|
(T/EH026) Comparison of two methods of quantitative and qualitative identification of phytoplankton in aquatic outdoor mesocosms. Ebke, K.-P.1, Börgel, C.1, Farrelly, E.2, Neugebaur-Büchler, K.3, Mitchell, G.C.4, 1 2 3 4 ABSTRACT- Two complementary methods were used to determine phytoplankton populations in an outdoor enclosure study conducted. Depth integrated water samples from the enclosures were taken and split into two subsamples. One subsample was fixed with Lugols and subsequently identified and enumerated using an invert microscope, and the other subsample analysed within hours using delayed fluorescence excitation spectroscopy (DF). DF-excitation spectroscopy is a novel technique to quantitatively estimate phytoplankton composition of freshwaters by determining photosynthetic activity in living cells. A deconvolution programme separates the detector output into algal groups each of which produce different excitation spectra. The four groups are Green algae (chlorophyceae, euglenophyceae, conjugatophyceae), Blue-green algae (cyanophyceae), Cryptophyta and Diatoms (bacillariophyceae, chrysophyceae, dinophyta, xanthophyceae). In addition calibration of the detector enables quantitative determination of pigment levels. Taxonomic data produced using invert microscope were compared with those generated using DF excitation spectroscopy and good correlation between the techniques was clearly demonstrated during the study. DF-excitation spectroscopy has the potential to provide quick and accurate quantitative and qualitative estimates of changes in phytoplankton population and composition. Key words: Phytoplankton, delayed fluorescence, mesocosm, chlorophyll |
