Plankton and primary production in the Lena river estuary and in the south-eastern Laptev sea

Primary production in the lower Lena River and its delta was high (50-160 mg Cm-3 day(-1)), while its integral values were moderate (0.1-0.3 g Cm-2 day(-1)) because of a low water transparency. In the river itself, phytoplankton was dominated by diatoms and picocyanobacteria with a biomass of 400-500 mg m(-3). In waters of the Lena Estuary (Buor-Haya Bay) with surface salinity of 2-7, the surface primary production ranged from 75 to 640 mg Cm-3 day(-1). The bulk of the surface primary production was contributed by the symbiotic ciliate Mesodinium rubrum which attained a biomass of 500-1500 mg m(-3), together with a biomass of algae of about 100 mg m(-3). In the open South-east Laptev Sea, influenced by the Lena and Yana Rivers, primary production at the surface was 37-98 mg Cm-3 day(-1). To the west, off the Novosibirsk Islands, primary production was moderate; 11-23 mg C m(-3) day(-1), decreasing at the shelf edge to 3-6 mg C m(-3) day(-1). The total number of bacteria in the River and Estuary was over 1.5 x 10(6) cells ml(-1), the wet biomass was over 150 mg m(-3), and daily production of bacteria was 10-50 mg m(-3). In the more saline waters of the open Laptev Sea, the microbial biomass was 5-10 times less than in the Estuary. The planktonic protozoa were represented by zooflagellates (biomass 70-100 mg m(-3)), by Strombidium and Tintinnopsis, genera of heterotrophic ciliates (biomass 10-70 mg m(-3)), and by the phototrophic symbiotic ciliate M. rubrum (biomass 300-1500 mg m(-3)). The mesozooplankton was scarce in the Lena River (20-60 mg m(-3)) while, in the brackish estuarine waters, its biomass Pose to 300-1700 mg m(-3). In the open Laptev Sea influenced by rivers, mesozooplankton biomass was also high; 300-400 mg m(-3). The influence of river drainage upon the pelagic ecosystem of an arctic estuarine basin is discussed in the present paper. (C) 1996 Academic Press Limited