Microbial activities and chemical gradients in the chemocline of a meromictic lake in relation to the precision of the sampling procedure

Abstract

The dark CO2 fixation rate, and sulfide and oxygen concentrations, were measured in the chemocline of the eutrophic, meromictic lake Saelenvannet in Western Norway. Sulfide and oxygen coexisted at a depth of 4–5 m in a narrow layer, only 2.5–10 cm wide. Coexistence of oxygen and sulfide coincided with an increase in the rate of dark CO2 fixation. Maximal potential for light-dependent CO2 fixation was found 2.5 cm below the sulfide and oxygen coexistence region. Our results demonstrate that a number of conventional sampling techniques are unsuitable for the study of such interfaces, and that very precise sampling techniques are needed to measure the chemical gradients and biological processes taking place in the chemocline of shallow meromictic lakes.