SS3.09 Climate-Lake Interactions
Date: Wednesday, June 12, 2002
Time: 10:15:00 AM
Location: Colwood
 
NõgesT, Institute of Zoology and Botany at the Estonian Agricultural University, Tartu County, Estonia, tnoges@zbi.ee
Nõges, P, , Institute of Zoology and Hydrobiology of University of Tartu, Tartu, Estonia, tnoges@zbi.ee
 
NORTH ATLANTIC OSCILLATION AFFECTS WATER LEVELS AND PHYTOPLANKTON IN LARGE SHALLOW TEMPERATE LAKES
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Periodicities in lake water level (WL) changes with spectral frequency maxima at 6-7 and 24-32 years have been reported from many of the large lakes in N-W Russia, Estonia, South Finland and North Germany. Smoothed WL changes in large shallow lakes Peipsi (Estonia/Russia, 3555 km2, mean depth 7.1 m) and Võrtsjärv (Estonia, 270 km2, mean depth 2.8 m) in 1885-2000 were in good accordance with changes in the North Atlantic Oscillation (NAO) index for winter. In L. Võrtsjärv where the annual amplitude of WL is 1.4 m and the absolute range is 3.2 m, hydrology is the main driving force for the ecosystem. Control of phytoplankton growth is mediated through ice conditions in winter and through WL in summer. The direct impact of winter conditions is restricted to a short postwinter period, the indirect influence is prolonged through the relationship with the mean depth of the lake. In deeper L. Peipsi the influence of WL on the ecosystem is less pronounced. This research was supported by ESF grant 4080, and by the EU projects ECOFRAME and MANTRA-East (EVK1-CT-1999-39 & EVK1-CT-2000-00076).