Some experiments on the sinking characteristics of two freshwater diatoms

The sinking rates of living and heat‐killed cells of Asterionella formosa and Tabellaria flocculosa and after treatment with CuSO4, NaHClO3, Formalin, Lugol’s solution, butanol, and isopropanol at 15°C are reported. Dead cells sank faster than living cells, particularly those of Tabellaria. Some interspecific differences were observed in the degree to which sinking is heightened after treatment with algicides. Sinking rates increased after exposure to certain concentrations of isopropanol and butanol. This was accomplished without loss of viability, suggesting that suspension may be partially regulated physiologically in these diatoms. The sinking rates fall within the range for growing and senescent populations of marine pennate diatoms having similar geometry. The results suggest that subtle physical or physiological conditions can influence diatom suspension, but these appear to be of secondary importance to vertical mixing in permitting their suspension.