Periphytic diatom ecological guilds in floodplain: Ten years after dam

Periphytic diatoms are a key primary producer in floodplain systems. In this study, we assessed the species and functional traits in the periphytic diatom community in three lentic environments directly connected to the Paraná River shortly after damming and a decade later. Samples were collected in 2001-2002 and 2010-2011 during high waters phase. Periphytic samples were obtained from Eichhornia azurea Kunth, found in the shore zone of these environments. We recorded a total of 90 diatom species. 47 taxa were exclusive during the period shortly after damming and 18 taxa were only found in 2010-2011. The analysis of the similarity, diversity, beta diversity and non-metric multidimensional scaling (NMDS) suggested that there were differences in the species and functional traits of the periphytic diatom community between the two study periods. Variations in water transparency and nutrient (including nitrogen and phosphorus forms) were the most important variables shaping diatom communities diatoms during the study periods. High and motile profiles were characteristic shortly after damming and taxa of high and low profiles predominated a decade later. High transparency, high water and nitrogen levels favored the development of high and low profile, such as Gomphonema augur var. augur, Synedra goulardii and Amphora sp., whereas taxa belonging to high-profile and motile algae (e.g., Eunotia indica, Nitzschia amphibia) were found in the opposite conditions. Species turnover was an important diversity component that was greatly influenced by limnologic differences over time, represented by environmental and temporal dissimilarities between the years. These changes reinforce the modifications that have occurred in the environmental component of the Upper Paraná River floodplain downstream of the dam from the start of its operation.