seuil d'apports admissibles

CONT: This section will consider the significance of these levels of chemical alterations, with emphasis on the levels of atmospheric input which can be viewed as having ""no effect"" on the most sensitive headwater streams and lakes. Evaluation of a ""no effect loading threshold"", or ""sustainable loading"" rate, which may yield moderate, but ""acceptable effects"", requires consideration not only of means pH trends, but also of the frequency and severity of brief periods during which much of the response to the loading dose may be expressed.