Water level as the mediator between climate change and phytoplankton composition in a large shallow temperate lake

We studied the effect of water level changes in Lake Võrtsjärv (270 km2, mean depth 2.8 m) on the abundance and composition of phytoplankton based on a 35-year database. Analysis of long time-series (since 1884) revealed a strong influence of the North Atlantic Oscillation on the water level in this lake. The registered maximum range of water level in L. Võrtsjärv is 3.2 m, which corresponds to 1.4 times difference in the lake area, 2.5 times difference in the mean depth and 3.5 times difference in volume. Cyanobacteria build up 2/3 of the average phytoplankton biomass during the ice-free period (May–October). On average 75% of the cyanophyte biomass is formed by four filamentous species. Centric diatoms from the genera Aulacoseira and Cyclotella dominate in the biomass of diatoms. Phytoplankton biomass was significantly lower in years of high water level and the changes were unrelated to nutrient loading. The share of filamentous blue-greens among phytoplankton followed the changes in the water level while there was a succession of dominants. Planktolyngbya limnetica reached its maximum in the low water period in the middle of the 1970s. Limnothrix redekei and L. planktonica started to dominate in the high water period in the 1980s while the total biomass decreased substantially in spite of high nutrient loading. During the low water period in the 1990s, the role of the nitrogen-fixing species Aphanizomenon skujae increased. The succession was caused by changes in light and nutrient availability in the fully mixed environment. As low light species, filamentous Limnothrix spp. were most successful in competition for light and phosphorus in deeper water while A. skujae was favoured by high light intensities and a low N/P ratio in shallow water.

[1]  Gordon A. Riley,et al.  Phytoplankton of the North Central Sargasso Sea, 1950–521 , 1957 .

[2]  U. Cubasch,et al.  The North Atlantic Oscillation as an indicator for greenhouse-gas induced regional climate change , 1999 .

[3]  J. Hurrell,et al.  The North Atlantic Oscillation , 2001, Science.

[4]  J. Hurrell.  Decadal Trends in the North Atlantic Oscillation: Regional Temperatures and Precipitation , 1995, Science.

[5]  H. Utermöhl.  Zur Vervollkommnung der quantitativen Phytoplankton-Methodik , 1958 .

[6]  Thomas L. Crisman,et al.  The role of water-level fluctuations in shallow lake ecosystems – workshop conclusions , 2003, Hydrobiologia.

[7]  L. Edler,et al.  Recommendations on methods for marine biological studies in the Baltic Sea. Phytoplankton and chlorophyll , 1979 .

[8]  D. G. George,et al.  Factors influencing the temporal coherence of five lakes in the English Lake District , 2000 .

[9]  M. Scheffer.  Ecology of Shallow Lakes , 1997, Population and Community Biology Series.

[10]  Frank H. Quinn,et al.  POTENTIAL EFFECTS OF CLIMATE CHANGES ON AQUATIC SYSTEMS: LAURENTIAN GREAT LAKES AND PRECAMBRIAN SHIELD REGION , 1997 .

[11]  Judit Padisák,et al.  Shallow lakes: the absolute, the relative, the functional and the pragmatic , 2003, Hydrobiologia.

[12]  The North Atlantic Oscillation: an enigmatic see-saw , 2000 .

[13]  C. Gibson,et al.  Photosynthetic characteristics of planktonic blue-green algae: Changes in photosynthetic capacity and pigmentation of Oscillatoria redekei van Goor under high and low light , 1982 .

[14]  M. Meffert.  In situ and in vitro photosynthesis of Limnothrix redekei (Cyanophyta) , 1989 .

[15]  C. Gibson.  The phytoplankton populations of Lough Neagh , 1993 .

[16]  D. Harbour,et al.  North Atlantic Oscillation and spring bloom phytoplankton composition in the English Channel , 2000 .

[17]  AFF1Tiina Nõges,et al.  The effect of extreme water level decrease on hydrochemistry and phytoplankton in a shallow eutrophic lake , 1999, Hydrobiologia.

[18]  T. Nõges,et al.  The Influence of Different Solvents and Extraction Regimes on the Recovery of Chlorophyll a from Freshwater Phytoplankton , 2000 .