Impact potentiel du flottage du bois sur le milieu aquatique

Some aspects are discussed of the consequences of logging operations on natural waters. The release into the aquatic environment of certain types of organic substances from logs can result in an increase in the colour and odour of the water. It appears that bark in particular is responsible for the deterioration of the water quality. Factors such as age and species of the tree and the environmental conditions of the water do mainly determine the nature and effectiveness of the microbial degradation of the tree trunk. Different constituents such as simple sugars, polysaccharides, cellulose, hemicellulose, pectins, lignins, amino acids, peptides, proteins, fatty and other organic acids, as well as phenols can, each to a different degree, be degraded by various types of microbes, in particular by fungi. Substances liberated from the bark and the wood, as well as their products of degradation could exert a stress on several types of organisms in the aquatic environment. Although no specific case of acute toxicity has as yet been reported, some laboratory studies have indicated sub-lethal effects involving fish (blockage of their respiratory system), fish eggs (reduction in the number of hatchings) and algae (reduction in growth rate). In certain instances these effects could be ascribed either to the presence of toxic organic substances or to low oxygen levels.