HR: 0830h
AN: B31C-0312    [PDF]
TI: Structure and Functioning of Phytoplankton Community of a Humic Lake Littoral Under Atmospheric Carbon Dioxide Enrichment
AU: * Ojala, A
EM: anne.ojala@helsinki.fi
AF: University of Helsinki, Lammi Biological Station, Paajarventie 320, Lammi, Ham FIN-16900 Finland
AU: Saarinen, T
EM: timo.saarinen@helsinki.fi
AF: University of Helsinki, Department of Ecology and Systematics, Division of Systematic Biology, P.O.Box 65, Helsinki, Uus FIN-00014 Finland
AU: Huotari, J
EM: jussi.huotari@helsinki.fi
AF: University of Helsinki, Department of Environmental and Ecological Sciences, Niemenkatu 73, Lahti, Ham FIN-15140 Finland
AU: Kairesalo, T
EM: timo.kairesalo@helsinki.fi
AF: University of Helsinki, Department of Environmental and Ecological Sciences, Niemenkatu 73, Lahti, Ham FIN-15140 Finland
AB: The flux of energy and carbon across the ecosystem can give an integrated measure of the whole-ecosystem response to environmental perturbation such as climate change. CLIMFRESH was an international, cooperative research project that focused on the response of lake ecosystems to increased atmospheric CO$_{2}$ concentration. The experimental set up where temperature was constantly kept $3\deg$C above the ambient was built in an experimental greenhouse (area ca. 550 m$^{2}$, volume ca. 1800 m$^{3}$) at Lammi Biological Station, southern Finland. The set up consisted of 4 experimental large-scale flow-through systems, which were each 7 m wide and 13 long with a water volume of ca. 65-70 m$^{3}$ and a retention time of 5-7 days. Each system had a very shallow littoral zone for emergent macrophytes and beyond that a zone for submerged plants with a maximum depth of ca. 1.5 m. The experiment was duplicated and two of the ponds were in the compartment with higher atmospheric CO$_{2}$ and two in the ambient CO$_{2}$ thus serving as controls. The target concentration of increased atmospheric CO$_{2}$ was 700 micromol mol$^{-1}$. Samples of water chemistry and on biological stock and process parameters were taken once a month throughout the three-year study period over the open-water period. Special interest was paid on studies on phytoplankton community and productivity. The results revealed that the exposure of the whole ecosystem to higher atmospheric CO$_{2}$ changed the phytoplankton community structure so that e.g. chrysophytes and cryptophytes were more abundant under higher CO$_{2}$ concentration. No clear changes in contribution of cyanobacteria were detected. There were time-dependent differences in N:P ratios of particulate matter so that in early summer the ratios were higher under exposure to extra CO$_{2}$. The same was true for N:P of inorganic nutrients as well as C:P ratios. These results indicate that climate change via increased atmospheric CO$_{2}$ concentrations can change the communities of planktonic primary producers in a way which can be reflected higher up in the food web.
DE: 0400 Biogeosciences
DE: 1615 Biogeochemical processes (4805)
DE: 1699 General or miscellaneous
DE: 1890 Wetlands
SC: Biogeosciences [B]
MN: 2003 Fall Meeting