Critical loads of acidity to surface waters in the Vosges massif (north-east of France)
Résumé
Acid clearwater fishless streams have been identified in the Vosges mountains. In order to evaluate the relationships between acidifying factors (such as atmospheric deposition), buffering factors (such as bedrock and soil type), and surface water acidity, an exhaustive survey of streamwater acidity in the Vosges mountains (N-E France) was performed. A network of 11 measurement stations of atmospheric deposition was used to estimate and map deposition over the whole massif (total area, #5000 km2). Data on bedrock, soil, superficial deposits, and vegetation were collected from published studies. Sensitive areas as well as acidifying environment factors were derived from the corresponding maps. Over the whole massif, 19% of streams showed baseflow alkalinity below 30 µeq.l-1 and 7.5 % were identified as acid (pH < 5.4). Acid streams occur on the north-westem side of the massif on quartz rich sandstone and acid granites. In each of these areas, we could clearly point out on one hand, the negative influence of conifer vegetation and glacial soil abrasion or induration, and on the other band the buffering effect of moraine deposits. A corresponding range of critical loads (< 0.2 to 2.0 Keq. ha-1.yr-1 ) for surface water was calculated using the Steady State Water Chemistry method (SSWC).