Strong dependence between phytoplankton and water chemistry in a large temperate lake: spatial and temporal perspective
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In lakes, spatial and temporal variability of water chemistry and phytoplankton are characteristic phenomena although often difficult to link together. This motivated us to study their interplay in Lake Vanajanselkä, a eutrophic lake in Finland. We hypothesized that in summer spatial and temporal differences in phytoplankton and water chemistry can be extended in comparison to spring and autumn. Therefore, chlorophyll a and water chemistry was examined by six sampling campaigns with 15 sampling sites over the lake in May–October 2009–2010. In summer, chlorophyll, pH, and oxygen were horizontally and vertically unevenly distributed in the lake, and in the epilimnion pH and oxygen showed a distinct diurnal variability suggesting high photosynthesis during the day. Daily >1 pH unit difference between the sites and 2.5 pH unit difference between the epi- and hypolimnion were found. In agreement with pH and oxygen, NO3-N and NH4-N could be unevenly distributed in the epilimnion. In autumn no spatial differences were found, however. The results emphasized that algae and cyanobacteria were responsible, at least partly, for the variability in water chemistry in the surface layer, and short- and long-term gradients in space and time need to be considered when productive lakes are studied.
KeywordsSpatial variability Temporal variability Chemistry Phytoplankton
We want to thank the field group from the Department of Physics and Lammi Biological Station (LBS) of the University of Helsinki (Kirsi Arvola, Mikko Heini, Jarmo Hinkkala, Elina Jaatinen, Ruibo Lei, John Loehr, Pertti Saaristo, Jussi Vilén and Yu Yang), and the laboratory technicians of LBS for the chemical measurements and determinations. The work was supported by the YMPANA research project (Development of a lake monitoring station). YMPANA was a part of the YMLI project and funded by the European Structural Fund Programmes (2008–2011). This work is also partly (Anniina Heini) supported by the Finnish Cultural Foundation, Häme Regional Fund. The Centre for Economic Development, Transport and the Environment of Häme provided logistic support during the study. We also thank Dr. John Loehr for his English corrections and comments on the manuscript.
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