Productivities of natural phytoplankton assemblages were significantly altered in passage through a cooling system of an electrical power station in mid-Chesapeake Bay, U.S.A. Carbon fixation in assemblages collected at the intake structure was significantly lower than rates noted at the discharge in June but significantly higher than rates observed at discharge in July through September. Productivity of a representative of the microflageUates, C1yptomonas acuta, was significantly reduced after passage through the plant (AT = 6 ° C) in July through September. Photosynthetic C incorporation rates for the dinoflagellate Prorocentrum mariae-lebouriae, the centric diatom Cyclotella caspia and the pennate diatom Thalassionema nitzschioides were not altered during entrainment. These data support previous observations of lower fixation rates and cell lysis in microflagellates than in more rigid diatoms following power plant entrainment.Water, Air, and Soil Pollution 21 (1984) 359-374. 0049-6979/84/0214-0359502.40.
Exponentially growing cultures of Thalassiosira fluviatilis Hustedt and Dunaliella tertiolecta Butcher were exposed to 4 min temperature shocks of 5° to 20°C above ambient (20°C). Photosynthetic carbon fixation, changes in in vivo fluorescence and fluorescence on the addition of the herbicide DCMU (3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea) were measured over the subsequent 24 h. The fluorescence ratio (R, DCMU‐enhanced fluorescence/in vivo fluorescence) paralleled changes in photosynthesis over this period; both were significantly reduced (P < 0.05) by temperature shocks of +15° and +20° C, but +5° and +10° C treatments had no inhibitory effect on either relative to the control. The instantaneous response obtained with the fluorescence ratio indicates that the technique might be applicable to routine bioassay procedures and thus replace the time consuming methods now used for the estimation of 14C‐incorporation and growth rates.
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