Influence of temporal changes on a diatom species in a floodplain lake: paleolimnological and biomonitoring approach

Long term anthropogenic and natural impacts may result in effects on hydrological and environmental variables in aquatic ecosystems, as floodplain lakes, causing changes in diatom populations and community composition. We hypothesized that temporal abiotic factors over time favoured the establishment and increase in relative abundance of the Achnanthidium minutissimum complex. For a greater understanding of variation in species abundance, we used biomonitoring and paleolimnological data, combining 18 years of data from periphyton samples and more than 60 years from sediment samples. To test the relationships between the environmental parameters and relative abundance of A. minutissimum from biomonitoring data, we used generalized linear models (GLM). Based on GLM, the relative abundance of A. minutissimum increased with lower water depth, lower temperature, higher turbidity, and high pH. These conditions coincide with periods of drought in the floodplain, which were more frequent and longer after the construction of dams near Lake Garças. Additionally, the paleolimnological data suggest that climatic and anthropogenic influences on abiotic factors, such as water level and turbidity may have been responsible for the increased abundance of A. minutissimum in Lake Garças, as well as its dominance in the periphytic community from 2000, after the last dam construction near the lake. This shows how the modification of an aquatic environment can change diatom populations, and highlights the importance of combining historical information, paleolimnological analyses and biomonitoring data to understand population and ecosystem processes over time.