Study of periphytic diatoms communities exposed to metallic contamination through complementary field and laboratory experiments

Abstract
Periphytic diatom communities are important primary producers in streams where their characteristics are influenced by many environmental factors. To study and cut off real effects of metal pollution (Cd, Zn) on these communities, complementary experiments were performed in order to precise short term effects of pollution during a four weeks colonization process. Early stage of diatom communities exposed to pollution was studied first in outdoor artificial streams connected to a subsystem of the Lot river (SW France), characterized by a polymetallic gradient. Colonization of glass substrates was followed each week in three sites contaminated between 0 to 10  g Cd.L ^-1. In a second step, an experiment was conducted into indoor artificial streams inseminated with homogenized periphyton suspension of the reference stream in situ. Initial development of communities was followed on glass substrates too and collected after two and four weeks of Cadmium exposure to three different metallic concentrations (control in laboratory, 10  g Cd.L ^-1 and 100  g Cd.L ^-1). Structure of diatom corrurtunities was assessed by studying density and taxonomie composition. Results of the different approaches are compared and point out marked effects of metallic pollution with clear decrease of diatom global density and perturbation of species composition.