The North Atlantic Oscillation and plankton dynamics in two European lakes- two variations on a general theme

Long-term data on water temperature, phytoplankton biovolume, Bosmina and D aphnia abundance and the timing of the clear-water phase were compared and analysed with respect to the influence of the North Atlantic Oscillation (N AO) in two strongly contrasting lakes in central Europe. In small, shallow, hypertrophic Muggelsee, spring water temperatures and Daphnia abundance bo th increased more rapidly than in large, deep, meso/oligotrophic Lake Const ance. Because of this, the clear-water phase commenced approximately three weeks earlier in Muggelsee than in Lake Constance. In Muggelsee, the phytop lankton biovolume during late winter/early spring was related to the NAO in dex. In Lake Constance, where phytoplankton growth was inhibited by intense downward mixing during all years studied, this was not the case. However, in both lakes, interannual variability in water temperature, in Daphnia spr ing population dynamics and in the timing of the clear-water phase, were al l related to the interannual variability of the NAO index. The Daphnia spri ng population dynamics and the timing of the clear-water phase appear to be synchronized by the NAO despite large differences between the lakes in mor phometry, trophic status and hushing and mixis regimes, and despite the gre at distance between the lakes (similar to 700 km). This suggests that a gre at variety of lakes in central Europe may possibly have exhibited similar i nterannual variability during the last 20 years.