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Seasonal dynamics of phytoplankton in the inner Neva Estuary in the 1980s and 1990s

Nikulina V. N.

Oceanologia

2003

No. 45 (1)

25-39

The phytoplankton in the inner Neva Estuary is described from data obtained from 1996 to 2000. The seasonal dynamics of the phytoplankton biomass are characterized by a bimodal curve with a summer maximum. The average seasonal biomass was approximately 3 mg l-1, the maximum biomass was 8-11 mg l-1. The species composition and quantitative parameters were compared to those observed in the 1980s. A notable, nearly 1.5-2 fold, increase in the biomass in the summer-autumn period and the predominance of Oscillatoria species among the blue-green algae were observed. A decline in the nutrient load in the water body at the end of the 1990s appeared to be insufficient to bring about a decrease in the proportion of Oscillatoria algae in the total species composition or a decline in the biomass of the entire phytoplankton community. In 2000 a certain change in the structural composition of the phytoplankton complex was noted. Species that had been predominant in the 1980s and had lost their advantage in the early 1990s, regained their earlier status.

Functional response of midsummer planktonic and benthic communities in the Neva Estuary (eastern Gulf of Finland) to anthropogenic stress

Golubkov S. M., Alimov A. F., Telesh I.V., Anokhina L. E., Maximov A. A., Nikulina V. N., Pavel'eva E. B., Panov V. E.

Oceanologia

2003

No. 45 (1)

53-66

Long-term hydrobiological research has shown that the functioning of the ecosystem of the Neva Estuary, one of the largest Baltic estuaries, has changed greatly since the beginning of the 20th century. Ineffective local water management in St. Petersburg during the last twenty years has stimulated the development of a natural "biological plug" in the salt barrier zone in the inner part of the estuary and has altered the ecosystem's functioning. These changes include an increase in primary production, in the primary production:organic matter decomposition ratio, and in pelagic-benthic coupling. It has also given rise to filamentous algae blooms and intensive secondary pollution in the coastal zone of the Neva Estuary. The primary production of phytoplankton in the inner part of the estuary has reached 2.3 gC m-2, that of the filamentous algae Cladophora glomerata 5.5 gC m-2 these figures are much higher than in other regions of the Gulf of Finland.