We aimed to evaluate the structure of periphytic algae communities, the trait distribution and the patterns of functional diversity in the last non-dammed stretch of the Upper Paraná River floodplain. We hypothesize that there is an increase in the functional diversity and a change of the traits and environmental variables structure along this floodplain. We expected an increase in the functional diversity due to the increase in tributaries propagule input leading to a functional divergence, provided by deterministic processes. The sampling was in channels, lakes and rivers in a floodplain area covering 230 km of extension of the main river. The periphyton was obtained from scraping petioles of the floating macrophyte Eichhornia azurea (Sw.) Kunth. The traits evaluated were life form and strength and form of adherence to the substrate. The functional diversity was calculated from a functional dendrogram and assembly rules. The hypotheses proposed in this study were partially accepted, since there was no increase in functional diversity along the sampled area, but we observed a change in the structure of the functional traits along the different stretches of the floodplain. The results showed diatoms as the dominant algae, and functional convergence as the assembly rule prevalent for this community. There was a large difference between local environmental factors along the floodplain. The protected areas housed the greatest functional diversity values, which was apparently influenced by the increase in functional diversity, which can be explained by the limnological factors and the input of propagules from the tributaries to the Paraná River. We noted the importance of the protected areas and local factors for assembly of this community.
Water level fluctuations result in changes in available habitat, affecting communities of algae and freshwater diatoms. Paleolimnological approaches assist in understanding the effects of hydrological regimes on communities over time. Therefore, the aim of this study was to identify the variation in water level due to the abundance of two diatom species, Diadesmis confervacea Kützing and Eunotia camelus Ehrenberg. Diadesmis confervacea has a periphytic habit and occurs primarily in shallow, marshy environments with high temperatures. Eunotia camelus has a planktonic habit and is mainly found in deeper environments. We analyzed the diatom fossils from sediment collected from a marsh located on Mutum Island, in the Upper Paraná River floodplain. The sediment core of 2 m was divided into layers of 2.5 cm and was dated to 830 PB using 14 C isotope. The relative abundances of the two species were obtained through quantitative analysis. The results showed a shift in the abundance of each species to the geomorphological changes and periods. The ratio of the opposing values of abundances of the two species might have been caused by changes in water levels due to ecological preferences. Competition for light between planktonic and periphytic communities also might affect algae abundance. Thus, we observed that D. confervacea and E. camelus are good indicators of hydrological changes. Therefore, our study contributes to better understand the effects of variation in water level and hydrological regime in the diatom species.
The number of periphytic algae species in floodplain lakes is strongly related to the flood pulse. Necessarily, algae dynamics are linked to some hydrological attributes such as the frequency, duration and intensity of the pulse. We analysed the variation in richness of the periphytic algae community over eight years (2000-2007). Our aims were (1) to examine periphytic algae richness and its relationship with the pulse regime and (2) to verify temporal changes of this richness in response to frequency, amplitude and intensity attributes. We analysed the potamophase and limnophase periods over the years using the fFITRAS function. Simple regressions were performed to reveal the influence of hydrological attributes on the richness of the periphytic algal community. The hydrological regime presented wide hydrometric-level variation among years, and we verified the predominance of the limnophase periods. Periphytic algae richness was high (371 taxa), presented wide oscillations ranging from 68 to 169 among the years and showed a tight correlation with flood pulse intensity. Our results highlight that the hydrological regime was the main factor structuring the richness pattern of the periphytic algae community in a floodplain environment. Furthermore, the results showed that temporal variations of the periphytic algae richness were related to shifts in flood pulse intensity, suggesting that this attribute is a key factor for periphytic algae communities in the floodplain environment and is important to be considered in studies covering long time series.
Considering the lack of knowledge regarding the paleolimnology and the diatom flora from the sediment in Brazilian aquatic environments, this study aimed to provide information about diatom biodiversity and autoecology in an environment located in the upper Paraná river floodplain. Sediment and periphytic samples were collected from a swamp located in an island of the upper Paraná river floodplain. Sediment samples were obtained by collecting a core of ~2 m with a calibrated date of 726 to 903 cal yr BP near the base. The core was sliced into layers of 2.5 cm, totaling 41 samples. Periphytic diatom samples were obtained by scraping macrophytes' petioles, totaling two samples. The community was represented by 31 species belonging to 15 genera. All of the taxa were found in the sediment record, and 15 were present in the periphyton. The three new records (Eunotia longicamelus, Planothidium bagualensis and Luticola hustedtii) reinforce the importance of paleolimnological and periphytic studies to increase information about the aquatic biodiversity.
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