated by means of the exposure index (IEX). The relationship between the macroinvertebrate communities and environmental variables was examined using CCA analysis. Conductivity, Cr, BOD and COD, were most strongly correlated with Axis 1, suggesting the existence of a gradient of environmental degradation. The most severely contaminated sites (IMRP= 1.1–2.5; IEX = 100–78%) were all characterized by a reduced community dominated by Nematoda and Oligochaeta. A moderate response was observed between 1400 and 1600 m from the coast (IMRP = 2.6–3.9; IEX = 36%) largely owing to the physico-chemical characteristics of the recipient river which contributed to moderating the effect of the anthopogenic perturbation. For statistical validation, this area was compared with historical physico-chemical and biological data, where OD and COD showed the same tendency throughout the 10-year period., Facultad de Ciencias Naturales y Museo, Instituto de Limnología "Dr. Raúl A. Ringuelet"

In this paper, Tributaries of the Río Paraná and Río de la Plata rivers (Arrecifes and Matanza-Riachuelo rivers, El Gato, El Pescado, Juan Blanco and Buriñigo streams). The System of Río Salado (Samborombón and Salado rivers, Las Garzas stream) and streams of Tandilia gills north-eastern slope stream (Napaleofú, Langueyú, Tandileofú, Chelforó and Vivoratá) were studied by analysing the zoobenthic community. Several streams tributaries of Rio de la Plata river are affected (to a different extent) by urban and industrial perturbations and they were compared with pristine streams of the region. Diversity and Biotic Indices were applied in the streams. Tolerant species and slow scores of the both indices were mainly registered in Matanza-Riachuelo river and El Gato stream, and the more sensitive taxa were identified in El Pescado and Juan Blanco streams. In Samborombon river there were salinity changes with taxa adapted to this condition (Polichaeta, Chasmagnatus granulata, Cyrtograpsus angulata, Cirripedia., Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) - Instituto de Limnología "Dr. Raul A. Ringuelet" (ILPLA)

Two invertebrate species (Hyalella curvispina and Palaemonetes argentinus) and one macrophyte (Egeria densa) from a naturally high nutrient content system (Pampean rivers of La Plata, Argentina) were evaluated for their potential use in situ assays aiming to assess changes in water quality. Invertebrates were individually placed in cylindrical chambers in polluted sections of rivers and in reference upstream sites. Mortality after 48 h was high in polluted and reduced in control sites. Mortality was also higher in situ assays than in laboratory static tests. Standard sections of the macrophyte were also deployed at the reference and control sites. Growth (7 days) in terms of mass increment (but not in length) was consistently reduced in polluted sites. Results of benthic invertebrate and periphitic algae surveys were consistent with the in situ tests: pollution resulted in a decrease in the number of taxa, taxa replacement and in changes in the value of the biotic indices Indice Biotico PAMPeano and Indice de Diatomeas Pampeano, indicating deterioration of water quality. In situ assays have a high potential as environmental tools in integrated approaches of bioassessment programs. Fil: Graça, Manuel A.S.. Universidad de Coimbra; Portugal Fil: Rodrigues Capitulo, Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología ; Argentina Fil: Ocon, Carolina Silvia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología ; Argentina Fil: Gomez, Nora. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología ; Argentina