This study represents a taxonomic survey of class Bacillariophyceae diatoms found in samples collected in the Iguacu River (Iguacu National Park, municipality of Foz do Iguacu, in the state of Parana, Brazil) between August 2007 and July 2008. Two sampling stations were utilized, the first located upstream of Iguacu Falls (Cais Bananeiras Station) and second downstream of the falls (Cais Macuco Safari Station). The study resulted in the identification of 86 taxa, including 74 at the specific level and seven taxonomic varieties. Two of these had never before been documented in the state of Parana: Gomphonema gibberum Hustedt and Pinnularia meridiana Metzeltin & Krammer. Nine are first-time records for Brazil: Cymbella charrua Metzeltin, Lange-Bertalot & Garcia-Rodriguez, Placoneis ovillus Metzeltin, Lange-Bertalot & Garcia-Rodriguez, Gomphonema affinopsis Metzeltin, Lange-Bertalot & Garcia-Rodriguez,, Gomphosphenia lingulatiformis (Lange-Bertalot & Reichardt) Lange-Bertalot, Luticola aequatorialis (Heiden) Lange-Bertalot & Ohtsuka, Sellaphora garciarodriguezii Metzeltin & Lange-Bertalot, Eolimna submuralis (Hustedt) Lange-Bertalot Kulikovskiy, Geissleria neosubtropica Metzeltin, Lange-Bertalot & Garcia-Rodriguez and Stauroneis cf. sylviabonillae Metzeltin, Lange-Bertalot & Garcia-Rodriguez

The evaluation of abiotic and biotic variables can provide information for understanding the structure and function of lotic systems. To obtain this information, measurements of 15 chemical and physical variables and of phytoplankton were conducted at two sampling stations. The present study aims to evaluate the temporal and spatial variation of planktonic diatoms in terms of abiotic variables and the trophic level of the river water and to select diatom species as descriptors of the physical and chemical conditions of the water upstream (S1) and downstream (S2) of the Iguassu River over an annual cycle. Sampling station S1 was classified as oligotrophic to mesotrophic, and S2 was classified as ultra-oligotrophic to oligotrophic. A total of 98 diatom species distributed among 39 genera was recorded, showing no dominant species but 36 abundant species. Although the differences of chemical and physical variables between S1 and S2 were limited to greater turbulence and turbidity, processes triggered by heavy rainfall exerted a significant influence on community structure, and a temporal change in composition was observed. At the end of the dry period, due to the recovery of nutrients and high transparency, there was an abundance of Cocconeis placentula var.lineata. In the rainy period, with increased turbulence and turbidity processes resulting from higher rainfall, there was an abundance ofAulacoseira granulata var. granulata.

A taxonomic survey was carried out on Coscinodiscophyceae and Fragilariophyceae found in the Iguaçu River catchment area within Iguaçu National Park, in the state of Paraná, Brazil. Between September 2007 and August 2008, we collected 24 samples from two stations on the Iguaçu River, upstream and downstream of the falls. We identified 37 taxa, including 22 specific and infraspecific taxa of Coscinodiscophyceae, together with 15 specific and infraspecific taxa of Fragilariophyceae. Melosira ruttneri Hustedt and Fragilaria alpestris Krasske ex Hustedt represent new records for Brazil.

In order to access environmental conditions, the use of bioindicators that have a close relationship with environmental stressors is a largely common practice, but when evaluating environmental inferences, the individual dominant taxa need to be interpreted. Humid regions such as the marshlands are fragile ecosystems and sustain communities of microalgae, often used as bioindicators, of which diatoms are a good example. Although they provide an excellent response to chemical and physical changes in water, diatom studies in surface sediments in wetlands are scarce worldwide. To determine whether diatom species have the potential to provide unambiguous inferences in the influence of environmental factors, we have evaluated diatom abundance in surface sediment, from three Pantanal lakes, against a set of environmental gradients: pH, dissolved oxygen, turbidity, conductivity, total dissolved solids, water temperature, index of trophic water status, total phosphorus and total nitrogen. The Ferradura lake presented an oligotrophic state and both Burro and Caracará lakes presented mesotrophic state. Diatoms were more abundant in the a mesotrophic conditions, but with higher species richness in the oligotrophic conditions. Depending on the N:P ratio, the nutrients nitrogen and phosphorus can also play the role of pollutants and may have negative and unpredictable effects in the environment, such as biotic homogenization. Despite the spatial variation in species, there was a greater richness of Eunotia Ehrenberg species, with the highest relative density of Eunotia formica Ehrenberg and E. pantropica Glushchenko, Kulikovskiy & Kociolek, due to the environmental acidic conditions, a determining characteristic of this genus. It was also observed that a small increase in the level of phosphorus generated an increase in the abundance of Aulacoseira Thwaites with the highest relative density of A. pusilla (Meister) Tuji & Houki and A. veraluciae Tremarin, Torgan & T.Ludwig. However, A. italica dominated in the moderately acidic environment. The results can help with decisions in impacted areas to solve socioeconomic problems, environmental management and biodiversity.

The study of the genus Melosira in plankton samples from the lower Iguaçu River revealed the presence of four taxa: Melosira undulata (Ehrenberg) Kützing var. undulata, M. undulata var. normanni Arnott, M. varians C. Agardh and M. muscigena Iwahashi. We present illustrations of the frustules using light microscopy (LM), descriptions, and comments about the morphology of the four taxa. The analysis of Melosira muscigena under scanning electron microscopy revealed unprecedented details of the ultrastructure, such as the shape and distribution of the rimoportulae at the valve mantle. This is the first record of Melosira undulata var. undulata and the second of M. muscigena in Brazil.

(1) Background: We analyzed the diatom community structure of the surface sediments, in three permanent ponds in the Pantanal of Mato Grosso, Brazil, to better understand how biota in these aquatic environments depend on structural connectivity and functional connectivity: (2) Methods: Ten samples sites were established in each pond, water and the sediment were taken during the flood period. Abiotic–biotic variables were determined and standardized; (3) Results: The three ponds presented acidic water and high concentration of nitrogen, with the highest acidity for Ferradura Pond (P1) and the highest trophic status index for Burro Pond (P2), but the greatest environmental variations occurred in Caracará Pond (P3). The variation in diversity between sites in the same pond is what contributes the most to gamma diversity. The most abundant species was Aulacoseiraitalica (Ehrenberg) Simonsen and the genus Eunotia Ehrenberg was the most representative in species. Ferradura Pond, there was a relationship between compositional and environmental dissimilarities with geographic distance, but there was no independent. Burro Pond, the relationship the compositional variation with environmental variables was not significant. Caracará Pond, there was a relationship of compositional dissimilarity both with geographical distance and with environmental; (4) Conclusions: The set of results suggests that the mechanisms that determine the metacommunity of each pond are different and that the environmental conditions and dispersion influenced the structure and composition. Since, diatom species were different between ponds, and ponds more eutrophic showed less diversity. The pH and oligotrophy were the main factors to maintain the greatest diversity of species of the genus Eunotia and the greatest abundance of Aulacoseira italica. Knowing the dynamics and structure of diatoms, which are at the beginning of the food chain, is essential for conserving, maintaining, or rehabilitating wetland ecosystems, such as the Pantanal, which is part La Plata river basin, which represents the second largest surface for water resources in South America and the Guarani Aquifer System, the biggest unified groundwater aquifer in the world.