Abundance of Diadesmis confervacea Kützing and Eunotia camelus Ehrenberg indicates the historical water level variation in a marsh

Abstract

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 14C 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.