Chlorophyll degradation in Lake Kinneret. Joint German-Israeli Research Project Final scientific report

Application of a high performance liquid chromatography (HPLC) method for analysis of pigments permitted the identification and quantification of chlorophylll degradation products in Lake Kinneret. Chlorophylle a was the major detectable degradation product of chlorophyll a varying between 1 and 9% of the chlorophyll a concentration, whereas phaeophytin was virtually lacking in the water column. Removal rate of pigments, estimated from analyses of pigment variations within sedimentation traps, indicated that the degradation of chlorophyll a via chlorophylle a is a dynamic process that continues during the sedimentation of the phytoplankton particles. Despite the fact that a significant signal of chlorophyllide a coexisted with the annual bloom of Peridinium, laboratory experiments failed to show in vitro chlorophyllase activity in this dinoflagellate. Only under extreme conditions of stationary phase culture and high temperatures, residual in vitro activities were observed, resulting in a chlorophyll a to chlorophyllide a ratio corresponding to the value measured in the lake water upon the collapse of the Peridinium bloom. Other phytoplankton species which represent various components of the lake population were examined for their in vitro chlorophyllase activity. Based on these experiments several species were defined as a potential source for chlorophyllase activity. Thus we postulated a chlorophyll degradation process which is based on interspecies interaction. Interestingly, the in vitro experimental system clearly indicated a reduction in chlorophyll a with disproportional increase in the concentration of chlorophyllide a and/or other chlorophyll a fluorescing derivatives. Multi-enzyme degradation processes with end products that do not fluoresce can be proposed to explain these results. However other degradation processes other than the hydrolysis of the phytol chain from a chlorophyll a molecule, should not be excluded. An excitation delayed fluorescence (DF) spectrometer was designed and manufactured to estimate the activity of the phytoplankton and its population composition. The instrument was first evaluated and examined by measuring controlled laboratory cultures and then was applied for in situ measurements of the phytoplankton populations in Lake Kinneret. It was possible to distinguish between major phytoplankton components using DF spectra as analytical signature. Furthermore DF spectra could provide good estimation on the relative abundance of the specific components of the phytoplankton assemblage. The DF intensity was positively correlated with the primary productivity at the depth of chlorophyll maxima, indicating that DF intensity may be used as a rapid probe to estimate aquatic productivity. (orig.)SIGLEAvailable from TIB Hannover: RR 9803(97,3) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany); Ministry of Science and Technology, Jerusalem (Israel); GSF -Forschungszentrum fuer Umwelt und Gesundheit GmbH, Neuherberg (Germany)DEGerman