Cryptogamie, Algologie
29 (3) - Pages 201-216We investigated the changes undergone by natural photosynthetic biofilms under metal exposure through field studies conducted on mature biofilms collected along gradients of organic and metal (cadmium, zinc) contaminations in the Decazeville watershed, South-West France. Biofilms grown under high nutrient conditions were as thick and dense with or without metal contamination. It suggested that the organic matrix acts like a barrier against deleterious effects of metals on diatom assemblages through various mechanisms: (i) gradients limiting metal diffusion in the inner parts of the biofilms, (ii) increased mortality of superficial cells creating a thin protective layer, and (iii) production of high amounts of metal-complexing exopolysaccharides by the constitutive microflora of the biofilms.