Changes in the elemental composition of Asterionella formosa during the diatom spring bloom

Changes in the elemental composition of the diatom Asterionellaformosa within mixed phytoplankton samples were determined overthe spring bloom period using energy dispersive X-ray microanalysis.Using a 10 kV electron microprobe, X-ray information from thetop 1–2 µm of the cell revealed overall mean concentrationsof: Si (4636 mmol kg^–1 dry wt), P (82), S (54), Cl (71)K (94) and Ca (90). Concentrations of all elements showed widevariation within each date sample, with unimodal frequency distributionsapproximating to a Normal distribution. Correlation of the entiredata set demonstrated clear statistical associations betweenelements, including Si, P and K. Uptake of Si during the courseof the diatom bloom led to a major fall in lake water concentration(1.0 to 0.07 mg l^–1), which correlated with a decreasein the mean cell Si concentration (6735 to 3107 mmol kg^–1dry wt) during the final phase of the bloom. Mean cell concentrationsof P and K also showed marked decreases with time, in closeparallel with cell Si. These changes in P and K were attributedto the high level of internal correlation with Si and not toany significant decrease in P and K availability in the environment.