Influence of atmospheric modes of variability on the limnological characteristics of large lakes south of the Alps: a new emerging paradigm

Winter air and spring surface water temperatures, spring epilimnetic phosphorus and hypolimnetic oxygen in the deep lakes south of the Alps (Garda, Iseo, Como, Lugano and Maggiore) showed a high degree of temporal coherence. The common temporal patterns were originating from the effects caused by winter climate, and from corresponding synchronisms in the interannual variations in the extent of the spring water renewal and replenishment of nutrients. In turn, the sequence of linked causal events was triggered by two atmospheric modes of variability relevant for the Mediterranean region, i.e. the East Atlantic pattern (EA) and the Eastern Mediterranean Pattern (EMP). The relationships between the North Atlantic Oscillation and the air and water temperatures were undetectable. In oligotrophic lakes, which were characterised by weak vertical nutrient gradients, the effects of the spring replenishment of P were negligible and difficult to detect (Maggiore), or detectable but of minor importance (Garda and Como) compared to those measured in more enriched lakes (Iseo and Lugano). The range of applicability of EA and EMP in the study of the impact of climate on aquatic ecosystems will require to be tested by expanding the number, typology and geographical location of water bodies in the Mediterranean region.