Effects of heavy metals (Cd, Hg) on periphytic diatom communities using artificial substrates in microcosms

The toxic effects of two metals (cadmium and mercury, as methylmercury) were studied on the periphytic compartment of experimental systems in association with a biotope made of two components - water column / natural sediment containing different aquatic species (plants, molluscs). Different conditions of contamination were studied in the protocols of the experiment with special attention given to the levels of exposure (several concentrations) and the initial source of contamination (water column or sediment). The equipment available enabled the measurement and control of the main environmental factors : temperature, photoperiode, luminous intensity, pH. The periphyton, essentially composed of diatoms, was allowed to grow on artificial substrata (glass slides) then collected after two periods of experimentation, 30 days (t1) and 72 days (t2). The disturbance generated on the periphyton by the contaminators is analysed in terms of population structure, density of population and the dynamics of evolution of the communities according to the condition under study (nature of the contaminators, concentration, contamination sources). During the experimentation, about 150 taxa were identified. Some of them, which are particularly interesting are here described.