A SIMPLE-MODEL OF REGIONAL ACIDIFICATION FOR HIGH-MOUNTAIN LAKES - APPLICATION TO THE PYRENEAN LAKES (NORTHEAST SPAIN)

In a sample of 102 lakes in the Pyrenees, 68% were sensitive to acidif ication in varying degrees. A model which describes the regional alkal inity distribution by using random variables to represent lake alkalin ity, chemical weathering and biological alkalinity generation, is prop osed to calculate the alkalinity loss due to acid deposition, and the critical and target acid loads. This model is kept simple to reduce th e input requirements and make the calibration procedures feasible on a regional scale. The relative simplicity of high mountain catchments l ying above the tree line, in particular the lack of well developed soi ls, makes such a model appropriate for these environments. The loss in alkalinity since the start of large scale industrial emissions was es timated to be 35 mu eq l(-1) on average. Assuming a scenario of increa sing nitrogen deposition, we estimate that a critical level of 10% of lakes with alkalinities below 20 mu eq l(-1) would be reached for a ni trogen deposition of 70-75 mu eq l(-1). According to the model, a 50% reduction of both nitrogen and sulphur deposition would be necessary t o ensure that all lakes are above the critical level. (C) 1998 Elsevie r Science Ltd. All rights reserved.