Physico-chemical control of the growth of a diatom, Asterionella formosa Hass., in a shallow eutrophic lake

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Abstract
Physico-chemical environmental control of the growth rate of an algal population, the pennate diatom Asterionella formasa Hass., was investigated for a year in natural water. This species occurred in vegetative form in the water column all the time, although its population density varied by five orders of magnitude from a maximum of 1.4×10 6 cells l −1 in February to a minimum of 0.8×10 1 cells l −1 in August. A mathematical model of a combination of multiplicative and Liebig types suggested that vegetative cells were severely limited in their growth rate, reaching almost 80% depression of the maximum rate between December and February by low temperatures and nearly 50% depression in warm seasons by light intensity. Nutrient limitations were only observed in May, August and September, although they were not as great as by temperature and light intensity in the study lake. Population changing rates of A.formosa determined in the lake were low and agreed well with the estimated growth rates during winter, but those in summer were low and disagreed with the estimated high growth rates. This suggests that population change of the species was highly dependent upon the specific growth rate in winter, but other factors became predominant in summer.