Qualité des eaux en bassins forestiers d'alimentation

Abstract

The characteristics of both subsurface and surface water resources are altered by human activities carried out within their catchment area. Forested areas give rise to water resource characteristics that may or may not be consistent with the demands of those responsible for managing these resources. Nitrate content is one of those characteristics. Beneath forest canopies, during the growth period when no felling is performed, nitrate contents of the water drained from these areas are low. Historical data pertaining to the Lorraine area give the mean value as being 4.2 mg NO3YI. No significant variation was observed in connection with the type of canopy involved, whether deciduous or coniferous. In catchment areas that support both forestry and farming activities, the proportion of forested land affects the degrees of freedom that can be allowed to agriculture to avoid deteriorating the water resource in the basin. A study on 33 agricultural and forestry basins in Lorraine that began in 1989, shows a critical value of approximately 35 % forests for the catchment area that is consistent with the "co-production" of drinking water, considering farming practices in the Lorraine agricultural systems at the close of the century. A deterioration in terms of nitrate content is observed under forest canopies where clear felling is practiced.