Summary of experimental results

The light absorbing capacity of phytoplankton, estimated from Fo, and its photosynthetic activity (estimated as Fv/Fm) are key characteristics of the primary processes of photosynthesis. We suggested a formula for calculation of the primary production of phytoplankton from these two characteristics and underwater irradiance. The probing data were used to plot vertical profiles of phytoplankton productivity in various regions of the Baltic, Norwegian, and South China Seas. The data obtained correlated with production values measured in parallel experiments with oxygen and radiocarbon methods (see Antal et al., 2001).

Investigation of a depth profile from the South extremity of the Sardinia Island along the shore of Sicily up to the Straight of Messina (60 km) (Tyrrhenian sea) revealed a zone of the upwelling of cold depth water enriched in mineral nutrients, characterized by an increased abundance and photosynthetic activity of phytoplankton (see figures).

In Norwegian Sea, meso- and micro-scale whirls were found to form in the mixing zone of North Atlantic Stream with depth water of the Norwegian Sea, which was characterized by enhanced photosynthetic activity and a low abundance of algae, which, taking in account of the number of the young population Calanus, indicated initiation of new phytoplankton populations in the whirl zones (see figures). These examples show the potentialities of the use of the submersible fluorometer in studies of the dynamic characteristics of aquatic systems.

Studies of the seasonl changes in phytoplankton in the Baikal Sea and Nhatrang Bay of the South China Sea showed that algal bloom was preceeded by a phase of enhanced phytoplankton activity, whereas the autumn depression of algae was accompanied by parallel decrease in their abundance and activity (see figures).

Investigation of dial changes in phytoplankton in Norwegian, Baltic, and Black Seas showed that the midday depression of phytoplankton activity near the surface was characterized by simultaneous decrease in its abundance and photosynthetic activity (see figures).

Investigation of the vertical distribution of phytoplankton in oligotrophic Issyk-Kul Lake showed a complex structure of phytoplankton population, which is due to pronounced water stratification. The lowest values of the abundance and photosynthetic activity were found in the upper layer under conditions of a high solar irradiation and low content of mineral nutrients. Low abundance and high activity of algal cells was found in the deep layers of the photic zone, which indicated the presence of a population of active algae, adapted to low light conditions (see figures). The similar data were obtained for oligotrophic regions of the South China Sea.

Biological monitoring of the effects of pollution on algal populations in natural water bodies and estimation of the limits of this effect and environment quality is an important problem. Probing of phytoplankton in the Baikal Lake near a discharge of industrial waste water clearly showed decrease in phytoplankton abundance (see figures).

However, investigation of phytoplankton in the Moscow River within urban area showed marked decrease in the photosynthetic activity near places of industrial sewage release, which was not accompanied by changes in the abundance of algae (see figures). A decrease in the photosynthetic activity without changes in the abundance of phytoplankton was also found in some bays of the Issyk-Kul Lake which were characterized by the presence of some heavy metals (Zn, Cd) at the maximum permissible levels (see figures). These data show that water pollution can be detected under conditions in which algal concentration does not yet decrease markedly, for example, at early stages of pollution or under low concentration of pollutants.

Detection of zones with increased content of mineral nutrients is of great importance for oligotrophic water bodies, particularly, in recreation and touring zones. Our studies in the Issyk-Kul Lake showed that, indeed, phytoplankton abundance and activity can be used as indicators water purity. For example, the highest values of phytoplankton abundance and photosynthetic activity were found in shore regions, particularly, near large tributaries rich in terrigenous elements (see figures).