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JOURNAL OF PLANKTON RESEARCH | VOLUME 18 | NUMBER 7 | PAGES 1201-1211 | 1996
© Oxford University Press

research-article

Production of dissolved organic carbon in phyloplankton cultures as measured by high-temperature catalytic oxidation and ultraviolet photo-oxidation methods

Wenhao Chen and Peter J. Wangersky1,2

Department of Oceanography, Dalhousie University Halifax, Nova Scotia, B3H 4J1, Canada 1Present address: School of Earth and Ocean Sciences, University of Victoria PO Box 1700, Victoria, BC, V8W 2Y2, Canada

2To whom correspondence should be addressed

Received on August 15, 1995; accepted on February 12, 1996 The production of dissolved organic carbon (DOC) in cultures of the diatoms Chaetoceros gracilis and Phaeodactylum tricornutum, the flagellate Isochrysis galbana, the dinoflagellate Alexandrium tamarense and a natural algal assemblage from the Northwest Arm, Halifax, Nova Scotia, Canada, was followed using a high-temperature catalytic oxidation (HTCO) and a UV photo-oxidation method. Molecular weight fractionation of the DOC was performed for two cultures: C.gracilis and I.galbana. While the DOC in the culture medium increased significantly during log-phase growth for all organisms except the dinoflagellate, this increase was proportional to the increase in cell numbers; the increase in DOC per cell was either small or zero. In all cultures, maximum release took place during stationary and senescent phases, usually after cell numbers had started to decrease. In both C.gracilis and I.galbana, a major portion (>65%) of the organic matter released to the medium during log-phase growth had mol. wts of <10 000 Da. The increase in DOC in the I.galbana culture in stationary and senescent phases was due to the release of high-molecular-weight materials. The differences in extracellular release of DOC between species and between different growth stages in the same species suggest that both the species composition and physiological state of phytoplankton populations must be known before interpretations and predictions based on field data can be made. In order to determine whether the differences in DOC values found by the HTCO and UV oxidation methods are caused by the resistance to UV oxidation of some compounds produced by phytoplankton, rather than by less than optimum efficiency of the UV unit used, standards must be based on naturally occurring compounds, rather than the pure compounds normally used.


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