The spring development of phytoplankton in Lake Erken: species composition, biomass, primary production and nutrient conditions — a review

Abstract

In Lake Erken climatic factors such as duration of ice cover, snow-depth and insolation govern the phytoplankton development and the species composition during the spring, with significant variations from year to year.

Generally the small diatom, Stephanodiscus hantzschii var. pusillus creates a conspicuous peak at ice-break. In some years motile dinoflagellates start to develop under the ice already in early March, which results in a much longer spring bloom.

The highest biomasses were recorded in 1954–1955 with values up to 11 mg 1^-1 of fresh weight. The chlorophyll a concentrations have at most reached an epilimnetic average of 30 μg 1^-1.

The primary production reached a maximum value of 2200 mg C m^-2 d^-1 in 1955 and the average production for two months during the spring varied from 30 to 64 mg C m^-3 d^-1.

Concerning nutrients, phosphorus was shown to be the limiting nutrient at the end of the spring bloom. This fact was confirmed by orthophosphate concentrations, algal surplus phosphorus content and alkaline phosphatase activity, as well as estimations of inorganic N: P and C: P ratios and nutrient enrichment experiments.