Drought events will become more frequent due the climate change. In floodplains, periphytic algae are responsible for part of the primary production, are the principal source of organic carbon deposition, play an important role in mineralization and nutrient cycling, and are the base of the food web for many organisms. As algae distribution in aquatic environments is a strong indicator of physical and chemical conditions of the sites, we aimed to determine the structure of periphytic algae in lentic and lotic environments during drought conditions and to uncover the main local abiotic factors in community structuring. We hypothesized diatoms would be more frequent than green algae and desmids at both sites, due to their resistance characteristics, and that higher periphyton algal richness, density and diversity would occur in the lake due to the greater availability of nutrients and the absence of flow. The study was carried out in the Finado Raimundo lake and the Ivinhema river in the Upper Paraná river floodplain during the low water period of 2011. Petioles of the aquatic macrophyte Eichhornia azurea (Sw.) Kunth were used as a substrate for periphytic algae. We found a total of 171 species, 104 species in the lake and 80 in the river. Diatoms were predominant at both sites due to their strategic traits, and between sites, there were different patterns in the periphytic algal community structure, owing to the distinctive physical and chemical characteristics of the lake and the river. Achnanthidium minutissimum (Kützing) Czarnecki and Nitzschia palea (Kützing) W. Smith were the most abundant species in both environments. Our results showed patterns of periphytic algae in a floodplain during drought conditions, which will assist in understanding their structuring during future drought scenarios.
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.
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.
A taxonomic study of species of the genus Gomphonema Ehrenberg (Bacillariophyceae) was performed in alotic environment (Ipoitã Channel) of the Upper Paraná River Floodplain. Samplings were performed in June, September and December 2013 and February 2014. Two petioles of Eichhornia azurea (Sw) Kunth were sampled at three different sites in the channel. Twelve species and two taxonomic varieties were identified. All species identified were recorded at the sampling site 3, loca ated close to the Ivinhema River. The lowest number of taxa occurred at the sampling site 1 (9 specific and infra specific taxa), in the confluence with the Paraná River. All taxa of Gomphonema were the first record for the Upper Paraná River Floodplain. Our results emphasize the lack of taxonomic studies for the region and the importance thereof to the knowledge of biodiversity.
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