Environmental factors that control the abundance of Cyclostephanos dubius (Bacillariophyceae) in Danish lakes, from seasonal to century scale

Studies of Cyclostephanos dubius were made using contemporary field data, lake surface-sediment samples and palaeolimnological records. Variations in the species' abundance (in time and across several lakes) in relation to environmental variables were explored using statistical methods. In five shallow, nutrient-rich, Danish lakes, the seasonal abundance of C. dubius was modelled using multiple linear regression techniques. Four significant variables (NO₂ + NO and silica concentrations, Secchi depth and zooplankton abundance) explained 24% of the variation in the seasonal diatom data. The abundance of C. dubius was positively correlated with [NO₂ + NO] and negatively correlated with [SiO2], Secchi depth and zooplankton abundance. In a dataset of 29 surface-sediment samples from Danish lakes, significant species response curves could be modelled for C. dubius with lake depth, and concentrations of total phosphorus (TP), silica and chlorophyll a. Analyses of species data over different timescales demonstrate that multiple, interactive factors and dynamic processes influence the abundance of the diatom in the phytoplankton and in sediment assemblages.