Resumo Objetivo: Identificar padrões espaciais em larga escala na limnologia dos corpos d’água laterais da bacia do Rio da Prata, considerando a presença dos barramentos e conglomerados urbanos. Métodos Amostragens foram feitas em uma ampla escala espacial (ao longo de 16 graus de latitude) durante dois períodos sazonais (23 locais no verão e 20 no inverno) para medições de variáveis físicas e químicas, clorofila a e biomassa do perifiton. Resultados A distância geográfica entre os locais foi significativamente correlacionada com a dissimilaridade ambiental (distância Euclidiana). Locais associados a reservatórios e planícies de inundação apresentaram menores concentrações de fósforo. Condições mais eutróficas estiveram associadas a áreas urbanas e regiões com atividades agropecuárias intensivas, como maior condutividade, concentrações de nitrogênio e clorofila a. Maior biomassa de perifiton ocorreu em locais sob influência de reservatórios. Material particulado inorgânico foi maior no verão e orgânico no inverno, devido à contrastante sazonalidade das chuvas na porção superior da bacia do rio Paraná. Não houve correlação significativa entre a dissimilaridade da vegetação e a dissimilaridade ambiental ou distância geográfica entre os locais amostrados. Conclusões As condições limnológicas nos ambientes fluviais laterais da bacia do Rio da Prata são altamente influenciadas pela construção de reservatórios, intensa ocupação urbana e sazonalidade na precipitação.

Abstract Aim: Identify large-scale limnological patterns in lateral water bodies of Río de La Plata Basin, considering the influence of river damming and urban conglomerates. Methods Samplings were performed in a broad spatial scale (along 16 latitude degrees) during two seasonal periods (23 sites in summer and 20 sites in winter) for measurements of physical and chemical variables, chlorophyll a and periphyton biomass. Results Geographical distance between sites was significantly correlated with the environmental dissimilarity (Euclidean distance). Reservoir and floodplain associated sites exhibited lower phosphorus concentration. Eutrophic conditions were higher in sites close to urban areas and regions with intensive agriculture and livestock activities, which exhibited higher conductivity, concentration of nitrogen and chlorophyll a. Sites associated to reservoirs had higher periphyton biomass. Inorganic suspended matter was higher in summer whereas organic suspended matter was higher in the winter, due to contrasting rain seasonality in the upper Paraná River sub-basin. No significant correlation between the dissimilarity of the vegetation and the environmental dissimilarity or geographical distance between sites was observed. Conclusions The limnological conditions in the fluvial lateral habitats in the Río de La Plata basin are highly influenced by reservoirs construction, intensive urban occupation and rain seasonality.

ABSTRACTRecent worldwide taxonomical research on Cladocera is discovering a number of new species but hardly in South America. The Río de La Plata is the second largest basin in the continent and the knowledge on cladocerans of the different sub-basins is uneven. The recent increase in the number of cladocerans species worldwide inspired this survey in the Río de La Plata basin. It was expected that new species, or at least a significant number of new records, could be found which would contribute to the richness of the least studied sub-basins. Twenty three sampling locations were selected and the Cladocera were analyzed in detail to the species level. The family Chydoridae was targeted due to its high species richness. Fifty species of Chydoridae were recorded, two of them probably new for science and a third one whose taxonomical status could not be further addressed, due to insufficient material for analysis. All sub-basins had at least one specimen of one or both new species. The contribution of new species was more homogeneous among sub-basins when compared to the total contribution of new registers. It was concluded that the improvement of the taxonomical resolution and extensive samplings are fundamental in assessing the real cladoceran richness in the basin and that knowledge based on just a few research centers is not enough to promote secure taxonomical and biogeographical considerations yet.