Effects of hydrological variables on structuring morphological trait (cell size) of diatom community in a lowland river

Diatoms are widely used as bio-indicators in water quality monitoring and ecological status assessment. Compare to chemical variables, the effects of hydrological variables on diatom dynamics have been rarely reported. In this study, we aimed to examine dynamics of diatoms based on the classification of a morphological trait (cell size) and to investigate the relationship between the diatom community and selected chemical and hydrological variables. We collected 339 daily-mixed samples by using an auto-sampler, from which we recorded 113 diatom taxa from 45 genera. Analysis of morphological trait showed variations among cell size classes throughout the year with big cells in winter and spring while small cells dominated in summer and autumn. Redundancy analysis (RDA) and partial RDA indicated that chemical and hydrological variables could jointly explain 50.2% of the diatom community variation, in which chemical variables explain 36.5% and hydrological variables explain 12.9%. The most important chemical variables were Orthophosphate-phosphorus (PO4-P) and Silicon (Si2+) concentrations, while the most significant hydrological variables were antecedent precipitation index (API) and base flow. We conclude that besides chemical variables (nutrients and metal ions) hydrological variables showed also remarkable effects on the diatom community variation, especially during wet conditions. A key implication of our findings for freshwater management is that future bio-monitoring protocols should take hydrological variables into consideration.