Evidence of Springwater Acidification in the Vosges Mountains (North-East of France): Influence of Bedrock Buffering Capacity

Investigations on springwater acidity were carried out in the Vosges mountains (north-eastern France). Acid or poorly buffered spring and streamwaters were detected in the same area. The proportion of acid springwaters (pH < 5.6) is about 20% among 220 springs. The springwater pH on granite are equally spread between 5.0 and 6.8 whereas on sandstone a majority of springs is in the range 5.6 to 6.2. As a whole, but mainly on sandstone, from the 1960's to 1990's, the shape of the pH distributions shifts toward greater acidity. In the sandstone area, trends in pH, alkalinity, total hardness (corresponding to divalent cations), sulfate and nitrate were considered over the 30 yr period (1963-1996) in relation to the bedrock chemical composition. Kendall seasonal tau coefficients indicate that decreasing trends were significant for the first three parameters. Linear regression on the smoothed mean value revealed 18 and 90% decrease for pH and alkalinity respectively, for springwaters draining poor-base cation sandstone whereas only 8 and 30% decrease respectively, was observed on clay-enriched sandstone. On silica-enriched sandstone, alkalinity began to decrease in the early 70's as well as pH. Loss of alkalinity only occurred in the early 80's for springs draining clay enriched sandstone. This can be interpreted as a titration process by acid atmospheric inputs of the buffering capacity of weathering and exchange processes in the soils and the catchment bedrock. The nitrate presents an increasing step in the early seventies but possibly as a result of change in analytical technics and/or increase in atmospheric inputs mainly resulting from increase in fertiliser inputs in agricultural areas or in car traffic. Surprisingly no change in sulfate was noticed in any groups of springs probably as a result of the adsorption/mobilisation in the soils. These long-term trends in spring waters (1963-1996) confirmed the soil and streamwater acidification trends already mentioned in this region, in relation to acid atmospheric inputs since no climate nor forestry practice changes have been detected over the period. Moreover, in spite of acid atmospheric input reductions, no recovery can presently be detected

Enhanced pavlovian aversive conditioning to positive emotional stimuli

Pavlovian aversive conditioning is an evolutionarily well-conserved adaptation enabling organisms to learn to associate environmental stimuli with biologically aversive events. However, mechanisms underlying preferential (or enhanced) Pavlovian aversive conditioning remain unclear. Previous research has suggested that only specific stimuli that have threatened survival across evolution (e.g., snakes and angry faces) are preferentially conditioned to threat. Here, we challenge this view by showing that positive stimuli with biological relevance (baby faces and erotic stimuli) are likewise readily associated with an aversive event (electric stimulation) during Pavlovian aversive conditioning, thereby reflecting a learning bias to these stimuli. Across three experiments, our results reveal an enhanced persistence of the conditioned response to both threat-relevant and positive relevant stimuli compared with the conditioned response to neutral stimuli. These findings support the existence of a general mechanism underlying preferential Pavlovian aversive conditioning that is shared across negative and positive stimuli with high relevance to the organism and provide new insights into the basic mechanisms underlying emotional learning in humans