Production of Benthic Microalgae in the Littoral Zone of a Eutrophic Lake

Abstract

Primary production by benthic microalgae of the sandy littoral zone in a Danish eutrophic lake, Fures0, was measured by means of the 14C method. Annual potential gross production was calculated as 297 g C m-2, with highest values in July (2,200 mg C m-2 day-'). Annual true gross production was estimated to be 143 g C m-2. Dark fixation was always relatively high (3-6 per cent). Sessile algae accounted for the bulk of primary production (70-90 per cent). Algae were mainly pennate diatoms. Diatoms with intact chromatophores were found down to a depth of 10 cm in the sediment. When cells from the anaerobic zone were brought into light, photosynthesis started immediately. During summer, the Ik-value was 9-10 klux, while the autumn population had a lower value (3-5 klux). Photoinhibition was demonstrated for the latter population at light intensities exceeding 25-30 klux. It seems to be characteristic for benthic algae, that light saturated photosynthesis takes place over a wide range of light intensities. Populations of benthic sessile diatoms appear to be rather stable.