Long-term nitrate concentrations in four perialpine lakes: regional coherence and the effects of climate change

摘要

Climate change is expected to result in increasing stress on aquatic ecosystems (Straile et al. 2003). Observations over the last few decades indicate the climate in much of Europe, especially in winter, has been undergoing change, with an increase in the frequency of unusually mild winters. These mild winters are thought to be associated with positive anomalies of the North Atlantic Oscillation (NAO; Hur-rell 1995). The NAO, which represents a large-scale fluctuation in the air pressure difference between the subtropical Azores High and the subpolar Iceland Low, is commonly quantified in terms of an index based on meridional surface air pressure differences over the North Atlantic (Hurrell 1995). Strong positive values of this index are associated with westerly winds and mild, wet winters over most of Europe, whereas negative values are associated with weak westerlies and cold, dry winters in Europe.