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|Title:||Increased nutrient loading and rapid changes in phytoplankton expected with climate change in stratified South European lakes: sensitivity of lakes with different trophic state and catchment properties|
|Authors:||NOGES Peeter; NOGES Tiina; GHIANI Michela; SENA Fabrizio; FRESNER Roswitha; FRIEDL Maria; MILDNER Johanna|
|Citation:||HYDROBIOLOGIA vol. 667 no. 1 p. 255-270|
|Type:||Articles in Journals|
|Abstract:||Within two years of contrasting temperature and precipitation regime, 2008 and 2009, we observed weekly the nutrient concentrations and phytoplankton development in two adjacent stratified lakes in northern Italy, the oligo-mesotrophic Lake Monate (2.5 km2, max. depth 34 m) and the eutrophic Lake Varese (14.8 km2, 26 m). The winter 2008-2009 was cold and wet followed by a wet spring. A heat wave starting in May turned the whole year 2009 the second hottest after 2003. We expected a deterioration of the ecological status of both lakes due to the supposed increase of nutrient loadings in spring and enhanced growing conditions for cyanobacteria in the eutrophic lake. In 2009 the hypolimnia of both lakes remained colder and the epilimnia became warmer compared to 2008. Dissolved oxygen concentrations were higher in colder hypolimnia in 2009. We observed a general increase in nutrient (N, P, Si) concentrations and a decrease of the N/P ratio in both lakes from 2008 to 2009. Inorganic P concentration in the hypolimnia in both lakes in November-December was positively related to bottom temperature showing a temperature coefficient (Q10) equal to 2.4. Chlorophyll a concentration increased from 2008 to 2009 in L. Monate, especially in the metalimnion, but dropped highly significantly in L. Varese. The Si limitation ceased in 2009 enabling an increase of the diatom biovolumes in spring in both lakes. In L. Monate there was no change in dominant species, but a three-fold increase in the annual maximum total biovolume. In L. Varese no cyanobacteria bloom occurred in 2009 and instead the dinoflagellate Ceratium furcoides, obviously flushed into the lake from an upstream lake, became a new dominant while the total phytoplankton biovolume decreased. The German multimetric Phyto-Lake-Index showed an increase in the trophic state in both lakes. The projected increase of winter precipitation in southern Europe is likely to increase the nutrient loadings to lakes and contribute to their eutrophication. Intense flushing of water bodies in spring in combination with the increasing thermal stability in summer may cause rapid and unexpected changes in phytoplankton abundance and community structure.|
|JRC Institute:||Institute for Environment and Sustainability|
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