MELIMEX,an experimental heavy metal pollution study: Effects of increased heavy metal load on uptake of glucose by natural planctonic communities

Glucose uptake in lake water samples has been determined with short-time¹⁴C-experiments at different additions of the single heavy metals Cu⁺⁺, Zn⁺⁺, Cd⁺⁺, Pb⁺⁺, Hg⁺⁺ and at different additions of a combination of all metals. The degree of a metal induced inhibition of glucose uptake varied from lake to lake and from season to season, whereby the addition of legally tolerated concentrations of 10 μg Cu/l and 200 μg Zn/l inhibited glucose uptake in most samples significantly, as well as the simultaneous addition of all metals. The legally tolerated limit of 1 μg Hg/l inhibited glucose uptake in Lake Lucerne samples almost completely, showed however no effect in samples of Lake Baldegg. The equimolar toxicity sequence of heavy metals for heterotrophic microorganisms has been determined as: Hg>Cu>Cd>(Zn. Pb). Glucose uptake of plankton sampled from metal polluted limno-corrals was less inhibited than that of the control plankton, when heavy metals were added to the samples singly or in combination. It is assumed that this effect is due to the natural selection of more resistant plankton species.